U.S. patent application number 12/864539 was filed with the patent office on 2011-01-13 for refrigeration apparatus.
This patent application is currently assigned to DAIKIN INDUSTRIES, LTD.. Invention is credited to Shuji Fujimoto, Atsushi Yoshimi.
Application Number | 20110005269 12/864539 |
Document ID | / |
Family ID | 40912725 |
Filed Date | 2011-01-13 |
United States Patent
Application |
20110005269 |
Kind Code |
A1 |
Fujimoto; Shuji ; et
al. |
January 13, 2011 |
REFRIGERATION APPARATUS
Abstract
A refrigeration apparatus includes a compression mechanism, a
heat source-side heat exchanger, a usage-side heat exchanger and an
intercooler. The compression mechanism has compression elements
arranged so that refrigerant discharged from a first-stage
compression element is sequentially compressed by a second-stage
compression element. The intercooler is connected to an
intermediate refrigerant tube arranged and configured to draw
refrigerant discharged from the first-stage compression element
into the second-stage compression element. The intercooler is
arranged and configured to cool the refrigerant discharged from the
first-stage compression element and drawn into the second-stage
compression element. The intercooler and the intermediate
refrigerant tube and are arranged and configured to perform wet
prevention control when a heat source temperature of the
intercooler or an outlet refrigerant temperature of the intercooler
is equal to or less than a saturation temperature of the
refrigerant fed from the first-stage compression element to the
second-stage compression element.
Inventors: |
Fujimoto; Shuji; ( Osaka,
JP) ; Yoshimi; Atsushi; ( 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: |
40912725 |
Appl. No.: |
12/864539 |
Filed: |
January 27, 2009 |
PCT Filed: |
January 27, 2009 |
PCT NO: |
PCT/JP2009/051235 |
371 Date: |
July 26, 2010 |
Current U.S.
Class: |
62/510 ;
62/513 |
Current CPC
Class: |
F25B 2400/13 20130101;
F25B 9/008 20130101; F25B 2313/0272 20130101; F25B 2400/075
20130101; F25B 2500/28 20130101; F25B 2400/072 20130101; F25B
2313/02741 20130101; F25B 2700/21 20130101; F25B 13/00 20130101;
F25B 2400/04 20130101; F25B 2309/061 20130101; F25B 1/10 20130101;
F25B 2400/23 20130101 |
Class at
Publication: |
62/510 ;
62/513 |
International
Class: |
F25B 1/10 20060101
F25B001/10; F25B 41/00 20060101 F25B041/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 30, 2008 |
JP |
2008-019764 |
Claims
1. A refrigeration apparatus comprising: a compression mechanism
having a plurality of compression elements configured and arranged
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 of the plurality
of compression elements; a heat source-side heat exchanger; a
usage-side heat exchanger; an intercooler connected to an
intermediate refrigerant tube arranged and configured to draw
refrigerant discharged from the first-stage compression element
into the second-stage compression element, the intercooler being
arranged and configured to cool the refrigerant discharged from the
first-stage compression element and drawn into the second-stage
compression element; and an intercooler bypass tube connected to
the intermediate refrigerant tube so as to bypass the intercooler,
the intercooler, the intermediate refrigerant tube and the
intercooler bypass tube being arranged and configured to perform
wet prevention control so that refrigerant does not flow to the
intercooler when a heat source temperature of the intercooler or an
outlet refrigerant temperature of the intercooler is equal to or
less than a saturation temperature of the refrigerant fed from the
first-stage compression element to the second-stage compression
element.
2. The refrigeration apparatus according to claim 1, wherein the
intercooler is a heat exchanger in which air is used as a heat
exchange medium.
3. The refrigeration apparatus according to claim 1, wherein the
intercooler is a heat exchanger in which water is used as a heat
exchange medium; and the intercooler, the intermediate refrigerant
tube and the intercooler bypass tube are arranged and configured
such that water fed to the intercooler is stopped during the wet
prevention control.
4. A refrigeration apparatus comprising: a compression mechanism
having a plurality of compression elements configured and arranged
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 of the plurality
of compression elements; a heat source-side heat exchanger; a
usage-side heat exchanger; and an intercooler which is a heat
exchanger having water as a heat exchange medium, the intercooler
being connected to an intermediate refrigerant tube arranged and
configured to draw refrigerant discharged from the first-stage
compression element into the second-stage compression element, and
the intercooler being arranged and configured to cool the
refrigerant discharged from the first-stage compression element and
drawn into the second-stage compression element, the intercooler
and the intermediate refrigerant tube being arranged and configured
to perform wet prevention control in which a flow rate of water
that flows through the intercooler is reduced when a heat source
temperature of the intercooler or an outlet refrigerant temperature
of the intercooler is equal to or less than a saturation
temperature of the refrigerant fed from the first-stage compression
element to the second-stage compression element.
5. The refrigeration apparatus according to claim 4, wherein, the
intercooler and the intermediate refrigerant tube being arranged
and configured such that the flow rate of water that flows through
the intercooler is controlled so that the outlet refrigerant
temperature of the intercooler is higher than the saturation
temperature of the refrigerant fed from the first-stage compression
element to the second-stage compression element during the wet
prevention control.
6. The refrigeration apparatus according to claim 1, further
comprising a second-stage injection tube arranged and configured to
branch refrigerant flowing between the heat source-side heat
exchanger and the usage-side heat exchanger and to return the
refrigerant to the second-stage compression element.
7. The refrigeration apparatus according to claim 4, further
comprising a second-stage injection tube arranged and configured to
branch refrigerant flowing between the heat source-side heat
exchanger and the usage-side heat exchanger and to return the
refrigerant to the second-stage compression element.
Description
TECHNICAL FIELD
[0001] The present invention relates to a refrigeration apparatus,
and particularly relates to a refrigeration apparatus which
performs a multistage compression refrigeration cycle.
BACKGROUND ART
[0002] As one conventional example of a refrigeration apparatus
which performs a multistage compression refrigeration cycle, Patent
Document 1 discloses an air-conditioning apparatus which performs a
two-stage compression refrigeration cycle. This air-conditioning
apparatus primarily has a compressor having two compression
elements connected in series, an outdoor heat exchanger, an
expansion valve, and an indoor heat exchanger.
[0003] <Patent Document 1>
[0004] Japanese Laid-open Patent Application No. 2007-232263
DISCLOSURE OF THE INVENTION
[0005] The refrigeration apparatus according to a first aspect of
the present invention comprises a compression mechanism, a heat
source-side heat exchanger, a usage-side heat exchanger, and an
intercooler, and an intercooler bypass 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
compressor in which a single compression element is incorporated
and/or a plurality of compressors 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
intercooler is provided to an intermediate refrigerant tube for
drawing refrigerant discharged from the first-stage compression
element into the second-stage compression element, and the
intercooler functions as a cooler of the refrigerant discharged
from the first-stage compression element and drawn into the
second-stage compression element. The intercooler bypass tube is
connected to the intermediate refrigerant tube so as to bypass the
intercooler. In the refrigeration apparatus, a wet prevention
control is performed using the intercooler bypass tube so that
refrigerant does not flow to the intercooler when the heat source
temperature of the intercooler or the outlet refrigerant
temperature of the intercooler is equal to or less than the
saturation temperature of the refrigerant fed from the first-stage
compression element to the second-stage compression element.
[0006] In a conventional air-conditioning apparatus, since the
refrigerant discharged from the first-stage compression element of
the compressor is drawn into the second-stage compression element
of the compressor and further compressed, the temperature of the
refrigerant discharged from the second-stage compression element of
the compressor is increased, there is a large difference in
temperature between the refrigerant and the air and/or water as a
heat source in, e.g., the outdoor heat exchanger functioning as a
refrigerant cooler, and the outdoor heat exchanger has much heat
radiation loss, which poses a problem in that it is difficult to
achieve a high operating efficiency.
[0007] As a countermeasure to such problems, the intercooler which
functions as a cooler of the refrigerant discharged from the
first-stage compression element and drawn into the second-stage
compression element is provided to the intermediate refrigerant
tube for drawing refrigerant discharged from the first-stage
compression element into the second-stage compression element,
thereby lowering the temperature of the refrigerant drawn into the
second-stage compression element. As a result, the temperature of
the refrigerant discharged from the second-stage compression
element is reduced, and a reduction in heat radiation loss in the
outdoor heat exchanger is conceivable.
[0008] However, in such a configuration, the refrigerant discharged
from the first-stage compression element and drawn into the
second-stage compression element is liable to be excessively cooled
under operating conditions in which the temperature of the water
and/or air as the heat source of the intercooler is low. Therefore,
the refrigerant drawn into the second-stage compression element
becomes wet, and the reliability of the compressor is liable to be
compromised.
[0009] In view of the above, this refrigeration apparatus uses the
intercooler bypass tube as wet prevention control that does not
allow refrigerant to flow to the intercooler when the heat source
temperature of the intercooler or the outlet refrigerant
temperature of the intercooler is equal to or less than the
saturation temperature of the refrigerant fed from the first-stage
compression element to the second-stage compression element.
[0010] Therefore, this refrigeration apparatus can prevent the
refrigerant drawn into the second-stage compression element from
becoming wet even under operating conditions in which the heat
source temperature of the intercooler is low.
[0011] The refrigeration apparatus according to a second aspect of
the present invention is the refrigeration apparatus according to
the first aspect of the present invention, wherein the intercooler
is a heat exchanger in which air is used as a heat source.
[0012] The refrigeration apparatus prevents the refrigerant drawn
into to the second-stage compression element from becoming wet even
under operating conditions in which the temperature of the air as
the heat source of the intercooler is low.
[0013] The refrigeration apparatus according to a third aspect of
the present invention is the refrigeration apparatus according to
the first aspect of the present invention, wherein the intercooler
is a heat exchanger in which water is used as a heat source; and
water fed to the intercooler is stopped during wet prevention
control.
[0014] The refrigeration apparatus can prevent the refrigerant
drawn into to the second-stage compression element from becoming
wet even under operating conditions in which the temperature of the
water as the heat source of the intercooler is low. Also, the
refrigeration apparatus can prevent refrigerant inside the
intercooler from liquefying and pooling because water fed to the
intercooler is stopped during wet prevention control.
[0015] The refrigeration apparatus according to a fourth aspect of
the present invention comprises a compression mechanism, a heat
source-side heat exchanger, a usage-side heat exchanger, and an
intercooler. 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 compressor in which a single
compression element is incorporated and/or a plurality of
compressors 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 intercooler is provided to an
intermediate refrigerant tube for drawing refrigerant discharged
from the first-stage compression element into the second-stage
compression element, and the intercooler functions as a cooler of
the refrigerant discharged from the first-stage compression element
and drawn into the second-stage compression element. The
refrigeration apparatus carries out wet prevention control for
reducing the flow rate of water that flows through the intercooler
when the heat source temperature of the intercooler or the outlet
refrigerant temperature of the intercooler is equal to or less than
the saturation temperature of the refrigerant fed from the
first-stage compression element to the second-stage compression
element. As used herein, the phrase "for reducing the flow rate of
water that flows through the intercooler" includes the meaning
"water fed to the intercooler is stopped."
[0016] In a conventional air-conditioning apparatus, since the
refrigerant discharged from the first-stage compression element of
the compressor is drawn into the second-stage compression element
of the compressor and further compressed, the temperature of the
refrigerant discharged from the second-stage compression element of
the compressor is increased, there is a large difference in
temperature between the refrigerant and the air and/or water as a
heat source in, e.g., the outdoor heat exchanger functioning as a
refrigerant cooler, and the outdoor heat exchanger has much heat
radiation loss, which poses a problem in that it is difficult to
achieve a high operating efficiency.
[0017] As a countermeasure to such problems, the intercooler which
functions as a cooler of the refrigerant discharged from the
first-stage compression element and drawn into the second-stage
compression element is provided to the intermediate refrigerant
tube for drawing refrigerant discharged from the first-stage
compression element into the second-stage compression element,
thereby lowering the temperature of the refrigerant drawn into the
second-stage compression element. As a result, the temperature of
the refrigerant discharged from the second-stage compression
element is reduced, and a reduction in heat radiation loss in the
outdoor heat exchanger is conceivable.
[0018] However, in such a configuration, the refrigerant discharged
from the first-stage compression element and drawn into the
second-stage compression element is liable to be excessively cooled
under operating conditions in which the temperature of the water
and/or air as the heat source of the intercooler is low. Therefore,
the refrigerant drawn into the second-stage compression element
becomes wet, and the reliability of the compressor is liable to be
compromised.
[0019] In view of the above, this refrigeration apparatus carries
out wet prevention control for reducing the flow rate of water that
flows through the intercooler when the heat source temperature of
the intercooler or the outlet refrigerant temperature of the
intercooler is equal to or less than the saturation temperature of
the refrigerant fed from the first-stage compression element to the
second-stage compression element.
[0020] The refrigeration apparatus thereby prevents the refrigerant
drawn into the second-stage compression element from becoming wet
even under operating conditions in which the temperature of the
water as the heat source of the intercooler is low.
[0021] The refrigeration apparatus according to a fifth aspect of
the present invention is the refrigeration apparatus according to
the fourth aspect of the present invention, wherein, in the wet
prevention control, the flow rate of water that flows through the
intercooler is controlled so that the outlet refrigerant
temperature of the intercooler is higher than the saturation
temperature of the refrigerant fed from the first-stage compression
element to the second-stage compression element.
[0022] The refrigeration apparatus controls the flow rate of water
that flows through the intercooler so that the outlet refrigerant
temperature of the intercooler is higher than the saturation
temperature of the refrigerant fed from the first-stage compression
element to the second-stage compression element in the wet
prevention control. Therefore, the refrigerant drawn into the
second-stage compression element can not only be prevented from
becoming wet, but the temperature of the refrigerant drawn into the
second-stage compression element can also be reduced, whereby the
temperature of the refrigerant discharged from the second-stage
compression element can be kept low, and the power consumption of
the compression mechanism can be reduced.
[0023] The refrigeration apparatus according to a sixth aspect of
the present invention is the refrigerant apparatus according to any
of the first to fifth aspects of the present invention, further
comprising a second-stage injection tubes for branching refrigerant
that flows between the heat source-side heat exchanger and the
usage-side heat exchanger after the refrigerant has been compressed
by the compression mechanism, and returning the refrigerant to the
second-stage compression element.
[0024] In addition to cooling the refrigerant drawn into the
second-stage compression element by the intercooler, the
refrigeration apparatus can reduce the temperature of the
refrigerant drawn into the second-stage compression element by
intermediate injection using a second-stage injection tube.
Therefore, the temperature of the refrigerant discharged from the
compression mechanism can be kept low, and the power consumption of
the compression mechanism can be reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a schematic structural diagram of an
air-conditioning apparatus as an embodiment of the refrigeration
apparatus according to the present invention.
[0026] FIG. 2 is a pressure-enthalpy graph representing the
refrigeration cycle during the air-cooling operation.
[0027] FIG. 3 is a temperature-entropy graph representing the
refrigeration cycle during the air-cooling operation.
[0028] FIG. 4 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 1.
[0029] FIG. 5 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 1.
[0030] FIG. 6 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 2.
[0031] FIG. 7 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 4.
[0032] FIG. 8 is a pressure-enthalpy graph representing the
refrigeration cycle during the air-cooling operation in the
air-conditioning apparatus according to Modification 4.
[0033] FIG. 9 is a temperature-entropy graph representing the
refrigeration cycle during the air-cooling operation in the
air-conditioning apparatus according to Modification 4.
[0034] FIG. 10 is a pressure-enthalpy graph representing the
refrigeration cycle during the air-warming operation in the
air-conditioning apparatus according to Modification 4.
[0035] FIG. 11 is a temperature-entropy graph representing the
refrigeration cycle during the air-warming operation in the
air-conditioning apparatus according to Modification 4.
[0036] FIG. 12 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 4.
[0037] FIG. 13 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 5.
[0038] FIG. 14 is a schematic structural diagram of an
air-conditioning apparatus according to Modification 5.
EXPLANATION OF THE REFERENCE NUMERALS
[0039] 1 Air-conditioning apparatus (refrigeration apparatus)
[0040] 2, 102 Compression mechanisms [0041] 4 Heat source-side heat
exchanger [0042] 6 Usage-side heat exchanger [0043] 7 Intercooler
[0044] 8 Intermediate refrigerant tube [0045] 9 Intercooler bypass
tube [0046] 18c First second-stage injection tube [0047] 19 Second
second-stage injection tube
BEST MODE FOR CARRYING OUT THE INVENTION
[0048] Embodiments of the refrigeration apparatus according to the
present invention are described hereinbelow with reference to the
drawings.
(1) Configuration of Air-Conditioning Apparatus
[0049] 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 so as to be
capable of an air-cooling 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.
[0050] The refrigerant circuit 10 of the air-conditioning apparatus
1 has primarily a compression mechanism 2, a heat source-side heat
exchanger 4, an expansion mechanism 5, a usage-side heat exchanger
6, and an intercooler 7.
[0051] 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
admit 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
admit the refrigerant discharged to the intermediate refrigerant
tube 8 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 refrigerant 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 2d 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 heat source-side heat exchanger 4, 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 depressurizing mechanism
41c for depressurizing the refrigerator oil flowing through the oil
return tube 41b. A capillary tube is used for the depressurizing
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 heat
source-side heat exchanger 4 and for blocking the flow of
refrigerant from the heat source-side heat exchanger 4 to the
discharge side of the compression mechanism 2, and a non-return
valve is used in the present embodiment.
[0052] 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.
[0053] The heat source-side heat exchanger 4 is a heat exchanger
that functions as a refrigerant cooler. One end of the heat
source-side heat exchanger 4 is connected to the compression
mechanism 2, and the other end is connected to the expansion
mechanism 5. The heat source-side heat exchanger is a heat
exchanger having air as a heat source (i.e., cooling source). The
air as the heat source is supplied to the heat source-side heat
exchanger 4 by a heat source-side fan (not shown).
[0054] The expansion mechanism 5 is a mechanism for depressurizing
the refrigerant, and an electric expansion valve is used in the
present embodiment. One end of the expansion mechanism 5 is
connected to the heat source-side heat exchanger 4, and the other
end is connected to the usage-side heat exchanger 6. In the present
embodiment, the expansion mechanism 5 depressurizes the
high-pressure refrigerant cooled in the heat source-side heat
exchanger 4 before feeding the refrigerant to the usage-side heat
exchanger 6.
[0055] The usage-side heat exchanger 6 is a heat exchanger that
functions as a heater of refrigerant. One end of the usage-side
heat exchanger 6 is connected to the expansion mechanism 5, and the
other end is connected to the compression mechanism 2. The
usage-side heat exchanger 6 is a heat exchanger having air and/or
water as a heat source (i.e., a heating source).
[0056] The intercooler 7 is provided to the intermediate
refrigerant tube 8, and is a heat exchanger which functions as a
cooler of refrigerant discharged from the compression element 2c on
the first-stage side and drawn into the compression element 2d. The
intercooler 7 is a heat exchanger having air as a heat source
(i.e., a cooling source). The air as the heat source is supplied to
the intercooler 7 by a heat source-side fan (not shown). There are
instances in which the intercooler 7 is integrated with the heat
source-side heat exchanger 4, in which case there are
configurations in which air used as a heat source is supplied by a
heat source-side fan shared between the heat source-side heat
exchanger 4 and the intercooler 7. Thus, it is acceptable to say
that the intercooler 7 is a cooler that uses an external heat
source, meaning that the intercooler does not use the refrigerant
that circulates through the refrigerant circuit 10.
[0057] An intercooler bypass tube 9 is connected to the
intermediate refrigerant tube 8 so as to bypass the intercooler 7.
This intercooler bypass tube 9 is a refrigerant tube for limiting
the flow rate of refrigerant flowing through the intercooler 7. The
intercooler bypass tube 9 is provided with an intercooler bypass
on/off valve 11. The intercooler bypass on/off valve 11 is an
electromagnetic valve in the present embodiment. The intercooler
bypass on/off valve 11 is essentially closed in the present
embodiment, except during temporary operation such as the
later-described wet prevention control.
[0058] The intermediate refrigerant tube 8 is provided with a
cooler on/off valve 12 in a position leading toward the intercooler
7 from the part connecting with the intercooler bypass tube 9
(i.e., in the portion leading from the part connecting with the
intercooler bypass tube 9 nearer the inlet of the intercooler 7 to
the connecting part nearer the outlet of the intercooler 7). The
cooler on/off valve 12 is a mechanism for limiting the flow rate of
refrigerant flowing through the intercooler 7. The cooler on/off
valve 12 is an electromagnetic valve in the present embodiment. The
cooler on/off valve 12 is essentially open in the present
embodiment, except during temporary operation such as the
later-described wet prevention control. In the present embodiment,
the cooler on/off valve 12 is provided in a position nearer the
inlet of the intercooler 7.
[0059] 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 discharge side of
the second-stage compression element 2d to the first-stage
compression element 2c. The non-return mechanism 15 is a non-return
valve in the present embodiment. In the present embodiment, the
non-return mechanism 15 is provided to the intermediate refrigerant
tube 8 in the portion leading away from the outlet of the
intercooler 7 toward the part connecting with the intercooler
bypass tube 9.
[0060] Furthermore, the air-conditioning apparatus 1 is provided
with various sensors. Specifically, the outlet of the intercooler 7
is provided with an intercooler outlet temperature sensor 52 for
detecting the temperature of refrigerant at the outlet of the
intercooler 7. 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 intercooler 7. An intermediate pressure
sensor 54 for detecting the intermediate pressure of the
compression mechanism, which is the pressure of the refrigerant
that flows through the intermediate refrigerant tube 8, is provided
to the intermediate refrigerant tube 8. Though not shown in the
drawings, the air-conditioning apparatus 1 has a controller for
controlling the actions of the compression mechanism 2, the
expansion mechanism 5, the intercooler bypass on/off valve 11, the
cooler on/off valve 12, and the other components constituting the
air-conditioning apparatus 1.
(2) Action of the Air-Conditioning Apparatus
[0061] Next, the action of the air-conditioning apparatus 1 of the
present embodiment will be described using FIGS. 1 through 3. FIG.
2 is a pressure-enthalpy graph representing the refrigeration cycle
during the air-cooling operation, and FIG. 3 is a
temperature-entropy graph representing the refrigeration cycle
during the air-cooling operation. Operation control during the
cooling operation described below and wet prevention control for
preventing refrigerant drawn into the second-stage compression
element from becoming wet due to cooling in the intercooler 7 are
carried out by the above-described 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. 2 and 3), the term "low pressure"
means a low pressure in the refrigeration cycle (specifically, the
pressure at points A and F in FIGS. 2 and 3), and the term
"intermediate pressure" and/or "intermediate pressure of the
compression mechanism" means an intermediate pressure in the
refrigeration cycle (specifically, the pressure at points B1 and C1
in FIGS. 2 and 3).
[0062] The opening degree of the expansion mechanism 5 is adjusted
during the air-cooling operation. The cooler on/off valve 12 is
opened and the intercooler bypass on/off valve 11 of the
intercooler bypass tube 9 is closed, thereby putting the
intercooler 7 into a state of functioning as a cooler.
[0063] When the compression mechanism 2 is driven while the
refrigerant circuit 10 is in this state, low-pressure refrigerant
(refer to point A in FIGS. 1 through 3) is drawn into the
compression mechanism 2 through the intake tube 2a, and after the
refrigerant is first compressed to an intermediate pressure by the
compression element 2c, the refrigerant is discharged to the
intermediate refrigerant tube 8 (refer to point B1 in FIGS. 1
through 3). The intermediate-pressure refrigerant discharged from
the first-stage compression element 2c is cooled in the intercooler
7 by undergoing heat exchange with the air as a cooling source
(refer to point C1 in FIGS. 1 through 3). The refrigerant cooled in
the intercooler 7 is then led to and further compressed in the
compression element 2d connected to the second-stage side of the
compression element 2c, and the refrigerant is then discharged from
the compression mechanism 2 to the discharge tube 2b (refer to
point D in FIGS. 1 through 3). The high-pressure refrigerant
discharged from the compression mechanism 2 is compressed to a
pressure exceeding a critical pressure (i.e., the critical pressure
Pcp at the critical point CP shown in FIG. 2) by the two-stage
compression action of the compression elements 2c, 2d. 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 led back 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 fed to the heat source-side heat exchanger 4
functioning as a refrigerant cooler. 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 (refer to point E in FIGS. 1 through 3). The high-pressure
refrigerant cooled in the heat source-side heat exchanger 4 is then
depressurized by the expansion mechanism 5 to become a low-pressure
gas-liquid two-phase refrigerant, which is fed to the usage-side
heat exchanger 6 functioning as a refrigerant heater (refer to
point F in FIGS. 1 through 3). 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 in
the usage-side heat exchanger 6, and the refrigerant evaporates as
a result (refer to point A in FIGS. 1 through 3). The low-pressure
refrigerant heated in the usage-side heat exchanger 6 is then led
back into the compression mechanism 2. In this manner the
air-cooling operation is performed.
[0064] Thus, in the air-conditioning apparatus 1, the intercooler 7
is provided to the intermediate refrigerant tube 8 for letting
refrigerant discharged from the compression element 2c into the
compression element 2d, and during the air-cooling operation, the
cooler on/off valve 12 is opened and the intercooler bypass on/off
valve 11 of the intercooler bypass tube 9 is closed, thereby
putting the intercooler 7 into a state of functioning as a cooler.
Therefore, the refrigerant drawn into the compression element 2d on
the second-stage side of the compression element 2c decreases in
temperature (refer to points B1 and C1 in FIG. 3) and the
refrigerant discharged from the compression element 2d also
decreases in temperature (refer to points D and D' in FIG. 3), in
comparison with cases in which no intercooler 7 is provided (in
this case, the refrigeration cycle is performed in the sequence in
FIGS. 2 and 3: point A.fwdarw.point B1.fwdarw.point D'.fwdarw.point
E.fwdarw.point F). Therefore, in the heat source-side heat
exchanger 4 functioning as a cooler of high-pressure refrigerant in
this air-conditioning apparatus 1, operating efficiency can be
improved over cases in which no intercooler 7 is provided, because
the temperature difference between the refrigerant and water or air
as the cooling source can be reduced, and heat radiation loss can
be reduced by an amount equivalent to the area enclosed by
connecting points B1, D', D, and C1 in FIG. 3.
[0065] <Wet Prevention Control>
[0066] In the cooling operation that accompanies cooling of the
intermediate-pressure refrigerant by the intercooler 7 as described
above, the refrigerant discharged from the first-stage compression
element 2c and drawn into the second-stage compression element 2d
is liable to be excessively cooled when under operating conditions
in which the temperature of the air as the heat source of the
intercooler 7 is low. Therefore, the refrigerant drawn into the
second-stage compression element 2d becomes wet, and the
reliability of the compressor 2 is liable to be compromised.
[0067] In view of the above, in the present embodiment, wet
prevention control uses the intercooler bypass tube 9 so that
refrigerant is not allowed to flow to the intercooler 7 when the
heat source temperature of the intercooler 7 is equal to or less
than the saturation temperature of the refrigerant fed from the
first-stage compression element 2c to the second-stage compression
element 2d. Specifically, in the present embodiment, when the
temperature of air as the heat source of the intercooler 7 detected
by the air temperature sensor 53 is equal to or less than the
saturation temperature obtained by converting the intermediate
pressure of the compression mechanism detected by the intermediate
pressure sensor 54, the intercooler bypass on/off valve 11 of the
intercooler bypass tube 9 is opened and the cooler on/off valve 12
is closed, whereby the refrigerant discharged from the first-stage
compression element 2c flows into the intake side of the
second-stage compression element 2d by way of the intercooler
bypass tube 9, and intermediate-pressure refrigerant does not flow
into the intercooler 7. In the case a refrigerant that operates in
the supercritical range is used such as in the present embodiment,
the pressure of the refrigerant discharged from the first-stage
compression element 2c is increased, and there may be cases in
which the operating conditions are such that the intermediate
pressure of the compression mechanism exceeds a critical pressure
(i.e., the critical pressure Pcp at the critical point CP shown in
FIG. 2). In such operating conditions, there is no longer the
concept of a saturated state in not only high-pressure refrigerant,
but also in intermediate-pressure refrigerant, and there is
therefore no further need for the wet prevention control described
above. Accordingly, in wet prevention control, it is determined
whether the intermediate pressure of the compression mechanism is
less than the critical pressure before a determination is made as
to whether the temperature of the air as the heat source is equal
to or less than the saturation temperature of the refrigerant fed
from the first-stage compression element 2c to the second-stage
compression element 2d. In the case that the intermediate pressure
of the compression mechanism is equal to or greater than the
critical pressure, the refrigerant is allowed to continue flowing
to the intercooler 7 to keep the temperature of the refrigerant
drawn into the second-stage compression element 2d as low as
possible. In the case that the intermediate pressure of the
compression mechanism is less than the critical pressure, it is
determined whether the temperature of the air as the heat source of
the intercooler 7 detected by the air temperature sensor 53 is
equal to or less than the saturation temperature obtained by
converting the intermediate pressure of the compression mechanism
detected by the intermediate pressure sensor 54. When the
temperature of the air as the heat source of the intercooler 7 is
equal to or less than the saturation temperature obtained by
converting the intermediate pressure of the compression mechanism,
the intermediate-pressure refrigerant is not allowed to flow to the
intercooler 7; and when the temperature of the air as the heat
source of the intercooler 7 is greater than the saturation
temperature obtained by converting the intermediate pressure of the
compression mechanism, the refrigerant is allowed to continue
flowing to the intercooler 7.
[0068] In this manner, with the air-conditioning apparatus 1 of the
present embodiment, when the temperature of the air as the heat
source of the intercooler 7 is equal to or less than the saturation
temperature of the intermediate-pressure refrigerant fed from the
first-stage compression element 2c to the second-stage compression
element 2d, wet prevention control that does not allow the
refrigerant to flow to the intercooler 7 is carried out using the
intercooler bypass tube 9. Therefore, the refrigerant drawn into
the second-stage compression element 2d can be prevented from
becoming wet, even under the operating conditions in which the
temperature of the air as the heat source of the intercooler 7 is
low.
[0069] With the air-conditioning apparatus 1, the cooler on/off
valve 12 disposed in the inlet side of the intercooler 7 is closed
when the temperature of the air as the heat source of the
intercooler 7 is equal to or less than the saturation temperature
of the intermediate-pressure refrigerant fed from the first-stage
compression element 2c to the second-stage compression element 2d.
Therefore, all of the refrigerant discharged from the first-stage
compression element 2c can be made to flow to the intercooler
bypass tube 9, and the intermediate-pressure refrigerant that flows
through the intermediate refrigerant tube 8 and the intercooler
bypass tube 9 can be prevented from flowing from the inlet side of
the intercooler 7 into the intercooler 7 and being retained inside
the intercooler 7. Also, in the present embodiment, since a
non-return mechanism 15 is provided to the outlet side of the
intercooler 7, the intermediate-pressure refrigerant that flows
through the intermediate refrigerant tube 8 and the intercooler
bypass tube 9 can be prevented from flowing from the outlet side of
the intercooler 7 to the intercooler 7 and being retained in the
intercooler 7. In a particular configuration in which the
intercooler 7 is integrally formed with the heat source-side heat
exchanger 4 and air as the heat source is fed to both the heat
source-side heat exchanger 4 and the intercooler 7 by a heat
source-side fan (not shown) shared by both the heat source-side
heat exchanger 4 and the intercooler 7, air as the heat source is
continuously fed to the intercooler 7 as well, as long as the air
as the heat source is fed to the heat source-side heat exchanger 4.
Therefore, it is effective to provide a cooler on/off valve 12 and
a non-return mechanism 15 because the intermediate-pressure
refrigerant is otherwise liable to flow into the intercooler 7 and
be retained inside the intercooler 7.
[0070] Instead of determining the necessity of wet prevention
control depending on whether the temperature of the air as the heat
source of the intercooler 7 is equal to or less than the saturation
temperature of the intermediate-pressure refrigerant fed from the
first-stage compression element 2c to the second-stage compression
element 2d, it is also possible to determine the necessity of wet
prevention control depending on whether the temperature of the
refrigerant (in this situation, the temperature of the refrigerant
detected by the intercooler outlet temperature sensor 52) in the
outlet of the intercooler 7 is equal to or less than the saturation
temperature of the intermediate-pressure refrigerant fed from the
first-stage compression element 2c to the second-stage compression
element 2d.
(3) Modification 1
[0071] In the embodiment described above, a heat exchanger is used
as the intercooler 7 in which air is the heat source, but a heat
exchanger may be used as the intercooler 7 in which water is used
as the heat source.
[0072] For example, in a configuration that feeds water to the
intercooler 7 via a water distribution tube 14 for intermediate
cooling, as shown in FIG. 4, wet prevention control may be carried
out so that a determination is made as to whether the temperature
of the water (in this case, the temperature of the water fed to the
intercooler 7 detected by a water temperature sensor 58 disposed in
the water inlet side of the intercooler 7) as the heat source of
the intercooler 7 is equal to or less than the saturation
temperature of the intermediate-pressure refrigerant fed from the
first-stage compression element 2c to the second-stage compression
element 2d, or whether the temperature of the refrigerant (in this
case, the temperature of the refrigerant detected by the
intercooler outlet temperature sensor 52) in the outlet of the
intercooler 7 is equal to or less than the saturation temperature
of the intermediate-pressure refrigerant fed from the first-stage
compression element 2c to the second-stage compression element 2d.
In the case that the temperature of the water as the heat source of
the intercooler 7 or the temperature of the refrigerant in the
outlet of the intercooler 7 is determined to be equal to or less
than the saturation temperature of the refrigerant fed from the
first-stage compression element 2c to the second-stage compression
element 2d, the refrigerant discharged from the first-stage
compression element 2c is allowed to flow to the intake side of the
second-stage compression element 2d via the intercooler bypass tube
9 by closing the cooler on/off valve 12 and opening the intercooler
bypass on/off valve 11 of the intercooler bypass tube 9 in the same
manner as the embodiment described above, whereby the
intermediate-pressure refrigerant is not allowed to flow to the
intercooler 7.
[0073] The same operational effects as those of the embodiment
described above can be achieved with the configuration of the
present modification, except that the heat source of the
intercooler 7 is water instead of air.
[0074] In a configuration that provides a water on/off valve 14a to
the water distribution tube 14 for intermediate cooling, as shown
in FIG. 5, control may be carried out so that the
intermediate-pressure refrigerant does not flow to the intercooler
7 by making use of the intercooler bypass tube 9 described above,
and control may be carried out for stopping the supply of water to
the intercooler 7 by closing the water on/off valve 14a. In this
case, the water on/off valve 14a is an electromagnetic valve
capable of on/off control.
[0075] In this case, refrigerant inside the intercooler 7 can
furthermore be prevented from being retained in a liquid state.
(4) Modification 2
[0076] Modification 1 described above is configured so that water
is fed to the intercooler 7 via a water distribution tube 14 for
intermediate cooling and so that a water on/off valve 14a is
provided to the water distribution tube 14 for intermediate
cooling; and in the case that it has determined that the
temperature of the water as the heat source of the intercooler 7 or
temperature of the refrigerant in the outlet of the intercooler 7
is equal to or less than the saturation temperature of the
refrigerant fed from the first-stage compression element 2c to the
second-stage compression element 2d, wet prevention control is
carried out by allowing intermediate-pressure refrigerant not to
flow to the intercooler 7 by using a intercooler bypass tube 9 and
water fed to the intercooler 7 is stopped by closing the water
on/off valve 14a (see FIG. 5). However, it is also possible to omit
the intercooler bypass tube 9 including the intercooler bypass
on/off valve 11, and/or a configuration such as the cooler on/off
valve 12 for allowing intermediate-pressure refrigerant not to flow
to the intercooler 7; and to instead use wet prevention control in
which the only control that is performed is to stop the feeding of
water to the intercooler 7.
[0077] In the configuration of the present modification, the
refrigerant constantly flows to the intercooler 7 but the water fed
to the intercooler 7 is stopped, which is different from
Modification 1 described above. The same operational effects as
those of Modification 1 described above can be achieved because,
essentially, the refrigerant that flows to the intercooler 7 is no
longer cooled by water.
(5) Modification 3
[0078] In the configuration of Modification 2 described above (see
FIG. 6), it is also possible to use a configuration in which the
water on/off valve 14a is composed of a valve whose degree of
opening can be adjusted, and when it has been determined that the
temperature of the refrigerant in the outlet of the intercooler 7
is equal to or less than the saturation temperature of the
refrigerant fed from the first-stage compression element 2c to the
second-stage compression element 2d, wet prevention control is
carried out so as to reduce the flow rate of water fed to the
intercooler 7 by reducing the degree of opening of the water on/off
valve 14a to prevent the refrigerant drawn into the second-stage
compression element 2d from becoming wet, and furthermore so as to
control the flow rate of the water that flows through the
intercooler 7 so that the temperature of the refrigerant in the
outlet of the intercooler 7 become greater than the saturation
temperature of the refrigerant fed from the first-stage compression
element 2c to the second-stage compression element 2d.
[0079] In the configuration of the present modification, not only
can the refrigerant drawn into the second-stage compression element
2d be prevented from becoming wet, but the temperature of the
refrigerant drawn into the second-stage compression element 2d can
also be kept low, whereby the temperature of the refrigerant
discharged from the second-stage compression element 2d can be kept
low and the power consumption of the compression mechanism 2 can be
reduced in the same manner as Modification 2 described above.
(6) Modification 4
[0080] In the refrigerant circuit 10 (see FIGS. 1, 4, 5, 6) in the
embodiment described above and the modifications thereof, a single
usage-side heat exchanger 6 is used and the configuration is
capable of air-cooling operation. However, there are cases in which
a configuration is provided with the aim of carrying out air
cooling and/or air-warming in accordance with the air-conditioning
load of a plurality of air-conditioning spaces, the configuration
having a switching mechanism 3 for switching between air-cooling
operation and air-warming operation, a plurality of usage-side heat
exchangers 6 mutually connected in parallel, and a receiver 18 for
temporarily retaining refrigerant that flows between the heat
source-side heat exchanger 4 and the usage-side heat exchangers 6.
Also, usage-side expansion mechanisms 5c are provided between the
usage-side heat exchangers 6 and the receiver 18 as a vapor-liquid
separator, so as to correspond to the usage-side heat exchangers 6
and so that the rate at which the refrigerant flows through the
usage-side heat exchangers 6 can be controlled and the required
refrigeration load can be obtained in the usage-side heat
exchangers 6 (e.g., a configuration that does not have second-stage
injection tubes 18c, 19 and an economizer heat exchanger 20 as in
the later-described FIGS. 7 and 12). In such a configuration,
intermediate pressure injection is carried out by returning the
refrigerant to the second-stage compression element 2d from the
receiver 18 as the vapor-liquid separator so as to merge with the
intermediate-pressure refrigerant of the compression mechanism
discharged from the first-stage compression element 2c of the
compression mechanism 2 and drawn into the second-stage compression
element 2d. Operating efficiency is thought to be improved because
the temperature of the refrigerant discharged from the second-stage
compression element 2d is reduced and power consumption of the
compression mechanism 2 is reduced.
[0081] However, in such a configuration in which a plurality of
usage-side heat exchangers 6 are connected to each other in
parallel, in which usage-side expansion mechanisms 5c as a
usage-side expansion valve are provided between the usage-side heat
exchangers 6 and the receiver 18 as a vapor-liquid separator so as
to correspond to the usage-side heat exchangers 6, and in which the
usage-side expansion mechanisms 5c control the flow rate of the
refrigerant that flows through the usage-side heat exchangers 6 so
that a required refrigeration load can be obtained in the
usage-side heat exchangers 6, the flow rate at which the
refrigerant flows through the usage-side heat exchangers 6 in an
air-warming operation is substantially determined by the degree of
opening of the usage-side expansion mechanisms 5c provided in the
downstream side of the usage-side heat exchangers 6 and in the
upstream side of the receiver 18. However, in this case, the degree
of opening of the usage-side expansion mechanisms 5c varies
depending not only on the flow rate of the refrigerant that flows
through the usage-side heat exchangers 6, but also on the state of
the flow rate distribution between the plurality of usage-side heat
exchangers 6. There are cases in which a state is produced in which
the degree of opening considerably varies among the plurality of
usage-side expansion mechanisms 5c, and a usage-side expansion
mechanism 5c may have a relatively small degree of opening.
Accordingly, there may be cases in which the vapor-liquid separator
pressure, which is the pressure of the refrigerant in the receiver
18, may be excessively reduced when the degree of opening of the
usage-side expansion mechanisms 5c is controlled during air-warming
operation. Also, when such an air-conditioning apparatus 1 is
configured as a separate-type air-conditioning apparatus in which a
heat source unit mainly including a compression mechanism 2, a heat
source-side heat exchanger 4, and a receiver 18, and a usage unit
mainly including usage-side heat exchangers 6 are connected by an
interconnecting pipe, the interconnecting pipe may become very long
depending on the arrangement of the usage unit and the heat source
unit. Due to the resulting pressure drop, this therefore adds to
the reduced pressure of the vapor-liquid separator, and the
pressure of the vapor-liquid separator is further reduced.
[0082] Accordingly, intermediate pressure injection by the receiver
18 as the vapor-liquid separator can be used even under conditions
in which the pressure difference between the pressure of the
vapor-liquid separator and the intermediate pressure of the
compression mechanism is small. Therefore, this is advantageous in
cases in which the pressure of the vapor-liquid separator is very
likely to be excessively reduced such as in the air-warming
operation in this configuration.
[0083] However, rather than carrying out an operation for
considerably reducing the pressure using other than the first
expansion mechanism 5a (e.g., see the first expansion mechanism 5a
of the later-described FIGS. 7 and 12) as the heat source-side
expansion mechanism between the time the refrigerant is cooled in
the heat source-side heat exchanger 4 and flows into the receiver
18 as the vapor-liquid separator, as in air-cooling operation,
there are preferably provided a second second-stage injection tube
19 for branching and returning the refrigerant that flows between
the heat source-side heat exchanger 4 and the first expansion
mechanism 5a to the second-stage compression element 2d, and an
economizer heat exchanger 20 for carrying out heat exchange between
the refrigerant that flows between the heat source-side heat
exchanger 4 and the first expansion mechanism 5a and the
refrigerant that flows through the second second-stage injection
tube 19. In conditions in which it is possible to use the pressure
difference between high pressure in the refrigeration cycle and
near-intermediate pressure in the refrigeration cycle, the
refrigerant that flows through the second second-stage injection
tube 19 after being heated by heat exchange in the economizer heat
exchanger 20 is returned (i.e., intermediate pressure injection is
carried out by the economizer heat exchanger 20) to the
second-stage compression element 2d (e.g., see the second
second-stage injection tube 19 and the economizer heat exchanger 20
of the later-described FIGS. 7 and 12). This is due to the fact
that intermediate pressure injection carried out by the economizer
heat exchanger 20 causes the flow rate of the refrigerant that can
be returned to the second-stage compression element 2d to fluctuate
based on the amount of heat exchange in the economizer heat
exchanger 20. Therefore, the amount of heat exchange in the
economizer heat exchanger 20 is reduced and the flow rate of the
refrigerant that can be returned to the second-stage compression
element 2d is reduced in the case that the pressure difference
between the pressure of the refrigerant in the inlet of the
economizer heat exchanger 20 and the intermediate pressure of the
compression mechanism is small, as in air-warming operation. While
such application is difficult, it is effective when the pressure
difference between the pressure of the refrigerant in the inlet of
the economizer heat exchanger 20 and the intermediate pressure of
the compression mechanism is large in that the amount of heat
exchange in the economizer heat exchanger 20 is increased and the
flow rate of the refrigerant that can be returned to the
second-stage compression element 2d is increased. In the particular
case that refrigerant such as carbon dioxide for operating in a
supercritical range is used, the pressure difference between the
intermediate pressure and the high pressure in the refrigeration
cycle is further increased because the high pressure in the
refrigeration cycle exceeds the critical pressure. Therefore,
intermediate pressure injection carried out by the economizer heat
exchanger 20 is advantageous. Also, in the case that refrigerant
such as carbon dioxide for operating in a supercritical range is
used, the pressure of the vapor-liquid separator increases to a
pressure that is greater than the critical pressure and the
refrigerant inside the receiver 18 as the vapor-liquid separator is
liable to enter a state in which gas refrigerant and liquid
refrigerant are difficult to separate. Therefore, considering this
point, intermediate pressure injection carried out by the
economizer heat exchanger 20 is preferably used in conditions in
which the pressure difference between the high pressure in the
refrigeration cycle and the near-intermediate pressure in the
refrigeration cycle can be used, as in air-cooling operation.
[0084] In view of the above, in the present modification, a
configuration is provided having a plurality of usage-side heat
exchangers 6 mutually connected in parallel and capable of
switching between air-cooling operation and air-warming operation,
as described above, and the usage-side expansion mechanisms 5c are
provided between the usage-side heat exchangers 6 and the receiver
18 as the vapor-liquid separator so as to correspond to the
usage-side heat exchangers 6 so that the flow rate of the
refrigerant that flows through the usage-side heat exchangers 6 can
be controlled and the required refrigeration load can be obtained
in the usage-side heat exchangers 6. Furthermore, during
air-warming operation, intermediate pressure injection carried out
by the receiver 18 as the vapor-liquid separator is used with
consideration given to the possibility that the pressure of the
refrigerant in the downstream side of the usage-side expansion
mechanisms 5c will be reduced; and during air-cooling operation,
intermediate pressure injection carried out by the economizer heat
exchanger 20 is used with consideration given to keeping the
pressure of the refrigerant high in the downstream side of the heat
source-side heat exchanger 4 and in the upstream side of the first
expansion mechanism 5a as the heat source-side expansion
mechanism.
[0085] For example, in the refrigerant circuit 10 (see FIG. 1)
having the intercooler bypass tube 9 and the intercooler 7 in which
air is used as a heat source in the embodiment described above, the
configuration has a switching mechanism 3 for making it possible to
switch between air-cooling operation and air-warming operation, and
a plurality of usage-side heat exchangers 6 mutually connected in
parallel, as shown in FIG. 7; and the first expansion mechanisms
5a, 5d as the heat source-side expansion mechanism and the
usage-side expansion mechanisms 5c as the usage-side expansion
valve are provided in place of the expansion mechanism 5.
Furthermore, it is possible to use a refrigerant circuit 610
provided with a bridge circuit 17, a receiver 18, a first
second-stage injection tube 18c, a second second-stage injection
tube 19, and a economizer heat exchanger 20.
[0086] The switching mechanism 3 is a mechanism for switching the
direction of refrigerant flow in the refrigerant circuit 610. In
order to allow the heat source-side heat exchanger 4 to function as
a cooler of refrigerant compressed by the compression mechanism 2
and to allow the usage-side heat exchanger 6 to function as a
heater 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. 7, this state of the switching
mechanism 3 is hereinbelow referred to as the "cooling operation
state"). In order to allow the usage-side heat exchanger 6 to
function as a cooler of refrigerant compressed by the compression
mechanism 2 and to allow the heat source-side heat exchanger 4 to
function as a heater 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. 7, this state of
the switching mechanism 3 is hereinbelow referred to as the
"heating operation state"). In the present modification, 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.
[0087] Thus, in terms of only the compression mechanism 2, the heat
source-side heat exchanger 4, the expansion mechanisms 5a, 5d, the
receiver 18, the usage-side expansion mechanisms 5c, and the
usage-side heat exchangers 6 that constitute the refrigerant
circuit 610, the switching mechanism 3 is configured so as to be
capable of switching between an air-cooling operation state and an
air-warming operation state. In the cooling operation state,
refrigerant is circulated in the sequence of the compression
mechanism 2, the heat source-side heat exchanger 4, the first
expansion mechanism 5a as the heat source-side expansion mechanism,
the receiver 18, the usage-side expansion mechanisms 5c, and the
usage-side heat exchangers 6. In the warming operation state, the
refrigerant is circulated in the sequence of the compression
mechanism 2, the usage-side heat exchangers 6, the usage-side
expansion mechanisms 5c as the usage-side expansion valve, the
receiver 18, a third expansion mechanism 5d as the heat-source side
expansion mechanism, and the heat source-side heat exchanger 4.
[0088] The bridge circuit 17 is provided 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 an inlet
of the receiver 18, and to a receiver outlet tube 18b connected to
an outlet of the receiver 18. The bridge circuit 17 has three
non-return valves 17a, 17b, 17c and a third expansion mechanism 5d
as a heat source-side expansion mechanism in the present
modification. The inlet non-return valve 17a is a non-return valve
for allowing refrigerant to flow only 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 for allowing refrigerant
to flow only from the usage-side heat exchanger 6 to the receiver
inlet tube 18a. In other words, the inlet non-return valves 17a,
17b have the function of allowing refrigerant to flow to the
receiver inlet tube 18a from either the heat source-side heat
exchanger 4 or the usage-side heat exchanger 6. The outlet
non-return valve 17c is a non-return valve for allowing refrigerant
to flow only from the receiver outlet tube 18b to the usage-side
heat exchanger 6. The third expansion mechanism 5d is a mechanism
for reducing the pressure of the refrigerant and constitutes a
portion of the bridge circuit 17. In other words, the outlet
non-return valves 17c and the third expansion mechanism 5d have the
function of allowing refrigerant to flow from the receiver outlet
tube 18b to the other of the heat source-side heat exchanger 4 and
the usage-side heat exchanger 6. Accordingly, the third expansion
mechanism 5d is fully closed during air-cooling operation in which
the switching mechanism 3 is set in the air-cooling operation
state, and is designed to reduce the pressure of the refrigerant
fed from the receiver outlet tube 18b to the heat source-side heat
exchanger 4 during air-warming operation in which the switching
mechanism 3 is set in the air-warming operation state. The third
expansion mechanism 5d is an electric expansion valve in the
present modification.
[0089] The first expansion mechanism 5a is a
refrigerant-depressurizing mechanism provided to the receiver inlet
tube 18a, and an electric expansion valve is used in the present
modification. One end of the first expansion mechanism 5a is
connected to the heat source-side heat exchanger 4 via the bridge
circuit 17, and the other end is connected to the receiver 18. In
the present modification, the first expansion mechanism 5a
depressurizes the high-pressure refrigerant cooled in the heat
source-side heat exchanger 4 before feeding the refrigerant to the
usage-side heat exchanger 6 during the air-cooling operation, and
depressurizes the high-pressure refrigerant cooled in the
usage-side heat exchanger 6 before feeding the refrigerant to the
heat source-side heat exchanger 4 during the air-warming operation.
An expansion mechanism bypass valve 5e is provided to the receiver
inlet tube 18a so as to bypass the first expansion mechanism 5a.
The expansion mechanism bypass valve 5e is an electromagnetic valve
in the present modification.
[0090] The receiver 18 is a container capable of temporarily
retaining refrigerant that has been depressurized in the first
expansion mechanism 5a, the inlet thereof connected to the receiver
inlet tube 18a, and the outlet thereof connected to the receiver
outlet tube 18b. The first second-stage injection tube 18c and an
intake return tube 18f is connected to the receiver 18. In this
case, the portions of the first second-stage injection tube 18c and
the intake return tube 18f that are on the receiver 18 side are
integrally formed.
[0091] The first second-stage injection tube 18c is a refrigerant
tube capable of carrying out intermediate pressure injection for
withdrawing 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, is
provided so as to connect the upper portion 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). A first second-stage injection on-off valve 18d and first
second-stage injection non-return mechanism 18e are provided to the
first second-stage injection tube 18c. The first second-stage
injection on-off valve 18d is a valve capable of open-close
operation, and is an electromagnetic valve in the present
modification. 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 the flow of refrigerant from the second-stage compression
element 2d to the receiver 18, and is a non-return valve in the
present modification.
[0092] The intake return tube 18f is a refrigerant tube capable of
withdrawing refrigerant from the receiver 18 and returning the
refrigerant to the first-stage compression element 2c of the
compression mechanism 2, and in the present modification, is
provided so as to connect the upper portion of the receiver 18 and
the intake tube 2a (i.e., the intake side of the first-stage
compression element 2c of the compression mechanism 2). The intake
return tube 18f is provided with an intake return on/off valve 18g.
The intake return on/off valve 18g is a valve capable of open-close
operation and is an electromagnetic valve in the present
modification.
[0093] The receiver 18 thus functions as a vapor-liquid separator
for separating the refrigerant that flows between the heat
source-side heat exchanger 4 and the usage-side heat exchangers 6
into vapor and gas between the usage-side expansion mechanisms 5c
and the expansion mechanisms 5a, 5d in the case that the first
second-stage injection tube 18c and/or the intake return tube 18f
are used by opening the first second-stage injection on-off valve
18d and/or the intake return on/off valve 18g; and is mainly
designed to be capable of returning the gas refrigerant obtained
from the vapor-liquid separation in the receiver 18 from the upper
portion of the receiver 18 to the first-stage compression element
2c and/or the second-stage compression element 2d of the
compression mechanism 2.
[0094] The usage-side expansion mechanisms 5c are mechanisms for
reducing the pressure of the refrigerant provided between the
usage-side heat exchangers 6 and the receiver 18 (more
specifically, the bridge circuit 17) as a vapor-liquid separator so
as to correspond to the usage-side heat exchangers 6, and is
electric expansion valve in the present modification. One end of
the usage-side expansion mechanisms 5c are connected to the
receiver 18 via the bridge circuit 17 and the other end is
connected to the usage-side heat exchangers 6. In the present
modification, the usage-side expansion mechanism 5c further
depressurizes the refrigerant depressurized by the first expansion
mechanism 5a to a low pressure before the refrigerant is fed to the
usage-side heat exchanger 6 during the air-cooling operation, and
during the air-warming operation, depressurizes the refrigerant
that has passed through the usage-side heat exchanger 6 before the
refrigerant is fed to the receiver 18.
[0095] The second second-stage injection tube 19 has a function for
branching off and returning the refrigerant that flows between the
heat source-side heat exchanger 4 and 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 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) 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. In this case, the portions of the first
second-stage injection tube 18c and the second second-stage
injection tube 19 that are on the intermediate refrigerant tube 8
side are integrally formed. 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 electric expansion valve in the present
modification.
[0096] The economizer heat exchanger 20 is a heat exchanger for
carrying out heat exchange between the refrigerant that flows
between the heat source-side heat exchanger 4 and 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 that
heat exchange is carried out between the refrigerant that flows in
the upstream-side position of the first expansion mechanism 5a of
the receiver inlet tube 18a (i.e., between the heat source-side
heat exchanger 4 and the first expansion mechanism 5a when the
switching mechanism 3 is set in the air-cooling operation state)
and the refrigerant that flows through the second second-stage
injection tube 19, and has flow channels through which both
refrigerants flow so as to oppose each other. In the present
modification, the economizer heat exchanger 20 is provided further
downstream from the position in which the second second-stage
injection tube 19 branches from the receiver inlet tube 18a.
Therefore, the refrigerant that flows between the heat source-side
heat exchanger 4 and the 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.
[0097] Thus, when the switching mechanism 3 is set in the cooling
operation state by the bridge circuit 17, the receiver 18, the
receiver inlet tube 18a, and the receiver outlet tube 18b, the
high-pressure refrigerant cooled in the heat source-side heat
exchanger 4 can be fed to the usage-side heat exchangers 6 through
the inlet non-return valve 17a of the bridge circuit 17, the first
expansion mechanism 5a of the receiver inlet tube 18a, the receiver
18, the outlet non-return valve 17c of the bridge circuit 17, and
the usage-side expansion mechanisms 5c. When the switching
mechanism 3 is set in the heating operation state, the
high-pressure refrigerant cooled in the usage-side heat exchangers
6 can be fed to the heat source-side heat exchanger 4 through the
usage-side expansion mechanisms 5c, the non-return valve 17b of the
bridge circuit 17, the expansion mechanism bypass valve 5e of the
receiver inlet tube 18a, the receiver 18, and the third expansion
mechanism 5d of the bridge circuit 17.
[0098] In the present modification, 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. A vapor-liquid separator temperature
sensor 57 for detecting the temperature of the refrigerant in the
receiver 18 is provided to the receiver inlet tube 18a in a
position nearer to the receiver 18 than the first expansion
mechanism 5a. The vapor-liquid separator temperature sensor 57 may
be provided to the receiver outlet tube 18b, or may be provided
directly to the receiver 18, e.g., the bottom portion of the
receiver 18.
[0099] Thus, in the present modification, it is possible to
separately use intermediate pressure injection carried out by the
receiver 18 for returning the refrigerant from the receiver 18 as
the vapor-liquid separator to the second-stage compression element
2d via the first second-stage injection tube 18c, and intermediate
pressure injection carried out by the economizer heat exchanger 20
for returning the refrigerant heated in the economizer heat
exchanger 20 to the second-stage compression element 2d via the
second second-stage injection tube 19
[0100] Next, the action of the air-conditioning apparatus 1 will be
described using FIGS. 7 through 11. FIG. 8 is a pressure-enthalpy
graph representing the refrigeration cycle during the air-cooling
operation in the present modification, FIG. 9 is a
temperature-entropy graph representing the refrigeration cycle
during the air-cooling operation in the present modification, FIG.
10 is a pressure-enthalpy graph representing the refrigeration
cycle during the air-warming operation in the present modification,
and FIG. 11 is a temperature-entropy graph representing the
refrigeration cycle during the air-warming operation in present
modification. Operation controls during the following air-cooling
operation and air-warming operation, and control for limiting
reduction in the pressure of the vapor-liquid separator are
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', E, and H in FIGS. 8 and 9, and the pressure at points
D, D', F, and H in FIGS. 10 and 11), the term "low pressure" means
a low pressure in the refrigeration cycle (specifically, the
pressure at points A, F in FIGS. 8 and 9, and the pressure at
points A and E in FIGS. 10 and 11), and the term "intermediate
pressure" means an intermediate pressure in the refrigeration cycle
(specifically, the pressure at points B1, C1, and G in FIGS. 8
through 11).
[0101] <Air-Cooling Operation>
[0102] During the air-cooling operation, the switching mechanism 3
is brought to the cooling operation state shown by the solid lines
in FIG. 7. The degree of opening of the first expansion mechanism
5a as the heat source-side expansion mechanism and the usage-side
expansion mechanisms 5c as the usage-side expansion valves is
adjusted. Also, the third expansion mechanism 5d and the expansion
mechanism bypass valve 5e are in a fully closed state. When the
switching mechanism 3 is set in an air-cooling operation state,
intermediate pressure injection carried out by the economizer heat
exchanger 20 for returning the refrigerant heated in the economizer
heat exchanger 20 to the second-stage compression element 2d via
the second second-stage injection tube 19 is performed without
carrying out intermediate pressure injection by the receiver 18 as
the vapor-liquid separator. More specifically, the first
second-stage injection on-off valve 18d is set in a closed state
and the degree of opening of the second second-stage injection
valve 19a is adjusted. Here, a 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. Furthermore, the cooler
on/off valve 12 is opened and the intercooler bypass on/off valve
11 of the intercooler bypass tube 9 is closed, thereby putting the
intercooler 7 into a state of functioning as a cooler.
[0103] When the compression mechanism 2 is driven while the
refrigerant circuit 610 is in this state, low-pressure refrigerant
(refer to point A in FIGS. 7 through 9) is drawn into the
compression mechanism 2 through the intake tube 2a, and after the
refrigerant is first compressed to an intermediate pressure by the
compression element 2c, the refrigerant is discharged to the
intermediate refrigerant tube 8 (refer to point B1 in FIGS. 7
through 9). The intermediate-pressure refrigerant discharged from
the first-stage compression element 2c is cooled by heat exchange
with air and/or water as a cooling source (refer to point C1 in
FIGS. 7 to 9). The refrigerant cooled in the intercooler 7 is
further cooled (refer to point G in FIGS. 7 to 9) 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. 7 to 9). Next, having been mixed with the
refrigerant returned from the second second-stage injection tube 19
(i.e., intermediate pressure injection 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 then discharged from the
compression mechanism 2 to the discharge tube 2b (refer to point D
in FIGS. 7 to 9). 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. 8). The high-pressure refrigerant discharged
from the compression mechanism 2 is fed via the switching mechanism
3 to the heat source-side heat exchanger 4 functioning as a
refrigerant cooler, and the refrigerant is cooled by heat exchange
with air and/or water as a cooling source (refer to point E in
FIGS. 7 to 9). 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. 7 to 9). The refrigerant flowing through the
receiver inlet tube 18a 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. 7 to 9). The refrigerant flowing
through the second second-stage injection tube 19 is heated by heat
exchange with the refrigerant flowing through the receiver inlet
tube 18a (refer to point K in FIGS. 7 to 9), and this refrigerant
is mixed with the refrigerant cooled in the intercooler 7 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. 7 to 9). The
refrigerant retained in the receiver 18 is fed to the receiver
outlet tube 18b, is fed to the usage-side expansion mechanisms 5c
via the receiver outlet tube 18b and the outlet non-return valve
17c of the bridge circuit 17, and is depressurized by the
usage-side expansion mechanism 5c to become a low-pressure
gas-liquid two-phase refrigerant (refer to point F in FIGS. 7 to
9). 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 A in FIGS. 7 to 9). The low-pressure
refrigerant heated in the usage-side heat exchanger 6 is then led
back into the compression mechanism 2 via the switching mechanism
3. In this manner the air-cooling operation is performed.
[0104] In the configuration of the present modification, in
addition to the cooling of the refrigerant drawn into the
second-stage compression element 2d by the intercooler 7, the
temperature of the refrigerant drawn into the second-stage
compression element 2d can be kept low by intermediate pressure
injection using the second second-stage injection tube 19 and the
economizer heat exchanger 20. Therefore, the temperature of the
refrigerant discharged from the compression mechanism 2 can be even
further reduced (refer to points D and D' in FIG. 9). The power
consumption of the compression mechanism 2 is thereby reduced and
operating efficiency can be improved.
[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 FIG. 7. The degree of opening of the third expansion mechanism
5d as the heat source-side expansion mechanism and the usage-side
expansion mechanisms 5c as usage-side expansion valves is adjusted.
The expansion mechanism bypass valve 5e is set in a fully opened
state, and depressurization is not performed by the first expansion
mechanism 5a. When the switching mechanism 3 is set in a heating
operation state, intermediate pressure injection is not carried out
by the economizer heat exchanger 20, and intermediate pressure
injection is carried out by the receiver 18 for returning the
refrigerant from the receiver 18 as the vapor-liquid separator to
the second-stage compression element 2d via the first second-stage
injection tube 18c. More specifically, the first second-stage
injection on-off valve 18d is set in an open state, and the second
second-stage injection valve 19a is set in a fully closed state.
Furthermore, the cooler on/off valve 12 is closed and the
intercooler bypass on/off valve 11 of the intercooler bypass tube 9
is opened, thereby putting the intercooler 7 into a state of not
functioning as a cooler.
[0107] When the compression mechanism 2 is driven while the
refrigerant circuit 610 is in this state, low-pressure refrigerant
(refer to point A in FIGS. 7, 10, and 11) 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 B1 in FIGS. 7, 10
and 11). Unlike the air-cooling operation, the
intermediate-pressure refrigerant discharged from the first-stage
compression element 2c passes through the intercooler bypass tube 9
(refer to point C1 in FIG. 7) without passing through the
intercooler 7 (i.e. without being cooled), and the refrigerant is
cooled (refer to point G in FIGS. 7, 10, and 11) by being mixed
with refrigerant being returned from the receiver 18 to the
second-stage compression element 2d via the first second-stage
injection tube 18c (refer to point M in FIGS. 7, 10, and 11). 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 led
to 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. 7, 10, and 11). 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. 10), similar to the air-cooling operation. The
high-pressure refrigerant discharged from the compression mechanism
2 is fed via the switching mechanism 3 to the usage-side heat
exchanger 6 functioning as a refrigerant cooler, and the
refrigerant is cooled by heat exchange with air or water as a
cooling source (refer to point F in FIGS. 7, 10, and 11). The
high-pressure refrigerant cooled in the usage-side heat exchanger 6
is depressurized by the usage-side expansion mechanisms 5c to
approximately intermediate pressure, is allowed to flow into the
receiver inlet tube 18a via the inlet non-return valve 17b of the
bridge circuit 17, and passes through the expansion mechanism
bypass valve 5e and temporarily retained and made to undergo
vapor-liquid separation inside the receiver 18 (refer to points I,
L, M in FIGS. 7, 10, 11). The gas refrigerant separated in
vapor-liquid separation in the receiver 18 is withdrawn by the
first second-stage injection tube 18c from the upper portion of the
receiver 18, and is 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 fed to the bridge circuit 17 via the receiver outlet tube
18b, is depressurized by the third expansion mechanism 5d to become
low-pressure gas-liquid two-phase refrigerant, and is fed to the
heat source-side heat exchanger 4 that functions as a refrigerant
heater (refer to point E in FIGS. 7, 10, 11). The low-pressure
gas-liquid two-phase refrigerant fed to the heat source-side heat
exchanger 4 is heated by heat exchange with water or air as a
heating source, and the refrigerant is evaporated as a result
(refer to point A in FIGS. 7, 10, and 11). The low-pressure
refrigerant heated in the heat source-side heat exchanger 4 is then
led back into the compression mechanism 2 via the switching
mechanism 3. In this manner the air-warming operation is
performed.
[0108] In the configuration of the present modification, the
temperature of the refrigerant discharged from the compression
mechanism 2 can be kept low because the temperature of the
refrigerant drawn into the second-stage compression element 2d can
be kept low by intermediate pressure injection using the receiver
18 and the first second-stage injection tube 18c (refer to points D
and D' in FIG. 11). The power consumption of the compression
mechanism 2 is thereby reduced and operating efficiency can be
improved. However, the intercooler 7 is not allowed to function as
a cooler, which is different from that during air-cooling
operation; and heat radiation loss by the intercooler 7 to the
exterior is suppressed and a reduction in heating ability in the
usage-side heat exchangers 6 is suppressed in comparison with the
case in which the intercooler 7 is made to function as a cooler in
the same manner as the air-cooling operation.
[0109] <Superheat Degree Control of Refrigerant Drawn into the
Second-Stage Compression Element>
[0110] In the present modification, the air-warming operation,
which is accompanied by intermediate pressure injection by the
receiver 18 as the vapor-liquid separator, produces operating
conditions in which a large amount of liquid refrigerant is
retained in the receiver 18 as the vapor-liquid separator, the
cause of which is unknown. When vapor-liquid separation becomes
difficult, liquid refrigerant is liable to become mixed with the
refrigerant that returns from the receiver 18 to the second-stage
compression element 2d via the first second-stage injection tube
18c, whereby the intermediate-pressure refrigerant drawn into the
second-stage compression element 2d becomes wet after intermediate
pressure injection has been carried out, and the reliability of the
compression mechanism 2 is liable to be compromised.
[0111] In view of the above, in the present modification, the
degree of superheat of the refrigerant drawn into the second-stage
compression element 2d is controlled by the open-close operation of
the first second-stage injection on-off valve 18d. Specifically, in
the present modification, the first second-stage injection on-off
valve 18d is opened and closed so that the degree of superheat of
the refrigerant drawn into the second-stage compression element 2d
after intermediate pressure injection has been carried out by the
receiver 18 does not become less than a predetermined value. Here,
the degree of superheat of the refrigerant drawn into the
second-stage compression element 2d is obtained by converting the
compression mechanism intermediate pressure detected by the
intermediate pressure sensor 54 to a saturation temperature and
subtracting the saturation temperature of the refrigerant that
corresponds to the compression mechanism intermediate pressure from
the temperature of the refrigerant detected by the intermediate
temperature sensor 56. The predetermined value of the degree of
superheat used in this control process is set to a value that is
greater than at least 0.degree., e.g., several .degree. C. to
several tens of .degree. C., so that the intermediate-pressure
refrigerant drawn into the second-stage compression element 2d does
not become wet. The open-close operation of the first second-stage
injection on-off valve 18d can be carried out by varying the time
ratio between time t1 in which the first second-stage injection
on-off valve 18d is set in an open-state and the time t2 at which
the closed-state is set. In the present modification, the first
second-stage injection on-off valve 18d is kept in an open-state by
setting the time ratio of time t2 in relation to time t1 to 0 in
order to positively carry out intermediate pressure injection by
the receiver 18 in the case that the degree of superheat of the
refrigerant drawn into the second-stage compression element 2d is
at a predetermined value or greater; and the time ratio of time t2
with respect to time t1 is changed in the increase direction (i.e.,
the time that the first second-stage injection on-off valve 18d is
in a closed state) in order to reduce the flow rate of the
refrigerant returning from the receiver 18 to the second-stage
compression element 2d in the case that the degree of superheat of
the refrigerant drawn into the second-stage compression element 2d
is less than a predetermined value. After the degree of superheat
of the refrigerant drawn into the second-stage compression element
2d has recovered to a predetermined value or higher, the time ratio
of time t2 with respect to time t1 is changed in the decrease
direction in order to cause the flow rate of the refrigerant
returned from the receiver 18 to the second-stage compression
element 2d to increase again.
[0112] Thus, in the present modification, the degree of superheat
of the refrigerant discharged from the first-stage compression
element 2c and drawn into the second-stage compression element 2d
is controlled by the open-close operation of the first second-stage
injection on-off valve 18d. Therefore, the refrigerant drawn into
the second-stage compression element 2d can be prevented from
becoming wet by reducing the flow rate of the refrigerant returned
from the receiver 18 to the second-stage compression element 2d,
even under operating conditions in which a large quantity of the
liquid refrigerant is retained in the receiver 18 as the
vapor-liquid separator and the liquid refrigerant mixes with the
refrigerant returned from the receiver 18 to the second-stage
compression element 2d. The reliability of the compression
mechanism 2 during air-warming operation is thereby improved in the
present modification.
[0113] In the present modification, intermediate pressure injection
carried out by the economizer heat exchanger 20 is performed during
air-cooling operation, and the degree of superheat of the
refrigerant returned from the second second-stage injection tube 19
to the second-stage compression element 2d is controlled by
adjusting the degree of opening of the second second-stage
injection valve 19a so as to achieve a target value. Accordingly,
in the present modification, the refrigerant drawn into the
second-stage compression element 2d can be prevented from becoming
wet due to the effect of the refrigerant returned to the
second-stage compression element 2d by intermediate pressure
injection carried out by the economizer heat exchanger 20 in the
air-cooling operation, whereby the reliability of the compression
mechanism 2 is improved.
[0114] Furthermore, in the present modification, wet prevention
control is carried out using the intercooler bypass tube 9 so that
refrigerant does not flow to the intercooler 7 when the temperature
of the air as the heat source of the intercooler 7 is equal to or
less than the saturation temperature of the intermediate-pressure
refrigerant fed from the first-stage compression element 2c to the
second-stage compression element 2d, as in the embodiment described
above. Therefore, the refrigerant drawn into the second-stage
compression element 2d can be prevented from becoming wet even
under operating conditions in which the temperature of the air as
the heat source of the intercooler 7 is low, whereby the
reliability of the compression mechanism 2 is improved.
[0115] Thus, in the present modification, the refrigerant drawn
into the second-stage compression element 2d can be prevented from
becoming wet due to the cooling operation of the intercooler 7
and/or the effect of the refrigerant returned to the second-stage
compression element 2d by intermediate pressure injection, whereby
the reliability of the compression mechanism 2 is improved in the
air-cooling operation and the air-warming operation.
[0116] In the refrigerant circuit 610 described above (see FIG. 7),
the first expansion mechanism 5a and the receiver 18 are connected
between the heat source-side heat exchanger 4 and the usage-side
heat exchangers 6 via the bridge circuit 17 (including the third
expansion mechanism 5d), but it is possible to use a refrigerant
circuit 710 configured so that the bridge circuit 17 is omitted and
the first expansion mechanism 5a is connected between the heat
source-side heat exchanger 4 and the receiver 18, as shown in FIG.
12, whereby the refrigerant that flows between the heat source-side
heat exchanger 4 and the usage-side heat exchangers 6 flows in
sequence through the first expansion mechanism 5a, the receiver 18,
and the usage-side expansion mechanisms 5c when the switching
mechanism 3 is set in the air-cooling operation state; and the
refrigerant that flows between the heat source-side heat exchanger
4 and the usage-side heat exchangers 6 flows in sequence through
the usage-side expansion mechanisms 5c, the receiver 18, and the
first expansion mechanism 5a when the switching mechanism 3 is set
in the heating operation state.
[0117] In this configuration, the differing points are that the
bridge circuit 17 is omitted and that the refrigerant that flows
between the heat source-side heat exchanger 4 and the usage-side
heat exchanger 6 does so in the sequence of the usage-side
expansion mechanisms 5c, the receiver 18, and the first expansion
mechanism 5a when the switching mechanism 3 is set in the heating
operation state (accordingly, the points I and L in FIGS. 10 and 11
change places); however, the same operational effects as those
described above can also be achieved.
[0118] The configuration of the intercooler 7 and the like in the
embodiment described above is used as the configuration of the
intercooler 7 and the like in the refrigerant circuits 610, 710
described above (see FIGS. 7 and 12), but no limitation is imposed
thereby; it also being possible to use the configuration of
Modifications 1 to 3.
(7) Modification 5
[0119] In the above-described embodiment and modifications thereof,
a two-stage compression-type compression mechanism 2 is configured
from the single compressor 21 having a single-shaft two-stage
compression structure, wherein two compression elements 2c, 2d are
provided and refrigerant discharged from the first-stage
compression element is sequentially compressed in the second-stage
compression element, but another possible option is to use a
multistage compression mechanism such as three-stage compression or
the like having more than two compression stages. Another possible
option is to configure a multistage compression mechanism by
connecting in series a plurality of compressors having a single
compression element and/or a plurality of compressors having a
plurality of compression elements. Yet another possible option is
to use a parallel multistage compression mechanism in which two or
more multistage compression mechanisms are connected in parallel in
the case that there is a need to increase the capacity of the
compression mechanism, such as the case in which several usage-side
heat exchangers 6 are connected.
[0120] For example, in a refrigerant circuit 610 (see FIG. 7) that
does not have the bridge circuit 17 of Modification 4 described
above, in place of the two-stage compression mechanism 2, it is
also possible to use a refrigerant circuit 810 having a compression
mechanism 102 in which two two-stage compression mechanisms 103,
104 are connected in parallel, as shown in FIG. 13.
[0121] 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 refrigerant thus drawn in 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 in through the first intake branch tube 104a,
the drawn-in 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 in 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
admitting 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
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 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 depressurizing mechanisms 141c, 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.
[0122] 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.
[0123] In the present modification, the intercooler 7 is provided
to the intermediate header tube 82 constituting the intermediate
refrigerant tube 8, and the intercooler 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.
Specifically, the intercooler 7 functions as a shared cooler for
two compression mechanisms 103, 104. Accordingly, the circuit
configuration is simplified around the compression mechanism 102
when the intercooler 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.
[0124] 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 104 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 81a, 84a. Therefore, even if either one
of the compression mechanisms 103, 104 has 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.
[0125] 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.
[0126] 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 has
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 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.
[0127] 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 has 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. 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.
[0128] The actions of the air-conditioning apparatus 1 of the
present modification during the air-cooling operation, the
air-warming operation, the wet prevention control, and the like are
essentially the same as the actions in the above-described
embodiment and modifications thereof (FIGS. 1 through 12 and the
relevant descriptions), except that the points modified by the
circuit configuration surrounding the compression mechanism 102 are
somewhat more complex due to the compression mechanism 102 being
provided instead of the compression mechanism 2, for which reason
the actions are not described herein.
[0129] The same operational effects as those of the above-described
embodiment and modifications thereof can also be achieved with the
configuration of the present modification.
[0130] In a refrigerant circuit 710 (see FIG. 12) that does not
have the bridge circuit 17 of Modification 4 described above, in
place of the two-stage compression-type compression mechanism 2, it
is also possible to use a refrigerant circuit 910 having a
compression mechanism 102 in which two two-stage compression-type
compression mechanisms 103, 104 are connected in parallel, as shown
in FIG. 14.
[0131] Since the bridge circuit 17 is omitted in this
configuration, the configuration is different from that of the
refrigerant circuit 810 (see FIG. 13) in that the refrigerant that
flows between the heat source-side heat exchanger 4 and the
usage-side heat exchanger 6 flows in the sequence of the usage-side
expansion mechanisms 5c, the receiver 18, and the first expansion
mechanism 5a when the switching mechanism 3 is set in the heating
operation state, but the same operational effects as those
described above can be achieved.
(8) Other Embodiments
[0132] Embodiments of the present invention and modifications
thereof are described above with reference to the drawings, but 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.
[0133] 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.
[0134] 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.
[0135] 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
[0136] If the present invention is used, it is possible to prevent
the refrigerant drawn into the second-stage compression element
from becoming wet in a refrigeration apparatus that carries out a
multistage compression refrigeration cycle, even under operation
conditions in which the temperature of the heat source of the
intercooler is low.
* * * * *