U.S. patent application number 14/402447 was filed with the patent office on 2015-06-04 for air-conditioning apparatus and method for controlling the same.
This patent application is currently assigned to Mitsubishi Electric Corporation. The applicant listed for this patent is Yohei Kato, Satoru Yanachi. Invention is credited to Yohei Kato, Satoru Yanachi.
Application Number | 20150153079 14/402447 |
Document ID | / |
Family ID | 49782383 |
Filed Date | 2015-06-04 |
United States Patent
Application |
20150153079 |
Kind Code |
A1 |
Yanachi; Satoru ; et
al. |
June 4, 2015 |
AIR-CONDITIONING APPARATUS AND METHOD FOR CONTROLLING THE SAME
Abstract
When operation of an air-conditioning apparatus starts, an
operation determination means determines whether the operation is a
cooling operation or a heating operation. If the operation is
determined not to be the cooling operation, a discharge gas cooling
unit does not perform cooling. On the other hand, if the operation
is determined to be the cooling operation, the discharge gas
cooling unit cools discharge gas.
Inventors: |
Yanachi; Satoru; (Tokyo,
JP) ; Kato; Yohei; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Yanachi; Satoru
Kato; Yohei |
Tokyo
Tokyo |
|
JP
JP |
|
|
Assignee: |
Mitsubishi Electric
Corporation
Tokyo
JP
|
Family ID: |
49782383 |
Appl. No.: |
14/402447 |
Filed: |
June 29, 2012 |
PCT Filed: |
June 29, 2012 |
PCT NO: |
PCT/JP2012/004235 |
371 Date: |
November 20, 2014 |
Current U.S.
Class: |
62/77 ;
62/324.6 |
Current CPC
Class: |
F25B 2313/02741
20130101; F25B 43/02 20130101; F25B 41/00 20130101; F25B 30/02
20130101; F24F 11/30 20180101; F25B 13/00 20130101; F25B 2313/006
20130101; F24F 11/62 20180101; F25B 40/02 20130101; F25B 6/04
20130101; F24F 11/65 20180101; F24F 2221/54 20130101; F24F 5/0089
20130101 |
International
Class: |
F25B 30/02 20060101
F25B030/02; F25B 41/00 20060101 F25B041/00; F25B 43/02 20060101
F25B043/02 |
Claims
1. An air-conditioning apparatus including a refrigerant circuit in
which a compressor, a discharge gas cooling unit, an oil separator,
a flow switching device, an indoor heat exchanger, an expansion
valve, and an outdoor heat exchanger are connected to each other in
a loop and capable of performing a cooling operation and a heating
operation by switching a channel with the flow switching device,
the air-conditioning apparatus comprising: a heat rejection control
means for controlling the discharge gas cooling unit such that the
discharge gas cooling unit cools discharge gas from the compressor
when the operating state is the cooling operation, and the
discharge gas cooling unit does not cool the discharge gas when the
operating state is the heating operation.
2. The air-conditioning apparatus of claim 1, wherein the heat
rejection control means has a function of detecting an operating
frequency of the compressor, and the heat rejection control means
controls the discharge gas cooling unit such that the discharge gas
cooling unit cools the discharge gas when the operating state is
the cooling operation and the operating frequency detected by the
heat rejection control means is greater than or equal to a
predetermined operating frequency, and the discharge gas cooling
unit does not cool the discharge gas if the operating frequency
detected by the heat rejection control means is less than the
predetermined operating frequency.
3. The air-conditioning apparatus of claim 1, wherein the discharge
gas cooling unit includes a pump that circulates a circulation
substance, a heat rejecter that is connected to the pump and
performs heat rejection from the circulation substance, and a heat
exchanger that is connected to the heat rejecter and the pump and
exchanges heat between the circulation substance and the discharge
gas, and the heat rejection control means controls the discharge
gas cooling unit such that the pump is driven to cool the discharge
gas in the heat exchanger in the cooling operation, and driving of
the pump is stopped so as not to cool the discharge gas in the heat
exchanger in the heating operation.
4. The air-conditioning apparatus of claim 1, wherein the discharge
gas cooling unit includes a heat exchanger including a refrigerant
channel in which the discharge gas from the compressor flows and a
cooling channel connected to a suction-side pipe of the compressor
such that suction gas to be sucked in the compressor flows into the
cooling channel, and a first three-way valve having two ports
connected to the suction-side pipe of the compressor and one port
connected to an outflow-side end of the cooling channel of the heat
exchanger, and the heat rejection control means controls the first
three-way valve such that the suction gas circulates in the cooling
channel of the heat exchanger so as to cool the discharge gas in
the cooling operation, and a flow of the suction gas into the
cooling channel of the heat exchanger is stopped so as not to cool
the discharge gas in the heating operation.
5. The air-conditioning apparatus of claim 1, wherein the outdoor
heat exchanger includes an air supply unit, the discharge gas
cooling unit includes a heat rejecter connected between a
discharge-side pipe of the compressor and the oil separator, and a
damper disposed between the heat rejecter and the air supply unit
and capable of opening and closing such that an air supply from the
air supply unit is shut or passed, and the heat rejection control
means controls the damper such that the damper is opened so as to
cause the air supply from the air supply unit to strike the heat
rejecter and cool the discharge gas in the cooling operation, and
the damper is closed so as to shut the air supply from the air
supply unit to the heat rejecter and not to cool the discharge gas
in the heating operation.
6. The air-conditioning apparatus of claim 1, wherein the discharge
gas cooling unit includes a pump that circulates a circulation
substance, a heat rejecter that is connected to the pump and
performs heat rejection from the circulation substance, a heat
exchanger that is connected to the heat rejecter and the pump and
exchanges heat between the circulation substance and the discharge
gas, and a second three-way valve having two ports connected
between a discharge-side pipe of the compressor and a suction-side
pipe of the heat exchanger and one port connected between the
discharge side of the heat exchanger and an inlet of the oil
separator, and the heat rejection control means controls the second
three-way valve such that the discharge gas passes through the heat
exchanger and is cooled in the cooling operation, and the discharge
gas does not pass through the heat exchanger and is not cooled in
the heating operation.
7. A method for controlling an air-conditioning apparatus including
a refrigerant circuit in which a compressor, a discharge gas
cooling unit, an oil separator, a flow switching device, an indoor
heat exchanger, an expansion valve, and an outdoor heat exchanger
are connected to each other in a loop and capable of performing a
cooling operation and a heating operation by switching a channel
with the flow switching device, the method comprising: controlling
the discharge gas cooling unit such that discharge gas from the
compressor is cooled when the operating state is the cooling
operation, and the discharge gas is not cooled when the operating
state is the heating operation.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a U.S. national stage application of
PCT/JP2012/004235 filed on Jun. 29, 2012, the contents of which are
incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to an air-conditioning
apparatus and a method for controlling the apparatus, and
particularly to an air-conditioning apparatus that performs a
cooling operation and a heating operation and a method for
controlling the air-conditioning apparatus.
BACKGROUND
[0003] In an air-conditioning apparatus, a compressor that
generates driving power for circulating refrigerant can be of a
reciprocating type, a screw type, a scroll type, or a rotary type,
for example. The compressor of any type encloses refrigerating
machine oil in order to lubricate a sliding portion. To obtain
reliability of the compressor, a predetermined amount of
refrigerating machine oil having a predetermined concentration or
more needs to be supplied to the compressor. In particular, in a
situation (e.g., in start-up) in which the oil concentration is
lowest with a decreased oil amount, refrigerating machine oil in a
necessary amount or more can be enclosed in some cases for stable
operation in order to continue the supply of the predetermined
amount of refrigerating machine oil in the predetermined
concentration or more.
[0004] The enclosure of the necessary amount or more of
refrigerating machine oil for stable operation increases the
oil-surface level in the compressor so that refrigerating machine
oil in the compressor can be easily discharged. With an increase in
amount of refrigerating machine oil with a high viscosity
circulating in refrigerant (hereinafter referred to as an oil
circulation rate), a pressure loss in pipes increases, resulting in
a decrease in COP capacity disadvantageously.
[0005] To solve this problem, in some proposed methods, an oil
separator is provided in a discharge part of the compressor in
order to separate refrigerating machine oil from refrigerant, and
the separated refrigerating machine oil returns to the compressor
so that the concentration of oil circulating in a refrigeration
cycle is reduced (see, for example, Patent Literatures 1 and 2). In
another proposed method, compressor discharge gas is cooled to
about a condensing temperature of refrigerant and refrigerating
machine oil in a gaseous state is separated so that the separation
efficiency is enhanced (see, for example, Patent Literature 3).
PATENT LITERATURE
[0006] Patent Literature 1: Japanese Unexamined Patent Application
Publication No. 62-80473
[0007] Patent Literature 2: Japanese Unexamined Utility Model
Registration Application Publication No. 2-131171
[0008] Patent Literature 3: Japanese Unexamined Patent Application
Publication No. 62-98170
[0009] There has been a need for an enhanced coefficient of
performance (COP) in recent air-conditioning apparatuses. As
described in Patent Literatures 1 to 3, a decrease in oil
circulation rate by separating refrigerant and oil has been
considered to enhance the COP. However, when focusing only on the
oil circulation rate, the COP might decrease disadvantageously.
SUMMARY
[0010] The present invention has been made to solve such a problem
as described above, and is intended to provide an air-conditioning
apparatus that can enhance a COP in both a cooling operation and a
heating operation and a method for controlling the air-conditioning
apparatus.
[0011] An air-conditioning apparatus according to the present
invention includes a refrigerant circuit in which a compressor, a
discharge gas cooling unit, an oil separator, a flow switching
device, an indoor heat exchanger, an expansion valve, and an
outdoor heat exchanger are connected to each other in a loop and
capable of performing a cooling operation and a heating operation
by switching a channel with the flow switching device, the
air-conditioning apparatus comprising: a heat rejection control
means for controlling the discharge gas cooling unit such that the
discharge gas cooling unit cools discharge gas from the compressor
when the operating state is the cooling operation, and the
discharge gas cooling unit does not cool the discharge gas when the
operating state is the heating operation.
[0012] In an oil separator and an air-conditioning apparatus
according to the present invention, in a cooling operation,
discharge gas is cooled by a discharge gas cooling unit and
separation in the oil separator is promoted so that the oil
circulation rate is reduced and the COP is enhanced, and in a
heating operation, cooling of the discharge gas is stopped so that
heat rejection in the discharge gas cooling unit is reduced and a
decrease in COP is reduced.
BRIEF DESCRIPTION OF DRAWINGS
[0013] FIG. 1 schematically illustrates a configuration of an
air-conditioning apparatus according to Embodiment 1 of the present
invention.
[0014] FIG. 2 is a graph showing a p-h diagram of an operating
state in a cooling operation of the air-conditioning apparatus
illustrated in FIG. 1.
[0015] FIG. 3 is a graph showing a p-h diagram of an operating
state in a heating operation of the air-conditioning apparatus
illustrated in FIG. 1.
[0016] FIG. 4 is a graph showing a relationship between a pressure
loss through a segment from an evaporator outlet to a compressor
inlet and a COP in the cooling operation of the air-conditioning
apparatus illustrated in FIG. 1.
[0017] FIG. 5 is a graph showing a relationship between an oil
circulation rate and a percentage to COP in the air-conditioning
apparatus illustrated in FIG. 1.
[0018] FIG. 6 is a graph showing a relationship between the amount
of heat rejection and a percentage to COP in a discharge gas
cooling unit in the heating operation of the air-conditioning
apparatus illustrated in FIG. 1.
[0019] FIG. 7 is a flowchart showing a method for controlling an
air-conditioning apparatus according to Embodiment 1 of the present
invention.
[0020] FIG. 8 is a flowchart showing a method for controlling an
air-conditioning apparatus according to Embodiment 2 of the present
invention.
[0021] FIG. 9 schematically illustrates a configuration of an
air-conditioning apparatus according to Embodiment 3 of the present
invention.
[0022] FIG. 10 schematically illustrates a configuration of an
air-conditioning apparatus according to Embodiment 4 of the present
invention.
[0023] FIG. 11 schematically illustrates a configuration of an
air-conditioning apparatus according to Embodiment 5 of the present
invention.
DETAILED DESCRIPTION
Embodiment 1
[0024] A preferred embodiment of an air-conditioning apparatus of
the present invention will be described with reference to the
drawings. FIG. 1 schematically illustrates an air-conditioning
apparatus according to Embodiment 1 of the present invention. An
air-conditioning apparatus 100 illustrated in FIG. 1 performs both
a cooling operation and a heating operation, and includes a
refrigerant circuit in which a compressor 1, a discharge gas
cooling unit 2, an oil separator 3, a four-way valve 4 serving as a
flow switching device, an indoor heat exchanger 6, an expansion
valve 8, and an outdoor heat exchanger 9 are connected to each
other in a loop. Among these components, the compressor 1, the
discharge gas cooling unit 2, the oil separator 3, the four-way
valve 4, the expansion valve 8, and the outdoor heat exchanger 9
constitute an outdoor unit 10, and an indoor heat exchanger 6
constitutes an indoor unit 11. The outdoor unit 10 and the indoor
unit 11 are connected to each other by a gas-side extension pipe 5
and a refrigerant-side extension pipe 7. Refrigerant circulates
between the outdoor unit 10 and the indoor unit 11 via the gas-side
extension pipe 5 and the refrigerant-side extension pipe 7.
[0025] The compressor 1 causes refrigerant from the four-way valve
4 to be a high-temperature high-pressure discharge gas. The
compressor 1 may be of various types. The compressor 1 that
generates driving power for circulating this refrigerant may be of
various types such as a reciprocating type, a screw type, a scroll
type, and a rotary type.
[0026] The discharge gas cooling unit 2 cools discharge gas from
the compressor 1, and includes a pump 12, a heat rejecter 13, and a
heat exchanger 14. The pump 12, the heat rejecter 13, and the heat
exchanger 14 constitute a circulation circuit in which water or
brine, for example, circulates. The pump 12 causes a circulation
substance such as water or brine to circulate between the heat
rejecter 13 and the heat exchanger 14. The heat rejecter 13 cools
(rejects heat from) water or brine, for example, circulating in the
circulation circuit. The heat exchanger 14 exchanges heat between
the discharge gas and water or brine, for example, flowing in the
circulation circuit. The heat exchanger 14 includes a refrigerant
channel through which the discharge gas from the compressor 1, for
example, flows and a cooling channel 14a through which the
circulation substance flows. The circulation substance flowing in
the cooling channel 14a takes the quantity of heat of the discharge
gas flowing in the refrigerant channel, thereby cooling the
discharge gas. The heat exchanger 14 may be of various known types
such as a shell-and-tube type, a shell-and-coil type, a dual-tube
type.
[0027] When the pump 12 starts operating, water or brine, for
example, circulates in the circulation circuit, and the heat
exchanger 14 exchanges heat between water, for example, and the
discharge gas. Water, for example, subjected to the heat exchange
is deprived of heat (i.e., cooled) by the heat rejecter 13. In this
manner, the discharge gas is cooled, in other words, heat is
radiated from the discharge gas. On the other hand, when the pump
12 stops, circulation of water, for example, in the circulation
circuit stops and the heat exchanger 14 does not exchange heat.
Thus, the discharge gas is not cooled. Operation of the pump 12 is
controlled by a heat rejection control means 22. By using the
control of on/off operation of the pump 12 by the heat rejection
control means 22, it is determined whether the discharge gas by the
discharge gas cooling unit 2 is cooled or not.
[0028] The oil separator 3 separates oil from the discharge gas,
and returns the separated oil to the compressor 1. The oil
separator 3, for example, includes an inflow pipe through which gas
discharged from the discharge gas cooling unit 2 flows into a
hollow container, a discharge pipe through which refrigerant gas is
discharged to the four-way valve 4, and a pipe which is located at
the bottom thereof and through which the separated oil returns to
the compressor 1. When gas flows from the inflow pipe into the
hollow container, oil is attached to the surface of the hollow
container, flows down toward the bottom surface of the hollow
container, and then returns to the compressor 1 through the pipe.
On the other hand, refrigerant gas is discharged from the discharge
pipe toward the four-way valve 4.
[0029] The higher the temperature of the refrigerant gas discharged
from the compressor 1, the larger amount of oil is separated from
refrigerant in the oil separator 3. Specifically, cooling of the
discharge gas by the discharge gas cooling unit 2 before the
discharge gas enters the discharge gas from the compressor 1 into
the oil separator 3 also reduces the temperature of oil included in
the discharge gas. The cooling of oil increases the viscosity and
the density of the oil, and accordingly, the oil can be more easily
attached to, and captured at, the surface of the hollow container
in the oil separator 3. Consequently, cooling of the discharge gas
by the discharge gas cooling unit 2 can promote separation between
oil and refrigerant in the oil separator 3.
[0030] The four-way valve 4 switches the direction of a flow of
refrigerant depending on the operation mode of the indoor unit 11.
Specifically, in a cooling operation, the four-way valve 4 is
switched to allow discharge gas to flow from the oil separator 3 to
the outdoor heat exchanger 9. On the other hand, in a heating
operation, the four-way valve 4 is switched to allow refrigerant to
flow from the oil separator 3 to the indoor heat exchanger 6. The
expansion valve (reducing valve) 8 narrows a refrigerant channel in
order to adjust the amount of refrigerant flowing into the
evaporator.
[0031] The indoor heat exchanger 6 exchanges heat between indoor
air and refrigerant. The outdoor heat exchanger 9 exchanges heat
between outdoor air and refrigerant. Specifically, in the cooling
operation, the indoor heat exchanger 6 serves as an evaporator and
the outdoor heat exchanger 9 serves as a condenser. In the indoor
heat exchanger 6, refrigerant absorbs heat from indoor air and cold
air is blown, whereas in the outdoor heat exchanger 9, refrigerant
rejects heat by outdoor air and hot air is released. On the other
hand, in the heating operation, the indoor heat exchanger 6 serves
as a condenser and the outdoor heat exchanger 9 serves as an
evaporator. In the indoor heat exchanger 6, refrigerant rejects
heat to indoor air and hot air is released, whereas in the outdoor
heat exchanger 9, outdoor air absorbs heat from refrigerant and
cold air is released.
[0032] The above-described operation of the outdoor unit 10 is
controlled by control unit 20. In particular, the control unit 20
includes an operation determination means 21 and a heat rejection
control means 22 in order to switch operation of the discharge gas
cooling unit 2 between a cooling operation and a heating operation.
The operation determination means 21 determines whether the
operating state is the cooling operation or the heating operation.
For example, the operation determination means 21 performs the
determination of the operating state on the basis of the switching
state of the four-way valve 4.
[0033] The heat rejection control means 22 controls cooling in the
discharge gas cooling unit 2 on the basis of the determination by
the operation determination means 21. Specifically, the heat
rejection control means 22 controls an on/off operation of the pump
12, thereby controlling heat rejection of refrigerant in the heat
exchanger 14. If the operation determination means 21 determines
that the operating state is the cooling operation, the heat
rejection control means 22 controls the pump 12 so that cooling in
the heat exchanger 14 is performed. If the operation determination
means 21 determines that the operating state is the heating
operation, the heat rejection control means 22 stops operation of
the pump 12 so that no cooling is performed.
[0034] FIG. 2 is a graph showing an example of a p-h diagram in the
cooling operation of the air-conditioning apparatus 100. Referring
now to FIGS. 1 and 2, an example operation in the cooling operation
of the air-conditioning apparatus 100 will be described. First,
refrigerant in the state of low-pressure gas is sucked in the
compressor 1 (state a), and the low-pressure gas is compressed by
the compressor 1 to be a high-temperature high-pressure gas (state
b). Discharge gas from the compressor 1 is cooled by the discharge
gas cooling unit 2 (state c), and is separated into refrigerant and
refrigerating machine oil in the oil separator 3. The refrigerating
machine oil obtained by the separation in the oil separator 3
returns to a suction port of the compressor 1. On the other hand,
refrigerant is condensed by the outdoor heat exchanger 9 to be
high-pressure liquid refrigerant (state d). The liquid refrigerant
becomes low-pressure two-phase refrigerant by the expansion valve 8
(state e), passes through the refrigerant-side extension pipe 7,
and becomes low-pressure gas in the indoor heat exchanger 6 (state
f). Thereafter, the low-pressure gas passes through the gas-side
extension pipe 5 and returns to the compressor 1 (state a).
[0035] FIG. 3 is a graph showing an example of a p-h diagram in the
heating operation of the air-conditioning apparatus 100. Referring
now to FIGS. 1 and 3, an example operation in the heating operation
of the air-conditioning apparatus 100 will be described. First,
low-pressure gas is sucked in the compressor 1 (state a10), is
compressed by the compressor 1, and then becomes high-temperature
high-pressure gas (state b10). The discharge gas cooling unit 2
performs no heat rejection, and the high-temperature high-pressure
gas is separated into refrigerant and refrigerating machine oil in
the oil separator 3. The refrigerating machine oil obtained by the
separation in the oil separator 3 returns to an inlet of the
compressor 1. On the other hand, refrigerant passes through the
gas-side extension pipe 5, is condensed in the indoor heat
exchanger 6, and becomes high-pressure liquid refrigerant (state
d10). The high-pressure liquid refrigerant becomes low-pressure
two-phase refrigerant in the expansion valve 8 (state e10). The
resulting refrigerant passes through the refrigerant-side extension
pipe 7, becomes low-pressure gas in the outdoor heat exchanger 9
(state f10), and returns to the compressor 1 (state a10).
[0036] As shown in FIG. 2, cooling by the discharge gas cooling
unit 2 in the cooling operation promotes separation of
refrigerating machine oil from refrigerant. Thus, in the cooling
operation, a pressure loss through a segment from an evaporator
outlet to the compressor inlet can be reduced, and the COP can be
enhanced by performing heat rejection of refrigerant in the
discharge gas cooling unit 2. On the other hand, as shown in FIG.
3, no cooling operation is performed in the discharge gas cooling
unit 2 in the heating operation, and thus, an enthalpy difference
in the outdoor heat exchanger (the condenser) can be reduced,
thereby reducing a decrease in COP.
[0037] FIG. 4 is a graph showing a relationship between a pressure
loss and a COP from the evaporator outlet to the compressor inlet.
In FIG. 4, the abscissa represents (pressure at evaporator
outlet)/(pressure at compressor inlet).times.100, which is 100%
when the pressure loss is 0 (zero). As the pressure loss increases
(i.e., the distance increases), the percentage (%) increases. The
ordinate represents the percentage to COP in a case where the
pressure loss is 0 (at 100% on the abscissa). FIG. 4 shows that the
COP decreases with an increase in the pressure loss through the
segment from the evaporator outlet to the compressor inlet.
[0038] As described above, in the cooling operation, the indoor
heat exchanger 6 serves as an evaporator and the outdoor heat
exchanger 9 serves as a condenser. On the other hand, in the
heating operation, the indoor heat exchanger 6 serves as a
condenser and the outdoor heat exchanger 9 serves as an evaporator.
Specifically, the distance from the evaporator outlet to the
compressor 1 refers to a distance from the indoor heat exchanger 6
of the indoor unit 11 to the compressor 1 of the outdoor unit 10 in
the cooling operation, and refers to a distance from the outdoor
heat exchanger 9 of the outdoor unit 10 to the compressor 1 of the
outdoor unit 10 in the heating operation.
[0039] In the cooling operation, the outdoor unit 10 and the indoor
unit 11 are connected to each other by using the long gas-side
extension pipe 5. Thus, a significant pressure loss, which is a
major cause of COP decrease for a refrigeration cycle, occurs
through a segment from the outlet of the evaporator (the indoor
heat exchanger 6) to the inlet of the compressor 1. On the other
hand, in the heating operation, although the outdoor heat exchanger
9 serves as an evaporator, the outdoor heat exchanger 9 and the
compressor 1 constitute the same outdoor unit 10, the pipe
connecting the outdoor heat exchanger 9 and the compressor 1 is
greatly shorter than the gas-side extension pipe 5 described above.
That is, unlike the cooling operation, a pipe that is a cause of a
significant pressure loss such as the gas-side extension pipe 5 is
not present between the evaporator outlet and the compressor inlet.
Thus, in the heating operation, a decrease in pressure loss through
a segment from the outlet of the evaporator (the outdoor heat
exchanger 9) to the inlet of the compressor 1 can be minimized.
[0040] FIG. 5 is a graph showing a relationship between the oil
circulation rate (={oil flow rate/(refrigerant flow rate+oil flow
rate)}.times.100) and the percentage to COP. In FIG. 5, as the oil
circulation rate increases, the percentage to COP decreases.
Specifically, as the amount of refrigerating machine oil separated
by the oil separator 3 from the discharge gas in the compressor 1
increases, the pressure loss in the gas-side extension pipe 5
decreases so that the COP increases. In other words, the COP can be
enhanced irrespective of the operating state by cooling the
discharge gas in the discharge gas cooling unit 2 and promoting
separation of oil in the oil separator 3. However, it was found
that cooling by the discharge gas cooling unit 2 in the heating
operation disadvantageously reduces the COP.
[0041] FIG. 6 is a graph showing a relationship between the amount
of heat rejection and the COP in the discharge gas cooling unit 2
in the heating operation. In FIG. 6, the abscissa represents the
percentage (the amount of heat rejection in the discharge gas
cooling unit 2/the amount of heat rejection in the entire
apparatus}.times.100) of the amount of heat rejection in the
discharge gas cooling unit 2 with respect to the amount of heat
rejection of the entire refrigerant in the heating operation. The
ordinate represents the percentage to COP in a case where the
amount of heat rejection in the discharge gas cooling unit 2 is 0
(zero). As shown in FIG. 6, as the amount of heat rejection
increases, the percentage to COP decreases.
[0042] Specifically, in the heating operation, cooling of discharge
gas from the compressor 1 by the discharge gas cooling unit 2 means
that the quantity of heat that is originally intended to be used
for heating the room with the indoor heat exchanger 6 is radiated
in the discharge gas cooling unit 2 located upstream of the indoor
heat exchanger 6. To compensate for the capacity necessary for
heating, operation of the compressor 1 needs to be accelerated,
which might cause cooling by the discharge gas cooling unit 2 to
reduce the percentage to COP.
[0043] In addition, as described above, even when the separation
efficiency in the oil separator 3 is increased, the efficiency in
increasing the COP is small because of an originally small pressure
loss thorough a segment from the outlet of the outdoor heat
exchanger (the evaporator) 9 to the inlet of the compressor 1 (see
FIG. 4). In other words, a decrease in COP caused by acceleration
of the compressor frequency for compensation for heat rejection in
the discharge gas cooling unit 2 exceeds the increase in COP
obtained by reducing the oil circulation rate with cooling of the
discharge gas. As a result, the COP decreases as a whole.
[0044] In view of this, the heat rejection control means 22
performs control such that the discharge gas cooling unit 2
performs cooling in the cooling operation. In this manner, the
discharge gas cooling unit 2 performs heat rejection with a
reduction of a pressure loss through the segment from the
evaporator outlet to the compressor inlet in the cooling operation,
thereby enhancing the COP. On the other hand, in the heating
operation, the heat rejection control means 22 performs control
such that the discharge gas cooling unit 2 does not perform
cooling. In this manner, a decrease in enthalpy difference in the
outdoor heat exchanger (the condenser) can be avoided, thereby
reducing a COP decrease.
[0045] Specifically, in an air-conditioning apparatus that always
performs a cooling operation, a heat exchanger is placed in a
cabinet such as a refrigerator, an outdoor unit is placed outside
the cabinet, and the heat exchanger in the cabinet is connected to
the outdoor unit by an extension pipe. In such an air-conditioning
apparatus, the long extension pipe increases a pressure loss
through a segment from an evaporator outlet to a compressor inlet,
which significantly affects the COP of the air-conditioning
apparatus. Thus, the COP can be significantly enhanced by reducing
the pressure loss through the segment from the evaporator outlet to
the compressor inlet due to an increase in separation efficiency.
In addition, the COP can also be enhanced by reducing the
condensing temperature with cooling of compressor discharge
gas.
[0046] On the other hand, in the air-conditioning apparatus 100,
such as an air conditioner, which performs a cooling operation and
a heating operation, the COP disadvantageously decreases in the
heating operation. In the air-conditioning apparatus 100, such as
an air conditioner, which performs cooling and heating, the
indoor-side heat exchanger 6 is placed inside the room and the
outdoor unit 10 is placed outside the room such that the indoor
heat exchanger 6 and the outdoor unit 10 are connected together by
the extension pipes 5 and 7. This configuration is similar to those
of, for example, a refrigerator. Thus, in the cooling operation,
cooling of gas discharged from the compressor reduces the
condensing temperature. Since the long extension pipe connects the
evaporator outlet to the compressor inlet, the COP is significantly
enhanced by reducing the oil circulation rate.
[0047] However, in the heating operation in which the indoor heat
exchanger serves as a condenser and the outdoor heat exchanger
serves as an evaporator, cooling of the discharge gas in the
compressor 1 leads to extraction of heat in an amount that is
originally intended to be used for heating in the indoor heat
exchanger 6. The pipe connecting the evaporator outlet and the
inlet of the compressor 1 together is short because the evaporator
and the compressor 1 are connected in the same outdoor unit. In
addition, the effect of enhancing the COP obtained by reducing the
oil circulation rate is very small. Thus, in the heating operation,
cooling of discharge gas of the compressor disadvantageously
reduces the COP.
[0048] In view of this, in the air-conditioning apparatus 100, the
discharge gas cooling unit 2 performs cooling in the cooling
operation. Thus, the COP can be enhanced by performing heat
rejection in the discharge gas cooling unit 2 with a reduced
pressure loss through the segment from the evaporator outlet to the
compressor inlet in the cooling operation. On the other hand, in
the heating operation, the discharge gas cooling unit 2 does not
perform cooling (heat rejection). Thus, a decrease in COP can be
reduced while avoiding a decrease in enthalpy difference in the
outdoor heat exchanger (the condenser).
[0049] FIG. 7 is a flowchart showing a preferred embodiment of a
method for controlling an air-conditioning apparatus according to
the present invention. Referring now to FIGS. 1 and 7, a method for
controlling an air-conditioning apparatus 100 will be described.
First, when operation starts (step ST1), the operation
determination means 21 determines whether the operation is a
cooling operation or a heating operation (step ST2). If the
operation is determined not to be the cooling operation but the
heating operation, the discharge gas cooling unit 2 performs
cooling (step ST3). On the other hand, if the operation is
determined to be the cooling operation, operation of the heat
rejection control means 22 allows the discharge gas cooling unit 2
to cool discharge gas.
[0050] In this manner, in the cooling operation, a pressure loss
through a segment from an evaporator outlet to a compressor inlet
is reduced, and heat rejection of refrigerant is performed in the
discharge gas cooling unit 2, thereby enhancing the COP. On the
other hand, since no cooling (heat rejection) is performed in the
discharge gas cooling unit 2 in the heating operation, a decrease
in enthalpy difference in the outdoor heat exchanger (the
condenser) 9 is avoided, thereby reducing a COP decrease.
Embodiment 2
[0051] FIG. 8 schematically shows an air-conditioning apparatus
according to Embodiment 2 of the present invention. Referring now
to FIGS. 1 and 8, the air-conditioning apparatus will be described.
In the method for controlling an air-conditioning apparatus shown
in FIG. 8, like reference signs designate the identical or
corresponding process steps in the method for controlling an
air-conditioning apparatus shown in FIG. 7, and detailed
description will not be repeated. The method for controlling an
air-conditioning apparatus shown in FIG. 8 differs from that for
the air-conditioning apparatus 100 shown in FIG. 1 in that
discharge gas is cooled by the discharge gas cooling unit 2 in a
case where an operating state is a cooling operation and an
operating frequency f is greater than or equal to an operating
frequency fref.
[0052] Specifically, the heat rejection control means 22
illustrated in FIG. 1 has the function of determining whether the
operating frequency f of the compressor 1 is greater than or equal
to a predetermined operating frequency fref. If the operating state
is a cooling operation and the compressor 1 operates at an
operating frequency greater than or equal to the predetermined
operating frequency fref, the heat rejection control means 22
controls the discharge gas cooling unit 2 such that the discharge
gas cooling unit 2 cools discharge gas. On the other hand, even if
the operating state is the cooling operation but the compressor 1
operates at an operating frequency less than or equal to the
predetermined operating frequency fref, the discharge gas cooling
unit 2 is controlled not to cool the discharge gas. The
predetermined operating frequency fref is determined in advance in
consideration of a reduction in pressure loss obtained by reducing
the oil circulation rate and increasing the output power of, for
example, a pump of the discharge gas cooling unit 2.
[0053] In this manner, it is possible to prevent the influence of a
decrease in COP caused by driving of a power source such as a pump
12 of the discharge gas cooling unit 2 from increasing.
Specifically, the operating frequency f of the compressor 1 and the
oil circulation rate are linearly related, that is, as the
operating frequency increases, the oil circulation rate also
increases. Thus, in a case where the operating frequency f of the
compressor 1 is low, the effect of enhancing the COP obtained by
reducing the oil circulation rate with the use of power of, for
example, the pump of the discharge gas cooling unit 2 might be
smaller than the influence of a reduced COP caused by power of, for
example, the pump of the discharge gas cooling unit 2. To prevent
this situation, a threshold process of the operating frequency f
can prevent the influence of a reduced COP caused by power of, for
example, the pump of the discharge gas cooling unit 2 from
increasing.
[0054] In the case of performing a cooling operation at an
operating frequency f around the predetermined operating frequency
fref, cooling in the discharge gas cooling unit 2 is switched
between on and off so that operation might be unstable. Thus, in a
case where the operating frequency becomes the predetermined
operating frequency or more even when a predetermined period in
which the operating frequency is less than or equal to the
predetermined operating frequency does not elapse, the heat
rejection control means 22 may control the discharge gas cooling
unit 2 such that the discharge gas cooling unit 2 promptly stops
cooling of discharge gas. Thereafter, when the operating time in
which the operating frequency is greater than or equal to the
predetermined operating frequency fref continues for a
predetermined period or longer, the heat rejection control means 22
may control the discharge gas cooling unit 2 such that the
discharge gas cooling unit 2 starts cooling of the discharge gas.
Alternatively, cooling operation of the discharge gas cooling unit
2 may not be promptly switched depending on the predetermined
operating frequency fref by using, for example, a variation rate of
the operating frequency f.
Embodiment 3
[0055] FIG. 9 schematically illustrates an air-conditioning
apparatus according to Embodiment 3 of the present invention.
Referring now to FIG. 9, an air-conditioning apparatus 200 will be
described. In the air-conditioning apparatus 200 illustrated in
FIG. 9, like reference signs designate the identical or
corresponding parts of the air-conditioning apparatus 100 shown in
FIG. 1, and detailed description will not be repeated. The
air-conditioning apparatus 200 illustrated in FIG. 9 differs from
the air-conditioning apparatus 100 illustrated in FIG. 1 in the
configuration of the discharge gas cooling unit.
[0056] A discharge gas cooling unit 202 illustrated in FIG. 9
includes a first three-way valve 215 and a heat exchanger 14. The
first three-way valve 215 and the heat exchanger 14 constitute a
circulation circuit. The first three-way valve 215 is connected to
a suction side of a compressor 1, a four-way valve 4, and the heat
exchanger 14. A pipe is branched such that suction gas flows into
both the compressor 1 and a cooling channel 14a of the heat
exchanger 14 at a side downstream of the three-way valve 215. Thus,
the discharge gas cooling unit 202 has a configuration that can
cool discharge gas flowing in a refrigerant circuit by circulating
un-compressed suction gas in the cooling channel 14a of the heat
exchanger 14.
[0057] A heat rejection control means 222 determines whether
suction gas that is yet to enter the compressor 1 circulates in the
cooling channel 14a of the heat exchanger 14 or not by switch
control with the first three-way valve 215. Specifically, the heat
rejection control means 222 controls switching of the three-way
valve 215 such that suction gas flows in the heat exchanger 14 in a
cooling operation. Then, heat exchange is performed between suction
gas and discharge gas from the compressor 1 in the heat exchanger
14, thereby cooling discharge gas. On the other hand, the heat
rejection control means 222 controls switching of the three-way
valve such that refrigerant that is yet to be compressed does not
flow in the heat exchanger 14 in a heating operation. Then, no
suction gas flows in the heat exchanger 14, and thus, discharge gas
from the compressor 1 is not cooled.
[0058] The above-described configuration of Embodiment 3 can also
reduce a pressure loss through a segment from an evaporator outlet
to a compressor inlet in the cooling operation and enhance the COP
by performing heat rejection of refrigerant in the discharge gas
cooling unit 202. On the other hand, since no cooling is performed
in the discharge gas cooling unit 202 in the heating operation, a
decrease in enthalpy difference in the outdoor heat exchanger (the
condenser) 9 can be avoided, thereby reducing a decrease in COP. In
addition, in performing heat rejection in the cooling operation,
refrigerant can be heated in the heat exchanger 14 before the
refrigerant is sucked in the compressor 1, and it is possible to
prevent liquid refrigerant from returning to the compressor 1 and
damaging the compressor 1.
Embodiment 4
[0059] FIG. 10 schematically illustrates an air-conditioning
apparatus according to Embodiment 4 of the present invention.
Referring now to FIG. 10, an air-conditioning apparatus 300 will be
described. In the description of the air-conditioning apparatus 300
illustrated in FIG. 10, like reference signs designate the
identical or corresponding parts of the air-conditioning apparatus
100 shown in FIG. 1, and detailed description will not be repeated.
The air-conditioning apparatus 300 illustrated in FIG. 10 differs
from the air-conditioning apparatus 100 illustrated in FIG. 1 in
the configuration of a discharge gas cooling unit 302.
[0060] The discharge gas cooling unit 302 illustrated in FIG. 10
includes a heat rejecter 13 connected between a discharge-side pipe
of a compressor 1 and an oil separator 3 and a damper 311 that
blocks or allows an air supply of part of air supplied from the air
supply unit 16 to the heat rejecter 13. A duct for conducting air
from the air supply unit 16 may be disposed between the air supply
unit 16 and the heat rejecter 13. The damper 311 has the function
of changing the wind direction between a direction in which air
from the air supply unit 16 strikes the heat rejecter 13 and a
direction in which air from the air supply unit 16 is blocked.
Operation of the damper 311 is controlled by the heat rejection
control means 322. The cooling effect can be enhanced by providing
a fin to the heat rejecter 13 so that the surface area is
increased.
[0061] The heat rejection control means 322 performs control such
that the damper 311 is opened in a cooling operation such that air
is sent to the heat rejecter 13. Then, the heat rejecter 13 cools
discharge gas. On the other hand, in a heating operation, the heat
rejection control means 322 closes the damper 311 so as to block an
air flow to the heat rejecter 13. Then, the discharge gas cooling
unit 2 does not cool discharge gas.
[0062] The above-described configuration of Embodiment 4 can also
promote separation of refrigerating machine oil from refrigerant,
and thus, a pressure loss through a segment from an evaporator
outlet to a compressor inlet is reduced in the cooling operation,
and the discharge gas cooling unit 302 performs heat rejection,
thereby enhancing the COP. On the other hand, in the heating
operation, the discharge gas cooling unit 302 does not perform
cooling (heat rejection), and thus, a decrease in enthalpy
difference in the outdoor heat exchanger (the condenser) 6 can be
avoided, thereby reducing a decrease in COP. The configuration
illustrated in FIG. 10 allows the adjustment of the amount of heat
rejection by the heat rejecter 13 to be performed only in the
outdoor unit 10.
Embodiment 5
[0063] FIG. 11 schematically illustrates an air-conditioning
apparatus according to Embodiment 5 of the present invention.
Referring now to FIG. 11, an air-conditioning apparatus 400 will be
described. In the air-conditioning apparatus 400 illustrated in
FIG. 11, like reference signs designate the identical or
corresponding parts of the air-conditioning apparatus 100 shown in
FIG. 1, and detailed description will not be repeated. The
air-conditioning apparatus 400 illustrated in FIG. 11 differs from
the air-conditioning apparatus 100 illustrated in FIG. 1 in the
configuration of a discharge gas cooling unit.
[0064] A discharge gas cooling unit 402 includes a pump 12, a heat
rejecter 13 connected to the pump 12, a heat exchanger 14 connected
to the heat rejecter 13 and configured to perform heat exchange
between discharge gas from a compressor 1 and circulating water,
for example, and a second three-way valve 418 having two ports
connected to a discharge pipe of the compressor 1 and the heat
exchanger 14 and the other port bypassing from the discharge pipe
of the compressor 1 to an inlet of an oil separator 3. That is, the
channel is switched between the channel in which discharge gas from
the compressor 1 passes through the heat exchanger 14 and the
channel in which the discharge gas bypasses the heat exchanger 14
and flows into the oil separator 3 by switching the second
three-way valve. The operation of the second three-way valve 418 is
controlled by the heat rejection control means 22.
[0065] The heat rejection control means 422 switches the second
three-way valve 418 such that discharge gas from the compressor 1
passes through the heat exchanger 14 in a cooling operation. Then,
the discharge gas is cooled in the heat exchanger 14. On the other
hand, the heat rejection control means 422 switches the second
three-way valve 418 such that the discharge gas bypasses the heat
exchanger 14 that exchanges heat with a discharge pipe of the
compressor 1 in a heating operation. Then, the discharge gas flows
into the oil separator 3 without passing through the heat exchanger
14, and the discharge gas is not cooled.
[0066] The above-described configuration of Embodiment 5 can also
promote separation of refrigerating machine oil from refrigerant,
and thus, a pressure loss through a segment from an evaporator
outlet to a compressor inlet is reduced in the cooling operation,
and the discharge gas cooling unit 402 performs heat rejection of
refrigerant, thereby enhancing the COP. On the other hand, in the
heating operation, the discharge gas cooling unit 402 does not
perform cooling (heat rejection), and thus, a decrease in enthalpy
difference in an outdoor heat exchanger (a condenser) 6 can be
avoided, thereby reducing a decrease in COP.
[0067] Embodiments of the present invention are not limited to
those described above. For example, in the above description, the
heat rejection control means 22, 222, 322, and 422 perform control
such that heat rejection is performed in a cooling operation but is
not performed in operations except the cooling operation.
Alternatively, the adjustment may be performed to increase or
decrease the amount of heat rejection in the cooling operation. For
example, as illustrated in FIG. 8, in a case where the operating
state is a cooling operation and the operating frequency is less
than the predetermined operating frequency fref, cooling may be
performed with a reduced flow rate at the cooling channel 14a of
the heat exchanger 14 or with a low cooling capacity by, for
example, controlling the damper 311 so as to reduce the amount of
air supplied to the heat rejecter 13 in FIG. 10.
[0068] In the above-described configuration of the oil separator 3,
a hollow container is used as an example. Alternatively, various
known techniques such as a technique of reducing the flow rate of
refrigerant gas in order to drop fine oil particles by utilizing
the dead weight thereof and a technique of providing a filter in an
oil separator so as to collect fine oil particles may be
employed.
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