U.S. patent application number 12/738924 was filed with the patent office on 2010-08-19 for refrigeration cycle apparatus.
This patent application is currently assigned to MITSUBISHI ELECTRIC CORPORATION. Invention is credited to Takashi Okazaki, Tomoyoshi Oobayashi, Fumitake Unezaki.
Application Number | 20100205987 12/738924 |
Document ID | / |
Family ID | 40678426 |
Filed Date | 2010-08-19 |
United States Patent
Application |
20100205987 |
Kind Code |
A1 |
Okazaki; Takashi ; et
al. |
August 19, 2010 |
REFRIGERATION CYCLE APPARATUS
Abstract
A refrigerant cycle apparatus comprising: a compressor 1, a
radiator 2, decompression means 3, a heat absorber 4, an internal
heat exchanger 5 that performs heat exchange between a refrigerant
at an outlet of said radiator and the refrigerant at an outlet of
said heat absorber, wherein first temperature detection means 30
for detecting a refrigerant temperature between an outlet of the
compressor 1 and an inlet of the radiator 2 and second temperature
detection means 31 for detecting the refrigerant temperature
between the outlet of the radiator 2 and a high-pressure side inlet
of the internal heat exchanger 5 are provided, and an opening
degree of decompression means 3 is controlled so that a temperature
difference (.DELTA.T) between a detection temperature by the first
temperature detection means 30 and the detection temperature by the
second temperature detection means 31 becomes a target value.
Inventors: |
Okazaki; Takashi; (Tokyo,
JP) ; Unezaki; Fumitake; (Tokyo, JP) ;
Oobayashi; Tomoyoshi; (Tokyo, JP) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
MITSUBISHI ELECTRIC
CORPORATION
TOKYO
JP
|
Family ID: |
40678426 |
Appl. No.: |
12/738924 |
Filed: |
November 20, 2008 |
PCT Filed: |
November 20, 2008 |
PCT NO: |
PCT/JP2008/071069 |
371 Date: |
April 20, 2010 |
Current U.S.
Class: |
62/190 |
Current CPC
Class: |
F25B 2309/061 20130101;
F25B 2700/2102 20130101; F25B 2700/21161 20130101; F25B 2600/17
20130101; F25B 2700/1933 20130101; F25B 2341/063 20130101; F25B
2700/21151 20130101; F25B 2339/047 20130101; F25B 2600/2513
20130101; F25B 40/00 20130101; F25B 2700/21174 20130101; F25B
2700/21152 20130101; F25B 9/008 20130101 |
Class at
Publication: |
62/190 |
International
Class: |
F25B 49/00 20060101
F25B049/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 2007 |
JP |
2007-310097 |
Claims
1. A refrigerant cycle apparatus comprising: at least a compressor,
a radiator, decompression means capable of changing an open degree,
a heat absorber, an internal heat exchanger that performs heat
exchange between a refrigerant at an outlet of said radiator and
the refrigerant at an outlet of said heat absorber, wherein first
refrigerant conditions detection means for detecting standard
conditions of at least said radiator and second refrigerant
conditions detection means for detecting refrigerant conditions
between an outlet of said radiator and a high-pressure side inlet
of said internal heat exchanger are provided, and an opening of
said decompression means is controlled so that a calculation value
calculated based on at least an output of said first refrigerant
conditions detection means and the output of said second
refrigerant conditions detection means becomes a target value.
2. The refrigerant cycle apparatus of claim 1 comprising: third
temperature detection means for detecting an inlet temperature of a
medium to be heated and fourth temperature detection means for
detecting an outlet temperature of the medium to be heated, wherein
the opening degree of said decompression means is controlled such
that a calculation value calculated based on outputs of said first
refrigerant condition detection means, said second refrigerant
condition detection means, said third temperature detection means,
and said fourth temperature detection means become a target
value.
3. A refrigerant cycle apparatus comprising: at least a compressor,
a radiator, decompression means capable of changing an open degree,
a heat absorber, an internal heat exchanger that performs heat
exchange between a refrigerant at an outlet of said radiator and
the refrigerant at an outlet of said heat absorber, wherein first
temperature detection means for detecting a refrigerant temperature
between an outlet of said compressor and an inlet of said radiator
and second temperature detection means for detecting the
refrigerant temperature between an outlet of said radiator and a
high-pressure side inlet of said internal heat exchanger are
provided, and an opening degree of said decompression means is
controlled such that a temperature difference (.DELTA.T) between a
detection temperature by said first temperature detection means and
the detection temperature by said second temperature detection
means becomes a target value.
4. The refrigerant cycle apparatus of claim 3 further comprising:
third temperature detection means for detecting an inlet
temperature of a medium to be heated and fourth temperature
detection means for detecting an outlet temperature of the medium
to be heated, wherein the opening degree of said decompression
means is controlled such that a calculation value calculated based
on outputs of said first temperature detection means, said second
temperature detection means, said third temperature detection
means, and said fourth temperature detection means, instead of said
temperature difference (.DELTA.T), become a target value.
5. A refrigerant cycle apparatus comprising: at least a compressor,
a radiator, decompression means capable of changing an open degree,
a heat absorber, an internal heat exchanger that performs heat
exchange between a refrigerant at an outlet of said radiator and
the refrigerant at an outlet of said heat absorber, wherein first
temperature detection means for detecting a refrigerant temperature
between an outlet of said compressor and an inlet of said radiator
and second temperature detection means for detecting the
refrigerant temperature between the outlet of said radiator and a
high-pressure side inlet of said internal heat exchanger, third
temperature detection means for detecting an inlet temperature of a
medium to be heated and fourth temperature detection means for
detecting the outlet temperature of the medium to be heated are
provided, and an opening degree of said decompression means is
controlled such that a sum (.SIGMA..DELTA.T) of a temperature
difference (.DELTA.T1) between a detection temperature by said
first temperature detection means and the detection temperature by
said fourth temperature detection means and the temperature
difference (.DELTA.T2) between the detection temperature by said
second temperature detection means and the detection temperature by
said third temperature detection means becomes a target value.
6. A refrigerant cycle apparatus comprising: at least a compressor,
a radiator, decompression means capable of changing an open degree,
a heat absorber, an internal heat exchanger that performs heat
exchange between a refrigerant at an outlet of said radiator and
the refrigerant at an outlet of said heat absorber, wherein first
temperature detection means for detecting a refrigerant temperature
between an outlet of said compressor and an inlet of said radiator
and second temperature detection means for detecting the
refrigerant temperature between the outlet of said radiator and a
high-pressure side inlet of said internal heat exchanger, third
temperature detection means for detecting an inlet temperature of a
medium to be heated and fourth temperature detection means for
detecting an outlet temperature of the medium to be heated are
provided, and an opening degree of said decompression means is
controlled such that a difference (.DELTA.T1-.DELTA.T2) between a
second temperature difference (.DELTA.T1) between a detection
temperature by said first temperature detection means and the
detection temperature by said fourth temperature detection means
and a third temperature difference (.DELTA.T2) between the
detection temperature by said second temperature detection means
and the detection temperature by said third temperature detection
means becomes a target value.
7. A refrigerant cycle apparatus comprising: at least a compressor,
a radiator, decompression means capable of changing an open degree,
a heat absorber, an internal heat exchanger that performs heat
exchange between a refrigerant at an outlet of said radiator and
the refrigerant at an outlet of said heat absorber, wherein first
pressure detection means for detecting a refrigeration pressure
between at least an outlet of said compressor and an inlet of said
decompression means and second temperature detection means for
detecting a refrigeration temperature between the outlet of said
radiator and a high-pressure side inlet of said internal heat
exchanger are provided, and an opening degree of said decompression
means is controlled such that a calculation value calculated based
on a detection pressure by said first pressure detection means and
a detection temperature by said second temperature detection means
becomes a target value.
8. A refrigerant cycle apparatus comprising: at least a compressor,
a radiator, decompression means capable of changing an open degree,
a heat absorber, an internal heat exchanger that performs heat
exchange between a refrigerant at an outlet of said radiator and
the refrigerant at an outlet of said heat absorber, wherein second
temperature detection means for detecting a refrigerant temperature
between an outlet of said radiator and a high-pressure side inlet
of said internal heat exchanger and internal heat exchanger outlet
temperature detection means for detecting the refrigerant
temperature between a high-pressure side outlet of said internal
heat exchanger and an inlet of said compression means are provided,
and an opening degree of said decompression means is controlled
such that a temperature difference (.DELTA.Thx) between a detection
temperature by said second temperature detection means and the
detection temperature by said internal heat exchanger outlet
temperature detection means becomes a target value.
9. The refrigerant cycle apparatus of claim 1, wherein sixth
temperature detection means for detecting the refrigerant
temperature between a low-pressure side outlet of said internal
heat exchanger and an inlet of said compressor is provided,
superheat degree of a compressor suction part is calculated from a
refrigerant saturation temperature at a detection point of said
sixth temperature detection means and a detection temperature by
said sixth temperature detection means, and the opening degree of
said decompression means is controlled such that said superheat
degree becomes the target value.
10. The refrigerant cycle apparatus of claim 9, wherein second
pressure detection means is provided between the low-pressure side
outlet of said internal heat exchanger and the inlet of said
compressor and said refrigerant saturation temperature is
calculated based on a detection value of said second pressure
detection means.
11. The refrigerant cycle apparatus of claim 9, wherein fifth
temperature detection means is provided between the inlet of said
heat absorber and the low-pressure side inlet of said internal heat
exchanger and said refrigerant saturation temperature is calculated
based on the detection temperature of said fifth temperature
detection means.
12. The refrigerant cycle apparatus of claim 9, wherein a priority
is given to control said superheat degree over said temperature
difference.
13. The refrigerant cycle apparatus of claim 1, wherein said
radiator is a heat exchanger that exchanges heat with water.
14. The refrigerant cycle apparatus of claim 1, wherein carbon
dioxide is used as a refrigerant.
15. The refrigerant cycle apparatus of claim 5, wherein sixth
temperature detection means for detecting the refrigerant
temperature between a low-pressure side outlet of said internal
heat exchanger and an inlet of said compressor is provided,
superheat degree of a compressor suction part is calculated from a
refrigerant saturation temperature at a detection point of said
sixth temperature detection means and a detection temperature by
said sixth temperature detection means, and the opening degree of
said decompression means is controlled such that said superheat
degree becomes the target value.
16. The refrigerant cycle apparatus of claim 6, wherein sixth
temperature detection means for detecting the refrigerant
temperature between a low-pressure side outlet of said internal
heat exchanger and an inlet of said compressor is provided,
superheat degree of a compressor suction part is calculated from a
refrigerant saturation temperature at a detection point of said
sixth temperature detection means and a detection temperature by
said sixth temperature detection means, and the opening degree of
said decompression means is controlled such that said superheat
degree becomes the target value.
17. The refrigerant cycle apparatus of claim 15, wherein second
pressure detection means is provided between the low-pressure side
outlet of said internal heat exchanger and the inlet of said
compressor and said refrigerant saturation temperature is
calculated based on a detection value of said second pressure
detection means.
18. The refrigerant cycle apparatus of claim 16, wherein second
pressure detection means is provided between the low-pressure side
outlet of said internal heat exchanger and the inlet of said
compressor and said refrigerant saturation temperature is
calculated based on a detection value of said second pressure
detection means.
19. The refrigerant cycle apparatus of claim 15, wherein fifth
temperature detection means is provided between the inlet of said
heat absorber and the low-pressure side inlet of said internal heat
exchanger and said refrigerant saturation temperature is calculated
based on the detection temperature of said fifth temperature
detection means.
20. The refrigerant cycle apparatus of claim 16, wherein fifth
temperature detection means is provided between the inlet of said
heat absorber and the low-pressure side inlet of said internal heat
exchanger and said refrigerant saturation temperature is calculated
based on the detection temperature of said fifth temperature
detection means.
Description
TECHNICAL FIELD
[0001] The present invention relates to a refrigeration cycle
apparatus using an internal heat exchanger, more particularly to a
refrigerant control for stably securing performance.
BACKGROUND ART
[0002] Descriptions will be given to prior art as follows.
[0003] Conventionally, a hot water supply apparatus is proposed as
a built-in refrigeration cycle apparatus such as:
[0004] a hot water supply apparatus comprising a refrigeration
cycle including a compressor, a hot water supply heat exchanger, an
electronic expansion valve, and a heat source side heat exchanger
whose heat source is an external air, and a hot water supply cycle
including a hot water supply heat exchanger and a hot water supply
tank,
[0005] wherein since ability control means that uses an
ability-variable type compressor and ability-controls the
compressor in response to changes in external environment
conditions of the heat source side heat exchanger is attached,
expansion valve opening degree control means for controlling an
opening degree of an electronic expansion valve so as to make a
discharge temperature of a compressor to be a target value in
response to changes in external environment conditions (an external
temperature, for example) of the heat source side heat exchanger
and rotation speed control means for controlling a rotation speed
of the compressor to be a target value in response to changes in
the external environment conditions of the heat source side heat
exchanger are attached, an opening of the electronic expansion
valve is controlled so as to make the discharge temperature of the
compressor becomes a target value in response to changes in the
external environment conditions (an external temperature, for
example) of the heat source side heat exchanger, and the rotation
speed of the compressor is controlled to be a target value in
response to changes in the external environment conditions of the
heat source side heat exchanger, an optimal operation condition can
be obtained in which a hot water supply ability and a hot water
supply load further match, and a coefficient of performance (COP)
can be improved and down-sizing of elements such as an heat
exchanger becomes possible. (For example, refer to Patent Document
1)
[0006] A water heater is also proposed such as:
a water heater for heating a hot water supply fluid in a
supercritical heat pump cycle where a refrigerant pressure in a
high pressure side becomes equal to or more than the critical
pressure of the refrigerant comprising:
[0007] a compressor,
[0008] a radiator that performs heat exchange between a refrigerant
discharged from the compressor and a hot water supply fluid and is
configured so that a refrigerant flow and the hot water supply
fluid flow opposes,
[0009] a decompressor for decompressing the refrigerant flowing out
of the radiator, and
[0010] an evaporator that makes the refrigerant that flows out of
the compressor evaporate, makes the refrigerant absorb a heat to
discharge it into a suction side of the compressor,
[0011] wherein a refrigerant pressure of a high-pressure side is
controlled so that a temperature difference (.DELTA.T) between the
refrigerant that flows out of the radiator and the hot water supply
fluid that flows therein becomes a predetermined temperature
difference (.DELTA.To). (For example, refer to Patent Document 2)
In this example of the prior art, a heat exchange efficiency of the
radiator can be enhanced to improve efficiency of a heat pump.
[0012] [Patent Document 1] Japanese Patent Gazette No. 3601369 (pp.
6; FIG. 1)
[0013] [Patent Document 2] Japanese Patent Gazette No. 3227651 (pp.
1-3; FIG. 2)
SUMMARY OF INVENTION
Problems to be Solved by the Invention
[0014] Both of the above examples of the prior art control
refrigerant conditions so that a discharge temperature of the
compressor or a temperature difference (.DELTA.T) between the
refrigerant that flows out of the radiator and the hot water supply
fluid that flows therein becomes a target value to achieve an
efficient operation. However, there was a problem that in the
vicinity where an efficiency (COP) of the refrigeration cycle
becomes maximum, a control based only on an inlet side (the above
discharge temperature) of the radiator or an outlet side (the above
temperature difference .DELTA.T) is difficult to achieve stable and
efficient operation conditions because changes in the discharge
temperature or the temperature difference .DELTA.T are small. In
addition, since an operation in which an internal heat exchanger
exists in the refrigerant circuit is not considered, there was a
problem that to control to achieve stable and efficient operation
conditions is difficult.
[0015] The present invention is made to solve the above problems in
the prior art. The object is to obtain a refrigeration cycle
apparatus capable of stably achieving efficient operation
conditions by controlling operation values based on standard
conditions of the radiator and outlet conditions of the radiator to
be a target value.
Means for Solving the Problems
[0016] In order to solve the above problems, the refrigeration
cycle apparatus according to the present invention includes at
least a compressor, a radiator, decompression means capable of
changing an open degree, a heat absorber, an internal heat
exchanger that performs heat exchange between a refrigerant at an
outlet of the radiator and the refrigerant at the outlet of the
heat absorber. The refrigeration cycle apparatus is characterized
in that at least first refrigerant conditions detection means for
detecting standard conditions of the radiator and second
refrigerant conditions detection means for detecting refrigerant
conditions between an outlet of the radiator and a high-pressure
side inlet of an internal heat exchanger are provided, and an
opening degree of decompression means is controlled so that a
calculation value calculated based on an output of the first
refrigerant conditions detection means and the output of the second
refrigerant conditions detection means becomes a target value.
EFFECT OF THE INVENTION
[0017] According to the present invention, the expansion valve
opening degree is controlled so that the COP becomes maximum based
on standard conditions of the radiator and refrigerant conditions
of the radiator outlet part, so that a refrigerant cycle apparatus
capable of stably achieving efficient operation can be
obtained.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 is a diagram showing a configuration of a
refrigeration cycle apparatus according to Embodiment 1 of the
present invention.
[0019] FIG. 2 is a diagram showing an operation behavior on a P-h
diagram according to Embodiment 1 of the present invention.
[0020] FIG. 3 is a diagram showing a temperature distribution of a
refrigerant and water in a water heat exchanger according to
Embodiment 1 of the present invention.
[0021] FIG. 4 is a diagram showing cycle conditions against an
expansion valve opening degree according to Embodiment 1 of the
present invention.
[0022] FIG. 5 is a diagram showing changes in each calculation
value, heating ability, and COP against an expansion valve opening
degree according to Embodiment 1 of the present invention.
[0023] FIG. 6 is a diagram showing changes in other calculation
value, heating ability, and COP against an expansion valve opening
degree according to Embodiment 1 of the present invention.
[0024] FIG. 7 is a diagram showing a control flowchart according to
Embodiment 1 of the present invention.
[0025] FIG. 8 is a diagram showing a refrigeration cycle apparatus
according to Embodiment 2 of the present invention.
[0026] FIG. 9 is a diagram showing an operation behavior on a P-h
diagram according to Embodiment 2 of the present invention.
DESCRIPTIONS OF CODES AND SYMBOLS
[0027] 1 compressor [0028] 2 radiator (water heat exchanger) [0029]
3 expansion valve [0030] 4 heat absorber (evaporator) [0031] 5
internal heat exchanger [0032] 20 hot water supply side pump [0033]
21 hot water storage tank [0034] 22 use side pump [0035] 23, 24, 25
on-off valve [0036] 29 blower [0037] 30, 31, 32, 33, 41, 42, 52
temperature detection means [0038] 35, 51 pressure detection means
[0039] 40 controller [0040] 50 heat source apparatus [0041] 60 hot
water storage apparatus
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1
[0042] Descriptions will be given to a refrigerant cycle apparatus
by Embodiment 1 according to the present invention.
[0043] FIG. 1 shows a configuration diagram of the refrigerant
cycle apparatus according to the present embodiment. In the figure,
the refrigerant cycle apparatus according to the present embodiment
is a hot water supply apparatus using carbon dioxide (hereinafter,
CO.sub.2) as a refrigerant, composed of a heat source apparatus 50,
a hot water storage apparatus 60, and a controller 40 for
controlling these. The present embodiment shows an example of the
hot water supply apparatus, however, it is not limited thereto. The
apparatus may be an air conditioner. In the same way, the
refrigerant is not limited to carbon dioxide but an HFC refrigerant
may be used.
[0044] The heat source apparatus 50 is composed of a compressor 1
for compressing the refrigerant, a radiator 2 (hereinafter,
referred to "water heat exchanger") for taking out heat of a
high-temperature high-pressure refrigerant compressed in the
compressor 1, an internal heat exchanger 5 for further cooling the
refrigerant output from the water heat exchanger 2, a decompressor
3 (hereinafter, referred to "expansion valve") that decompresses
the refrigerant and whose opening degree can be changed, an
heat-absorber 4 (hereinafter, referred to "evaporator") for
evaporating the refrigerant decompressed in the expansion valve 3,
and an internal heat exchanger 5 for further heating the
refrigerant flowed out of the evaporator 4. That is, the internal
heat exchanger 5 is a heat exchanger that heat-exchanges the
refrigerant at an outlet of the water heat exchanger 2 with the
refrigerant at the outlet of the evaporator 4. A blower 29 is
provided for sending air on an outer surface of the evaporator 4.
There are also provided first temperature detection means 30 for
detecting a discharge temperature of the compressor 1, second
temperature detection means 31 for detecting an outlet temperature
of the water heat exchanger 2, fifth temperature detection means 32
for detecting an inlet refrigerant temperature of the evaporator 4,
and sixth temperature detection means 33 for detecting a suction
temperature of the compressor 1. In addition, the first temperature
detection means 30 and the second temperature detection means 31
correspond to a first refrigerant conditions detection means and
second refrigerant conditions detection means respectively in an
example of control in FIG. 7 to be described later.
[0045] A hot water storage apparatus 60 is connected with the water
heat exchanger 2, which is a radiator, via piping, being composed
of a heat source side pump 20, a hot water storage tank 21, a use
side pump 22, and on-off valves 23, 24, 25. Here, on-off valves 23,
24, 25 may be a simple valve only for switching operation or an
opening variable valve. When a water level of the hot water storage
tank 21 drops, the on-off valves 24, 25 are closed, the on-off
valve 23 is opened, and hot water storage operation is performed in
which supplied water is heated up to a predetermined temperature.
When a heat dissipation loss is large and the temperature in the
hot water storage tank 21 decreases such as in winter, the on-off
valves 23, 25 are closed, the on-off valve 24 is opened, and
circulation heating operation is performed in which low-temperature
hot water in the hot water storage tank 21 is re-boiled. At the
time of using the hot water supply, the on-off valves 23, 24 are
closed, the on-off valve 25 is opened, the use side pump 22 starts
operation to transfer stored hot water to the use side. At an inlet
side of the water heat exchanger 2, third temperature detection
means 41 is attached for detecting an inlet temperature of a medium
(water) to be heated. At an outlet side of the water heat exchanger
2, fourth temperature detection means 42 is attached for detecting
the outlet temperature of the medium (water) to be heated.
[0046] A controller 40 performs calculation using detected values
from first temperature detection means 30, second temperature
detection means 31, fifth temperature detection means 32, sixth
temperature detection means 33, third temperature detection means
41, and fourth temperature detection means 42 to control an opening
degree of the expansion valve 3, a rotation speed of the compressor
1, and the rotation speed of the hot water supply side pump 20,
respectively.
[0047] FIG. 2 is a P-h diagram describing cycle conditions during
hot water storage operation in the refrigeration cycle apparatus
shown in FIG. 1. In FIG. 2, solid lines denote refrigerant
conditions at a certain expansion valve opening degree and A, B, C,
D, and E denote refrigerant conditions in the hot water storage
operation. At the time of the hot water storage operation, a
high-temperature high-pressure refrigerant (A) discharged from the
compressor 1 flows into the water heat exchanger 2. In the water
heat exchanger 2, the refrigerant heats supplied water while
dissipating heat to water circulating the hot water storage circuit
to decrease the own temperature. A refrigerant (B) flowed out of
the water heat exchanger 2 dissipates heat in the internal heat
exchanger 5 to further decrease (C) the temperature, being
decompressed (D) by the expansion valve 3 to turn into a
low-temperature low-pressure refrigerant. The low-temperature
low-pressure refrigerant absorbs heat from the air in the
evaporator 4 to evaporate (E). The refrigerant flowed out of the
evaporator 4 is heated in the internal heat exchanger 5 to turn
into a gas (F) and sucked by the compressor 1 to form a
refrigeration cycle.
[0048] Here, the expansion valve 3 is controlled so that a suction
superheat degree of the compressor 1 becomes a target value (for
example, 5 to 10.degree. C.). Specifically, based on a detection
value of fifth temperature detection means 32 detecting an inlet
refrigerant temperature of the evaporator 4, a temperature decrease
amount due to a pressure loss in the evaporator 4 and the internal
heat exchanger 5 is corrected, an evaporation temperature (ET) is
estimated, a suction superheat degree SH.sub.s is calculated by the
following formula using a detection value (T.sub.s) of sixth
temperature detection means 33 detecting a suction temperature of
the compressor 1.
SH.sub.s=T.sub.s-ET
[0049] Using the above formula, an opening degree of the expansion
valve 3 is controlled so that SH.sub.s becomes a target value. An
example is given in which an evaporation temperature (ET) is
estimated based on the detection value of the fifth temperature
detection means 32, however, it is not limited thereto. Pressure
detection means (second pressure detection means) 51 (refer to FIG.
1) is installed between a low-pressure side outlet of the internal
heat exchanger 5 and the inlet of the compressor 1, and from the
detection value, a refrigerant saturation temperature may be
obtained. A suction superheat degree control precedes other high
efficiency operation control because a function to prevent liquid
return of the compressor 1 precedes a function to efficiently
operate the water heat exchanger 2 from the viewpoint of securing
reliability of the equipment.
[0050] Next, operation on the P-h diagram in the case when the
opening degree of the expansion valve 3 is made smaller is denoted
by broken lines in FIG. 2. When the opening degree of expansion
valve 3 is made smaller, the refrigerant flow amount flowing from
the expansion valve 3 to the evaporator 4 decreases and the suction
superheat degree of the compressor 1 temporarily increases. In
addition, since the refrigerant shifts to a high pressure side, the
pressure on the high pressure side increases and a discharge
temperature becomes high. At the same time, a water heat exchanger
output temperature decreases so that a temperature difference in
the becomes constant. When the water heat exchanger output
temperature decreases, a heat exchange amount in the internal heat
exchanger 5 decreases, and as a result, the suction superheat
degree becomes almost the same state as that of before the opening
degree of the expansion valve 3 is made smaller to indicate a
constant value. That is, a change in opening degree of the
expansion valve 3 is absorbed by the heat exchange amount of the
internal heat exchanger 5 (the heat exchange amount varies in
response to the opening degree of the expansion valve 3) to make a
change in the suction superheat degree small. Accordingly, control
of the suction superheat degree of the compressor 1 alone cannot
secure heating ability in the water heat exchanger 2 and efficiency
is lowered. Therefore, new control is required in order to secure
heating ability and improve operation efficiency.
[0051] Next, descriptions will be given to why a local maximal
value occurs in performance (COP) using a temperature distribution
in the water heat exchanger shown in FIG. 3.
[0052] FIG. 3 shows a refrigerant and water temperature
distribution in the water heat exchanger 2. In the figure, thick
solid lines show a change in refrigerant temperature, and a thin
solid lines denote a change in water temperature. .DELTA.T1 denotes
a temperature difference between the water heat exchanger inlet
temperature and water outlet temperature, and .DELTA.T2 denotes a
temperature difference between the water heat exchanger outlet
temperature and water inlet temperature. .DELTA.Tp is a temperature
difference at a pinch point where the temperature difference
between a refrigerant and water in the water heat exchanger 2
becomes minimum. .DELTA.T denotes a temperature difference between
the water heat exchanger inlet temperature and the water heat
exchanger outlet temperature. As shown by a cycle state against the
expansion valve opening degree in FIG. 4, when a discharge
temperature is increased by decreasing the expansion valve 3
opening degree, under a condition when heating ability in the water
heat exchanger 2 is almost constant, the outlet temperature of the
water heat exchanger 2 decreases so that an average temperature
difference of the refrigerant and water in the water heat exchanger
2 is maintained, and the temperature difference .DELTA.Tp of pinch
point also decreases. Further, as the refrigerant amount shifts to
a high pressure side, a discharge pressure rises to increase an
input and COP is lowered. To the contrary, when the expansion valve
3 opening degree is made large and the discharge temperature is
lowered, the outlet temperature of the water heat exchanger 2
increases so that an average temperature difference between the
refrigerant and water in the water heat exchanger 2 is maintained.
The temperature difference .DELTA.Tp at the pinch point also
increases, however, a heating ability ratio becomes small and COP
is lowered. Accordingly, as shown by broken lines in the figure, a
suitable expansion opening degree exists that makes COP
maximum.
[0053] Next, FIG. 5 shows changes in operation values obtained from
the temperature of each part when the opening degree of the
expansion valve 3 changes. In FIG. 5, the horizontal axis
represents the opening degree (%) of the expansion valve 3, and the
vertical axis represents the suction superheat degree, discharge
temperature, temperature difference .DELTA.T2 between the outlet
temperature of the water heat exchanger and water inlet
temperature, heating ability ratio, COP ratio. The heating ability
ratio and COP ratio show a ratio when a maximum value against the
expansion valve opening degree is set as 100%, respectively.
Against changes in the opening degree of the expansion valve 3,
changes in the suction superheat degree can be regarded as almost a
constant value, so that it is understood that changes in the
heating ability ratio and the COP ratio cannot be judged by the
suction superheat degree. When controlling the COP to be maximum
based on the temperature difference .DELTA.T2 between the discharge
temperature and the outlet temperature of the water heat exchanger
and water inlet temperature, changes in the discharge temperature
and temperature difference .DELTA.T2 are small in the vicinity of
the expansion valve opening degree when the COP reaches maximum as
shown by a dotted line in the figure, so that it is found that a
high accuracy temperature measurement is required for controlling
COP to be maximum.
[0054] Next, FIG. 6 shows changes in other operation values
obtained from temperatures of each part when the opening degree of
the expansion valve 3 is changed. In FIG. 6, the horizontal axis
represents the opening degree (%) of the expansion valve 3. The
vertical axis represents an outlet/inlet temperature difference
.DELTA.Thx of the internal heat exchanger, a temperature difference
.DELTA.T between a discharge temperature and an outlet temperature
of the water heat exchanger, a total temperature difference
.SIGMA..DELTA.T of the above .DELTA.T1 and .DELTA.T2, heating
ability, and a COP ratio, respectively. Characteristics of FIG. 6
shows that operation can be performed in the vicinity where the COP
becomes maximum by either controlling a heat exchange amount of the
internal heat exchanger 5 based on the temperature difference
.DELTA.Thx between the outlet and inlet of the internal heat
exchanger or controlling the heat exchange amount of the water heat
exchanger 2 based on the total temperature difference
.SIGMA..DELTA.T of .DELTA.T1 and .DELTA.T2 of the water heat
exchanger 2. Further, the temperature difference .DELTA.T between
the discharge temperature and the outlet temperature of the water
heat exchanger significantly changes in the vicinity of the
expansion valve opening degree at which the COP becomes maximum, so
that it is understood that a deviation from the maximum value of
the COP could be controlled to be small based on the temperature
difference .DELTA.T. Here, only the case of the temperature
difference .DELTA.T is shown, however, the same effect can be
expected by controlling based on the difference
(.DELTA.T1-.DELTA.T2) of the temperature differences .DELTA.T1 and
.DELTA.T2.
[0055] Thus, it is possible to achieve an operation in the vicinity
of the maximum efficiency by adopting a high-pressure side outlet
temperature of the internal heat exchanger 5 for .DELTA.Thx, the
discharge temperature for .DELTA.T, and the discharge temperature
and a water side outlet/inlet temperatures for .SIGMA..DELTA.T.
[0056] As is understood from FIG. 6, a total temperature difference
.SIGMA..DELTA.T of the temperature difference .DELTA.T1 between the
water heat exchanger inlet temperature and water outlet temperature
and the temperature difference .DELTA.T2 between the water heat
exchanger outlet temperature and water inlet temperature becomes a
minimum. The control based on such an index has a physical meaning
and being reasonable. However, high-precision temperature detection
is required because change in temperature is small in the vicinity
where the COP becomes a maximum compared with the temperature
difference .DELTA.T. Further, from FIG. 3, it is considered that
when the COP becomes a maximum value, a temperature difference
.DELTA.Tp at a pinch point is almost the same as that of .DELTA.T2
between the water heat exchanger outlet temperature and water inlet
temperature. This is because a maximum performance is shown when
two temperature differences that become minimum in the water heat
exchanger 2 become equal without being biased to either of them
when considering characteristics of the heat exchanger.
Accordingly, it is allowable to control the expansion valve 3 so as
to make .DELTA.Tp and .DELTA.T2 to be equal.
[0057] Next, descriptions will be given to an example of a control
operation of the refrigeration cycle apparatus of FIG. 1 in which
an expansion valve opening degree is controlled so as to make a
suction superheat degree and the above temperature difference
.DELTA.T to converge at target values.
[0058] FIG. 7 is a flowchart showing a control operation of the
refrigeration cycle apparatus. With the present invention, for the
purpose of giving a priority to reliability of products, the
suction superheat degree (SHs) control of the compressor 1 precedes
the temperature difference .DELTA.T control for securing the
heating ability.
[0059] Firstly, when the suction superheat degree (SHs) is smaller
than a target value (SHm) by a preset convergence range .DELTA.SH
or less (S101), the expansion valve opening degree is lowered until
the suction superheat degree (SHs) converges. Thus, when the
suction superheat degree (SHs) is secured, the temperature
difference .DELTA.T is made to converge at the target value.
Specifically, when the temperature difference .DELTA.T is smaller
than a target value (.DELTA.Tm) by a preset convergence range
.delta.T or less (S102), the expansion opening degree is lowered
and .DELTA.T is made to converge. Thus, lower limit values of the
suction superheat degree (SHs) and the temperature difference
.DELTA.T can be suppressed.
[0060] Next, when the suction superheat degree (SHs) is larger than
the target value (SHm) by a preset convergence range .DELTA.SH or
more (S103), the expansion valve opening degree is increased until
the suction superheat degree (SHs) converges. Thus, when the
suction superheat degree (SHs) is converged, the temperature
difference .DELTA.T is made to converge at the target value. Thus,
when the suction superheat degree (SHs) is converged, the
temperature difference .DELTA.T is made to converge at the target
value. Specifically, when the temperature difference .DELTA.T is
larger than the target value (.DELTA.Tm) by a preset convergence
range .delta.T or more (S104), the expansion opening degree is
increased and .DELTA.T is made to converge. Thus, upper limit
values of the suction superheat degree (SHs) and the temperature
difference .DELTA.T can be suppressed. An example is shown in which
a priority is given to control the suction superheat degree,
however, it is not limited thereto when using a compressor which is
resistant to liquid return. The same effect can be expected even
when the priority order is exchanged. Through the above control,
the suction superheat degree (SHs) and the temperature difference
.DELTA.T are converged at target values.
[0061] In the above, descriptions are given to an example in which
the suction superheat degree (SHs) and the temperature difference
.DELTA.T are controlled to converge at target values (SHm,
.DELTA.Tm), however, it is allowable that, in place of the
temperature difference .DELTA.T, a total temperature difference
.SIGMA..DELTA.T of .DELTA.T1 and .DELTA.T2, a difference between
.DELTA.T1 and .DELTA.T2 (.DELTA.T1-.DELTA.T2), or .DELTA.Thx can be
used to control them to converge at a target value, respectively.
When using .SIGMA..DELTA.T and (.DELTA.T1-.DELTA.T2), they are
obtained by calculating detection temperatures by the first
temperature detection means 30, the second temperature detection
means 31, the third temperature detection means 41, and the fourth
temperature detection means 42. When using .DELTA.Thx, internal
heat exchanger outlet temperature detection means 52 is attached
(refer to FIG. 1) between a high-pressure side outlet of the
internal heat exchanger 5 and an inlet of the expansion valve 3,
the temperature difference .DELTA.Thx is obtained from a detection
temperatures by the second temperature detection means 31 and the
internal heat exchanger outlet temperature detection means 52.
[0062] Since, in the present embodiment, in addition to suction
superheat degree control of the compressor, the expansion valve
opening degree is made to be controlled so that the COP becomes
maximum based on a temperature difference .DELTA.T (or
.SIGMA..DELTA.T, .DELTA.T1-.DELTA.T2, .DELTA.Thx) between the
discharge temperature and the water heat exchanger outlet
temperature, a high efficiency refrigeration cycle apparatus can be
obtained.
[0063] A refrigerant saturation temperature (ET) is obtained based
on an output of the fifth temperature detection means 32 or
pressure detection means, the suction superheat degree (SHs) is
obtained by the detection temperature (Ts) of the sixth temperature
detection means and the refrigerant saturation temperature (ET),
and the expansion valve opening degree is controlled so that the
suction superheat degree (SHs) becomes a target value, so that the
superheat degree of the suction part of the compressor 1 is
secured, liquid return to the compressor 1 can be prevented, and
reliability can be secured. In the example of FIG. 1, descriptions
are given to an example in which the fifth temperature detection
means 32 is provided between the expansion valve 3 and the
evaporator 4, it can be disposed at any position between the inlet
of the evaporator 4 and a low-pressure side inlet of the internal
heat exchanger 5.
[0064] In the present embodiment, when controlling the superheat
degree and the above temperature differences (.DELTA.T,
.SIGMA..DELTA.T, .DELTA.T1-.DELTA.T2, .DELTA.Thx), the control of
the superheat degree precedes the control of the above temperature
differences. From this point, the reliability of the compressor 1
is secured.
[0065] In the present embodiment, the radiator is composed of the
water heat exchanger, so that a high efficiency hot water supply
apparatus can be obtained.
Embodiment 2
[0066] Descriptions will be given to a refrigeration cycle
apparatus according to Embodiment 2 of the present invention as
follows.
[0067] FIG. 8 is a drawing showing a configuration of the
refrigeration cycle apparatus according to the present invention.
What is different from Embodiment 1 is that a first pressure
detection means 35 is provided in place of the first temperature
detection means 30 for detecting the discharge temperature of the
compressor 1. Based on the first pressure detection means 35, a
virtual saturation temperature is obtained, which is a standard
condition of the water heat exchanger 2. The pressure detection
means 35 can be shared with a pressure sensor provided, for
example, to prevent an abnormal rise in high pressure. Descriptions
on an operation behavior will be omitted because they are the same
as Embodiment 1.
[0068] In the present embodiment, like a conventional HFC
refrigerant, a virtual superheat degree of the water heat exchanger
2 outlet is calculated to control the refrigerant conditions
thereof. Specifically, from first pressure detection means 35
provided in place of the first temperature detection means 30, a
virtual saturation temperature is calculated as a standard
condition of the water heat exchanger 2 and from the difference
between a virtual saturation temperature Tsat and outlet
temperature Tcount of the water heat exchanger 2 detected by the
second temperature detection means 31, a virtual superheat degree
SC is obtained from the following formula.
SC=Tsat-Tcount
[0069] In the present embodiment, the opening degree of the
expansion valve 3 is controlled in the same way as the flowchart of
FIG. 7 so that the SC obtained by the above formula becomes a
target value (SCm) whose efficiency is maximum.
[0070] Here, how to obtain the virtual saturation temperature will
be explained.
[0071] FIG. 9 is a diagram showing an operation behavior of the
refrigeration cycle apparatus according to the present invention on
a P-h diagram. The virtual saturation temperature can be freely
defined by demonstrating a definition such as a pseudo critical
temperature trajectory connecting flexion points of isothermal
lines like a dashed line .alpha. and a vertical line like a dotted
line .beta. extended with an enthalpy at a critical point being a
constant. However, in order to operate the refrigeration cycle
apparatus stably and at the maximum efficiency, a virtual
saturation temperature should be selected under which the
temperature difference becomes large in the vicinity of the maximum
efficiency as mentioned above. Then, the virtual saturation
temperature can be obtained as an intersection of a constant
pressure line with a pressure at a point B, which is a detection
value by first pressure detection means 35 and the dashed line
.alpha., or as an intersection of a constant pressure line with a
pressure at a point B, which is a detection value by first pressure
detection means 35 and the dotted line .beta..
[0072] In the present embodiment, since the virtual saturation
temperature is used in place of the discharge temperature of the
compressor 1, first temperature detection means 30 in FIG. 1 can be
omitted and low cost can be achieved. Like the conventional HFC
refrigerant, superheat degree of the outlet of the water heat
exchanger 2 is controlled, therefore, control of the expansion
valve can be applied as it is, which has been conventionally
used.
* * * * *