U.S. patent application number 12/988554 was filed with the patent office on 2011-02-10 for refrigeration apparatus.
This patent application is currently assigned to DAIKIN INDUSTRIES, LTD.. Invention is credited to Shuji Fujimoto, Atsushi Yoshimi.
Application Number | 20110030407 12/988554 |
Document ID | / |
Family ID | 41216821 |
Filed Date | 2011-02-10 |
United States Patent
Application |
20110030407 |
Kind Code |
A1 |
Yoshimi; Atsushi ; et
al. |
February 10, 2011 |
REFRIGERATION APPARATUS
Abstract
A refrigeration apparatus uses supercritical range refrigerant,
and includes a multi-stage compression mechanism, a heat
source-side heat exchanger, a usage-side heat exchanger, a
switching mechanism switchable between cooling and heating
operation states, and a second-stage injection tube. The
second-stage injection tube branches off refrigerant, which has
radiated heat in the heat source-side heat exchanger or the
usage-side heat exchanger, and returns the refrigerant to the
second-stage compression element. Refrigerant is prevented from
returning to the second-stage compression element through the
second-stage injection tube at least during a beginning of a
reverse cycle defrosting operation, which is performed to defrost
the heat source-side heat exchanger by switching the switching
mechanism to the cooling operation state.
Inventors: |
Yoshimi; Atsushi; (Osaka,
JP) ; Fujimoto; Shuji; (Osaka, JP) |
Correspondence
Address: |
GLOBAL IP COUNSELORS, LLP
1233 20TH STREET, NW, SUITE 700
WASHINGTON
DC
20036-2680
US
|
Assignee: |
DAIKIN INDUSTRIES, LTD.
Osaka-shi, Osaka
JP
|
Family ID: |
41216821 |
Appl. No.: |
12/988554 |
Filed: |
April 20, 2009 |
PCT Filed: |
April 20, 2009 |
PCT NO: |
PCT/JP2009/057836 |
371 Date: |
October 19, 2010 |
Current U.S.
Class: |
62/324.5 |
Current CPC
Class: |
F25B 47/025 20130101;
F25B 2400/23 20130101; F25B 9/008 20130101; F25B 13/00 20130101;
F25B 2400/13 20130101; F25B 2313/02741 20130101; F25B 1/10
20130101; F25B 2313/0272 20130101; F25B 2309/061 20130101 |
Class at
Publication: |
62/324.5 |
International
Class: |
F25B 13/00 20060101
F25B013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 22, 2008 |
JP |
2008-111544 |
Claims
1. A refrigeration apparatus that uses a refrigerant that operates
in a supercritical range, the refrigeration apparatus comprising: a
compression mechanism having a plurality of compression elements
arranged and configured so that refrigerant discharged from a
first-stage compression element of the plurality of compression
elements is sequentially compressed by a second-stage compression
element; a heat source-side heat exchanger using air as a heat
source and being arranged and configured to operate as a radiator
or evaporator of refrigerant; a usage-side heat exchanger arranged
and configured to operate as a evaporator or radiator of
refrigerant; a switching mechanism arranged and configured to
switch between a cooling operation state in which the refrigerant
is circulated through the compression mechanism, the heat
source-side heat exchanger, and the usage-side heat exchanger in
order, and a heating operation state in which the refrigerant is
circulated through the compression mechanism, the usage-side heat
exchanger, and the heat source-side heat exchanger in order; and a
second-stage injection tube arranged and configured to branch off
the refrigerant, which has radiated heat in the heat source-side
heat exchanger or the usage-side heat exchanger, and to return the
refrigerant to the second-stage compression element the
second-stage injection tube being arranged and configured such that
refrigerant is prevented from returning to the second-stage
compression element through the second-stage injection tube at
least during a beginning of a reverse cycle defrosting operation,
which is performed to defrost the heat source-side heat exchanger
by switching the switching mechanism to the cooling operation
state.
2. The refrigeration apparatus according to claim 1, wherein the at
least the beginning of the reverse cycle defrosting operation is a
time period from a start of the reverse cycle defrosting operation
until a predetermined time duration elapses, and the predetermined
time duration is set according to a length of a refrigerant tube
between the usage-side heat exchanger and the switching
mechanism.
3. The refrigeration apparatus according to claim 1, wherein the at
least the beginning of the reverse cycle defrosting operation is a
time period from a start of the reverse cycle defrosting operation
until a temperature of the refrigerant in the usage-side heat
exchanger decreases to a predetermined temperature or lower.
4. The refrigeration apparatus according to claim 1, wherein the at
least the beginning of the reverse cycle defrosting operation is a
time period from a start of the reverse cycle defrosting operation
until a pressure of the refrigerant in the intake side of the
compression mechanism decreases to a predetermined pressure or
lower.
5. The refrigeration apparatus according to claim 1, wherein the
refrigerant that operates in the supercritical range is carbon
dioxide.
6. The refrigeration apparatus according to claim 2, wherein the
refrigerant that operates in the supercritical range is carbon
dioxide.
7. The refrigeration apparatus according to claim 3, wherein the
refrigerant that operates in the supercritical range is carbon
dioxide.
8. The refrigeration apparatus according to claim 4, wherein the
refrigerant that operates in the supercritical range is carbon
dioxide.
Description
TECHNICAL FIELD
[0001] The present invention relates to a refrigeration apparatus,
and particularly relates to a refrigeration apparatus which has a
refrigerant circuit configured to be capable of switching between a
cooling operation and a heating operation and which performs a
multistage compression refrigeration cycle by using a refrigerant
that operates in a supercritical range.
BACKGROUND ART
[0002] As one conventional example of a refrigeration apparatus
which has a refrigerant circuit configured to be capable of
switching between a cooling operation and a heating operation and
which performs a multistage compression refrigeration cycle by
using a refrigerant that operates in a supercritical range, Patent
Document 1 discloses an air-conditioning apparatus which has a
refrigerant circuit configured to be capable of switching between
an air-cooling operation and an air-warming operation and which
performs a two-stage compression refrigeration cycle by using
carbon dioxide as a refrigerant. This air-conditioning apparatus
has primarily a compressor having two compression elements
connected in series, a four-way switching valve for switching
between an air-cooling operation and an air-warming operation, an
outdoor heat exchanger, and an indoor heat exchanger. This
air-conditioning apparatus also has a gas-liquid separator for
performing gas-liquid separation on refrigerant flowing between the
outdoor heat exchanger and the indoor heat exchanger, and a
second-stage injection tube for returning the refrigerant from the
gas-liquid separator to the second-stage compression element.
[0003] <Patent Document 1>
[0004] Japanese Laid-open Patent Publication No. 2007-232263
SUMMARY OF INVENTION
[0005] A refrigeration apparatus according to a first aspect of the
present invention comprises a compression mechanism, a heat
source-side heat exchanger which functions as a radiator or
evaporator of refrigerant, a usage-side heat exchanger which
functions as an evaporator or radiator of refrigerant, a switching
mechanism, and a second-stage injection tube. The compression
mechanism has a plurality of compression elements and is configured
so that the refrigerant discharged from the first-stage compression
element, which is one of a plurality of compression elements, is
sequentially compressed by the second-stage compression element. As
used herein, the term "compression mechanism" refers to a
compressor in which a plurality of compression elements are
integrally incorporated, or a configuration that includes a
compression mechanism in which a single compression element is
incorporated and/or a plurality of compression mechanisms in which
a plurality of compression elements have been incorporated are
connected together. The phrase "the refrigerant discharged from a
first-stage compression element, which is one of the plurality of
compression elements, is sequentially compressed by a second-stage
compression element" does not mean merely that two compression
elements connected in series are included, namely, the "first-stage
compression element" and the "second-stage compression element;"
but means that a plurality of compression elements are connected in
series and the relationship between the compression elements is the
same as the relationship between the aforementioned "first-stage
compression element" and "second-stage compression element." The
switching mechanism is a mechanism for switching between a cooling
operation state, in which the refrigerant is circulated through the
compression mechanism, the heat source-side heat exchanger, and the
usage-side heat exchanger in a stated order; and a heating
operation state, in which the refrigerant is circulated through the
compression mechanism, the usage-side heat exchanger, and the heat
source-side heat exchanger in a stated order. The heat source-side
heat exchanger is a heat exchanger having air as a heat source. The
second-stage injection tube is a refrigerant tube for branching off
the refrigerant whose heat has been radiated in the heat
source-side heat exchanger or the usage-side heat exchanger and
returning the refrigerant to the second-stage compression element.
In this refrigeration apparatus, refrigerant is prevented from
returning to the second-stage compression element through the
second-stage injection tube, at least during the beginning of a
reverse cycle defrosting operation for defrosting the heat
source-side heat exchanger by switching the switching mechanism to
the cooling operation state.
[0006] With conventional air-conditioning apparatuses, in cases in
which a heat exchanger having air as a heat source is used as the
outdoor heat exchanger, when the heating operation is performed
while the air as the heat source is low in temperature, frost
deposits form on the outdoor heat exchanger functioning as an
evaporator of the refrigerant, and a defrosting operation for
defrosting the outdoor heat exchanger must therefore be performed
by causing the outdoor heat exchanger to function as a radiator of
the refrigerant. In cases in which a reverse cycle defrosting
operation is used as the defrosting operation, wherein the outdoor
heat exchanger is made to function as a radiator of refrigerant by
switching the switching mechanism from an air-warming operation
state to an air-cooling operation state, the indoor heat exchanger
is made to function as an evaporator of refrigerant regardless of
the intention being to cause the indoor heat exchanger to function
as a radiator of refrigerant, and a problem is encountered in that
the temperature decreases on the indoor side. Therefore, to avoid
this temperature decrease on the indoor side, a considered
possibility is to reduce the flow rate of the refrigerant flowing
through the indoor heat exchanger by using the second-stage
injection tube to ensure that the refrigerant fed from the outdoor
heat exchanger to the indoor heat exchanger is returned to the
second-stage compression element also when the reverse cycle
defrosting operation is performed, during both the air-cooling
operation and the air-warming operation.
[0007] However, when the second-stage injection tube is used to
reduce the flow rate of the refrigerant flowing through the indoor
heat exchanger as described above, the refrigerant tube or the like
between the indoor heat exchanger and the four-way switching valve
is heated and made to store heat by the high-temperature
refrigerant discharged from the compressor through the air-warming
operation which had been performed until immediately before the
reverse cycle defrosting operation, and the defrosting capacity
cannot be improved because this stored heat is not sufficiently
utilized when the reverse cycle defrosting operation is performed.
Particularly with an air-conditioning apparatus using refrigerant
that operates in the supercritical range, it is preferable to
sufficiently utilize this stored heat because the high pressure in
the refrigeration cycle comes to exceed the critical pressure and
the temperature of the refrigerant discharged from the refrigerant
becomes extremely high.
[0008] In view of this, in the refrigeration apparatus according to
a first aspect of the present invention, refrigerant is prevented
from returning to the second-stage compression element through the
second-stage injection tube, at least at the beginning of the
reverse cycle defrosting operation. Thereby, in the refrigerant
circuit in this refrigeration apparatus, circulation is performed
whereby the refrigerant discharged from the compression mechanism
is actively drawn into the compression mechanism through the
usage-side heat exchanger. At this time, sufficient use is made of
the heat stored in the refrigerant tube or the like between the
usage-side heat exchanger and the switching mechanism due to the
heating operation performed until immediately before the reverse
cycle defrosting operation was performed, the temperature of the
low-pressure refrigerant in the refrigeration cycle drawn into the
compression mechanism increases, and the refrigerant is prevented
from returning to the second-stage compression element through the
second-stage injection tube, thereby minimizing the decrease in the
temperature of the intermediate-pressure refrigerant in the
refrigeration cycle drawn into the second-stage compression
element. Therefore, the temperature of the high-pressure
refrigerant in the refrigeration cycle discharged from the
compression mechanism can be greatly increased, and the defrosting
capacity per unit flow rate of the refrigerant when the reverse
cycle defrosting operation is performed can be improved. Moreover,
it is at least in the beginning of the reverse cycle defrosting
operation that a state is created in which refrigerant does not
return to the second-stage compression element through the
second-stage injection tube, and circulation for drawing
refrigerant into the compression mechanism through the usage-side
heat exchanger is not continued excessively in the refrigerant
circuit after the amount of heat stored in the refrigerant tube or
the like between the usage-side heat exchanger and the switching
mechanism has decreased and the effect of improving the defrosting
capacity can no longer be sufficiently achieved; therefore, the
temperature decrease on the usage side can be minimized.
[0009] Thus, in this refrigeration apparatus, when the reverse
cycle defrosting operation is performed, defrosting capacity can be
improved while the temperature decrease on the usage side is
minimized.
[0010] The refrigeration apparatus according to a second aspect is
the refrigeration apparatus according to the first aspect, wherein
the phrase "at least the beginning of the reverse cycle defrosting
operation" refers to a time starting from the start of the reverse
cycle defrosting operation to the elapsing of a predetermined time
duration set according to the length of a refrigerant tube between
the usage-side heat exchanger and the switching mechanism.
[0011] In this refrigeration apparatus, the fact that at least the
beginning of the reverse cycle defrosting operation is a time
period from the start of the reverse cycle defrosting operation to
when a predetermined time duration set according to the length of a
refrigerant tube between the usage-side heat exchanger and the
switching mechanism has elapsed makes it possible to determine the
point in time at which the amount of heat stored in the refrigerant
tube or the like between the usage-side heat exchanger and the
switching mechanism has decreased and the effect of improving the
defrosting capacity can no longer be sufficiently achieved,
according to the length of the refrigerant tube between the
usage-side heat exchanger and the switching mechanism.
[0012] The refrigeration apparatus according to a third aspect is
the refrigeration apparatus according to the first aspect, wherein
the phrase "at least the beginning of the reverse cycle defrosting
operation" refers to a time period from the start of the reverse
cycle defrosting operation until the temperature of the refrigerant
in the usage-side heat exchanger decreases to a predetermined
temperature or lower.
[0013] In this refrigeration apparatus, the fact that at least the
beginning of the reverse cycle defrosting operation is a time
period from the start of the reverse cycle defrosting operation
until the temperature of the refrigerant in the usage-side heat
exchanger decreases to a predetermined temperature or lower makes
it possible to determine, in terms of the temperature decrease on
the usage side, whether or not the amount of heat stored in the
refrigerant tube or the like between the usage-side heat exchanger
and the switching mechanism has decreased and the effect of
improving the defrosting capacity can no longer be sufficiently
achieved.
[0014] The refrigeration apparatus according to a fourth aspect is
the refrigeration apparatus according to the first aspect, wherein
the phrase "at least the beginning of the reverse cycle defrosting
operation" refers to a time period from the start of the reverse
cycle defrosting operation until the pressure of the refrigerant in
the intake side of the compression mechanism decreases to a
predetermined pressure or lower.
[0015] In this refrigeration apparatus, the fact that at least the
beginning of the reverse cycle defrosting operation is a time
period from the start of the reverse cycle defrosting operation
until the pressure of the refrigerant in the intake side of the
compression mechanism decreases to a predetermined pressure or
lower makes it possible to determine, in terms of the decrease in
the flow rate of the refrigerant drawn into the compression
mechanism that occurs with the temperature decrease on the usage
side, whether or not the amount of heat stored in the refrigerant
tube or the like between the usage-side heat exchanger and the
switching mechanism has decreased and the effect of improving the
defrosting capacity can no longer be sufficiently achieved.
[0016] The refrigeration apparatus according to a fifth aspect is
the refrigeration apparatus according to the first through fourth
aspects, wherein the refrigerant for operating in the supercritical
range is carbon dioxide.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIG. 1 is a schematic structural diagram of an
air-conditioning apparatus as an embodiment of the refrigeration
apparatus according to the present invention.
[0018] FIG. 2 is a diagram showing the flow of refrigerant within
the air-conditioning apparatus during the air-cooling
operation.
[0019] FIG. 3 is a pressure-enthalpy graph representing the
refrigeration cycle during the air-cooling operation.
[0020] FIG. 4 is a temperature-entropy graph representing the
refrigeration cycle during the air-cooling operation.
[0021] FIG. 5 is a diagram showing the flow of refrigerant within
the air-conditioning apparatus during the air-warming
operation.
[0022] FIG. 6 is a flowchart of the defrosting operation.
[0023] FIG. 7 is a diagram showing the flow of refrigerant within
the air-conditioning apparatus at the start of the defrosting
operation.
[0024] FIG. 8 is a pressure-enthalpy graph representing the
refrigeration cycle during the defrosting operation.
[0025] FIG. 9 is a temperature-entropy graph representing the
refrigeration cycle during the defrosting operation.
[0026] FIG. 10 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 1.
[0027] FIG. 11 is a diagram showing the flow of refrigerant within
the air-conditioning apparatus during the air-cooling
operation.
[0028] FIG. 12 is a pressure-enthalpy graph representing the
refrigeration cycle during the air-cooling operation in the
air-conditioning apparatus according to Modification 1.
[0029] FIG. 13 is a temperature-entropy graph representing the
refrigeration cycle during the air-cooling operation in the
air-conditioning apparatus according to Modification 1.
[0030] FIG. 14 is a diagram showing the flow of refrigerant within
the air-conditioning apparatus during the air-warming
operation.
[0031] FIG. 15 is a diagram showing the flow of refrigerant within
the air-conditioning apparatus at the start of the defrosting
operation.
[0032] FIG. 16 is a pressure-enthalpy graph representing the
refrigeration cycle during the defrosting operation in the
air-conditioning apparatus according to Modification 1.
[0033] FIG. 17 is a temperature-entropy graph representing the
refrigeration cycle during the defrosting operation in the
air-conditioning apparatus according to Modification 1.
[0034] FIG. 18 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 2.
[0035] FIG. 19 is a diagram showing the flow of refrigerant within
the air-conditioning apparatus during the air-cooling
operation.
[0036] FIG. 20 is a pressure-enthalpy graph representing the
refrigeration cycle during the air-cooling operation in the
air-conditioning apparatus according to Modification 2.
[0037] FIG. 21 is a temperature-entropy graph representing the
refrigeration cycle during the air-cooling operation in the
air-conditioning apparatus according to Modification 2.
[0038] FIG. 22 is a diagram showing the flow of refrigerant within
the air-conditioning apparatus during the air-warming
operation.
[0039] FIG. 23 is a diagram showing the flow of refrigerant within
the air-conditioning apparatus at the start of the defrosting
operation.
[0040] FIG. 24 is a diagram showing the flow of refrigerant within
the air-conditioning apparatus in the defrosting operation after
defrosting of the intermediate heat exchanger is complete.
[0041] FIG. 25 is a diagram showing the flow of refrigerant within
the air-conditioning apparatus in the defrosting operation after
defrosting of the intermediate heat exchanger and utilization of
the stored heat are complete.
[0042] FIG. 26 is a pressure-enthalpy graph representing the
refrigeration cycle during the defrosting operation in the
air-conditioning apparatus according to Modification 2.
[0043] FIG. 27 is a temperature-entropy graph representing the
refrigeration cycle during the defrosting operation in the
air-conditioning apparatus according to Modification 2.
[0044] FIG. 28 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 3.
[0045] FIG. 29 is a diagram showing the flow of refrigerant within
the air-conditioning apparatus during the air-cooling
operation.
[0046] FIG. 30 is a pressure-enthalpy graph representing the
refrigeration cycle during the air-cooling operation in the
air-conditioning apparatus according to Modification 3.
[0047] FIG. 31 is a temperature-entropy graph representing the
refrigeration cycle during the air-cooling operation in the
air-conditioning apparatus according to Modification 3.
[0048] FIG. 32 is a diagram showing the flow of refrigerant within
the air-conditioning apparatus during the air-warming
operation.
[0049] FIG. 33 is a diagram showing the flow of refrigerant within
the air-conditioning apparatus at the start of the defrosting
operation.
[0050] FIG. 34 is a diagram showing the flow of refrigerant within
the air-conditioning apparatus in the defrosting operation after
defrosting of the intermediate heat exchanger is complete.
[0051] FIG. 35 is a diagram showing the flow of refrigerant within
the air-conditioning apparatus in the defrosting operation after
defrosting of the intermediate heat exchanger and utilization of
the stored heat are complete.
[0052] FIG. 36 is a pressure-enthalpy graph representing the
refrigeration cycle during the defrosting operation in the
air-conditioning apparatus according to Modification 3.
[0053] FIG. 37 is a temperature-entropy graph representing the
refrigeration cycle during the defrosting operation in the
air-conditioning apparatus according to Modification 3.
[0054] FIG. 38 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 4.
DESCRIPTION OF EMBODIMENTS
[0055] Embodiments of the refrigeration apparatus according to the
present invention are described hereinbelow with reference to the
drawings.
(1) Configuration of Air-Conditioning Apparatus
[0056] FIG. 1 is a schematic structural diagram of an
air-conditioning apparatus 1 as an embodiment of the refrigeration
apparatus according to the present invention. The air-conditioning
apparatus 1 has a refrigerant circuit 10 configured to be capable
of switching between an air-cooling operation and an air-warming
operation, and the apparatus performs a two-stage compression
refrigeration cycle by using a refrigerant (carbon dioxide in this
case) for operating in a supercritical range.
[0057] The refrigerant circuit 10 of the air-conditioning apparatus
1 has primarily a compression mechanism 2, a switching mechanism 3,
a heat source-side heat exchanger 4, a bridge circuit 17, a
receiver 18, a first expansion mechanism 5a, a second expansion
mechanism 5b, a first second-stage injection tube 18c, and a
usage-side heat exchanger 6.
[0058] In the present embodiment, the compression mechanism 2 is
configured from a compressor 21 which uses two compression elements
to subject a refrigerant to two-stage compression. The compressor
21 has a hermetic structure in which a compressor drive motor 21b,
a drive shaft 21c, and compression elements 2c, 2d are housed
within a casing 21a. The compressor drive motor 21b is linked to
the drive shaft 21c. The drive shaft 21c is linked to the two
compression elements 2c, 2d. Specifically, the compressor 21 has a
so-called single-shaft two-stage compression structure in which the
two compression elements 2c, 2d are linked to a single drive shaft
21c and the two compression elements 2c, 2d are both rotatably
driven by the compressor drive motor 21b. In the present
embodiment, the compression elements 2c, 2d are rotary elements,
scroll elements, or another type of positive displacement
compression elements. The compressor 21 is configured so as to draw
refrigerant through an intake tube 2a, to discharge this
refrigerant to an intermediate refrigerant tube 8 after the
refrigerant has been compressed by the compression element 2c, to
drawhe intermediate-pressure refrigerant discharged to the
intermediate refrigerant tube 8 in the refrigeration cycle into the
compression element 2d, and to discharge the refrigerant to a
discharge tube 2b after the refrigerant has been further
compressed. The intermediate refrigerant tube 8 is a refrigerant
tube for taking the intermediate-pressure refrigerant in the
refrigeration cycle into the compression element 2d connected to
the second-stage side of the compression element 2c after the
refrigerant has been discharged from the compression element 2c
connected to the first-stage side of the compression element 2c.
The discharge tube 2b is a refrigerant tube for feeding refrigerant
discharged from the compression mechanism 2 to the switching
mechanism 3, and the discharge tube 2b is provided with an oil
separation mechanism 41 and a non-return mechanism 42. The oil
separation mechanism 41 is a mechanism for separating refrigerator
oil accompanying the refrigerant from the refrigerant discharged
from the compression mechanism 2 and returning the oil to the
intake side of the compression mechanism 2, and the oil separation
mechanism 41 has primarily an oil separator 41a for separating
refrigerator oil accompanying the refrigerant from the refrigerant
discharged from the compression mechanism 2, and an oil return tube
41b connected to the oil separator 41a for returning the
refrigerator oil separated from the refrigerant to the intake tube
2a of the compression mechanism 2. The oil return tube 41b is
provided with a depressurization mechanism 41c for depressurizing
the refrigerator oil flowing through the oil return tube 41b. A
capillary tube is used for the depressurization mechanism 41c in
the present embodiment. The non-return mechanism 42 is a mechanism
for allowing the flow of refrigerant from the discharge side of the
compression mechanism 2 to the switching mechanism 3 and for
blocking the flow of refrigerant from the switching mechanism 3 to
the discharge side of the compression mechanism 2, and a non-return
valve is used in the present embodiment.
[0059] Thus, in the present embodiment, the compression mechanism 2
has two compression elements 2c, 2d and is configured so that among
these compression elements 2c, 2d, refrigerant discharged from the
first-stage compression element is compressed in sequence by the
second-stage compression element.
[0060] The switching mechanism 3 is a mechanism for switching the
direction of refrigerant flow in the refrigerant circuit 10. In
order to allow the heat source-side heat exchanger 4 to function as
a radiator of refrigerant compressed by the compression mechanism 2
and to allow the usage-side heat exchanger 6 to function as an
evaporator of refrigerant cooled in the heat source-side heat
exchanger 4 during the air-cooling operation, the switching
mechanism 3 is capable of connecting the discharge side of the
compression mechanism 2 and one end of the heat source-side heat
exchanger 4 and also connecting the intake side of the compressor
21 and the usage-side heat exchanger 6 (refer to the solid lines of
the switching mechanism 3 in FIG. 1, this state of the switching
mechanism 3 being referred to below as the "cooling operation
state"). In order to allow the usage-side heat exchanger 6 to
function as a radiator of refrigerant compressed by the compression
mechanism 2 and to allow the heat source-side heat exchanger 4 to
function as an evaporator of refrigerant cooled in the usage-side
heat exchanger 6 during the air-warming operation, the switching
mechanism 3 is capable of connecting the discharge side of the
compression mechanism 2 and the usage-side heat exchanger 6 and
also of connecting the intake side of the compression mechanism 2
and one end of the heat source-side heat exchanger 4 (refer to the
dashed lines of the switching mechanism 3 in FIG. 1, this state of
the switching mechanism 3 being referred to below as the "heating
operation state"). In the present embodiment, the switching
mechanism 3 is a four-way switching valve connected to the intake
side of the compression mechanism 2, the discharge side of the
compression mechanism 2, the heat source-side heat exchanger 4, and
the usage-side heat exchanger 6. The switching mechanism 3 is not
limited to a four-way switching valve, and may be configured so as
to have a function for switching the direction of the flow of the
refrigerant in the same manner as described above by using, e.g., a
combination of a plurality of electromagnetic valves.
[0061] Thus, focusing solely on the compression mechanism 2, the
heat source-side heat exchanger 4, and the usage-side heat
exchanger 6 constituting the refrigerant circuit 10; the switching
mechanism 3 is configured to be capable of switching between a
cooling operation state in which the refrigerant is circulated
sequentially through the compression mechanism 2, the heat
source-side heat exchanger 4 functioning as a radiator of
refrigerant, and the usage-side heat exchanger 6 functioning as an
evaporator of refrigerant; and a heating operation state in which
the refrigerant is circulated sequentially through the compression
mechanism 2, the usage-side heat exchanger 6 functioning as a
radiator of refrigerant, and the heat source-side heat exchanger 4
functioning as an evaporator of refrigerant.
[0062] The heat source-side heat exchanger 4 is a heat exchanger
that functions as a radiator or an evaporator of refrigerant. One
end of the heat source-side heat exchanger 4 is connected to the
switching mechanism 3, and the other end is connected to the first
expansion mechanism 5a via the bridge circuit 17. The heat
source-side heat exchanger 4 is a heat exchanger that uses air as a
heat source (i.e., a cooling source or a heating source), and a
fin-and-tube heat exchanger is used in the present embodiment. The
air as the heat source is supplied to the heat source-side heat
exchanger 4 by a heat source-side fan 40. The heat source-side fan
40 is driven by a fan drive motor 40a.
[0063] The bridge circuit 17 is disposed between the heat
source-side heat exchanger 4 and the usage-side heat exchanger 6,
and is connected to a receiver inlet tube 18a connected to the
inlet of the receiver 18 and to a receiver outlet tube 18b
connected to the outlet of the receiver 18. The bridge circuit 17
has four non-return valves 17a, 17b, 17c, and 17d in the present
embodiment. The inlet non-return valve 17a is a non-return valve
that allows only the flow of refrigerant from the heat source-side
heat exchanger 4 to the receiver inlet tube 18a. The inlet
non-return valve 17b is a non-return valve that allows only the
flow of refrigerant from the usage-side heat exchanger 6 to the
receiver inlet tube 18a. In other words, the inlet non-return
valves 17a, 17b have a function for allowing refrigerant to flow
from one among the heat source-side heat exchanger 4 or the
usage-side heat exchanger 6 to the receiver inlet tube 18a. The
outlet non-return valve 17c is a non-return valve that allows only
the flow of refrigerant from the receiver outlet tube 18b to the
usage-side heat exchanger 6. The outlet non-return valve 17d is a
non-return valve that allows only the flow of refrigerant from the
receiver outlet tube 18b to the heat source-side heat exchanger 4.
In other words, the outlet non-return valves 17c, 17d have a
function for allowing refrigerant to flow from the receiver outlet
tube 18b to the heat source-side heat exchanger 4 or the usage-side
heat exchanger 6.
[0064] The first expansion mechanism 5a is a mechanism for
depressurizing the refrigerant, is provided to the receiver inlet
tube 18a, and is an electrically driven expansion valve in the
present embodiment. In the present embodiment, during the
air-cooling operation, the first expansion mechanism 5a
depressurizes the high-pressure refrigerant in the refrigeration
cycle that has been cooled in the heat source-side heat exchanger 4
nearly to the saturation pressure of the refrigerant before the
refrigerant is fed to the usage-side heat exchanger 6 via the
receiver 18; and during the air-warming operation, the first
expansion mechanism 5a depressurizes the high-pressure refrigerant
in the refrigeration cycle that has been cooled in the usage-side
heat exchanger 6 nearly to the saturation pressure of the
refrigerant before the refrigerant is fed to the heat source-side
heat exchanger 4 via the receiver 18.
[0065] The receiver 18 is a container provided in order to
temporarily retain the refrigerant that has been depressurized by
the first expansion mechanism 5a so as to allow storage of excess
refrigerant produced according to the operation states, such as the
quantity of refrigerant circulating in the refrigerant circuit 10
being different between the air-cooling operation and the
air-warming operation, and the inlet of the receiver 18 is
connected to the receiver inlet tube 18a, while the outlet is
connected to the receiver outlet tube 18b. Also connected to the
receiver 18 are the first second-stage injection tube 18c and a
first intake return tube 18f. The first second-stage injection tube
18c and the first intake return tube 18f are integrated in the
portion near the receiver 18.
[0066] The first second-stage injection tube 18c is a refrigerant
tube capable of performing intermediate pressure injection for
extracting refrigerant from the receiver 18 and returning the
refrigerant to the second-stage compression element 2d of the
compression mechanism 2, and in the present modification, the first
second-stage injection tube 18c is provided so as to connect the
top part of the receiver 18 and the intermediate refrigerant tube 8
(i.e., the intake side of the second-stage compression element 2d
of the compression mechanism 2). The first second-stage injection
tube 18c is provided with a first second-stage injection on/off
valve 18d and a first second-stage injection non-return mechanism
18e. The first second-stage injection on/off valve 18d is a valve
capable of opening and closing, and is an electromagnetic valve in
the present embodiment. The first second-stage injection non-return
mechanism 18e is a mechanism for allowing refrigerant to flow from
the receiver 18 to the second-stage compression element 2d and
blocking refrigerant from flowing from the second-stage compression
element 2d to the receiver 18, and a non-return valve is used in
the present embodiment.
[0067] The first intake return tube 18f is connected so as to be
capable of withdrawing refrigerant from inside the receiver 18 and
returning the refrigerant to the intake tube 2a of the compression
mechanism 2 (i.e., to the intake side of the compression element 2c
on the first-stage side of the compression mechanism 2). A first
intake return on/off valve 18g is provided to this first intake
return tube 18f. The first intake return on/off valve 18g is an
electromagnetic valve in the present embodiment.
[0068] Thus, when the first second-stage injection tube 18c is used
by opening the first second-stage injection on/off valve 18d, the
receiver 18 functions as a gas-liquid separator for performing
gas-liquid separation between the first expansion mechanism 5a and
the second expansion mechanism 5b on the refrigerant flowing
between the heat source-side heat exchanger 4 and the usage-side
heat exchanger 6, and intermediate pressure injection can be
performed by the receiver 18 for returning the gas refrigerant
resulting from gas-liquid separation in the receiver 18 from the
top part of the receiver 18 to the second-stage compression element
2d of the compression mechanism 2.
[0069] The second expansion mechanism 5b is a mechanism provided to
the receiver outlet tube 18b and used for depressurizing the
refrigerant, and is an electrically driven expansion valve in the
present embodiment. In the present embodiment, during the
air-cooling operation, the second expansion mechanism 5b further
depressurizes the refrigerant depressurized by the first expansion
mechanism 5a to a low pressure in the refrigeration cycle before
the refrigerant is fed to the usage-side heat exchanger 6 via the
receiver 18; and during the air-warming operation, the second
expansion mechanism 5b further depressurizes the refrigerant
depressurized by the first expansion mechanism 5a to a low pressure
in the refrigeration cycle before the refrigerant is fed to the
heat source-side heat exchanger 4 via the receiver 18.
[0070] The usage-side heat exchanger 6 is a heat exchanger that
functions as a radiator or an evaporator of refrigerant. One end of
the usage-side heat exchanger 6 is connected to the first expansion
mechanism 5a via the bridge circuit 17, and the other end is
connected to the switching mechanism 3. The usage-side heat
exchanger 6 is a heat exchanger that uses water and/or air as a
heat source (i.e., a cooling source or a heating source).
[0071] Furthermore, the air-conditioning apparatus 1 is provided
with various sensors. Specifically, the heat source-side heat
exchanger 4 is provided with a heat source-side heat exchange
temperature sensor 51 for detecting the temperature of the
refrigerant flowing through the heat source-side heat exchanger 4.
The usage-side heat source-side heat exchanger 6 is provided with a
usage-side heat exchange temperature sensor 61 for detecting the
temperature of the refrigerant flowing through the usage-side heat
exchanger 6. An intake pressure sensor 60 for detecting the
pressure of the refrigerant flowing through the intake side of the
compression mechanism 2 is provided to either the intake tube 2a or
the compression mechanism 2. The air-conditioning apparatus 1 is
provided with an air temperature sensor 53 for detecting the
temperature of the air as a heat source for the heat source-side
heat exchanger 4. Though not shown in the drawings, the
air-conditioning apparatus 1 also has a controller for controlling
the actions of the compression mechanism 2, the switching mechanism
3, the expansion mechanism 5, the heat source-side fan 40, the
first second-stage injection on/off valve 18d, the first intake
return on/off valve 18g, and the other components constituting the
air-conditioning apparatus 1.
(2) Action of the Air-Conditioning Apparatus
[0072] Next, the action of the air-conditioning apparatus 1 of the
present embodiment will be described using FIGS. 1 through 9. FIG.
2 is a diagram showing the flow of refrigerant within the
air-conditioning apparatus 1 during the air-cooling operation, FIG.
3 is a pressure-enthalpy graph representing the refrigeration cycle
during the air-cooling operation, FIG. 4 is a temperature-entropy
graph representing the refrigeration cycle during the air-cooling
operation, FIG. 5 is a diagram showing the flow of refrigerant
within the air-conditioning apparatus 1 during the air-warming
operation, FIG. 6 is a flowchart of the defrosting operation, FIG.
7 is a diagram showing the flow of refrigerant within the
air-conditioning apparatus 1 at the start of the defrosting
operation, FIG. 8 is a pressure-enthalpy graph representing the
refrigeration cycle during the defrosting operation, and FIG. 9 is
a temperature-entropy graph representing the refrigeration cycle
during the defrosting operation. Operation control in the
air-cooling operation, the air-warming operation, and the
defrosting operation described hereinbelow is performed by the
aforementioned controller (not shown). In the following
description, the term "high pressure" means a high pressure in the
refrigeration cycle (specifically, the pressure at points D, D',
and E in FIGS. 3, 4, 8, and 9), the term "low pressure" means a low
pressure in the refrigeration cycle (specifically, the pressure at
points A, F, W in FIGS. 3, 4, 8, and 9), and the term "intermediate
pressure" means an intermediate pressure in the refrigeration cycle
(specifically, the pressure at points B, G, G', I, L, and M in
FIGS. 3, 4, 8, and 9).
[0073] <Air-Cooling Operation>
[0074] During the air-cooling operation, the switching mechanism 3
is brought to the cooling operation state shown by the solid lines
in FIGS. 1 and 2. The opening degrees of the first expansion
mechanism 5a and the second expansion mechanism 5b are adjusted.
The first second-stage injection on/off valve 18d is brought to an
open state.
[0075] When the refrigerant circuit 10 is in this state,
low-pressure refrigerant (refer to point A in FIGS. 1 through 4) is
drawn into the compression mechanism 2 through the intake tube 2a,
and after the refrigerant is first compressed by the compression
element 2c to an intermediate pressure, the refrigerant is
discharged to the intermediate refrigerant tube 8 (refer to point A
in FIGS. 1 through 4). The intermediate-pressure refrigerant
discharged from the first-stage compression element 2c is cooled
(refer to point G in FIGS. 1 through 4) by mixing with the
refrigerant returned from the receiver 18 to the second-stage
compression element 2d through the first second-stage injection
tube 18c (refer to point M in FIGS. 1 through 4). Next, having been
mixed with the refrigerant returning from the first second-stage
injection tube 18c (i.e., intermediate pressure injection is
carried out by the receiver 18 which acts as a gas-liquid
separator), the intermediate-pressure refrigerant is drawn into and
further compressed in the compression element 2d connected to the
second-stage side of the compression element 2c, and the
refrigerant is discharged from the compression mechanism 2 to the
discharge tube 2b (refer to point D in FIGS. 1 through 4). The
high-pressure refrigerant discharged from the compression mechanism
2 is compressed by the two-stage compression action of the
compression elements 2c, 2d to a pressure exceeding a critical
pressure (i.e., the critical pressure Pcp at the critical point CP
shown in FIG. 3). The high-pressure refrigerant discharged from the
compression mechanism 2 flows into the oil separator 41a
constituting the oil separation mechanism 41, and the accompanying
refrigeration oil is separated. The refrigeration oil separated
from the high-pressure refrigerant in the oil separator 41a flows
into the oil return tube 41b constituting the oil separation
mechanism 41 wherein it is depressurized by the depressurization
mechanism 41c provided to the oil return tube 41b, and the oil is
then returned to the intake tube 2a of the compression mechanism 2
and drawn once more into the compression mechanism 2. Next, having
been separated from the refrigeration oil in the oil separation
mechanism 41, the high-pressure refrigerant is passed through the
non-return mechanism 42 and the switching mechanism 3, and is fed
to the heat source-side heat exchanger 4 functioning as a
refrigerant radiator. The high-pressure refrigerant fed to the heat
source-side heat exchanger 4 is cooled in the heat source-side heat
exchanger 4 by heat exchange with air as a cooling source supplied
by the heat source-side fan 40 (refer to point E in FIGS. 1 through
4). The high-pressure refrigerant cooled in the heat source-side
heat exchanger 4 then flows through the inlet non-return valve 17a
of the bridge circuit 17 into the receiver inlet tube 18a, and the
refrigerant is depressurized to a nearly saturated pressure by the
first expansion mechanism 5a and is temporarily retained in the
receiver 18 (refer to point I in FIGS. 1 through 4). The
refrigerant retained in the receiver 18 is fed to the receiver
outlet tube 18b and is depressurized by the second expansion
mechanism 5b to become a low-pressure gas-liquid two-phase
refrigerant, and is then fed through the outlet non-return valve
17c of the bridge circuit 17 to the usage-side heat exchanger 6
functioning as a refrigerant evaporator (refer to point F in FIGS.
1 through 4). The low-pressure gas-liquid two-phase refrigerant fed
to the usage-side heat exchanger 6 is heated by heat exchange with
water or air as a heating source, and the refrigerant is evaporated
as a result (refer to point W in FIGS. 1 through 4). The
low-pressure refrigerant heated in the usage-side heat exchanger 6
is then drawn once more into the compression mechanism 2 via the
switching mechanism 3 (refer to point A in FIGS. 1 through 4). In
this manner the air-cooling operation is performed.
[0076] Thus, in the air-conditioning apparatus 1 (refrigeration
apparatus) of the present embodiment, since the first second-stage
injection tube 18c is provided to branch off the refrigerant whose
heat has been radiated in the heat source-side heat exchanger 4 and
return the refrigerant to the second-stage compression element 2d,
the temperature of the refrigerant drawn into the second-stage
compression element 2d can be kept even lower (refer to points B
and G in FIG. 4) without heat being radiated to the exterior. The
temperature of the refrigerant discharged from the compression
mechanism 2 is thereby minimized (refer to points D and D' in FIG.
4), and it is possible to further reduce the heat radiation loss
equivalent to the area enclosed by connecting points B, D', D, and
G in FIG. 4 more than in cases in which the first second-stage
injection tube 18c is not provided; therefore, the power
consumption of the compression mechanism 2 can be further reduced,
and operating efficiency can be further improved.
[0077] <Air-Warming Operation>
[0078] During the air-warming operation, the switching mechanism 3
is brought to the heating operation state shown by the dashed lines
in FIGS. 1 and 5. The opening degrees of the first expansion
mechanism 5a and the second expansion mechanism 5b are also
adjusted. Furthermore, the first second-stage injection on/off
valve 18d is brought to the open state similar to during the
air-cooling operation.
[0079] When the refrigerant circuit 10 is in this state,
low-pressure refrigerant (refer to point A in FIGS. 1 and 3 through
5) is drawn into the compression mechanism 2 through the intake
tube 2a, and after the refrigerant is first compressed by the
compression element 2c to an intermediate pressure, the refrigerant
is discharged to the intermediate refrigerant tube 8 (refer to
point B in FIGS. 1 and 3 through 5). This intermediate-pressure
refrigerant discharged from the first-stage compression element 2c
is cooled (refer to point G in FIGS. 1 and 3 through 5) by mixing
with the refrigerant returning from the receiver 18 to the
second-stage compression element 2d through the first second-stage
injection tube 18c (refer to point M in FIGS. 1 and 3 through 5).
Next, having been mixed with the refrigerant returning from the
first second-stage injection tube 18c (i.e., intermediate pressure
injection is carried out by the receiver 18 which acts as a
gas-liquid separator), the intermediate-pressure refrigerant is
drawn into and further compressed in the compression element 2d
connected to the second-stage side of the compression element 2c,
and the refrigerant is discharged from the compression mechanism 2
to the discharge tube 2b (refer to point D in FIGS. 1 and 3 through
5). The high-pressure refrigerant discharged from the compression
mechanism 2 is compressed by the two-stage compression action of
the compression elements 2c, 2d to a pressure exceeding a critical
pressure (i.e., the critical pressure Pcp at the critical point CP
shown in FIG. 3), similar to the air-cooling operation. The
high-pressure refrigerant discharged from the compression mechanism
2 flows into the oil separator 41a constituting the oil separation
mechanism 41, and the accompanying refrigeration oil is separated.
The refrigeration oil separated from the high-pressure refrigerant
in the oil separator 41a flows into the oil return tube 41b
constituting the oil separation mechanism 41 wherein it is
depressurized by the depressurization mechanism 41c provided to the
oil return tube 41b, and the oil is then returned to the intake
tube 2a of the compression mechanism 2 and drawn once more into the
compression mechanism 2. Next, having been separated from the
refrigeration oil in the oil separation mechanism 41, the
high-pressure refrigerant is passed through the non-return
mechanism 42 and the switching mechanism 3, fed to the usage-side
heat exchanger 6 functioning as a radiator of refrigerant, and
cooled by heat exchange with the water and/or air as a cooling
source (refer to point F in FIGS. 1 and 5, and read point E as
point F in FIGS. 3 and 4). The high-pressure refrigerant cooled in
the usage-side heat exchanger 6 then flows through the inlet
non-return valve 17b of the bridge circuit 17 into the receiver
inlet tube 18a, and the refrigerant is depressurized to a nearly
saturated pressure by the first expansion mechanism 5a and
temporarily retained in the receiver 18 (refer to point I in FIGS.
1 and 3 through 5). The refrigerant retained in the receiver 18 is
fed to the receiver outlet tube 18b where it is depressurized by
the second expansion mechanism 5b into a low-pressure gas-liquid
two-phase refrigerant, which is passed through the outlet
non-return valve 17d of the bridge circuit 17 and fed to the heat
source-side heat exchanger 4 functioning as an evaporator of
refrigerant (refer to point E in FIGS. 1 and 5, and read point F as
point E in FIGS. 3 and 4). The low-pressure gas-liquid two-phase
refrigerant fed to the heat source-side heat exchanger 4 is heated
and evaporated in the heat source-side heat exchanger 4 by heat
exchange with the air as a heat source supplied by the heat
source-side fan 40 (refer to point A in FIGS. 1 and 3 through 5).
The low-pressure refrigerant heated and evaporated in the heat
source-side heat exchanger 4 is then drawn once more into the
compression mechanism 2 via the switching mechanism 3. In this
manner the air-warming operation is performed.
[0080] Thus, in the air-conditioning apparatus 1 (refrigeration
apparatus) of the present embodiment, since the first second-stage
injection tube 18c is provided to branch off the refrigerant whose
heat has been radiated in the usage-side heat exchanger 6 and
return the refrigerant to the second-stage compression element 2d,
similar to during the air-cooling operation, the temperature of the
refrigerant drawn into the second-stage compression element 2d can
be kept even lower (refer to points B and G in FIG. 4) without heat
being radiated to the exterior. The temperature of the refrigerant
discharged from the compression mechanism 2 is thereby minimized
(refer to points D and D' in FIG. 4), and it is possible to further
reduce the heat radiation loss equivalent to the area enclosed by
connecting points B, D', D, and G in FIG. 4 more than in cases in
which the first second-stage injection tube 18c is not provided;
therefore, the power consumption of the compression mechanism 2 can
be further reduced, and operating efficiency can be further
improved.
[0081] <Defrosting Operation>
[0082] First, in step S1, a decision is made as to whether or not
frost deposits have formed in the heat source-side heat exchanger 4
during the air-warming operation. This is determined based on the
temperature of the refrigerant flowing through the heat source-side
heat exchanger 4 as detected by the heat source-side heat exchange
temperature sensor 51, and/or on the cumulative time of the
air-warming operation. For example, in cases in which the
temperature of refrigerant in the heat source-side heat exchanger 4
as detected by the heat source-side heat exchange temperature
sensor 51 is equal to or less than a predetermined temperature
equivalent to conditions at which frost deposits occur, or in cases
in which the cumulative time of the air-warming operation has
elapsed past a predetermined time, it is determined that frost
deposits have formed in the heat source-side heat exchanger 4. In
cases in which these temperature conditions or time conditions are
not met, it is determined that frost deposits have not formed in
the heat source-side heat exchanger 4. Since the predetermined
temperature and predetermined time depend on the temperature of the
air as a heat source, the predetermined temperature and
predetermined time are preferably set as a function of the air
temperature detected by the air temperature sensor 53. In cases in
which a temperature sensor is provided to the inlet or outlet of
the heat source-side heat exchanger 4, the refrigerant temperature
detected by these temperature sensors may be used in the
determination of the temperature conditions instead of the
refrigerant temperature detected by the heat source-side heat
exchange temperature sensor 51. In cases in which it is determined
in step Si that frost deposits have occurred in the heat
source-side heat exchanger 4, the process advances to step S2.
[0083] Next, in step S2, the defrosting operation is started. The
defrosting operation is a reverse cycle defrosting operation in
which the heat source-side heat exchanger 4 is made to function as
a refrigerant radiator by switching the switching mechanism 3 from
the heating operation state (i.e., the air-warming operation) to
the cooling operation state.
[0084] In the present embodiment, when the reverse cycle defrosting
operation is performed, a problem arises with the temperature
decrease on the usage side due to the usage-side heat exchanger 6
being made to function as an evaporator of refrigerant. Therefore,
to avoid this temperature decrease on the usage side, a considered
possibility is to reduce the flow rate of the refrigerant flowing
through the usage-side heat exchanger 6 by creating a state in
which intermediate pressure injection by the receiver 18 as a
gas-liquid separator is used (i.e., ensuring that refrigerant
returns to the second-stage compression element 2d through the
first second-stage injection tube 18c), during both the air-cooling
operation and the air-warming operation.
[0085] However, when the first second-stage injection tube 18c is
used to reduce the flow rate of the refrigerant flowing through the
usage-side heat exchanger 6 as described above, the refrigerant
tube (hereinbelow, the refrigerant tube connecting the usage-side
heat exchanger 6 and the switching mechanism 3 is referred to as
the refrigerant tube 1d) or the like between the usage-side heat
exchanger 6 and the switching mechanism 3 is heated and made to
store heat by the high-temperature refrigerant discharged from the
compressor through the air-warming operation which had been
performed until immediately before the reverse cycle defrosting
operation, and the defrosting capacity cannot be improved because
this stored heat is not sufficiently utilized when the reverse
cycle defrosting operation is performed. Particularly with an
air-conditioning apparatus 1 which uses refrigerant that operates
in the supercritical range, such as that of the present embodiment,
it is preferable to sufficiently utilize this stored heat because
the high pressure in the refrigeration cycle comes to exceed the
critical pressure and the temperature of the refrigerant discharged
from the refrigerant becomes extremely high, further increasing the
amount of stored heat. In cases in which the refrigerant circuit 10
in the present embodiment is configured by connecting the heat
source unit (a unit installed outdoors or the like, having
primarily the compression mechanism 2, the switching mechanism 3,
the heat source-side heat exchanger 4, the expansion mechanisms 5a,
5b, the intermediate refrigerant tube 8, the bridge circuit 17, the
receiver 18, the first second-stage injection tube, the first
intake return tube 18f, the heat source-side fan 40, and other
components) and the usage unit (a unit installed indoors or the
like, having primarily the usage-side heat exchanger 6) via a
refrigerant communication tube, there are cases in which the length
of the refrigerant communication tube is extremely long, the tube
length of the refrigerant tube 1d also accordingly becomes
extremely long, and the amount of stored heat increases further. It
is therefore preferable to sufficiently utilize the stored
heat.
[0086] In view of this, in step S2 (the start of the defrosting
operation) in the present embodiment, first, a state is created in
which intermediate pressure injection by the receiver 18 as a
gas-liquid separator is not used (i.e., refrigerant is prevented
from returning to the second-stage compression element 2d through
the first second-stage injection tube 18c), the switching mechanism
3 is switched from the heating operation state to the cooling
operation state, and the reverse cycle defrosting operation is
performed (refer to the refrigeration cycle shown by the solid
lines in FIGS. 7, 8, and 9).
[0087] Thereby, in the refrigerant circuit 10, circulation is
performed whereby the refrigerant discharged from the compression
mechanism 2 is actively drawn into the compression mechanism 2
through the usage-side heat exchanger 6; therefore, the
low-pressure refrigerant heated and evaporated in the usage-side
heat exchanger 6 (refer to point W in the lines indicating the
refrigeration cycle shown by the solid lines in FIGS. 8 and 9) is
drawn into the compression mechanism 2 via the switching mechanism
3 (refer to point A in the lines indicating the refrigeration cycle
shown by the solid lines in FIGS. 8 and 9) after being heated by
the refrigerant tube 1d or the like. That is, sufficient
utilization is made of the heat stored in the refrigerant tube 1d
or the like between the usage-side heat exchanger 6 and the
switching mechanism 3 by the air-warming operation that had been
performed until immediately before the defrosting operation.
Thereby, the temperature of the low-pressure refrigerant in the
refrigeration cycle drawn into the compression mechanism 2
increases (refer to point B in the lines indicating the
refrigeration cycle shown by the solid lines in FIG. 9), and the
refrigerant is prevented from returning to the second-stage
compression element 2d through the first second-stage injection
tube 18c, whereby the decrease in the temperature of the
intermediate-pressure refrigerant in the refrigeration cycle drawn
into the second-stage compression element 2d is minimized (refer to
points B and G in the lines indicating the refrigeration cycle
shown by the solid lines in FIG. 9), the temperature of the
high-pressure refrigerant in the refrigeration cycle discharged
from the compression mechanism 2 can therefore be increased (refer
to point D in the lines indicating the refrigeration cycle shown by
the solid lines in FIG. 9), and the defrosting capacity per unit
flow rate of the refrigerant when the reverse cycle defrosting
operation is performed can be improved.
[0088] However, if the reverse cycle defrosting operation in step
S2 described above is continued, there is a high risk that a state
will arise in which the amount of heat stored in the refrigerant
tube 1d or the like between the usage-side heat exchanger 6 and the
switching mechanism 3 will gradually decrease and the effect of
improving the defrosting capacity will not be sufficiently achieved
before it is determined in step S6 described hereinafter that
defrosting of the heat source-side heat exchanger 4 is complete.
When such a state arises, the temperature of the refrigerant in the
usage-side heat exchanger 6 decreases (refer to points F and W in
the lines indicating the refrigeration cycle shown by the solid
lines in FIG. 9, and points F and W in the lines indicating the
refrigeration cycle shown by the dashed lines in FIG. 9), the low
pressure in the refrigeration cycle decreases, and the flow rate of
the refrigerant drawn from the first-stage compression element 2c
decreases (refer to points A, F, and W in the lines indicating the
refrigeration cycle shown by the solid lines in FIG. 8, and points
A, F, and W in the lines indicating the refrigeration cycle shown
by the dashed lines in FIG. 8); therefore, a problem emerges that
the temperature decreases on the usage side, the flow rate of the
refrigerant circulating through the refrigerant circuit 10
decreases, and the defrosting capacity cannot be guaranteed.
[0089] In view of this, in step S3 in the present embodiment, a
decision is made as to whether or not utilization of the stored
heat in the refrigerant tube 1d or the like between the usage-side
heat exchanger 6 and the switching mechanism 3 has concluded. If it
is determined that utilization of the stored heat has concluded,
the process advances to step S5, and a state is created in which
intermediate pressure injection by the receiver 18 as a gas-liquid
separator is used (i.e., the refrigerant is prevented from
returning to the second-stage compression element 2d through the
first second-stage injection tube 18c), similar to during the
air-cooling operation, thereby switching to the reverse cycle
defrosting operation in which the flow rate of the refrigerant
flowing through the usage-side heat exchanger 6 is reduced (refer
to the refrigeration cycle shown by the dashed lines in FIGS. 2, 8,
and 9).
[0090] The process of step S4, which is performed ahead of the
process of step S5, is a process for avoiding numerous repeated
performances of the process of step S5 when the determination in
step S3 is repeatedly performed, regardless of whether or not the
process of step S5 has already been performed. The determination in
step S3 described above of whether or not the stored heat in the
refrigerant tube 1d or the like between the usage-side heat
exchanger 6 and the switching mechanism 3 has finished being
utilized is made based on the tube length of the refrigerant tube
1d between the usage-side heat exchanger 6 and the switching
mechanism 3 (optionally, the tube length of the refrigerant
communication tube in cases in which the air-conditioning apparatus
1 is configured by connecting the heat source unit and the usage
unit via the refrigerant communication tube), the temperature of
the refrigerant in the usage-side heat exchanger 6 as detected by
the usage-side heat exchange temperature sensor 61, and/or the
temperature of the refrigerant in the intake side of the
compression mechanism 2 as detected by the intake pressure sensor
60. For example, as a decision based on the tube length of the
refrigerant tube 1d between the usage-side heat exchanger 6 and the
switching mechanism 3, a predetermined time duration is designated
according to the tube length of the refrigerant tube 1d between the
usage-side heat exchanger 6 and the switching mechanism 3, the
predetermined time duration being equivalent to the point in time
after the start of the reverse cycle defrosting operation when the
amount of stored heat in the refrigerant tube 1d or the like
between the usage-side heat exchanger 6 and the switching mechanism
3 decreases and the effect of improving the defrosting capacity is
not sufficiently achieved; and it can be determined that
utilization of the stored heat in the refrigerant tube 1d or the
like between the usage-side heat exchanger 6 and the switching
mechanism 3 has concluded when this predetermined time duration has
elapsed after the start of the reverse cycle defrosting operation
of step S2. For example, one possibility is to designate the
predetermined time duration as a short time duration when the tube
length is short (therefore, when the tube length is extremely
short, the defrosting operation of step S2 is substantially not
performed), and to designate the predetermined time duration as a
long time duration when the tube length is long. Thus, in cases in
which the decision of whether or not utilization of the stored heat
in the refrigerant tube 1d or the like between the usage-side heat
exchanger 6 and the switching mechanism 3 has concluded is made
based on the tube length of the refrigerant tube 1d between the
usage-side heat exchanger 6 and the switching mechanism 3, the
decision can be made in view of the extent of the amount of stored
head corresponding to the tube length of the refrigerant tube 1d
(or the refrigerant communication tube). As a decision based on the
temperature of the refrigerant in the usage-side heat exchanger 6,
a predetermined temperature of the refrigerant in the usage-side
heat exchanger 6 is designated, the predetermined temperature
corresponding to a state in which the amount of stored heat in the
refrigerant tube 1d or the like between the usage-side heat
exchanger 6 and the switching mechanism 3 decreases and the effect
of improving the defrosting capacity is not sufficiently achieved
after the start of the reverse cycle defrosting operation of step
S2; and it can be determined that utilization of the stored heat in
the refrigerant tube 1d or the like between the usage-side heat
exchanger 6 and the switching mechanism 3 has concluded when the
temperature of the refrigerant in the usage-side heat exchanger 6
decreases to this predetermined temperature or lower after the
start of the reverse cycle defrosting operation of step S2. Thus,
when the decision of whether or not utilization of the stored heat
in the refrigerant tube 1d or the like between the usage-side heat
exchanger 6 and the switching mechanism 3 has concluded is made
based on the temperature of the refrigerant in the usage-side heat
exchanger 6, the decision can be made in view of the temperature
decrease on the usage side. As a decision based on the pressure of
the refrigerant in the intake side of the compression mechanism 2,
a predetermined pressure of the refrigerant in the intake side of
the compression mechanism 2 is designated, the predetermined
pressure corresponding to a state in which the amount of stored
heat in the refrigerant tube 1d or the like between the usage-side
heat exchanger 6 and the switching mechanism 3 decreases and the
effect of improving the defrosting capacity is not sufficiently
achieved after the start of the reverse cycle defrosting operation
of step S2; and it can be determined that utilization of the stored
heat in the refrigerant tube 1d or the like between the usage-side
heat exchanger 6 and the switching mechanism 3 is complete when the
pressure of the refrigerant in the intake side of the compression
mechanism 2 decreases to this predetermined pressure or lower after
the start of the reverse cycle defrosting operation of step S2.
Thus, when the decision of whether or not utilization of the stored
heat in the refrigerant tube 1d or the like between the usage-side
heat exchanger 6 and the switching mechanism 3 has concluded is
made based on the pressure of the refrigerant in the intake side of
the compression mechanism 2, the decision can be made in view of
the fact that the flow rate of the refrigerant drawn into the
compression mechanism 2 decreases along with the temperature
decrease on the usage side. The determination in step S3 may use
any one of the three determination methods described above, or it
may use a combination of any two or all three of the three
determination methods described above. For example, it is
considered more preferable when the decision based on the
predetermined time duration designated according to the tube length
of the refrigerant tube 1d is combined with either the decision
based on the temperature of the refrigerant in the usage-side heat
exchanger 6 or the decision based on the pressure of the
refrigerant in the intake side of the compression mechanism 2 (in
this case, the decision is made according to the elapse of the
predetermined time duration and either the decrease of the
refrigerant temperature to or below the predetermined temperature
or the decrease of the refrigerant pressure to or below the
predetermined pressure), because the decision can be made in view
of both the temperature decrease on the usage side and the amount
of heat stored.
[0091] The temperature decrease on the usage side can thereby be
minimized in the refrigerant circuit 10 because circulation through
the usage-side heat exchanger 6 into the compression mechanism 2 no
longer continues excessively. Moreover, the temperature of the
intermediate-pressure refrigerant in the refrigeration cycle drawn
into the second-stage compression element 2d decreases (refer to
points B and G in the lines indicating the refrigeration cycle
shown by the dashed lines of FIG. 9) and the temperature of the
refrigerant discharged from the compression mechanism 2 decreases
(refer to point D in the lines indicating the refrigeration cycle
shown by the dashed lines of FIG. 9) due to the refrigerant
returning to the second-stage compression element 2d through the
first second-stage injection tube 18c, whereby the defrosting
capacity per unit flow rate of the refrigerant when the reverse
cycle defrosting operation is performed decreases, but the flow
rate of the refrigerant discharged from the second-stage
compression element 2d increases, and as much defrosting capacity
as is possible can be guaranteed.
[0092] Next, in cases in which it is determined by the process in
steps S3 to S5 that utilization of the stored heat has not
concluded, or in cases in which it is determined that utilization
of the stored heat has concluded and a switch is made to the
defrosting operation, a decision is made in step S6 as to whether
or not defrosting of the heat source-side heat exchanger 4 is
complete. This decision is made based on the temperature of
refrigerant flowing through the heat source-side heat exchanger 4
as detected by the heat source-side heat exchange temperature
sensor 51, and/or on the operation time of the defrosting
operation. For example, in the case that the temperature of
refrigerant in the heat source-side heat exchanger 4 as detected by
the heat source-side heat exchange temperature sensor 51 is equal
to or greater than a temperature equivalent to conditions at which
frost deposits do not occur, or in the case that the defrosting
operation has continued for a predetermined time or longer, it is
determined that defrosting of the heat source-side heat exchanger 4
has concluded. In the case that the temperature conditions or time
conditions are not met, it is determined that defrosting of the
heat source-side heat exchanger 4 is not complete. In the case that
a temperature sensor is provided to the inlet or outlet of the heat
source-side heat exchanger 4, the temperature of the refrigerant as
detected by either of these temperature sensors may be used in the
determination of the temperature conditions instead of the
refrigerant temperature detected by the heat source-side heat
exchange temperature sensor 51. In cases in which it is determined
in step S6 that defrosting of the heat source-side heat exchanger 4
has not concluded, the process returns once again to steps S3 to
S5, and in cases in which it is determined that defrosting of the
heat source-side heat exchanger 4 has concluded, the process
advances to step S7, the defrosting operation is ended, and a
process is again performed for restarting the air-warming
operation. More specifically, a process is performed for switching
the switching mechanism 3 from the cooling operation state to the
heating operation state (i.e. the air-warming operation).
[0093] Thus, in the air-conditioning apparatus 1 (refrigeration
apparatus) of the present embodiment, during at least the beginning
of the reverse cycle defrosting operation, which takes place from
the start of the defrosting operation until the amount of stored
heat in the refrigerant tube 1d or the like between the usage-side
heat exchanger 6 and the switching mechanism 3 decreases and a
state arises in which the effect of improving the defrosting
capacity is not sufficiently achieved, a state is created in which
refrigerant does not return to the second-stage compression element
2d through the first second-stage injection tube 18c (refer to
steps S2, S3, and S6), and sufficient utilization is made of the
heat stored in the refrigerant tube 1d or the like between the
usage-side heat exchanger 6 and the switching mechanism 3 by the
air-warming operation which was being performed until immediately
before the reverse cycle defrosting operation was performed to
improve the defrosting capacity per unit flow rate of the
refrigerant during the reverse cycle defrosting operation. After
the amount of stored heat in the refrigerant tube 1d or the like
between the usage-side heat exchanger 6 and the switching mechanism
3 decreases and a state has arisen in which the effect of improving
the defrosting capacity is not sufficiently achieved, a state is
created in which refrigerant does not return to the second-stage
compression element 2d through the first second-stage injection
tube 18c (refer to steps S3 to S6), similar to the air-cooling
operation, and in the refrigerant circuit 10, the temperature
decrease on the usage side is minimized by preventing the
circulation through the usage-side heat exchanger 6 into the
compression mechanism 2 from continuing excessively, while as much
defrosting capacity as possible is guaranteed by increasing the
flow rate of the refrigerant discharged from the second-stage
compression element 2d. Specifically, in this air-conditioning
apparatus 1, when the reverse cycle defrosting operation is
performed, it is possible to improve the defrosting capacity while
minimizing the temperature decrease on the usage side.
(3) Modification 1
[0094] In the embodiment described above, in the air-conditioning
apparatus 1 configured to be capable of switching between the
air-cooling operation and the air-warming operation via the
switching mechanism 3, the first second-stage injection tube 18c is
provided for performing intermediate pressure injection through the
receiver 18 as a gas-liquid separator, and intermediate pressure
injection is performed by the receiver 18 as a gas-liquid
separator, but instead of intermediate pressure injection by the
receiver 18, another possible option is to provide a second
second-stage injection tube 19 and an economizer heat exchanger 20
and to perform intermediate pressure injection through the
economizer heat exchanger 20.
[0095] For example, as shown in FIG. 10, a refrigerant circuit 110
can be used which is provided with a second second-stage injection
tube 19 and an economizer heat exchanger 20 instead of the first
second-stage injection tube 18c in the embodiment described
above.
[0096] The second second-stage injection tube 19 has a function for
branching off and returning the refrigerant cooled in the heat
source-side heat exchanger 4 or the usage-side heat exchanger 6 to
the second-stage compression element 2d of the compression
mechanism 2. In the present modification, the second second-stage
injection tube 19 is provided so as to branch off refrigerant
flowing through the receiver inlet tube 18a and return the
refrigerant to the second-stage compression element 2d. More
specifically, the second second-stage injection tube 19 is provided
so as to branch off and return the refrigerant from a position
(i.e., between the heat source-side heat exchanger 4 and the first
expansion mechanism 5a when the switching mechanism 3 is in the
cooling operation state, or between the usage-side heat exchanger 6
and the first expansion mechanism 5a when the switching mechanism 3
is in the heating operation state) on the upstream side of the
first expansion mechanism 5a of the receiver inlet tube 18a to a
position on the downstream side of the intercooler 7 of the
intermediate refrigerant tube 8. The second second-stage injection
tube 19 is provided with a second second-stage injection valve 19a
whose opening degree can be controlled. The second second-stage
injection valve 19a is an electrically driven expansion valve in
the present modification.
[0097] The economizer heat exchanger 20 is a heat exchanger for
carrying out heat exchange between the refrigerant from which heat
has been released in the heat source-side heat exchanger 4 or the
usage-side heat exchanger 6 and the refrigerant that flows through
the second second-stage injection tube 19 (more specifically, the
refrigerant that has been depressurized to near intermediate
pressure in the second second-stage injection valve 19a). In the
present modification, the economizer heat exchanger 20 is provided
so as to perform heat exchange between the refrigerant flowing
through a position in the receiver inlet tube 18a upstream of the
first expansion mechanism 5a (i.e., between the heat source-side
heat exchanger 4 and the first expansion mechanism 5a when the
switching mechanism 3 is in the cooling operation state, or between
the usage-side heat exchanger 6 and the first expansion mechanism
5a when the switching mechanism 3 is in the heating operation
state) and the refrigerant flowing through the second second-stage
injection tube 19, and the economizer heat exchanger 20 has a
passage through which both refrigerants flow against each other. In
the present modification, the economizer heat exchanger 20 is
provided upstream of the second second-stage injection tube 19 of
the receiver inlet tube 18a. Therefore, the refrigerant from which
heat has been released in the heat source-side heat exchanger 4 or
usage-side heat exchanger 6 is branched off in the receiver inlet
tube 18a into the second second-stage injection tube 19 before
undergoing heat exchange in the economizer heat exchanger 20, and
heat exchange is then conducted in the economizer heat exchanger 20
with the refrigerant flowing through the second second-stage
injection tube 19.
[0098] Furthermore, the air-conditioning apparatus 1 of the present
modification is provided with various sensors. Specifically, the
intermediate refrigerant tube 8 or the compression mechanism 2 is
provided with an intermediate pressure sensor 54 for detecting the
pressure of the refrigerant that flows through the intermediate
refrigerant tube 8. The outlet of the second second-stage injection
tube 19 side of the economizer heat exchanger 20 is provided with
an economizer outlet temperature sensor 55 for detecting the
temperature of the refrigerant at the outlet of the second
second-stage injection tube 19 side of the economizer heat
exchanger 20.
[0099] Next, the action of the air-conditioning apparatus 1 will be
described using FIGS. 6 and 10 through 17. FIG. 11 is a diagram
showing the flow of refrigerant within the air-conditioning
apparatus 1 during the air-cooling operation, FIG. 12 is a
pressure-enthalpy graph representing the refrigeration cycle during
the air-cooling operation, FIG. 13 is a temperature-entropy graph
representing the refrigeration cycle during the air-cooling
operation, FIG. 14 is a diagram showing the flow of refrigerant
within the air-conditioning apparatus 1 during the air-warming
operation, FIG. 15 is a diagram showing the flow of refrigerant
within the air-conditioning apparatus 1 at the start of the
defrosting operation, FIG. 16 is a pressure-enthalpy graph
representing the refrigeration cycle during the defrosting
operation, and FIG. 17 is a temperature-entropy graph representing
the refrigeration cycle during the defrosting operation. Operation
control in the air-cooling operation, the air-warming operation,
and the defrosting operation described hereinbelow is performed by
the aforementioned controller (not shown) in the present
embodiment. In the following description, the term "high pressure"
means a high pressure in the refrigeration cycle (specifically, the
pressure at points D, D', E, and H in FIGS. 12, 13, 16, and 17),
the term "low pressure" means a low pressure in the refrigeration
cycle (specifically, the pressure at points A, F, W in FIGS. 12,
13, 16, and 17), and the term "intermediate pressure" means an
intermediate pressure in the refrigeration cycle (specifically, the
pressure at points B, G, G', J, and K in FIGS. 12, 13, 16, and
17).
[0100] <Air-Cooling Operation>
[0101] During the air-cooling operation, the switching mechanism 3
is brought to the cooling operation state shown by the solid lines
in FIGS. 10 and 11. The opening degrees of the first expansion
mechanism 5a and the second expansion mechanism 5b are adjusted.
Furthermore, the opening degree of the second second-stage
injection valve 19a is also adjusted. More specifically, in the
present modification, so-called superheat degree control is
performed wherein the opening degree of the second second-stage
injection valve 19a is adjusted so that a target value is achieved
in the degree of superheat of the refrigerant at the outlet in the
second second-stage injection tube 19 side of the economizer heat
exchanger 20. In the present modification, the degree of superheat
of the refrigerant at the outlet in the second second-stage
injection tube 19 side of the economizer heat exchanger 20 is
obtained by converting the intermediate pressure detected by the
intermediate pressure sensor 54 to a saturation temperature and
subtracting this refrigerant saturation temperature value from the
refrigerant temperature detected by the economizer outlet
temperature sensor 55. Though not used in the present embodiment,
another possible option is to provide a temperature sensor to the
inlet in the second second-stage injection tube 19 side of the
economizer heat exchanger 20, and to obtain the degree of superheat
of the refrigerant at the outlet in the second second-stage
injection tube 19 side of the economizer heat exchanger 20 by
subtracting the refrigerant temperature detected by this
temperature sensor from the refrigerant temperature detected by the
economizer outlet temperature sensor 55. The opening degree
adjustment of the second second-stage injection valve 19a is not
limited to superheat degree control; the opening degree may be
opened to a predetermined opening degree in accordance with the
flow rate of refrigerant circulating in the refrigerant circuit 110
or other factors, for example.
[0102] When the refrigerant circuit 110 is in this state,
low-pressure refrigerant (refer to point A in FIGS. 10 through 13)
is drawn into the compression mechanism 2 through the intake tube
2a, and after the refrigerant is first compressed by the
compression element 2c to an intermediate pressure, the refrigerant
is discharged to the intermediate refrigerant tube 8 (refer to
point A in FIGS. 10 through 13). The intermediate-pressure
refrigerant discharged from the first-stage compression element 2c
is cooled (refer to point G in FIGS. 10 through 13) by being mixed
with refrigerant being returned from the second second-stage
injection tube 19 to the second-stage compression element 2d (refer
to point K in FIGS. 10 through 13). Next, having been mixed with
the refrigerant returning from the second second-stage injection
tube 19 (i.e., intermediate pressure injection is carried out by
the economizer heat exchanger 20), the intermediate-pressure
refrigerant is drawn into and further compressed in the compression
element 2d connected to the second-stage side of the compression
element 2c, and the refrigerant is discharged from the compression
mechanism 2 to the discharge tube 2b (refer to point D in FIGS. 10
through 13). The high-pressure refrigerant discharged from the
compression mechanism 2 is compressed by the two-stage compression
action of the compression elements 2c, 2d to a pressure exceeding a
critical pressure (i.e., the critical pressure Pcp at the critical
point CP shown in FIG. 12). The high-pressure refrigerant
discharged from the compression mechanism 2 flows into the oil
separator 41a constituting the oil separation mechanism 41, and the
accompanying refrigeration oil is separated. The refrigeration oil
separated from the high-pressure refrigerant in the oil separator
41a flows into the oil return tube 41b constituting the oil
separation mechanism 41 wherein it is depressurized by the
depressurization mechanism 41c provided to the oil return tube 41b,
and the oil is then returned to the intake tube 2a of the
compression mechanism 2 and drawn once more into the compression
mechanism 2. Next, having been separated from the refrigeration oil
in the oil separation mechanism 41, the high-pressure refrigerant
is passed through the non-return mechanism 42 and the switching
mechanism 3, and is fed to the heat source-side heat exchanger 4
functioning as a refrigerant radiator. The high-pressure
refrigerant fed to the heat source-side heat exchanger 4 is cooled
in the heat source-side heat exchanger 4 by heat exchange with air
as a cooling source supplied by the heat source-side fan 40 (refer
to point E in FIGS. 10 through 13). The high-pressure refrigerant
cooled in the heat source-side heat exchanger 4 flows through the
inlet non-return valve 17a of the bridge circuit 17 into the
receiver inlet tube 18a, and some of the refrigerant is branched
off into the second second-stage injection tube 19. The refrigerant
flowing through the second second-stage injection tube 19 is
depressurized to a nearly intermediate pressure in the second
second-stage injection valve 19a and is then fed to the economizer
heat exchanger 20 (refer to point J in FIGS. 10 through 13). After
being branched off into the second second-stage injection tube 19,
the refrigerant flows into the economizer heat exchanger 20, where
it is cooled by heat exchange with the refrigerant flowing through
the second second-stage injection tube 19 (refer to point H in
FIGS. 10 through 13). The refrigerant flowing through the second
second-stage injection tube 19 is heated by heat exchange with the
high-pressure refrigerant cooled in the heat source-side heat
exchanger 4 as a radiator (refer to point K in FIGS. 10 through
13), and is mixed with the intermediate-pressure refrigerant
discharged from the first-stage compression element 2c as described
above. The high-pressure refrigerant cooled in the economizer heat
exchanger 20 is depressurized to a nearly saturated pressure by the
first expansion mechanism 5a and is temporarily retained in the
receiver 18 (refer to point I in FIGS. 10 and 11). The refrigerant
retained in the receiver 18 is fed to the receiver outlet tube 18b
and is depressurized by the second expansion mechanism 5b to become
a low-pressure gas-liquid two-phase refrigerant, and is then fed
through the outlet non-return valve 17c of the bridge circuit 17 to
the usage-side heat exchanger 6 functioning as a refrigerant
evaporator (refer to point F in FIGS. 10 through 13). The
low-pressure gas-liquid two-phase refrigerant fed to the usage-side
heat exchanger 6 is heated by heat exchange with water or air as a
heating source, and the refrigerant is evaporated as a result
(refer to point W in FIGS. 10 through 13). The low-pressure
refrigerant heated in the usage-side heat exchanger 6 is then drawn
once more into the compression mechanism 2 via the switching
mechanism 3 (refer to point A in FIGS. 10 through 13). In this
manner the air-cooling operation is performed.
[0103] Thus, in the air-conditioning apparatus 1 of the present
modification, the second second-stage injection tube 19 and the
economizer heat exchanger 20 are provided to branch off the
refrigerant whose heat has been radiated in the heat source-side
heat exchanger 4 and return the refrigerant to the second-stage
compression element 2d, and the temperature of the refrigerant
drawn into the second-stage compression element 2d can therefore be
kept even lower without heat being radiated to the exterior (refer
to points C and G in FIG. 13), similar to the embodiment described
above. The temperature of the refrigerant discharged from the
compression mechanism 2 is thereby minimized (refer to points D and
D' in FIG. 13), and it is possible to further reduce the heat
radiation loss equivalent to the area enclosed by connecting points
C, D', D, and G in FIG. 13 more than in cases in which the second
second-stage injection tube 19 and the economizer heat exchanger 20
are not provided; therefore, the power consumption of the
compression mechanism 2 can be further reduced, and operating
efficiency can be further improved.
[0104] Moreover, the intermediate pressure injection by the
economizer heat exchanger 20 used in the present modification is
more beneficial than the intermediate pressure injection by the
receiver 18 as a gas-liquid separator used in the embodiment
described above, because in a refrigerant circuit configuration in
which no significant depressurizing operations are performed except
for the first expansion mechanism 5a as a heat source-side
expansion mechanism after the refrigerant is cooled in the heat
source-side heat exchanger 4 as a radiator and the pressure
difference from the high pressure in the refrigeration cycle to the
nearly intermediate pressure of the refrigeration cycle can be
used, the quantity of heat exchanged in the economizer heat
exchanger 20 can be increased, and the flow rate of the refrigerant
passing through the second second-stage injection tube 19 and
returning to the second-stage compression element 2d can thereby be
increased. Particularly in cases in which refrigerant that operates
in the supercritical range is used as in the present modification,
the intermediate pressure injection by the economizer heat
exchanger 20 is extremely beneficial because there is an extremely
large pressure difference from the high pressure in the
refrigeration cycle to the nearly intermediate pressure of the
refrigeration cycle.
[0105] <Air-Warming Operation>
[0106] During the air-warming operation, the switching mechanism 3
is brought to the heating operation state shown by the dashed lines
in FIGS. 1 and 5. The opening degrees of the first expansion
mechanism 5a and the second expansion mechanism 5b are adjusted.
Furthermore, the opening degree of the second second-stage
injection valve 19a is adjusted in the same manner as in the
air-cooling operation.
[0107] When the refrigerant circuit 110 is in this state,
low-pressure refrigerant (refer to point A in FIGS. 10 and 12
through 14) is drawn into the compression mechanism 2 through the
intake tube 2a, and after the refrigerant is first compressed by
the compression element 2c to an intermediate pressure, the
refrigerant is discharged to the intermediate refrigerant tube 8
(refer to point B in FIGS. 10 and 12 through 14). This
intermediate-pressure refrigerant discharged from the first-stage
compression element 2c is cooled (refer to point G in FIGS. 10 and
12 through 14) by mixing with the refrigerant returned from the
second second-stage injection tube 19 to the second-stage
compression element 2d (refer to point K in FIGS. 10 and 12 through
14). Next, having been mixed with the refrigerant returning from
the second second-stage injection tube 19 (i.e., intermediate
pressure injection is carried out by the economizer heat exchanger
20), the intermediate-pressure refrigerant is drawn into and
further compressed in the compression element 2d connected to the
second-stage side of the compression element 2c, and the
refrigerant is discharged from the compression mechanism 2 to the
discharge tube 2b (refer to point D in FIGS. 10 and 12 through 14).
The high-pressure refrigerant discharged from the compression
mechanism 2 is compressed by the two-stage compression action of
the compression elements 2c, 2d to a pressure exceeding a critical
pressure (i.e., the critical pressure Pcp at the critical point CP
shown in FIG. 12), similar to the air-cooling operation. The
high-pressure refrigerant discharged from the compression mechanism
2 flows into the oil separator 41a constituting the oil separation
mechanism 41, and the accompanying refrigeration oil is separated.
The refrigeration oil separated from the high-pressure refrigerant
in the oil separator 41a flows into the oil return tube 41b
constituting the oil separation mechanism 41 wherein it is
depressurized by the depressurization mechanism 41c provided to the
oil return tube 41b, and the oil is then returned to the intake
tube 2a of the compression mechanism 2 and drawn once more into the
compression mechanism 2. Next, having been separated from the
refrigeration oil in the oil separation mechanism 41, the
high-pressure refrigerant is passed through the non-return
mechanism 42 and the switching mechanism 3, fed to the usage-side
heat exchanger 6 functioning as a radiator of refrigerant, and
cooled by heat exchange with the water and/or air as a cooling
source (refer to point F in FIGS. 10 and 14, and read point E as
point F in FIGS. 12 and 13). The high-pressure refrigerant cooled
in the usage-side heat exchanger 6 flows through the inlet
non-return valve 17b of the bridge circuit 17 into the receiver
inlet tube 18a, and some of the refrigerant is branched off into
the second second-stage injection tube 19. The refrigerant flowing
through the second second-stage injection tube 19 is depressurized
to a nearly intermediate pressure in the second second-stage
injection valve 19a and is then fed to the economizer heat
exchanger 20 (refer to point J in FIGS. 10 and 12 through 14). The
refrigerant after being branched off to the second second-stage
injection tube 19 then flows into the economizer heat exchanger 20,
where it is cooled by heat exchange with the refrigerant flowing
through the second second-stage injection tube 19 (refer to point H
in FIGS. 10 and 12 through 14). The refrigerant flowing through the
second second-stage injection tube 19 is heated by heat exchange
with the high-pressure refrigerant cooled in the usage-side heat
exchanger 6 functioning as a radiator (refer to point K in FIGS. 10
and 12 through 14), and is mixed with the intermediate-pressure
refrigerant discharged from the first-stage compression element 2c
as described above. The high-pressure refrigerant cooled in the
economizer heat exchanger 20 is depressurized to a nearly saturated
pressure by the first expansion mechanism 5a and is temporarily
retained in the receiver 18 (refer to point I in FIGS. 10 and 14).
The refrigerant retained in the receiver 18 is fed to the receiver
outlet tube 18b where it is depressurized by the second expansion
mechanism 5b to a low-pressure gas-liquid two-phase refrigerant,
which is fed through the outlet non-return valve 17d of the bridge
circuit 17 to the heat source-side heat exchanger 4 functioning as
an evaporator of refrigerant (refer to point E in FIGS. 10 and 14,
and read point F as point E in FIGS. 12 and 13). The low-pressure
gas-liquid two-phase refrigerant fed to the heat source-side heat
exchanger 4 is then heated and evaporated in the heat source-side
heat exchanger 4 by heat exchange with the air as a heating source
supplied by the heat source-side fan 40 (refer to point A in FIGS.
10 and 12 through 14). The low-pressure refrigerant heated and
evaporated in the heat source-side heat exchanger 4 is then drawn
once more into the compression mechanism 2 via the switching
mechanism 3. In this manner the air-warming operation is
performed.
[0108] Thus, in the air-conditioning apparatus 1 of the present
modification, similar to the embodiment described above, the second
second-stage injection tube 19 and economizer heat exchanger 20 are
provided to branch off the refrigerant whose heat has been radiated
in the usage-side heat exchanger 6 and return the refrigerant to
the second-stage compression element 2d similar to the air-cooling
operation; therefore, the temperature of the refrigerant drawn into
the second-stage compression element 2d can be further minimized
without heat being radiated to the exterior (refer to points C and
G FIG. 13). Thereby, the temperature of the refrigerant discharged
from the compression mechanism 2 is kept lower (refer to points D
and D' in FIG. 13), and the heat radiation loss equivalent to the
area enclosed by connecting points C, D', D, and G in FIG. 13 can
be further reduced in comparison with cases in which the second
second-stage injection tube 19 and the economizer heat exchanger 20
are not provided; therefore, the power consumption of the
compression mechanism 2 can be further reduced and operating
efficiency can be further improved.
[0109] Moreover, the intermediate pressure injection by the
economizer heat exchanger 20 used in the present modification is
more beneficial than the intermediate pressure injection by the
receiver 18 as a gas-liquid separator used in the embodiment
described above, similar to the air-cooling operation, because in a
refrigerant circuit configuration in which no significant
depressurizing operations are performed except for the first
expansion mechanism 5a as a heat source-side expansion mechanism
after the refrigerant is cooled in the usage-side heat exchanger 6
as a radiator and the pressure difference from the high pressure in
the refrigeration cycle to the nearly intermediate pressure of the
refrigeration cycle can be used, the quantity of heat exchanged in
the economizer heat exchanger 20 can be increased, and the flow
rate of the refrigerant passing through the second second-stage
injection tube 19 and returning to the second-stage compression
element 2d can thereby be increased. Particularly in cases in which
refrigerant that operates in the supercritical range is used as in
the present modification, the intermediate pressure injection by
the economizer heat exchanger 20 is extremely beneficial because
there is an extremely large pressure difference from the high
pressure in the refrigeration cycle to the nearly intermediate
pressure of the refrigeration cycle.
[0110] <Defrosting Operation>
[0111] In the present modification, the second second-stage
injection tube 19 and the economizer heat exchanger 20 are provided
and intermediate pressure injection by the economizer heat
exchanger 20 is used, which is different from the embodiment
described above in which intermediate pressure injection by the
receiver 18 as a gas-liquid separator is used, but the modification
and embodiment are similar in having the objectives of reducing the
temperature on the usage side when the reverse cycle defrosting
operation is performed and/or utilizing the stored heat in the
refrigerant tube 1d or the like between the usage-side heat
exchanger 6 and the switching mechanism 3.
[0112] In view of this, in the present modification, in step S2
shown in FIG. 6, a state is created in which intermediate pressure
injection by the economizer heat exchanger 20 is not used (i.e.,
refrigerant is prevented from returning to the second-stage
compression element 2d through the second second-stage injection
tube 19), while the switching mechanism 3 is switched from the
heating operation state to the cooling operation state and the
reverse cycle defrosting operation is performed (refer to the
refrigeration cycle shown by the solid lines in FIGS. 15, 16, and
17).
[0113] Thereby, as in the embodiment described above, during at
least the beginning of the reverse cycle defrosting operation,
which takes place from the start of the defrosting operation until
the amount of stored heat in the refrigerant tube 1d or the like
between the usage-side heat exchanger 6 and the switching mechanism
3 decreases and a state arises in which the effect of improving the
defrosting capacity is not sufficiently achieved, circulation is
performed in the refrigerant circuit 110 in which the refrigerant
discharged from the compression mechanism 2 is actively drawn into
the compression mechanism 2 through the usage-side heat exchanger
6, and the low-pressure refrigerant heated and evaporated in the
usage-side heat exchanger 6 (refer to point W in the lines
indicating the refrigeration cycle shown by the solid lines in
FIGS. 16 and 17) is therefore drawn into the compression mechanism
2 via the switching mechanism 3 (refer to point A in the lines
indicating the refrigeration cycle shown by the solid lines in
FIGS. 16 and 17) after being heated by the refrigerant tube 1d or
the like. Specifically, sufficient utilization is made of the heat
stored in the refrigerant tube 1d or the like between the
usage-side heat exchanger 6 and the switching mechanism 3 by the
air-warming operation that had been performed until immediately
before the defrosting operation was performed. The low-pressure
refrigerant in the refrigeration cycle drawn into the compression
mechanism 2 thereby increases in temperature (refer to point B in
the lines indicating the refrigeration cycle shown by the solid
lines in FIG. 17) and the refrigerant is prevented from returning
to the second-stage compression element 2d through the second
second-stage injection tube 19, thereby minimizing the decrease in
the temperature of the intermediate-pressure refrigerant in the
refrigeration cycle drawn into the second-stage compression element
2d (refer to points B and G in the lines indicating the
refrigeration cycle shown by the solid lines in FIG. 17).
Therefore, the temperature of the high-pressure refrigerant in the
refrigeration cycle discharged from the compression mechanism 2 can
be greatly increased (refer to point D in the lines indicating the
refrigeration cycle shown by the solid lines in FIG. 17), and the
defrosting capacity per unit flow rate of the refrigerant during
the reverse cycle defrosting operation can be improved.
[0114] In the present modification, in step S5 shown in FIG. 6, a
state is created in which intermediate pressure injection by the
economizer heat exchanger 20 is used (i.e., the refrigerant returns
to the second-stage compression element 2d through the second
second-stage injection tube 19), similar to the air-cooling
operation, thereby switching to the reverse cycle defrosting
operation in which the flow rate of the refrigerant flowing through
the usage-side heat exchanger 6 is reduced (refer to the
refrigeration cycle shown by the dashed lines in FIGS. 11, 16, and
17). Opening degree control is herein performed so that the opening
degree of the second second-stage injection valve 19a is greater
than the opening degree of the second second-stage injection valve
19a during the air-cooling operation and/or the air-warming
operation. In a case in which the opening degree of the second
second-stage injection valve 19a when fully close is 0%, the
opening degree when fully open is 100%, and the second second-stage
injection valve 19a is controlled during the air-cooling operation
and air-warming operation within the opening-degree range of 50% or
less, for example; the second second-stage injection valve 19a in
step S2 is controlled so that the opening degree increases up to
about 70%, and this opening degree is kept constant until it is
determined in step S3 that defrosting of the heat source-side heat
exchanger 4 is complete.
[0115] Thereby, as in the embodiment described above, after the
amount of stored heat in the refrigerant tube 1 d or the like
between the usage-side heat exchanger 6 and the switching mechanism
3 decreases and a state has arisen in which the effect of improving
the defrosting capacity is not sufficiently achieved, the
temperature decrease on the usage side is minimized in the
refrigerant circuit 110 because the circulation through the
usage-side heat exchanger 6 into the compression mechanism 2 no
longer continues excessively. Moreover, the refrigerant is made to
return to the second-stage compression element 2d through the
second second-stage injection tube 19, whereby the temperature of
the intermediate-pressure refrigerant in the refrigeration cycle
drawn into the second-stage compression element 2d decreases (refer
to points B and G in the lines indicating the refrigeration cycle
shown by the dashed lines in FIG. 17) and the temperature of the
refrigerant discharged from the compression mechanism 2 decreases
(refer to point D in the lines indicating the refrigeration cycle
shown by the dashed lines in FIG. 17). The defrosting capacity per
unit flow rate of the refrigerant during the reverse cycle
defrosting operation thereby decreases, but since the flow rate of
the refrigerant discharged from the second-stage compression
element 2d increases, the defrosting capacity can be guaranteed as
much as is possible. Furthermore, in the present modification,
since it is possible to control the flow rate of the refrigerant
returned to the second-stage compression element 2d through the
second second-stage injection tube 19 by controlling the opening
degree of the second second-stage injection valve 19a, the flow
rate of the refrigerant returning to the second-stage compression
element 2d can be greatly increased by performing opening degree
control so that the opening degree of the second second-stage
injection valve 19a is greater than during the air-cooling
operation and/or the air-warming operation as described above, for
example, whereby the flow rate of the refrigerant flowing through
the heat source-side heat exchanger 4 can be further increased
while further reducing the flow rate of the refrigerant flowing
through the usage-side heat exchanger 6.
[0116] Thus, in the present modification, the same effects as those
of the defrosting operation of the embodiment described above are
achieved, and since intermediate pressure injection by the
economizer heat exchanger 20 is used, the effect of minimizing the
temperature decrease on the usage side can be improved more so than
in the case of using intermediate pressure injection by the
receiver 18 in the embodiment described above.
[0117] The other steps S1, S3, S4, S6, and S7 of the defrosting
operation in the present modification are identical to those of the
defrosting operation in the embodiment described above, and are
therefore not described herein.
(4) Modification 2
[0118] In the refrigerant circuits 10 and 110 (FIGS. 1 and 10) in
the embodiment and Modification 1 described above, intermediate
pressure injection by the receiver 18 as a gas-liquid separator or
intermediate pressure injection by the economizer heat exchanger 20
is performed, whereby the temperature of the refrigerant discharged
from the second-stage compression element 2d is reduced, the power
consumption of the compression mechanism 2 is reduced, and
operating efficiency is improved, but in addition to this
configuration, the intermediate refrigerant tube 8 for drawing the
refrigerant discharged from the first-stage compression element 2c
into the second-stage compression element 2d may also be provided
with an intermediate heat exchanger 7 that functions as a cooler of
refrigerant discharged from the first-stage compression element 2c
and drawn into the second-stage compression element 2d.
[0119] For example, the refrigerant circuit 110 of Modification 1
described above can be replaced by a refrigerant circuit 210
provided with the intermediate heat exchanger 7 and an intermediate
heat exchanger bypass tube 9, as shown in FIG. 18.
[0120] The intermediate heat exchanger 7 herein is a heat exchanger
which is provided to the intermediate refrigerant tube 8 and which
functions as a cooler of refrigerant discharged from the
first-stage compression element 2c and drawn into the compression
element 2d, and a fin-and-tube heat exchanger is used in the
present modification. The intermediate heat exchanger 7 is
integrated with the heat source-side heat exchanger 4. More
specifically, the intermediate heat exchanger 7 is integrated by
sharing heat transfer fins with the heat source-side heat exchanger
4. In the present modification, the air as the heat source is
supplied by the heat source-side fan 40 for supplying air to the
heat source-side heat exchanger 4. Specifically, the heat
source-side fan 40 is designed so as to supply air as a heat source
to both the heat source-side heat exchanger 4 and the intermediate
heat exchanger 7.
[0121] An intermediate heat exchanger bypass tube 9 is connected to
the intermediate refrigerant tube 8 so as to bypass the
intermediate heat exchanger 7. This intermediate heat exchanger
bypass tube 9 is a refrigerant tube for limiting the flow rate of
refrigerant flowing through the intermediate heat exchanger 7. The
intermediate heat exchanger bypass tube 9 is provided with an
intermediate heat exchanger bypass on/off valve 11. The
intermediate heat exchanger bypass on/off valve 11 is an
electromagnetic valve in the present modification. In the present
modification, the intermediate heat exchanger bypass on/off valve
11 essentially is controlled so as to close when the switching
mechanism 3 is set for the cooling operation state, and to open
when the switching mechanism 3 is set for the heating operation
state. In other words, excluding cases in which temporary
operations such as the hereinafter-described defrosting operation
are performed, the intermediate heat exchanger bypass on/off valve
11 essentially is controlled so as to close when the air-cooling
operation is performed and to open when the air-warming operation
is performed.
[0122] In the intermediate refrigerant tube 8, an intermediate heat
exchanger on/off valve 12 is provided to the portion extending from
the connection with the end of the intermediate heat exchanger
bypass tube 9 near the first-stage compression element 2c to the
end of the intermediate heat exchanger 7 near the first-stage
compression element 2c. This intermediate heat exchanger on/off
valve 12 is a mechanism for limiting the flow rate of refrigerant
flowing through the intermediate heat exchanger 7. The intermediate
heat exchanger on/off valve 12 is an electromagnetic valve in the
present modification. Excluding cases in which temporary operations
such as the hereinafter-described defrosting operation are
performed, in the present modification the intermediate heat
exchanger on/off valve 12 is essentially controlled so as to open
when the switching mechanism 3 is set for the cooling operation
state, and to close when the switching mechanism 3 is set for the
heating operation state. In other words, the intermediate heat
exchanger on/off valve 12 is controlled so as to open when the
air-cooling operation is performed and close when the air-warming
operation is performed.
[0123] The intermediate refrigerant tube 8 is also provided with a
non-return mechanism 15 for allowing refrigerant to flow from the
discharge side of the first-stage compression element 2c to the
intake side of the second-stage compression element 2d and for
blocking the refrigerant from flowing from the intake side of the
second-stage compression element 2d to the discharge side of the
first-stage compression element 2c. The non-return mechanism 15 is
a non-return valve in the present modification. In the present
modification, the non-return mechanism 15 is provided to the
portion of the intermediate refrigerant tube 8 extending from the
end of the intermediate heat exchanger 7 near the second-stage
compression element 2d to the connection with the end of the
intermediate heat exchanger bypass tube 9 near the second-stage
compression element 2d.
[0124] Furthermore, an intermediate heat exchange outlet
temperature sensor 52 for detecting the temperature of the
refrigerant in the outlet of the intermediate heat exchanger 7 is
provided to the outlet of the intermediate heat exchanger 7.
[0125] Next, the action of the air-conditioning apparatus 1 will be
described using FIGS. 6, 12, 13 and 16 through 27. FIG. 19 is a
diagram showing the flow of refrigerant within the air-conditioning
apparatus 1 during the air-cooling operation, FIG. 20 is a
pressure-enthalpy graph representing the refrigeration cycle during
the air-cooling operation, FIG. 21 is a temperature-entropy graph
representing the refrigeration cycle during the air-cooling
operation, FIG. 22 is a diagram showing the flow of refrigerant
within the air-conditioning apparatus 1 during the air-warming
operation, FIG. 23 is a diagram showing the flow of refrigerant
within the air-conditioning apparatus 1 at the start of the
defrosting operation, FIG. 24 is a diagram showing the flow of
refrigerant within the air-conditioning apparatus 1 in the
defrosting operation after defrosting of the intermediate heat
exchanger 7 has concluded, FIG. 25 is a diagram showing the flow of
refrigerant within the air-conditioning apparatus 1 in the
defrosting operation after defrosting of the intermediate heat
exchanger 7 and utilization of the stored heat have concluded, FIG.
26 is a pressure-enthalpy graph representing the refrigeration
cycle during the defrosting operation, and FIG. 27 is a
temperature-entropy graph representing the refrigeration cycle
during the defrosting operation. Operation control in the
air-cooling operation, the air-warming operation, and the
defrosting operation described hereinbelow is performed by the
aforementioned controller (not shown) in the present embodiment. In
the following description, the term "high pressure" means a high
pressure in the refrigeration cycle (specifically, the pressure at
points D, D', E, and H in FIGS. 20, 21, 12, 13, 16, 17, 26, and
27), the term "low pressure" means a low pressure in the
refrigeration cycle (specifically, the pressure at points A, F, Win
FIGS. 20, 21, 12, 13, 16, 17, 26, and 27), and the term
"intermediate pressure" means an intermediate pressure in the
refrigeration cycle (specifically, the pressure at points B, C, C',
G, G', J, and K in FIGS. 20, 21, 12, 13, 16, 17, 26, and 27).
[0126] <Air-Cooling Operation>
[0127] During the air-cooling operation, the switching mechanism 3
is brought to the cooling operation state shown by the solid lines
in FIGS. 18 and 19. The opening degrees of the first expansion
mechanism 5a and the second expansion mechanism 5b are adjusted.
Since the switching mechanism 3 is in the cooling operation state,
the intermediate heat exchanger on/off valve 12 of the intermediate
refrigerant tube 8 is opened and the intermediate heat exchanger
bypass on/off valve 11 of the intermediate heat exchanger bypass
tube 9 is closed, thereby creating a state in which the
intermediate heat exchanger 7 functions as a cooler. Furthermore,
the opening degree of the second second-stage injection valve 19a
is adjusted in the same manner as in Modification 1 described
above.
[0128] When the refrigerant circuit 210 is in this state,
low-pressure refrigerant (refer to point A in FIGS. 18 through 21)
is drawn into the compression mechanism 2 through the intake tube
2a, and after the refrigerant is first compressed by the
compression element 2c to an intermediate pressure, the refrigerant
is discharged to the intermediate refrigerant tube 8 (refer to
point A in FIGS. 18 through 21). The intermediate-pressure
refrigerant discharged from the first-stage compression element 2c
is cooled in the intermediate heat exchanger 7 by undergoing heat
exchange with the air as a cooling source supplied by the heat
source-side fan 40 (refer to point C in FIGS. 18 through 21). The
refrigerant cooled in the intermediate heat exchanger 7 is further
cooled (refer to point G in FIGS. 18 through 21) by being mixed
with refrigerant being returned from the second second-stage
injection tube 19 to the second-stage compression element 2d (refer
to point K in FIGS. 18 through 21). Next, having been mixed with
the refrigerant returning from the second second-stage injection
tube 19 (i.e., intermediate pressure injection is carried out by
the economizer heat exchanger 20), the intermediate-pressure
refrigerant is drawn into and further compressed in the compression
element 2d connected to the second-stage side of the compression
element 2c, and the refrigerant is discharged from the compression
mechanism 2 to the discharge tube 2b (refer to point D in FIGS. 18
through 21). The high-pressure refrigerant discharged from the
compression mechanism 2 is compressed by the two-stage compression
action of the compression elements 2c, 2d to a pressure exceeding a
critical pressure (i.e., the critical pressure Pcp at the critical
point CP shown in FIG. 20). The high-pressure refrigerant
discharged from the compression mechanism 2 flows into the oil
separator 41 a constituting the oil separation mechanism 41, and
the accompanying refrigeration oil is separated. The refrigeration
oil separated from the high-pressure refrigerant in the oil
separator 41a flows into the oil return tube 41b constituting the
oil separation mechanism 41 wherein it is depressurized by the
depressurization mechanism 41c provided to the oil return tube 41b,
and the oil is then returned to the intake tube 2a of the
compression mechanism 2 and drawn once more into the compression
mechanism 2. Next, having been separated from the refrigeration oil
in the oil separation mechanism 41, the high-pressure refrigerant
is passed through the non-return mechanism 42 and the switching
mechanism 3, and is fed to the heat source-side heat exchanger 4
functioning as a refrigerant radiator. The high-pressure
refrigerant fed to the heat source-side heat exchanger 4 is cooled
in the heat source-side heat exchanger 4 by heat exchange with air
as a cooling source supplied by the heat source-side fan 40 (refer
to point E in FIGS. 18 through 21). The high-pressure refrigerant
cooled in the heat source-side heat exchanger 4 flows through the
inlet non-return valve 17a of the bridge circuit 17 into the
receiver inlet tube 18a, and some of the refrigerant is branched
off into the second second-stage injection tube 19. The refrigerant
flowing through the second second-stage injection tube 19 is
depressurized to a nearly intermediate pressure in the second
second-stage injection valve 19a and is then fed to the economizer
heat exchanger 20 (refer to point J in FIGS. 18 through 21). The
refrigerant after being branched off into the second second-stage
injection tube 19 then flows into the economizer heat exchanger 20,
where it is cooled by heat exchange with the refrigerant flowing
through the second second-stage injection tube 19 (refer to point H
in FIGS. 18 through 21). The refrigerant flowing through the second
second-stage injection tube 19 is heated by heat exchange with the
high-pressure refrigerant cooled in the heat source-side heat
exchanger 4 as a radiator (refer to point K in FIGS. 18 through
21), and is mixed with the intermediate-pressure refrigerant
discharged from the first-stage compression element 2c as described
above. The high-pressure refrigerant cooled in the economizer heat
exchanger 20 is depressurized to a nearly saturated pressure by the
first expansion mechanism 5a and is temporarily retained in the
receiver 18 (refer to point I in FIGS. 18 and 19). The refrigerant
retained in the receiver 18 is fed to the receiver outlet tube 18b
and is depressurized by the second expansion mechanism 5b to become
a low-pressure gas-liquid two-phase refrigerant, and is then fed
through the outlet non-return valve 17c of the bridge circuit 17 to
the usage-side heat exchanger 6 functioning as a refrigerant
evaporator (refer to point F in FIGS. 18 through 21). The
low-pressure gas-liquid two-phase refrigerant fed to the usage-side
heat exchanger 6 is heated by heat exchange with water or air as a
heating source, and the refrigerant is evaporated as a result
(refer to point W in FIGS. 18 through 21). The low-pressure
refrigerant heated in the usage-side heat exchanger 6 is then drawn
once more into the compression mechanism 2 via the switching
mechanism 3 (refer to point A in FIGS. 18 through 21). In this
manner the air-cooling operation is performed.
[0129] Thus, in the air-conditioning apparatus 1 of the present
modification, in addition to the configuration of the intermediate
pressure injection (as performed by the second second-stage
injection tube 19 and the economizer heat exchanger 20 herein), the
intermediate heat exchanger 7 is provided to the intermediate
refrigerant tube 8 for drawing the refrigerant discharged from the
compression element 2c into the compression element 2d, and in the
air-cooling operation, the intermediate heat exchanger on/off valve
12 is opened and the intermediate heat exchanger bypass on/off
valve 11 of the intermediate heat exchanger bypass tube 9 is
closed, thereby bringing the intermediate heat exchanger 7 to a
state of functioning as a cooler. Therefore, the temperature of the
refrigerant drawn into the compression element 2d on the
second-stage side of the compression element 2c decreases (refer to
points G and G' in FIG. 21) and the temperature of the refrigerant
discharged from the compression element 2d also decreases (refer to
points D and D' in FIG. 21), more so than in cases in which the
intermediate heat exchanger 7 is not provided (in this case, the
refrigeration cycle is performed in the following sequence shown in
FIGS. 20 and 21: point A.fwdarw.point B, C'.fwdarw.point
G'.fwdarw.point D'.fwdarw.point E.fwdarw.point H.fwdarw.point F).
Therefore, in the heat source-side heat exchanger 4 functioning as
a radiator of the refrigerant in this air-conditioning apparatus 1,
operating efficiency can be improved over cases in which no
intermediate heat exchanger 7 is provided, because the temperature
difference between the refrigerant and water or air as the cooling
source can be further reduced, and heat radiation loss can be
reduced by an amount equivalent to the area enclosed by connecting
points G', D', D, and Gin FIG. 21.
[0130] <Air-Warming Operation>
[0131] During the air-warming operation, the switching mechanism 3
is brought to the heating operation state shown by the dashed lines
in FIGS. 18 and 22. The opening degrees of the first expansion
mechanism 5a and the second expansion mechanism 5b are adjusted.
Since the switching mechanism 3 is in the heating operation state,
the intermediate heat exchanger on/off valve 12 of the intermediate
refrigerant tube 8 is closed and the intermediate heat exchanger
bypass on/off valve 11 of the intermediate heat exchanger bypass
tube 9 is opened, thereby creating a state in which the
intermediate heat exchanger 7 does not function as a cooler.
Furthermore, the opening degree of the second second-stage
injection valve 19a is adjusted in the same manner as in the
air-cooling operation.
[0132] When the refrigerant circuit 210 is in this state,
low-pressure refrigerant (refer to point A in FIGS. 18, 22, 12, and
13) is drawn into the compression mechanism 2 through the intake
tube 2a, and after the refrigerant is first compressed by the
compression element 2c to an intermediate pressure, the refrigerant
is discharged to the intermediate refrigerant tube 8 (refer to
point B in FIGS. 18, 22, 12, and 13). The intermediate-pressure
refrigerant discharged from the first-stage compression element 2c
passes through the intermediate heat exchanger bypass tube 9 (refer
to point C' in FIGS. 18 and 22) without passing through the
intermediate heat exchanger 7 (i.e., without being cooled), unlike
during the air-cooling operation. This intermediate-pressure
refrigerant that has passed through the intermediate heat exchanger
bypass tube 9 without being cooled by the intermediate heat
exchanger 7 is further cooled (refer to point G in FIGS. 18, 22,
12, and 13) by being mixed with refrigerant being returned from the
second second-stage injection tube 19 to the second-stage
compression element 2d (refer to point K in FIGS. 18, 22, 12, and
13). Next, having been mixed with the refrigerant returning from
the second second-stage injection tube 19 (i.e., intermediate
pressure injection is carried out by the economizer heat exchanger
20), the intermediate-pressure refrigerant is drawn into and
further compressed in the compression element 2d connected to the
second-stage side of the compression element 2c, and the
refrigerant is discharged from the compression mechanism 2 to the
discharge tube 2b (refer to point D in FIGS. 18, 22, 12, and 13).
The high-pressure refrigerant discharged from the compression
mechanism 2 is compressed by the two-stage compression action of
the compression elements 2c, 2d to a pressure exceeding a critical
pressure (i.e., the critical pressure Pcp at the critical point CP
shown in FIG. 12), similar to the air-cooling operation. The
high-pressure refrigerant discharged from the compression mechanism
2 flows into the oil separator 41a constituting the oil separation
mechanism 41, and the accompanying refrigeration oil is separated.
The refrigeration oil separated from the high-pressure refrigerant
in the oil separator 41a flows into the oil return tube 41b
constituting the oil separation mechanism 41 wherein it is
depressurized by the depressurization mechanism 41 c provided to
the oil return tube 41b, and the oil is then returned to the intake
tube 2a of the compression mechanism 2 and drawn once more into the
compression mechanism 2. Next, having been separated from the
refrigeration oil in the oil separation mechanism 41, the
high-pressure refrigerant is passed through the non-return
mechanism 42 and the switching mechanism 3, fed to the usage-side
heat exchanger 6 functioning as a radiator of refrigerant, and
cooled by heat exchange with the water and/or air as a cooling
source (refer to point F in FIGS. 18 and 22, and read point E as
point F in FIGS. 12 and 13). The high-pressure refrigerant cooled
in the usage-side heat exchanger 6 flows through the inlet
non-return valve 17b of the bridge circuit 17 into the receiver
inlet tube 18a, and some of the refrigerant is branched off into
the second second-stage injection tube 19. The refrigerant flowing
through the second second-stage injection tube 19 is depressurized
to a nearly intermediate pressure in the second second-stage
injection valve 19a and is then fed to the economizer heat
exchanger 20 (refer to point J in FIGS. 18, 22, 12, and 13). The
refrigerant after being branched off to the second second-stage
injection tube 19 then flows into the economizer heat exchanger 20,
where it is cooled by heat exchange with the refrigerant flowing
through the second second-stage injection tube 19 (refer to point H
in FIGS. 18, 22, 12, and 13). The refrigerant flowing through the
second second-stage injection tube 19 is heated by heat exchange
with the high-pressure refrigerant cooled in the usage-side heat
exchanger 6 functioning as a radiator (refer to point K in FIGS.
18, 22, 12, and 13), and is mixed with the intermediate-pressure
refrigerant discharged from the first-stage compression element 2c
as described above. The high-pressure refrigerant cooled in the
economizer heat exchanger 20 is depressurized to a nearly saturated
pressure by the first expansion mechanism 5a and is temporarily
retained in the receiver 18 (refer to point I in FIGS. 18 and 22).
The refrigerant retained in the receiver 18 is fed to the receiver
outlet tube 18b and is depressurized by the second expansion
mechanism 5b to become a low-pressure gas-liquid two-phase
refrigerant, and is then fed through the outlet non-return valve
17d of the bridge circuit 17 to the heat source-side heat exchanger
4 functioning as a refrigerant evaporator (refer to point E in
FIGS. 18 and 22, and read point F as point E in FIGS. 12 and 13).
The low-pressure gas-liquid two-phase refrigerant fed to the heat
source-side heat exchanger 4 is heated in the heat source-side heat
exchanger 4 by heat exchange with air as a heating source supplied
by the heat source-side fan 40, and the refrigerant is evaporated
(refer to point A in FIGS. 18, 22, 12, and 13). The low-pressure
refrigerant heated and evaporated in the heat source-side heat
exchanger 4 is then drawn once more into the compression mechanism
2 via the switching mechanism 3. In this manner the air-warming
operation is performed.
[0133] Thus, in the air-conditioning apparatus 1 of the present
modification, in addition to the configuration of the intermediate
pressure injection (as performed by the second second-stage
injection tube 19 and the economizer heat exchanger 20 herein), the
intermediate heat exchanger 7 is provided to the intermediate
refrigerant tube 8 for drawing the refrigerant discharged from the
compression element 2c into the compression element 2d, and in the
air-warming operation, the intermediate heat exchanger on/off valve
12 is closed and the intermediate heat exchanger bypass on/off
valve 11 of the intermediate heat exchanger bypass tube 9 is
opened, thereby bringing the intermediate heat exchanger 7 to a
state of not functioning as a cooler. Therefore, the decrease in
the temperature of the refrigerant discharged from the compression
mechanism 2 is minimized, more so than in cases in which the
intermediate heat exchanger 7 is made to function as a cooler,
similar to the air-cooling operation described above. Therefore, in
the air-conditioning apparatus 1, heat radiation to the exterior
can be minimized, temperature decreases can be minimized in the
refrigerant supplied to the usage-side heat exchanger 6 functioning
as a refrigerant cooler, loss of heating performance in the
usage-side heat exchanger 6 can be reduced, and loss of operating
efficiency can be prevented, in comparison with cases in which the
intermediate heat exchanger 7 is made to function as a radiator
similar to the air-cooling operation described above.
[0134] <Defrosting Operation>
[0135] In the present modification, since the intermediate heat
exchanger 7 is provided to the intermediate refrigerant tube 8 for
drawing the refrigerant discharged from the compression element 2c
into the compression element 2d, a heat exchanger having air as a
heat source is used as the intermediate heat exchanger 7, and the
intermediate heat exchanger 7 is integrated with the heat
source-side heat exchanger 4; there is a risk of frost deposition
occurring on the intermediate heat exchanger 7, although the frost
deposition is not much in comparison with the heat source-side heat
exchanger 4, and it is therefore preferable for refrigerant to flow
not only to the heat source-side heat exchanger 4 but to the
intermediate heat exchanger 7 as well and for defrosting of the
intermediate heat exchanger 7 to be performed.
[0136] In view of this, in the present modification, in step S2
shown in FIG. 6, a state is created in which intermediate pressure
injection is not used (herein, refrigerant is prevented from
returning to the second-stage compression element 2d through the
second second-stage injection tube 19), a state in which the
intermediate heat exchanger 7 is not made to function as a cooler
is created by opening the intermediate heat exchanger on/off valve
12 and closing the intermediate heat exchanger bypass on/off valve
11, similar to the air-cooling operation described above; the
switching mechanism 3 is switched from the heating operation state
to the cooling operation state, and the reverse cycle defrosting
operation is performed (refer to the refrigeration cycle shown by
the solid lines in FIGS. 23, 26, and 27).
[0137] Defrosting of the intermediate heat exchanger 7 is thereby
performed along with defrosting of the heat source-side heat
exchanger 4. Since the amount of frost deposition in the
intermediate heat exchanger 7 is small, defrosting of the
intermediate heat exchanger 7 will be complete before defrosting of
the heat source-side heat exchanger 4 is complete and before
utilization of the stored heat in the refrigerant tube 1d or the
like between the usage-side heat exchanger 6 and the switching
mechanism 3 is determined to be complete in step S3 shown in FIG.
6. However, if refrigerant continues to flow to the intermediate
heat exchanger 7 even after defrosting of the intermediate heat
exchanger 7 is complete, heat is radiated from the intermediate
heat exchanger 7 to the exterior and the temperature of the
refrigerant drawn into the second-stage compression element 2d
decreases, and as a result, the temperature of the refrigerant
discharged from the compression mechanism 2 decreases, creating a
problem of the loss of defrosting capacity of the heat source-side
heat exchanger 4.
[0138] In view of this, in the present modification, in step S6
shown in FIG. 6, a decision is made as to whether or not defrosting
of the intermediate heat exchanger 7 is complete, and when
defrosting of the intermediate heat exchanger 7 is determined to be
complete, the intermediate heat exchanger 7 is brought to a state
of not functioning as a cooler by closing the intermediate heat
exchanger on/off valve 12 and opening the intermediate heat
exchanger bypass on/off valve 11, and the process therefore returns
to step S3 shown in FIG. 6. The decision of whether or not
defrosting of the intermediate heat exchanger 7 has concluded is
made based on the temperature of the refrigerant in the outlet of
the intermediate heat exchanger 7. For example, when the
temperature of the refrigerant in the outlet of the intermediate
heat exchanger 7 as detected by the intermediate heat exchange
outlet temperature sensor 52 is detected as being equal to or
greater than a predetermined temperature, defrosting of the
intermediate heat exchanger 7 is determined to have concluded, and
when such temperature conditions are not met, defrosting of the
intermediate heat exchanger 7 is determined not to have
concluded.
[0139] Heat radiation from the intermediate heat exchanger 7 to the
exterior thereby does not take place, the decrease in the
temperature of the refrigerant drawn into the second-stage
compression element 2d is therefore minimized, and as a result, the
decrease in the temperature of the refrigerant discharged from the
compression mechanism 2 can be minimized, and the decrease in the
defrosting capacity of the heat source-side heat exchanger 4 can be
minimized (Refer to the refrigeration cycle shown by the solid
lines in FIGS. 24, 16, and 17).
[0140] In the present modification, in step S5 shown in FIG. 6, a
state of using intermediate pressure injection is created
(refrigerant returns to the second-stage compression element 2d
through the second second-stage injection tube 19) in the same
manner as in Modification 1 described above, thereby switching to
the reverse cycle defrosting operation in which the flow rate of
refrigerant flowing through the usage-side heat exchanger 6 is
reduced (refer to the refrigeration cycle shown by the dashed lines
in FIGS. 25, 26, and 27).
[0141] Thereby, as in Modification 1 described above, after a state
has arisen in which the amount of stored heat in the refrigerant
tube 1d or the like between the usage-side heat exchanger 6 and the
switching mechanism 3 decreases and the effect of improving the
defrosting capacity is not sufficiently achieved, circulation
through the usage-side heat exchanger 6 into the compression
mechanism 2 is no longer continued excessively in the refrigerant
circuit 210, the temperature decrease on the usage side can
therefore be minimized, and as much defrosting capacity as possible
can be guaranteed because the flow rate of the refrigerant
discharged from the second-stage compression element 2d
increases.
[0142] Thus, in the present modification, the same effects as those
of the defrosting operation of Modification 1 described above are
achieved, the heat stored in the refrigerant tube 1 d or the like
between the usage-side heat exchanger 6 and the switching mechanism
3 can be utilized to efficiently defrost the intermediate heat
exchanger 7, and after defrosting of the intermediate heat
exchanger 7 is complete, the refrigerant bypasses so as not to flow
to the intermediate heat exchanger 7, whereby needless heat
radiation to the exterior is suppressed, and the loss of defrosting
capacity of the heat source-side heat exchanger 4 can be
minimized.
[0143] The other steps S1, S3, S4, and S7 of the defrosting
operation in the present modification are the same as in the
defrosting operation of Modification 1 described above, and are
therefore not described herein.
(5) Modification 3
[0144] In the refrigerant circuits 110 and 210 (see FIGS. 10 and
18) in Modifications 1 and 2 described above, in both the
air-cooling operation in which the switching mechanism 3 is brought
to the cooling operation state and the air-warming operation in
which the switching mechanism 3 is brought to the heating operation
state, the temperature of the refrigerant discharged from the
second-stage compression element 2d is reduced, the power
consumption of the compression mechanism 2 is reduced, and
operating efficiency can be improved by performing intermediate
pressure injection by the economizer heat exchanger 20 as described
above. The intermediate pressure injection by the economizer heat
exchanger 20 is believed to be beneficial in a refrigerant circuit
configuration having a single usage-side heat exchanger 6, wherein
the pressure difference from the high pressure in the refrigeration
cycle to the nearly intermediate pressure of the refrigeration
cycle can be used.
[0145] However, there are cases in which the configuration has a
plurality of usage-side heat exchangers 6 connected to each other
in parallel with the objective of performing air cooling and/or air
warming corresponding to air-conditioning loads for a plurality of
air-conditioned spaces, and usage-side expansion mechanisms 5c are
provided between the receiver 18 as a gas-liquid separator and the
usage-side heat exchangers 6 so as to correspond to each of the
usage-side heat exchangers 6, in order to make it possible to
control the flow rates of refrigerant flowing through each of the
usage-side heat exchangers 6 and obtain the refrigeration loads
required in each of the usage-side heat exchangers 6.
[0146] For example, although the details are not shown, in the
refrigerant circuit 210 (see FIG. 18) having a bridge circuit 17 in
Modifications 1 and 2 described above, another possibility is to
provide a plurality (two in this case) of usage-side heat
exchangers 6 connected to each other in parallel, to provide
usage-side expansion mechanisms 5c (see FIG. 28) between the
receiver 18 as a gas-liquid separator (more specifically, the
bridge circuit 17) and the usage-side heat exchangers 6 so as to
correspond to each of the usage-side heat exchangers 6, to omit the
second expansion mechanism 5b that had been provided to the
receiver outlet tube 18b, and to provide a third expansion
mechanism (not shown) for depressurizing the refrigerant to a low
pressure in the refrigeration cycle during the air-warming
operation instead of the outlet non-return valve 17d of the bridge
circuit 17.
[0147] In such a configuration, intermediate pressure injection by
the economizer heat exchanger 20 is beneficial, similar to
Modification 2 described above, in conditions in which the pressure
difference from the high pressure in the refrigeration cycle to the
nearly intermediate pressure of the refrigeration cycle can be used
without any significant depressurizing operations being performed
except for the first expansion mechanism 5a as a heat source-side
expansion mechanism after the refrigerant is cooled in the heat
source-side heat exchanger 4 as a radiator, as in the case in the
air-cooling operation in which the switching mechanism 3 is brought
to the cooling operation state.
[0148] However, in conditions in which each of the usage-side
expansion mechanisms 5c control the flow rate of the refrigerant
flowing through each of the usage-side heat exchangers 6 as
radiators so as to obtain the refrigeration loads required in each
of the usage-side heat exchangers 6 as radiators, and the flow rate
of the refrigerant passing through each of the usage-side heat
exchangers 6 as radiators is mostly determined by depressurizing
the refrigerant by controlling the opening degrees of the
usage-side expansion mechanisms 5c provided downstream of each of
the usage-side heat exchangers 6 as radiators and upstream of the
economizer heat exchanger 20, as in the case in the air-warming
operation in which the switching mechanism 3 is brought to the
heating operation state; the extent to which the refrigerant is
depressurized by controlling the opening degrees of the usage-side
expansion mechanisms 5c fluctuates not only according to the flow
rate of the refrigerant flowing through each of the usage-side heat
exchangers 6 as radiators but also according to the state of the
flow rate distribution among the plurality of usage-side heat
exchangers 6 as radiators, and there are cases in which a state
arises in which the extent of depressurization differs greatly
among the plurality of usage-side expansion mechanisms 5c, or the
extent of depressurization in the usage-side expansion mechanisms
5c is comparatively large. Therefore, there is a risk that the
pressure of the refrigerant in the inlet of the economizer heat
exchanger 20 will decrease, in which case there is a risk that the
rate of heat exchange in the economizer heat exchanger 20 (i.e.,
the flow rate of the refrigerant flowing through the second
second-stage injection tube 19) will decrease and use will be
difficult. Particularly in cases in which this type of
air-conditioning apparatus 1 is configured as a separate-type
air-conditioning apparatus in which a heat source unit including
primarily the compression mechanism 2, the heat source-side heat
exchanger 4, and the receiver 18 is connected by a communication
tube with a usage unit including primarily the usage-side heat
exchanger 6, the communication tube could be extremely long
depending on the arrangement of the usage unit and the heat source
unit; therefore, the pressure drop has an effect, and the pressure
of the refrigerant in the inlet of the economizer heat exchanger 20
decreases further. In cases in which there is a risk that the
pressure of the refrigerant in the inlet of the economizer heat
exchanger 20 will decrease, it is beneficial to use intermediate
pressure injection by the receiver 18 as a gas-liquid separator in
the embodiment described above, which can be used even in
conditions in which there is a small pressure difference between
the pressure in the receiver 18 and the intermediate pressure in
the refrigeration cycle (the pressure of the refrigerant flowing
through the intermediate refrigerant tube 8 in this case).
[0149] In cases in which the configuration has a plurality of
usage-side heat exchangers 6 connected to each other in parallel
with the objective of performing air cooling and/or air warming
corresponding to air-conditioning loads for a plurality of
air-conditioned spaces, and a configuration is used which is
provided with usage-side expansion mechanisms 5c between the
receiver 18 and the usage-side heat exchangers 6 so as to
correspond to each of the usage-side heat exchangers 6 in order to
make it possible to control the flow rates of refrigerant flowing
through each of the usage-side heat exchangers 6 and obtain the
refrigeration loads required in each of the usage-side heat
exchangers 6 as described above; during the air-cooling operation,
the refrigerant depressurized by the first expansion mechanism 5a
to a nearly saturated pressure and temporarily retained in the
receiver 18 (refer to point L in FIG. 28) is distributed to each of
the usage-side expansion mechanisms 5c, but if the refrigerant fed
from the receiver 18 to each of the usage-side expansion mechanisms
5c is in a gas-liquid two-phase state, there is a risk of the flow
being uneven when the refrigerant is distributed among the
usage-side expansion mechanisms 5c, and it is therefore preferable
that the refrigerant fed from the receiver 18 to each of the
usage-side expansion mechanisms 5c is brought as much as possible
to a subcooled state.
[0150] In view of this, in the present modification, the
configuration of Modification 2 described above (see FIG. 18) is
replaced by a refrigerant circuit 310 in which the first
second-stage injection tube 18c is connected to the receiver 18 in
order to allow the receiver 18 to function as a gas-liquid
separator and enable intermediate pressure injection to be
performed, intermediate pressure injection by the economizer heat
exchanger 20 can be performed during the air-cooling operation,
intermediate pressure injection by the receiver 18 as a gas-liquid
separator can be performed during the air-warming operation, and a
subcooling heat exchanger 96 as a cooler and a second intake return
tube 95 are between the receiver 18 and the usage-side expansion
mechanisms 5c, as shown in FIG. 28.
[0151] The second intake return tube 95 herein is a refrigerant
tube for branching off the refrigerant fed from the heat
source-side heat exchanger 4 as a radiator to the usage-side heat
exchangers 6 and returning the refrigerant to the intake side of
the compression mechanism 2 (i.e., the intake tube 2a). In the
present modification, the second intake return tube 95 is provided
so as to branch off the refrigerant fed from the receiver 18 to the
usage-side expansion mechanisms 5c. More specifically, the second
intake return tube 95 is provided so as to branch off the
refrigerant from a position upstream of the subcooling heat
exchanger 96 (i.e., between the receiver 18 and the subcooling heat
exchanger 96) and return the refrigerant to the intake tube 2a.
This second intake return tube 95 is provided with a second intake
return valve 95a whose opening degree can be controlled. The second
intake return valve 95a is an electrically driven expansion valve
in the present modification.
[0152] The subcooling heat exchanger 96 is a heat exchanger for
performing heat exchange between the refrigerant fed from the heat
source-side heat exchanger 4 as a radiator to the usage-side heat
exchangers 6 as evaporators and the refrigerant flowing through the
second intake return tube 95 (more specifically, the refrigerant
that has been depressurized in the second intake return valve 95a
to a nearly low pressure). In the present modification, the
subcooling heat exchanger 96 is provided so as to perform heat
exchange between the refrigerant flowing through a position
upstream of the usage-side expansion mechanisms 5c (i.e., between
the position where the second intake return tube 95 branches off
and the usage-side expansion mechanisms 5c) and the refrigerant
flowing through the second intake return tube 95. In the present
modification, the subcooling heat exchanger 96 is provided farther
downstream than the position where the second intake return tube 95
branches off. Therefore, the refrigerant cooled in the heat
source-side heat exchanger 4 as a radiator is branched off to the
second intake return tube 95 after passing through the economizer
heat exchanger 20 as a cooler, and in the subcooling heat exchanger
96, heat exchange is performed with the refrigerant flowing through
the second intake return tube 95.
[0153] The first second-stage injection tube 18c and the first
intake return tube 18f are integrated in the portion near the
receiver 18, similar to the embodiment described above. The first
second-stage injection tube 18c and the second second-stage
injection tube 19 are integrated in the portion near the
intermediate refrigerant tube 8. The first intake return tube 18f
and the second intake return tube 95 are integrated in the portion
on the intake side of the compression mechanism 2. In the present
modification, the usage-side expansion mechanisms 5c are
electrically driven expansion valves. In the present modification,
since the second second-stage injection tube 19 and the economizer
heat exchanger 20 are used during the air-cooling operation, and on
the other hand the first second-stage injection tube 18c is used
during the air-warming operation as described above, there is no
need for the direction of refrigerant flow to the economizer heat
exchanger 20 to be constant during both the air-cooling operation
and the air-warming operation, and the bridge circuit 17 can
therefore be omitted to simplify the configuration of the
refrigerant circuit 310.
[0154] The outlet of the subcooling heat exchanger 96 on the side
near the second intake return tube 95 is provided with a subcooling
heat exchange outlet temperature sensor 59 for detecting the
temperature of the refrigerant in the outlet of the subcooling heat
exchanger 96 on the side near the second intake return tube 95.
[0155] Next, the action of the air-conditioning apparatus 1 will be
described using FIGS. 3, 4, 16, 17 and 28 through 37. FIG. 29 is a
diagram showing the flow of refrigerant within the air-conditioning
apparatus 1 during the air-cooling operation, FIG. 30 is a
pressure-enthalpy graph representing the refrigeration cycle during
the air-cooling operation, FIG. 31 is a temperature-entropy graph
representing the refrigeration cycle during the air-cooling
operation, FIG. 32 is a diagram showing the flow of refrigerant
within the air-conditioning apparatus 1 during the air-warming
operation, FIG. 33 is a diagram showing the flow of refrigerant
within the air-conditioning apparatus 1 at the start of the
defrosting operation, FIG. 34 is a diagram showing the flow of
refrigerant within the air-conditioning apparatus 1 in the
defrosting operation after defrosting of the intermediate heat
exchanger 7 is complete, FIG. 35 is a diagram showing the flow of
refrigerant within the air-conditioning apparatus 1 in the
defrosting operation after defrosting of the intermediate heat
exchanger 7 and utilization of the stored heat have concluded, FIG.
36 is a pressure-enthalpy graph representing the refrigeration
cycle during the defrosting operation, and FIG. 37 is a
temperature-entropy graph representing the refrigeration cycle
during the defrosting operation. Operation control in the
air-cooling operation, the air-warming operation, and the
defrosting operation described hereinbelow is performed by the
aforementioned controller (not shown) in the present embodiment. In
the following description, the term "high pressure" means a high
pressure in the refrigeration cycle (specifically, the pressure at
points D, D', E, H, I, R in FIGS. 30, 31, 16, 17, 36, and 37, and
the pressure at points D, D', and E in FIGS. 3 and 4), the term
"low pressure" means a low pressure in the refrigeration cycle
(specifically, the pressure at points A, F, S, U, and W in FIGS.
30, 31, 16, 17, 36, and 37, and the pressure at points A and F in
FIGS. 3 and 4), and the term "intermediate pressure" means an
intermediate pressure in the refrigeration cycle (specifically, the
pressure at points B, C, C', G, G', J, and K in FIGS. 30, 31, 16,
17, 36, and 37, and the pressure at points B, C, C', G, G', I, L,
and M in FIGS. 3 and 4).
[0156] <Air-Cooling Operation>
[0157] During the air-cooling operation, the switching mechanism 3
is brought to the cooling operation state shown by the solid lines
in FIGS. 28 and 29. The opening degrees of the first expansion
mechanism 5a and the second expansion mechanism 5b are adjusted.
Since the switching mechanism 3 is in the cooling operation state,
the intermediate heat exchanger on/off valve 12 of the intermediate
refrigerant tube 8 is opened and the intermediate heat exchanger
bypass on/off valve 11 of the intermediate heat exchanger bypass
tube 9 is closed, thereby creating a state in which the
intermediate heat exchanger 7 functions as a cooler. When the
switching mechanism 3 is brought to the cooling operation state,
intermediate pressure injection by the receiver 18 as a gas-liquid
separator is not performed, but intermediate pressure injection is
performed by the economizer heat exchanger 20 which returns to the
second-stage compression element 2d the refrigerant that has been
passed through the second second-stage injection tube 19 and heated
in the economizer heat exchanger 20. More specifically, the first
second-stage injection on/off valve 18d is closed, and the opening
degree of the second second-stage injection valve 19a is adjusted
in the same manner as in Modification 2 described above.
Furthermore, when the switching mechanism 3 is in the cooling
operation state, the opening degree of the second intake return
valve 95a is adjusted as well because the subcooling heat exchanger
96 is used. More specifically, in the present modification,
so-called superheat degree control is performed wherein the opening
degree of the second intake return valve 95a is adjusted so that a
target value is achieved in the degree of superheat of the
refrigerant at the outlet in the second intake return tube 95 side
of the subcooling heat exchanger 96. In the present modification,
the degree of superheat of the refrigerant at the outlet in the
second intake return tube 95 side of the subcooling heat exchanger
96 is obtained by converting the low pressure detected by the
intake pressure sensor 60 to a saturation temperature and
subtracting this refrigerant saturation temperature value from the
refrigerant temperature detected by the subcooling heat exchanger
outlet temperature sensor 59. Though not used in the present
modification, another possible option is to provide a temperature
sensor to the inlet in the second intake return tube 95 side of the
subcooling heat exchanger 96, and to obtain the degree of superheat
of the refrigerant at the outlet in the second intake return tube
95 side of the subcooling heat exchanger 96 by subtracting the
refrigerant temperature detected by this temperature sensor from
the refrigerant temperature detected by the subcooling heat
exchanger outlet temperature sensor 59. Adjusting the opening
degree of the second intake return valve 95a is not limited to the
superheat degree control, and the second intake return valve 95a
may be opened to a predetermined opening degree in accordance with
the flow rate of refrigerant circulating within the refrigerant
circuit 310, for example.
[0158] When the refrigerant circuit 310 is in this state,
low-pressure refrigerant (refer to point A in FIGS. 28 through 31)
is drawn into the compression mechanism 2 through the intake tube
2a, and after the refrigerant is first compressed by the
compression element 2c to an intermediate pressure, the refrigerant
is discharged to the intermediate refrigerant tube 8 (refer to
point A in FIGS. 28 through 31). The intermediate-pressure
refrigerant discharged from the first-stage compression element 2c
is cooled in the intermediate heat exchanger 7 by undergoing heat
exchange with the air as a cooling source supplied by the heat
source-side fan 40 (refer to point C in FIGS. 28 through 31). The
refrigerant cooled in the intermediate heat exchanger 7 is further
cooled (refer to point G in FIGS. 28 through 31) by being mixed
with refrigerant being returned from the second second-stage
injection tube 19 to the second-stage compression element 2d (refer
to point K in FIGS. 28 through 31). Next, having been mixed with
the refrigerant returning from the second second-stage injection
tube 19 (i.e., intermediate pressure injection is carried out by
the economizer heat exchanger 20), the intermediate-pressure
refrigerant is drawn into and further compressed in the compression
element 2d connected to the second-stage side of the compression
element 2c, and the refrigerant is discharged from the compression
mechanism 2 to the discharge tube 2b (refer to point D in FIGS. 28
through 31). The high-pressure refrigerant discharged from the
compression mechanism 2 is compressed by the two-stage compression
action of the compression elements 2c, 2d to a pressure exceeding a
critical pressure (i.e., the critical pressure Pcp at the critical
point CP shown in FIG. 30). The high-pressure refrigerant
discharged from the compression mechanism 2 flows into the oil
separator 41a constituting the oil separation mechanism 41, and the
accompanying refrigeration oil is separated. The refrigeration oil
separated from the high-pressure refrigerant in the oil separator
41a flows into the oil return tube 41b constituting the oil
separation mechanism 41 wherein it is depressurized by the
depressurization mechanism 41c provided to the oil return tube 41b,
and the oil is then returned to the intake tube 2a of the
compression mechanism 2 and drawn once more into the compression
mechanism 2. Next, having been separated from the refrigeration oil
in the oil separation mechanism 41, the high-pressure refrigerant
is passed through the non-return mechanism 42 and the switching
mechanism 3, and is fed to the heat source-side heat exchanger 4
functioning as a refrigerant radiator. The high-pressure
refrigerant fed to the heat source-side heat exchanger 4 is cooled
in the heat source-side heat exchanger 4 by heat exchange with air
as a cooling source supplied by the heat source-side fan 40 (refer
to point E in FIGS. 28 through 31). Some of the high-pressure
refrigerant cooled in the heat source-side heat exchanger 4 is then
branched off to the second second-stage injection tube 19. The
refrigerant flowing through the second second-stage injection tube
19 is depressurized to a nearly intermediate pressure in the second
second-stage injection valve 19a and is then fed to the economizer
heat exchanger 20 (refer to point J in FIGS. 28 through 31). The
refrigerant after being branched off to the second second-stage
injection tube 19 then flows into the economizer heat exchanger 20,
where it is cooled by heat exchange with the refrigerant flowing
through the second second-stage injection tube 19 (refer to point H
in FIGS. 28 through 31). The refrigerant flowing through the second
second-stage injection tube 19 is heated by heat exchange with the
high-pressure refrigerant cooled in the heat source-side heat
exchanger 4 as a radiator (refer to point K in FIGS. 28 through
31), and is mixed with the intermediate-pressure refrigerant
discharged from the first-stage compression element 2c as described
above. The high-pressure refrigerant cooled in the economizer heat
exchanger 20 is depressurized to a nearly saturated pressure by the
first expansion mechanism 5a and is temporarily retained in the
receiver 18 (refer to point I in FIGS. 28 through 31). Some of the
refrigerant retained in the receiver 18 is then branched off to the
second intake return tube 95. The refrigerant flowing through the
second intake return tube 95 is depressurized to a nearly low
pressure in the second intake return valve 95a and is then fed to
the subcooling heat exchanger 96 (refer to point S in FIGS. 28
through 31). The refrigerant branched off into the second intake
return tube 95 then flows into the subcooling heat exchanger 96,
where it is further cooled by heat exchange with the refrigerant
flowing through the second intake return tube 95 (refer to point R
in FIGS. 28 through 31). The refrigerant flowing through the second
intake return tube 95 is heated by heat exchange with the
high-pressure refrigerant cooled in the economizer heat exchanger
20 (refer to point U in FIGS. 28 through 31), and is mixed with the
refrigerant flowing through the intake side of the compression
mechanism 2 (here, the intake tube 2a). The refrigerant cooled in
the subcooling heat exchanger 96 is then fed to the usage-side
expansion mechanisms 5c and depressurized by the usage-side
expansion mechanisms 5c to become a low-pressure gas-liquid
two-phase refrigerant, and is then fed to the usage-side heat
exchangers 6 functioning as evaporators of refrigerant (refer to
point F in FIGS. 28 through 31). The low-pressure gas-liquid
two-phase refrigerant fed to the usage-side heat exchanger 6 is
heated by heat exchange with water or air as a heating source, and
the refrigerant is evaporated as a result (refer to point W in
FIGS. 28 through 31). The low-pressure refrigerant heated in the
usage-side heat exchanger 6 is then drawn once more into the
compression mechanism 2 via the switching mechanism 3 (refer to
point A in FIGS. 28 through 31). In this manner the air-cooling
operation is performed.
[0159] Thus, in the air-conditioning apparatus 1 of the present
modification, in addition to the intermediate heat exchanger 7
being made to function as a cooler similar to the air-cooling
operation in Modification 2 described above, the second
second-stage injection tube 19 and the economizer heat exchanger 20
are provided to ensure that the refrigerant whose heat has been
radiated in the heat source-side heat exchanger 4 is branched off
and returned to the second-stage compression element 2d, and the
temperature of the refrigerant drawn into the second-stage
compression element 2d can therefore be kept even lower without
radiating heat to the exterior, similar to Modification 2 described
above. Thereby, the temperature of the refrigerant discharged from
the compression mechanism 2 is kept low, and the power consumption
of the compression mechanism 2 can be further reduced and operating
efficiency further improved in comparison with cases in which the
second second-stage injection tube 19 and the economizer heat
exchanger 20 are not provided, because heat radiation loss can be
further reduced.
[0160] Moreover, in the present modification, since the refrigerant
fed from the receiver 18 to the usage-side expansion mechanisms 5c
(refer to point I in FIGS. 28 through 31) can be cooled by the
subcooling heat exchanger 96 to a subcooled state (refer to point R
in FIGS. 30 and 31), it is possible to reduce the risk of the flows
being uneven when the refrigerant is distributed to each of the
usage-side expansion mechanisms 5c.
[0161] <Air-Warming Operation>
[0162] During the air-warming operation, the switching mechanism 3
is brought to the heating operation state shown by the dashed lines
in FIGS. 28 and 32. The opening degrees of the first expansion
mechanism 5a and the second expansion mechanism 5b are adjusted.
Since the switching mechanism 3 is in the heating operation state,
the intermediate heat exchanger on/off valve 12 of the intermediate
refrigerant tube 8 is closed and the intermediate heat exchanger
bypass on/off valve 11 of the intermediate heat exchanger bypass
tube 9 is opened, thereby creating a state in which the
intermediate heat exchanger 7 does not function as a cooler. When
the switching mechanism 3 is brought to the heating operation
state, intermediate pressure injection by the economizer heat
exchanger 20 is not performed, but intermediate pressure injection
is performed by the receiver 18 whereby the refrigerant is passed
through the first second-stage injection tube 18c and returned from
the receiver 18 as a gas-liquid separator to the second-stage
compression element 2d. More specifically, the first second-stage
injection on/off valve 18d is brought to an opened state and the
second second-stage injection valve 19a is brought to a fully
closed state. Furthermore, when the switching mechanism 3 is
brought to the heating operation state, the second intake return
valve 95a is also brought to the fully closed state because the
subcooling heat exchanger 96 is not used.
[0163] When the refrigerant circuit 310 is in this state,
low-pressure refrigerant (refer to point A in FIGS. 28, 32, 3, and
4) is drawn into the compression mechanism 2 through the intake
tube 2a, and after the refrigerant is first compressed by the
compression element 2c to an intermediate pressure, the refrigerant
is discharged to the intermediate refrigerant tube 8 (refer to
point B in FIGS. 28, 32, 3, and 4). This intermediate-pressure
refrigerant discharged from the first-stage compression element 2c
passes through the intermediate heat exchanger bypass tube 9 (refer
to point C' in FIGS. 28 and 32) without passing through the
intermediate heat exchanger 7 (i.e., without being cooled), similar
to the air-warming operation in Modification 2 described above.
This intermediate-pressure refrigerant that has passed through the
intermediate heat exchanger bypass tube 9 without being cooled by
the intermediate heat exchanger 7 is cooled (refer to point G in
FIGS. 28, 32, 3, and 4) by mixing with the refrigerant returned
from the receiver 18 through the first second-stage injection tube
18c to the second-stage compression element 2d (refer to point M in
FIGS. 28, 32, 3, and 4). Next, having been mixed with the
refrigerant returning from the first second-stage injection tube
18c (i.e., intermediate pressure injection is carried out by the
receiver 18 which acts as a gas-liquid separator), the
intermediate-pressure refrigerant is drawn into and further
compressed in the compression element 2d connected to the
second-stage side of the compression element 2c, and the
refrigerant is discharged from the compression mechanism 2 to the
discharge tube 2b (refer to point D in FIGS. 28, 32, 3, and 4). The
high-pressure refrigerant discharged from the compression mechanism
2 is compressed by the two-stage compression action of the
compression elements 2c, 2d to a pressure exceeding a critical
pressure (i.e., the critical pressure Pcp at the critical point CP
shown in FIG. 3), similar to the air-cooling operation. The
high-pressure refrigerant discharged from the compression mechanism
2 flows into the oil separator 41a constituting the oil separation
mechanism 41, and the accompanying refrigeration oil is separated.
The refrigeration oil separated from the high-pressure refrigerant
in the oil separator 41a flows into the oil return tube 41b
constituting the oil separation mechanism 41 wherein it is
depressurized by the depressurization mechanism 41c provided to the
oil return tube 41b, and the oil is then returned to the intake
tube 2a of the compression mechanism 2 and drawn once more into the
compression mechanism 2. Next, after the refrigeration oil has been
separated in the oil separation mechanism 41, the high-pressure
refrigerant is fed through the non-return mechanism 42 and the
switching mechanism 3 to the usage-side heat exchangers 6
functioning as radiators of refrigerant, and the refrigerant is
cooled by heat exchange with the water and/or air as a cooling
source (refer to point F in FIGS. 28 and 32, and read point E as
point F in FIGS. 3 and 4). After the high-pressure refrigerant
cooled in the usage-side heat exchangers 6 is then depressurized to
a nearly intermediate pressure by the usage-side expansion
mechanisms 5c, the refrigerant is temporarily retained in the
receiver 18 and subjected to gas-liquid separation (refer to points
I, L, and M in FIGS. 28, 32, 3, and 4). The gas refrigerant that
has undergone gas-liquid separation in the receiver 18 is then
extracted out from the top part of the receiver 18 by the first
second-stage injection tube 18c and mixed with the
intermediate-pressure refrigerant discharged from the first-stage
compression element 2c as described above. The liquid refrigerant
retained in the receiver 18 is then depressurized by the first
expansion mechanism 5a into a low-pressure gas-liquid two-phase
refrigerant, which is fed to the heat source-side heat exchanger 4
functioning as an evaporator of refrigerant (refer to point E in
FIGS. 28 and 32, and read point F as point E in FIGS. 3 and 4). The
low-pressure gas-liquid two-phase refrigerant fed to the heat
source-side heat exchanger 4 is then heated and evaporated in the
heat source-side heat exchanger 4 by heat exchange with the air as
a heat source supplied by the heat source-side fan 40 (refer to
point A in FIGS. 28, 32, 3, and 4). The low-pressure refrigerant
heated and evaporated in the heat source-side heat exchanger 4 is
then drawn once more into the compression mechanism 2 via the
switching mechanism 3. In this manner the air-warming operation is
performed.
[0164] Thus, in the air-conditioning apparatus 1 of the present
modification, the intermediate heat exchanger 7 is brought to a
state of not functioning as a cooler similar to the air-warming
operation in Modification 2 described above, and the first
second-stage injection tube 18c is provided to branch off the
refrigerant whose heat has been radiated in the heat source-side
heat exchanger 4 and return the refrigerant to the second-stage
compression element 2d, similar to the air-warming operation in the
embodiment described above; therefore, the temperature of the
refrigerant drawn into the second-stage compression element 2d can
be kept lower without heat being radiated to the exterior, similar
to the embodiment described above. Thereby, although the
temperature of the refrigerant discharged from the compression
mechanism 2 decreases and the heating capacity per unit flow rate
of the refrigerant in the usage-side heat exchangers 6 decreases,
the flow rate of the refrigerant discharged from the second-stage
compression element 2d increases, the decrease in the heating
capacity of the usage-side heat exchangers 6 is therefore
minimized, and as a result, the power consumption of the
compression mechanism 2 can be reduced and operating efficiency can
be improved.
[0165] <Defrosting Operation>
[0166] In the present modification, the second intake return tube
95 and the subcooling heat exchanger 96 are provided so that
refrigerant fed from the receiver 18 to the usage-side expansion
mechanisms 5c during the air-cooling operation can be cooled to a
subcooled state. Therefore, in step S2 shown in FIG. 6, when a
state of using the subcooling heat exchanger 96 is created, some of
the refrigerant fed from the receiver 18 to the usage-side heat
exchangers 6 returns to the compression mechanism 2 through the
second intake return tube 95 without passing through the
refrigerant tube 1d or the like between the usage-side heat
exchangers 6 and the switching mechanism 3, which is not preferable
in terms of utilizing the stored heat in the refrigerant tube 1d or
the like between the usage-side heat exchangers 6 and the switching
mechanism 3.
[0167] In view of this, in the present modification, in step S2
shown in FIG. 6, intermediate pressure injection is not used
(herein, refrigerant is prevented from returning to the
second-stage compression element 2d through the first second-stage
injection tube 18c and the second second-stage injection tube 19),
a state is created in which the intermediate heat exchanger 7 is
made to function as a cooler by opening the intermediate heat
exchanger on/off valve 12 and closing the intermediate heat
exchanger bypass on/off valve 11, similar to the air-cooling
operation described above, the switching mechanism 3 is switched
from the heating operation state to the cooling operation state,
the subcooling heat exchanger 96 is also not used (that is, the
second intake return valve 95a is shut off and refrigerant is
prevented from returning to the second-stage compression element 2d
through the second intake return tube 95), and the reverse cycle
defrosting operation is performed (refer to the refrigeration cycle
shown by the solid lines in FIGS. 33, 34, 36, and 37).
[0168] Thereby, in the refrigerant circuit 310, the second intake
return tube 95 and the subcooling heat exchanger 96 no longer pose
a hindrance to utilizing the heat stored in the refrigerant tube 1d
or the like between the usage-side heat exchangers 6 and the
switching mechanism 3.
[0169] In the present modification, intermediate pressure injection
by the economizer heat exchanger 20 and intermediate pressure
injection by the receiver 18 as a gas-liquid separator are used
according to the characteristics in the air-cooling operation and
the air-warming operation. Therefore, in step S5 shown in FIG. 6,
either intermediate pressure injection by the economizer heat
exchanger 20 or intermediate pressure injection by the receiver 18
as a gas-liquid separator can be used.
[0170] In view of this, in the present modification, taking into
account the possibility of controlling the opening degree of the
second second-stage injection valve 19a, a state of using
intermediate pressure injection by the economizer heat exchanger 20
is created (that is, refrigerant is returned to the second-stage
compression element 2d through the second second-stage injection
tube 19), similar to Modifications 1 and 2 described above, the
flow rate of the refrigerant flowing through the usage-side heat
exchangers 6 is further reduced, and the flow rate of the
refrigerant flowing through the heat source-side heat exchanger 4
is further increased (refer to the refrigeration cycle shown by the
dashed lines in FIGS. 35, 36, and 37). Moreover, in the present
modification, since some of the refrigerant fed from the receiver
18 to the usage-side heat exchangers 6 can be returned to the
compression mechanism 2 through the second intake return tube 95
without passing through the refrigerant tube 1d or the like between
the usage-side heat exchangers 6 and the switching mechanism 3 by
creating a state in which the subcooling heat exchanger 96 is used
as described above, this fact can be used to create a state in
which intermediate pressure injection by the economizer heat
exchanger 20 is used, to create a state in which the subcooling
heat exchanger 96 is used, and also to reduce the flow rate of the
refrigerant flowing through the usage-side heat exchangers 6 and
further minimize the temperature decrease on the usage side in step
S5 shown in FIG. 6 (refer to the refrigeration cycle shown by the
dashed lines in FIGS. 35, 36, and 37).
[0171] Thus, in the present modification, the same effects as those
of the defrosting operation of Modification 2 described above are
achieved, it is possible to promote utilization of the stored heat
in the refrigerant tube 1 d or the like between the usage-side heat
exchangers 6 and the switching mechanism 3 and to minimize the
temperature decrease on the usage side by appropriately switching
the second intake return tube 95 and the subcooling heat exchanger
96 between use and non-use, and taking into account the fact that
the opening degree of the second second-stage injection valve 19a
can be controlled, a state of using intermediate pressure injection
by the economizer heat exchanger 20 can be created to effectively
minimize the temperature decrease on the usage side when the
reverse cycle defrosting operation is performed during a state of
using intermediate pressure injection.
[0172] The other steps S1, S3, S4, S6, and S7 of the defrosting
operation in the present modification are similar to those of the
defrosting operation in Modification 2 described above, and are
therefore not described herein.
(6) Modification 4
[0173] In the above-described embodiment and the modifications
thereof, a two-stage compression-type compression mechanism 2 is
configured such that the refrigerant discharged from the
first-stage compression element of two compression elements 2c, 2d
is sequentially compressed in the second-stage compression element
by one compressor 21 having a single-axis two-stage compression
structure, but other options include using a compression mechanism
having more stages than a two-stage compression system, such as a
three-stage compression system or the like; or configuring a
multistage compression mechanism by connecting in series a
plurality of compressors incorporated with a single compression
element and/or compressors incorporated with a plurality of
compression elements. In cases in which the capacity of the
compression mechanism must be increased, such as cases in which
numerous usage-side heat exchangers 6 are connected, for example, a
parallel multistage compression-type compression mechanism may be
used in which two or more multistage compression-type compression
mechanisms are connected in parallel.
[0174] For example, the refrigerant circuit 310 in Modification 3
described above (see FIG. 28) may be replaced by a refrigerant
circuit 410 that uses a compression mechanism 102 in which
two-stage compression-type compression mechanisms 103, 104 are
connected in parallel instead of the two-stage compression-type
compression mechanism 2, as shown in FIG. 38.
[0175] In the present modification, the first compression mechanism
103 is configured using a compressor 29 for subjecting the
refrigerant to two-stage compression through two compression
elements 103c, 103d, and is connected to a first intake branch tube
103a which branches off from an intake header tube 102a of the
compression mechanism 102, and also to a first discharge branch
tube 103b whose flow merges with a discharge header tube 102b of
the compression mechanism 102. In the present modification, the
second compression mechanism 104 is configured using a compressor
30 for subjecting the refrigerant to two-stage compression through
two compression elements 104c, 104d, and is connected to a second
intake branch tube 104a which branches off from the intake header
tube 102a of the compression mechanism 102, and also to a second
discharge branch tube 104b whose flow merges with the discharge
header tube 102b of the compression mechanism 102. Since the
compressors 29, 30 have the same configuration as the compressor 21
in the embodiment and modifications thereof described above,
symbols indicating components other than the compression elements
103c, 103d, 104c, 104d are replaced with symbols beginning with 29
or 30, and these components are not described. The compressor 29 is
configured so that refrigerant is drawn from the first intake
branch tube 103a, the drawn refrigerant is compressed by the
compression element 103c and then discharged to a first inlet-side
intermediate branch tube 81 that constitutes the intermediate
refrigerant tube 8, the refrigerant discharged to the first
inlet-side intermediate branch tube 81 is caused to be drawn into
the compression element 103d by way of an intermediate header tube
82 and a first outlet-side intermediate branch tube 83 constituting
the intermediate refrigerant tube 8, and the refrigerant is further
compressed and then discharged to the first discharge branch tube
103b. The compressor 30 is configured so that refrigerant is drawn
through the second intake branch tube 104a, the drawn refrigerant
is compressed by the compression element 104c and then discharged
to a second inlet-side intermediate branch tube 84 constituting the
intermediate refrigerant tube 8, the refrigerant discharged to the
second inlet-side intermediate branch tube 84 is drawn into the
compression element 104d via the intermediate header tube 82 and a
second outlet-side intermediate branch tube 85 constituting the
intermediate refrigerant tube 8, and the refrigerant is further
compressed and then discharged to the second discharge branch tube
104b. In the present modification, the intermediate refrigerant
tube 8 is a refrigerant tube for drawing refrigerant discharged
from the compression elements 103c, 104c connected to the
first-stage sides of the compression elements 103d, 104d into the
compression elements 103d, 104d connected to the second-stage sides
of the compression elements 103c, 104c, and the intermediate
refrigerant tube 8 primarily comprises the first inlet-side
intermediate branch tube 81 connected to the discharge side of the
first-stage compression element 103c of the first compression
mechanism 103, the second inlet-side intermediate branch tube 84
connected to the discharge side of the first-stage compression
element 104c of the second compression mechanism 104, the
intermediate header tube 82 whose flow merges with both inlet-side
intermediate branch tubes 81, 84, the first discharge-side
intermediate branch tube 83 branching off from the intermediate
header tube 82 and connected to the intake side of the second-stage
compression element 103d of the first compression mechanism 103,
and the second outlet-side intermediate branch tube 85 branching
off from the intermediate header tube 82 and connected to the
intake side of the second-stage compression element 104d of the
second compression mechanism 104. The discharge header tube 102b is
a refrigerant tube for feeding refrigerant discharged from the
compression mechanism 102 to the switching mechanism 3. A first oil
separation mechanism 141 and a first non-return mechanism 142 are
provided to the first discharge branch tube 103b connected to the
discharge header tube 102b. A second oil separation mechanism 143
and a second non-return mechanism 144 are provided to the second
discharge branch tube 104b connected to the discharge header tube
102b. The first oil separation mechanism 141 is a mechanism whereby
refrigeration oil that accompanies the refrigerant discharged from
the first compression mechanism 103 is separated from the
refrigerant and returned to the intake side of the compression
mechanism 102. The first oil separation mechanism 141 mainly has a
first oil separator 141a for separating from the refrigerant the
refrigeration oil that accompanies the refrigerant discharged from
the first compression mechanism 103, and a first oil return tube
141b that is connected to the first oil separator 141a and that is
used for returning the refrigeration oil separated from the
refrigerant to the intake side of the compression mechanism 102.
The second oil separation mechanism 143 is a mechanism whereby
refrigeration oil that accompanies the refrigerant discharged from
the second compression mechanism 104 is separated from the
refrigerant and returned to the intake side of the compression
mechanism 102. The second oil separation mechanism 143 mainly has a
second oil separator 143a for separating from the refrigerant the
refrigeration oil that accompanies the refrigerant discharged from
the second compression mechanism 104, and a second oil return tube
143b that is connected to the second oil separator 143a and that is
used for returning the refrigeration oil separated from the
refrigerant to the intake side of the compression mechanism 102. In
the present modification, the first oil return tube 141b is
connected to the second intake branch tube 104a, and the second oil
return tube 143c is connected to the first intake branch tube 103a.
Accordingly, a greater amount of refrigeration oil returns to the
compression mechanism 103, 104 that has the lesser amount of
refrigeration oil even when there is an imbalance between the
amount of refrigeration oil that accompanies the refrigerant
discharged from the first compression mechanism 103 and the amount
of refrigeration oil that accompanies the refrigerant discharged
from the second compression mechanism 104, which is due to the
imbalance in the amount of refrigeration oil retained in the first
compression mechanism 103 and the amount of refrigeration oil
retained in the second compression mechanism 104. The imbalance
between the amount of refrigeration oil retained in the first
compression mechanism 103 and the amount of refrigeration oil
retained in the second compression mechanism 104 is therefore
resolved. In the present modification, the first intake branch tube
103a is configured so that the portion leading from the flow
juncture with the second oil return tube 143b to the flow juncture
with the intake header tube 102a slopes downward toward the flow
juncture with the intake header tube 102a, while the second intake
branch tube 104a is configured so that the portion leading from the
flow juncture with the first oil return tube 141b to the flow
juncture with the intake header tube 102a slopes downward toward
the flow juncture with the intake header tube 102a. Therefore, even
if either one of the two-stage compression-type compression
mechanisms 103, 104 is stopped, refrigeration oil being returned
from the oil return tube corresponding to the operating compression
mechanism to the intake branch tube corresponding to the stopped
compression mechanism is returned to the intake header tube 102a,
and there will be little likelihood of a shortage of oil supplied
to the operating compression mechanism. The oil return tubes 141b,
143b are provided with depressurization mechanisms 141 c, 143c for
depressurizing the refrigeration oil that flows through the oil
return tubes 141b, 143b. The non-return mechanism 142, 144 are
mechanisms for allowing refrigerant to flow from the discharge side
of the compression mechanisms 103, 104 to the switching mechanism
3, and for cutting off the flow of refrigerant from the switching
mechanism 3 to the discharge side of the compression mechanisms
103, 104.
[0176] Thus, in the present modification, the compression mechanism
102 is configured by connecting two compression mechanisms in
parallel; namely, the first compression mechanism 103 having two
compression elements 103c, 103d and configured so that refrigerant
discharged from the first-stage compression element of these
compression elements 103c, 103d is sequentially compressed by the
second-stage compression element, and the second compression
mechanism 104 having two compression elements 104c, 104d and
configured so that refrigerant discharged from the first-stage
compression element of these compression elements 104c, 104d is
sequentially compressed by the second-stage compression
element.
[0177] In the present modification, the intermediate heat exchanger
7 is provided to the intermediate header tube 82 constituting the
intermediate refrigerant tube 8, and the intermediate heat
exchanger 7 is a heat exchanger for cooling the conjoined flow of
the refrigerant discharged from the first-stage compression element
103c of the first compression mechanism 103 and the refrigerant
discharged from the first-stage compression element 104c of the
second compression mechanism 104 during the air-cooling operation.
Specifically, the intermediate heat exchanger 7 functions as a
shared cooler for two compression mechanisms 103, 104 during
air-cooling operation. Accordingly, the circuit configuration is
simplified around the compression mechanism 102 when the
intermediate heat exchanger 7 is provided to the
parallel-multistage-compression-type compression mechanism 102 in
which a plurality of multistage-compression-type compression
mechanisms 103, 104 are connected in parallel.
[0178] The first inlet-side intermediate branch tube 81
constituting the intermediate refrigerant tube 8 is provided with a
non-return mechanism 81a for allowing the flow of refrigerant from
the discharge side of the first-stage compression element 103c of
the first compression mechanism 103 toward the intermediate header
tube 82 and for blocking the flow of refrigerant from the
intermediate header tube 82 toward the discharge side of the
first-stage compression element 103c, while the second inlet-side
intermediate branch tube 84 constituting the intermediate
refrigerant tube 8 is provided with a non-return mechanism 84a for
allowing the flow of refrigerant from the discharge side of the
first-stage compression element 104c of the second compression
mechanism 103 toward the intermediate header tube 82 and for
blocking the flow of refrigerant from the intermediate header tube
82 toward the discharge side of the first-stage compression element
104c. In the present modification, non-return valves are used as
the non-return mechanisms 81 a, 84a. Therefore, even if either one
of the compression mechanisms 103, 104 is stopped, there are no
instances in which refrigerant discharged from the first-stage
compression element of the operating compression mechanism passes
through the intermediate refrigerant tube 8 and travels to the
discharge side of the first-stage compression element of the
stopped compression mechanism. Therefore, there are no instances in
which refrigerant discharged from the first-stage compression
element of the operating compression mechanism passes through the
interior of the first-stage compression element of the stopped
compression mechanism and exits out through the intake side of the
compression mechanism 102, which would cause the refrigeration oil
of the stopped compression mechanism to flow out, and it is thus
unlikely that there will be insufficient refrigeration oil for
starting up the stopped compression mechanism. In the case that the
compression mechanisms 103, 104 are operated in order of priority
(for example, in the case of a compression mechanism in which
priority is given to operating the first compression mechanism
103), the stopped compression mechanism described above will always
be the second compression mechanism 104, and therefore in this case
only the non-return mechanism 84a corresponding to the second
compression mechanism 104 need be provided.
[0179] In cases of a compression mechanism which prioritizes
operating the first compression mechanism 103 as described above,
since a shared intermediate refrigerant tube 8 is provided for both
compression mechanisms 103, 104, the refrigerant discharged from
the first-stage compression element 103c corresponding to the
operating first compression mechanism 103 passes through the second
outlet-side intermediate branch tube 85 of the intermediate
refrigerant tube 8 and travels to the intake side of the
second-stage compression element 104d of the stopped second
compression mechanism 104, whereby there is a danger that
refrigerant discharged from the first-stage compression element
103c of the operating first compression mechanism 103 will pass
through the interior of the second-stage compression element 104d
of the stopped second compression mechanism 104 and exit out
through the discharge side of the compression mechanism 102,
causing the refrigeration oil of the stopped second compression
mechanism 104 to flow out, resulting in insufficient refrigeration
oil for starting up the stopped second compression mechanism 104.
In view of this, an on/off valve 85a is provided to the second
outlet-side intermediate branch tube 85 in the present
modification, and when the second compression mechanism 104 is
stopped, the flow of refrigerant through the second outlet-side
intermediate branch tube 85 is blocked by the on/off valve 85a. The
refrigerant discharged from the first-stage compression element
103c of the operating first compression mechanism 103 thereby no
longer passes through the second outlet-side intermediate branch
tube 85 of the intermediate refrigerant tube 8 and travels to the
intake side of the second-stage compression element 104d of the
stopped second compression mechanism 104; therefore, there are no
longer any instances in which the refrigerant discharged from the
first-stage compression element 103c of the operating first
compression mechanism 103 passes through the interior of the
second-stage compression element 104d of the stopped second
compression mechanism 104 and exits out through the discharge side
of the compression mechanism 102 which causes the refrigeration oil
of the stopped second compression mechanism 104 to flow out, and it
is thereby made even more unlikely that there will be insufficient
refrigeration oil for starting up the stopped second compression
mechanism 104. An electromagnetic valve is used as the on/off valve
85a in the present modification.
[0180] In the case of a compression mechanism which prioritizes
operating the first compression mechanism 103, the second
compression mechanism 104 is started up in continuation from the
starting up of the first compression mechanism 103, but at this
time, since a shared intermediate refrigerant tube 8 is provided
for both compression mechanisms 103, 104, the starting up takes
place from a state in which the pressure in the discharge side of
the first-stage compression element 103c of the second compression
mechanism 104 and the pressure in the intake side of the
second-stage compression element 103d are greater than the pressure
in the intake side of the first-stage compression element 103c and
the pressure in the discharge side of the second-stage compression
element 103d, and it is difficult to start up the second
compression mechanism 104 in a stable manner. In view of this, in
the present modification, there is provided a startup bypass tube
86 for connecting the discharge side of the first-stage compression
element 104c of the second compression mechanism 104 and the intake
side of the second-stage compression element 104d, and an on/off
valve 86a is provided to this startup bypass tube 86. In cases in
which the second compression mechanism 104 is stopped, the flow of
refrigerant through the startup bypass tube 86 is blocked by the
on/off valve 86a and the flow of refrigerant through the second
outlet-side intermediate branch tube 85 is blocked by the on/off
valve 85a. When the second compression mechanism 104 is started up,
a state in which refrigerant is allowed to flow through the startup
bypass tube 86 can be restored via the on/off valve 86a, whereby
the refrigerant discharged from the first-stage compression element
104c of the second compression mechanism 104 is drawn into the
second-stage compression element 104d via the startup bypass tube
86 without being mixed with the refrigerant discharged from the
first-stage compression element 103c of the first compression
mechanism 103, a state of allowing refrigerant to flow through the
second outlet-side intermediate branch tube 85 can be restored via
the on/off valve 85a at a point in time when the operating state of
the compression mechanism 102 has been stabilized (e.g., a point in
time when the intake pressure, discharge pressure, and intermediate
pressure of the compression mechanism 102 have been stabilized),
the flow of refrigerant through the startup bypass tube 86 can be
blocked by the on/off valve 86a, and operation can transition to
the normal air-cooling operation or air-warming operation. In the
present modification, one end of the startup bypass tube 86 is
connected between the on/off valve 85a of the second outlet-side
intermediate branch tube 85 and the intake side of the second-stage
compression element 104d of the second compression mechanism 104,
while the other end is connected between the discharge side of the
first-stage compression element 104c of the second compression
mechanism 104 and the non-return mechanism 84a of the second
inlet-side intermediate branch tube 84, and when the second
compression mechanism 104 is started up, the startup bypass tube 86
can be kept in a state of being substantially unaffected by the
intermediate pressure portion of the first compression mechanism
103. An electromagnetic valve is used as the on/off valve 86a in
the present modification.
[0181] The actions of the air-cooling operation, air-warming
operation, and/or defrosting operation of the air-conditioning
apparatus 1 of the present modification are not described herein
because they are essentially the same as the actions in
Modification 3 described above (FIGS. 3, 4, 16, 17, 28 through 37,
and their relevant descriptions), except for the points of
modification owing to the somewhat higher level of complexity of
the circuit configuration surrounding the compression mechanism 102
due to the compression mechanism 102 being provided instead of the
compression mechanism 2.
[0182] The same operational effects as those of Modification 3
described above can also be achieved with the configuration of the
present modification.
(7) Other Embodiments
[0183] Embodiments of the present invention and modifications
thereof are described above with reference to the drawings;
however, the specific configuration is not limited to these
embodiments or their modifications, and can be changed within a
range that does not deviate from the scope of the invention.
[0184] For example, in the above-described embodiment and
modifications thereof, the present invention may be applied to a
so-called chiller-type air-conditioning apparatus in which water or
brine is used as a heating source or cooling source for conducting
heat exchange with the refrigerant flowing through the usage-side
heat exchanger 6, and a secondary heat exchanger is provided for
conducting heat exchange between indoor air and the water or brine
that has undergone heat exchange in the usage-side heat exchanger
6.
[0185] The present invention can also be applied to other types of
refrigeration apparatuses besides the above-described chiller-type
air-conditioning apparatus, as long as the apparatus performs a
multistage compression refrigeration cycle by using a refrigerant
that operates in a supercritical range as its refrigerant.
[0186] The refrigerant that operates in a supercritical range is
not limited to carbon dioxide; ethylene, ethane, nitric oxide, and
other gases may also be used.
INDUSTRIAL APPLICABILITY
[0187] If the present invention is used, when the reverse cycle
defrosting operation is performed in a refrigeration apparatus
which has a refrigerant circuit configured to be capable of
switching between a cooling operation and a heating operation and
which uses a refrigerant that operates in the supercritical range
to perform a multistage compression-type refrigeration cycle, the
temperature decrease on the usage side can be minimized, and the
defrosting capacity can be improved.
REFERENCE SIGNS LIST
[0188] 1 Air-conditioning apparatus (refrigeration apparatus)
[0189] 2, 102 Compression mechanisms
[0190] 3 Switching mechanism
[0191] 4 Heat source-side heat exchanger
[0192] 6 Usage-side heat exchanger
[0193] 18c First second-stage injection tube
[0194] 19 Second second-stage injection tube
* * * * *