EP3705809A1

EP3705809A1 - Heat pump

Info

Publication number: EP3705809A1
Application number: EP18877203.2A
Authority: EP
Inventors: Takayuki Kobayashi; Yohei Katsurayama
Original assignee: Kansai Electric Power Co Inc; Chubu Electric Power Co Inc; Mitsubishi Heavy Industries Thermal Systems Ltd
Current assignee: Kansai Electric Power Co Inc; Chubu Electric Power Co Inc; Mitsubishi Heavy Industries Thermal Systems Ltd
Priority date: 2017-11-08
Filing date: 2018-11-08
Publication date: 2020-09-09
Also published as: JP6916716B2; CN111316048B; CN111316048A; JP2019086237A; EP3705809A4; WO2019093422A1

Abstract

Provided is a heat pump that includes: a low-stage compressor (3); a high-stage compressor (4) connected in series to a downstream side of the low-stage compressor (3); a condenser (5) connected to a downstream side of the high-stage compressor (4); expansion elements (6) each connected to a downstream side of the condenser (5); an evaporator (10) connected to downstream sides of the expansion elements (6); a second valve (18) and a third valve (19) allowing a refrigerant (R) to be selectively introduced into either the low-stage compressor (3) or the high-stage compressor (4) from the evaporator (10); a low-stage gas-liquid separator (21) installed at an inlet of the low-stage compressor (3) and configured to separate a liquid phase of the refrigerant (R) and to allow a gas phase to be introduced into the low-stage compressor (3); and a high-stage gas-liquid separator (22) installed at an inlet of the high-stage compressor (4) and configured to separate the liquid phase of the refrigerant (R) and to allow the gas phase to be introduced into the high-stage compressor (4).

Description

Technical Field

The present invention relates to a heat pump provided with a refrigerant circuit.
Priority is claimed on Japanese Patent Application No. 2017-215657, filed November 8, 2017 , the contents of which are incorporated herein by reference.

Background Art

A refrigeration cycle in which a refrigerant circuit repeats compression and expansion and circulates a refrigerant, i.e., a heat pump, has been known for a long time. In this heat pump, as described in, for instance, Patent Document 1as follows, the refrigerant may be subjected to two-stage compression by a low-stage compressor that compresses the refrigerant and a high-stage compressor that further compresses the refrigerant discharged from the low-stage compressor.
In this heat pump, an evaporator that evaporates the refrigerant is installed on an upstream side of the low-stage compressor. The evaporator is a heat exchanger in which heat exchange is conducted, for instance, between the refrigerant and a heating medium such as water or air.

Citation List

Patent Document

Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2016-90102

Summary of Invention

Technical Problem

Here, the heat pump of Patent Document 1 is configured such that the refrigerant from the evaporator is made to be introduced into the low-stage compressor and is then introduced into the high-stage compressor.
However, a heat exchange amount at the evaporator is not necessarily constant and is likely to be changed by, for instance, environmental factors. For this reason, in some cases, a temperature of the refrigerant introduced into the low-stage compressor from the heat exchanger is not constant, the refrigerant introduced into the low-stage compressor is not in a state optimal for compression at the low-stage compressor, and the heat pump cannot perform an efficient operation as a whole.
Furthermore, in the case where the refrigerant from the evaporator includes a liquid phase, there is a risk of occurrence of liquid compression at the low-stage compressor and the high-stage compressor, and it is also difficult to perform efficient operation.
Thus, the present invention provides a heat pump which introduces a refrigerant in a state optimal for compression into a low-stage compressor and a high-stage compressor and in which efficient operation is possible.

Solution to Problem

A heat pump according to a first aspect of the present invention includes: a low-stage compressor; a high-stage compressor which is connected in series to a downstream side of the low-stage compressor; a condenser which is connected to a downstream side of the high-stage compressor; expansion elements which are each connected to a downstream side of the condenser; an evaporator which is connected to downstream sides of the expansion elements; selector valves which are configured to allow a refrigerant to be selectively introduced into either the low-stage compressor or the high-stage compressor from the evaporator; a low-stage gas-liquid separator which is installed at an inlet of the low-stage compressor and which is configured to separate a liquid phase of the refrigerant to allow a gas phase to be introduced into the low-stage compressor; and a high-stage gas-liquid separator which is installed at an inlet of the high-stage compressor and which is configured to separate the liquid phase of the refrigerant to allow the gas phase to be introduced into the high-stage compressor.
According to this heat pump, the refrigerant can be selectively introduced into either the low-stage compressor or the high-stage compressor from the evaporator. Accordingly, depending on a state of the refrigerant flowing out of the evaporator, an introduction path of the refrigerant can be switched to a compressor in which optimal compression is possible.
Furthermore, even in the case where the refrigerant from the evaporator is introduced into either the low-stage compressor or the high-stage compressor, after gas-liquid separation from the refrigerant at the inlet of the low-stage compressor is performed by the low-stage gas-liquid separator or the gas-liquid separation from the refrigerant at the inlet of the high-stage compressor is performed by the high-stage gas-liquid separator, the gas phase can be introduced into the low-stage compressor or the high-stage compressor.
A heat pump according to a second aspect of the present invention may further include, in the first aspect, an interstage flow passage which is installed between the low-stage compressor and the high-stage compressor. The high-stage gas-liquid separator may be installed on the interstage flow passage.
In this way, the high-stage gas-liquid separator is installed on the interstage flow passage, and thereby in the case where the refrigerant from the evaporator is introduced into the high-stage compressor via the low-stage compressor, the gas-liquid separation of the refrigerant can be performed, and a risk of liquid compression at the high-stage compressor can be further reduced.
A heat pump according to a third aspect of the present invention may further include, in the first aspect, high-stage flow passages which are configured to connect between the evaporator and the high-stage compressor without passing through the low-stage compressor. The high-stage gas-liquid separator may be installed on the high-stage flow passages.
In the case where the refrigerant from the evaporator is introduced into the high-stage compressor via the low-stage compressor, the refrigerant does not flow through the high-stage flow passage. In this case, the high-stage gas-liquid separator may be installed on the high-stage flow passages, and thereby the refrigerant does not pass through the high-stage gas-liquid separator. Accordingly, pressure loss occurring in the case where the refrigerant discharged from the low-stage compressor passing through the high-stage gas-liquid separator can be avoided. Accordingly, a coefficient of performance (COP) of the heat pump, i.e., operation efficiency, can be improved.
A heat pump according to a fourth aspect of the present invention may be configured in any of the first to third aspects such that a plurality of the evaporators are provided to the heat pump, and the selector valves are respectively installed to the corresponding evaporators such that the refrigerant are selectively introduced into either the low-stage compressor or the high-stage compressor from the evaporators.
The plurality of evaporators are provided to the heat pump, accordingly the heat pump has a multi-source type refrigerant circuit that includes a plurality of heat exchangers that are different from each other in terms of a heat exchange amount or an installation environment.
Here, a heat exchange amount is changed at each of the evaporators and a temperature of the refrigerant is changed, a state of the refrigerant directed to the low-stage compressor and the high-stage compressor may not be a state optimal for compression at the low-stage compressor and the high-stage compressor. Thus, in the present aspect, the refrigerant cannot only be introduced into the low-stage compressor from each of the evaporators by the selector valves, but also directly introduced into the high-stage compressor by bypassing the low-stage compressor.
Furthermore, concurrently with switching of the introduction path of the refrigerant from one evaporator to the compressor, switching of the introduction path of the refrigerant from the other evaporator to the compressor is also possible. Accordingly, depending on a state of the refrigerant flowing out of each of the evaporators, the introduction path of the refrigerant can be switched to the compressor in which optimal compression is possible.

Advantageous Effects of Invention

According to the heat pump, a refrigerant in a state optimal for compression is introduced into the low-stage compressor and the high-stage compressor, and efficient operation is made possible.

Brief Description of Drawings

FIG. 1 is an overall constitutional view of a heat pump of a first embodiment of the present invention.
FIG. 2 is an overall constitutional view of a heat pump of a second embodiment of the present invention.

Description of Embodiments

Hereinafter, a heat pump 1 of a first embodiment of the present invention will be described.
As illustrated in FIG. 1, the heat pump 1 according to the present embodiment has a refrigerant circuit 2 that operates in a two-stage compression cycle. The refrigerant circuit 2 has a low-stage compressor 3, a high-stage compressor 4, a condenser 5, expansion valves (expansion elements) 6, and an evaporator 10, and these components are connected by a pipe 15 in this order. For example, a refrigerant R such as carbon dioxide circulates through the refrigerant circuit 2. Here, the refrigerant R is not particularly limited to carbon dioxide.
The low-stage compressor 3 sucks in the refrigerant R and compresses the refrigerant R. The low-stage compressor 3 is, for instance, a rotary compressor or a scroll compressor.
The high-stage compressor 4 is connected in series to the low-stage compressor 3 and further compresses the refrigerant R discharged from the low-stage compressor 3 to a higher pressure. The pipe 15 between the low-stage compressor 3 and the high-stage compressor 4 serves as an interstage flow passage CM. The high-stage compressor 4 is, for instance, a rotary compressor or a scroll compressor.
The condenser 5 conducts heat exchange between the high-temperature high-pressure refrigerant R discharged from the high-stage compressor 4 and a heating medium R1, such as air or water, and cools and condenses the refrigerant R.
Each of the expansion valve 6 adiabatically expands the refrigerant R from the condenser 5 to reduce a pressure of the refrigerant R. The expansion valve 6 is configured such that a plurality of expansion valves (in the present embodiment, two expansion valves) are provided corresponding to first and second evaporators 11 and 12 (to be described below) on an upstream side (an inlet side) of the evaporator 10.
In the present embodiment, the first evaporator 11 and the second evaporator 12 are provided as the evaporator 10. The first evaporator 11 and the second evaporator 12 are installed in parallel. However, the number of evaporators 10 is not limited to the case of the present embodiment.
The first evaporator 11 is an air heat exchanger that conducts heat exchange between the refrigerant R that has passed through the expansion valve 6 and, for instance, air as a heating medium R2.
The pipe 15 between the first evaporator 11 and an upstream side (a suction side) of the low-stage compressor 3 serves as a first flow passage C1. A first valve 17, which can switch a flowing direction of the refrigerant R, is installed on the first flow passage C1. In the present embodiment, the first valve 17 is a four-way valve.
Further, the pipe 15 between the first evaporator 11 and an upstream side of the high-stage compressor 4 (which is a suction side of the high-stage compressor 4, and a discharge side of the low-stage compressor 3) serves as a second flow passage (a high-stage flow passage) C2. Here, a second valve (a selector valve) 18 is installed on the first flow passage C1 at a position between the first valve 17 and the first evaporator 11. The second flow passage C2 connects the second valve 18 and the interstage flow passage CM. The second valve 18 is a three-way valve. Depending on whether the refrigerant R flows toward the downstream of the first flow passage C1 or toward the second flow passage C2, the flowing direction of the refrigerant R can be switched by the second valve 18. In the case where the refrigerant R flows through the second flow passage C2, the refrigerant R does not pass the low-stage compressor 3.
The second evaporator 12 is a water heat exchanger that conducts heat exchange between the refrigerant R that has passed through the expansion valve 6 and, for instance, water as a heating medium R3.
The pipe 15 between the second evaporator 12 and an upstream side (a suction side) of the low-stage compressor 3 serves as a third flow passage C3. To be specific, the third flow passage C3 has an upstream portion C3a that connects a downstream outlet of the second evaporator 12 and the first flow passage C1 at a position upstream of the first valve 17. Further, the third flow passage C3 has a downstream portion C3b that connects the first valve 17 and an upstream inlet of the low-stage compressor 3. In addition, a third valve (a selector valve) 19 is installed on the upstream portion C3a. In the present embodiment, the second valve 18 and the third valve 19 are three-way valves, but are not limited thereto. The second valve 18 and the third valve 19 only needs to be any valves that can switch the flowing direction of the refrigerant R.
Further, the pipe 15 between the second evaporator 12 and an upstream inlet of the high-stage compressor 4 serves as a fourth flow passage (a high-stage flow passage) C4. The fourth flow passage C4 connects the third valve 19 and an intermediate position of the second flow passage C2, and thereby connects the third valve 19 and the interstage flow passage CM via the second flow passage C2. Depending on whether the refrigerant R flows toward the downstream of the upstream portion C3a or toward the fourth flow passage C4, the flowing direction of the refrigerant R can be switched by the third valve 19. In the case where the refrigerant R flows through the fourth flow passage C4, the refrigerant R does not pass the low-stage compressor 3.
Here, the refrigerant circuit 2 further includes a low-stage gas-liquid separator 21 and a high-stage gas-liquid separator 22.
The low-stage gas-liquid separator 21 is a device called an accumulator and is installed on the downstream portion C3b of the third flow passage C3 at the inlet of the low-stage compressor 3. The low-stage gas-liquid separator 21 can separate a liquid phase of the refrigerant R at an inlet of the low-stage gas-liquid separator 21 and introduce a gas phase into the low-stage compressor 3. The liquid phase of the refrigerant R which is separated at the low-stage gas-liquid separator 21 may be introduced into the low-stage compressor 3 by a device (not illustrated).
Like the low-stage gas-liquid separator 21, the high-stage gas-liquid separator 22 is a device called an accumulator, and is installed on the interstage flow passage CM between an outlet of the low-stage compressor 3 and the inlet of the high-stage compressor 4. The high-stage gas-liquid separator 22 can separate a liquid phase of the refrigerant R to introduce a gas phase into the high-stage compressor 4. The liquid phase of the refrigerant R which is separated at the high-stage gas-liquid separator 22 may be introduced into the high-stage compressor 4 by a device (not illustrated).
According to the heat pump 1 of the present embodiment described above, the refrigerant R from the first evaporator 11 and the second evaporator 12 can be selectively introduced into either the low-stage compressor 3 or the high-stage compressor 4.
To be specific, when switching between the case where the refrigerant R is introduced into the low-stage compressor 3 from the first evaporator 11 and the case where the refrigerant R is introduced into the high-stage compressor 4 from the first evaporator 11, the second valve 18 is operated. The operation of the second valve 18 may be performed by a controller (not illustrated) or manually performed.
Further, when switching between the case where the refrigerant R is introduced into the low-stage compressor 3 from the second evaporator 12 and the case where the refrigerant R is introduced into the high-stage compressor 4 from the second evaporator 12, the third valve 19 is operated. The operation of the third valve 19 may be performed by a controller (not illustrated) or manually performed.
In this way, a flow path of the refrigerant R from the first evaporator 11 and the second evaporator 12 can be appropriately changed, and thereby the refrigerant R can be introduced into the compressor, in which optimal compression is possible, of the low-stage compressor 3 and the high-stage compressor 4 depending on a state of the refrigerant R flowing out of each of the evaporators 10.
Furthermore, even in the case where the refrigerant R from the evaporators 10 (11, 12) is introduced into either the low-stage compressor 3 or the high-stage compressor 4, after gas-liquid separation of the refrigerant R is performed at the inlet of the low-stage compressor 3 by the low-stage gas-liquid separator 21, or after the gas-liquid separation of the refrigerant R is performed at the inlet of the high-stage compressor 4 by the high-stage gas-liquid separator 22, a gas phase can be introduced into the low-stage compressor 3 or the high-stage compressor 4. That is, even in the case where the refrigerant R from the first evaporator 11 and the second evaporator 12 is introduced into either the low-stage compressor 3 or the high-stage compressor 4, the gas-liquid separation of the refrigerant R is performed without fail.
Therefore, since the refrigerant R that is in a state optimal for compression is introduced into the low-stage compressor 3 and the high-stage compressor 4, and liquid compression at the low-stage compressor 3 and the high-stage compressor 4 can be avoided, efficient operation is made possible.
Furthermore, in the present embodiment, the plurality of evaporators 10 are provided, and thereby the heat pump 1 has a multi-source type refrigerant circuit 2 that includes a plurality of heat exchangers that are different from each other in terms of a heat exchange amount or an installation environment.
Here, a heat exchange amount is changed at each of the first evaporator 11 and the second evaporator 12 and a temperature of the refrigerant R is changed, and thereby a state of the refrigerant R directed to the low-stage compressor 3 and the high-stage compressor 4 may not be a state optimal for compression at the low-stage compressor 3 and the high-stage compressor 4. Thus, in the present embodiment, the refrigerant R can not only be introduced into the low-stage compressor 3 from the evaporators 10 by the second valve 18 and the third valve 19, but also directly introduced into the high-stage compressor 4 by bypassing the low-stage compressor 3. Accordingly, efficient operation is made possible.
Furthermore, concurrently with switching of the flow path of the refrigerant R from the first evaporator 11, switching of the flow path of the refrigerant R from the second evaporator 12 is also possible. Accordingly, depending on a state of the refrigerant R flowing out of each of the first evaporator 11 and the second evaporator 12, the introduction path of the refrigerant R can be switched to the compressor, in which optimal compression is possible, of the low-stage compressor 3 and the high-stage compressor 4. Accordingly, operation efficiency can be improved.
Next, a heat pump 1A of a second embodiment of the present invention will be described with reference to FIG. 2. In the second embodiment to be described below, the same portion as in the first embodiment will be given the same reference sign and described, and duplicate description will be omitted. The second embodiment is different from the first embodiment with regard to an installation place of a high-stage gas-liquid separator 22A.
The high-stage gas-liquid separator 22A is installed on a second flow passage C2 at an inlet of a high-stage compressor 4. That is, in the case where a refrigerant R is introduced into the high-stage compressor 4 from a first evaporator 11 (a second evaporator 12) without passing through a low-stage compressor 3, the high-stage gas-liquid separator 22A is installed just before the refrigerant R that does not pass through the low-stage compressor 3 joins a refrigerant R discharged from the low-stage compressor 3 (on an upstream side).
According to the heat pump 1A of the present embodiment, in the case where the refrigerant R from the first evaporator 11 is introduced into the high-stage compressor 4 without passing through the low-stage compressor 3, gas-liquid separation of the refrigerant R is performed at the high-stage gas-liquid separator 22A, and a gas phase can be introduced into the high-stage compressor 4. Accordingly, the risk of liquid compression at the high-stage compressor 4 can be reduced.
Furthermore, the high-stage gas-liquid separator 22A is installed on the second flow passage C2, and thereby in the case where the refrigerant R from the first evaporator 11 and the second evaporator 12 is introduced into the high-stage compressor 4 via the low-stage compressor 3, the refrigerant R does not flow through the second flow passage C2. Accordingly, in this case, since the refrigerant R does not pass through the high-stage gas-liquid separator 22A, the occurrence of pressure loss caused by the refrigerant R discharged from the low-stage compressor 3 passing through the high-stage gas-liquid separator 22A can be avoided. Accordingly, the COP of the heat pump 1A, i.e., operation efficiency, can be improved.
Although the embodiments of the present invention have been described with reference to the drawings, the components and combinations thereof in the embodiments are one example, and additions, omissions, substitutions, and other modifications of the constitutions are possible without departing from the spirit of the present invention. The present invention is not limited by the embodiments, but is only limited by the claims.
For example, in the embodiment, the example in which the first evaporator 11 and the second evaporator 12 are provided as the evaporator 10 has been described. However, the number of evaporators 10 is not limited to the case of the above embodiments, only one may be provided, or three or more may be provided.

Industrial Applicability

According to the heat pump, the refrigerant that is in the state optimal for compression is introduced into the low-stage compressor and the high-stage compressor, and thereby efficient operation is possible.

Reference Signs List

1, 1A: Heat pump
2: Refrigerant circuit
3: Low-stage compressor
4: High-stage compressor
5: Condenser
6: Expansion valve
10: Evaporator
11: First evaporator
12: Second evaporator
15: Pipe
17: First valve
18: Second valve (selector valve)
19: Third valve (selector valve)
21: Low-stage gas-liquid separator
22, 22A: High-stage gas-liquid separator
R1: Heating medium
R2: Heating medium
R3: Heating medium
C1: First flow passage
C2: Second flow passage (high-stage flow passage)
C3: Third flow passage
C3a: Upstream portion
C3b: Downstream portion
C4: Fourth flow passage (high-stage flow passage)
CM: Interstage flow passage
R: Refrigerant

Claims

A heat pump comprising:
a low-stage compressor;

a high-stage compressor which is connected in series to a downstream side of the low-stage compressor;

a condenser which is connected to a downstream side of the high-stage compressor;

expansion elements which are each connected to a downstream side of the condenser;

an evaporator which is connected to downstream sides of the expansion elements;

selector valves which are configured to allow a refrigerant to be selectively introduced into either the low-stage compressor or the high-stage compressor from the evaporator;

a low-stage gas-liquid separator which is installed at an inlet of the low-stage compressor and which is configured to separate a liquid phase of the refrigerant to allow a gas phase to be introduced into the low-stage compressor; and

a high-stage gas-liquid separator which is installed at an inlet of the high-stage compressor and which is configured to separate the liquid phase of the refrigerant to allow the gas phase to be introduced into the high-stage compressor.
The heat pump according to claim 1, further comprising an interstage flow passage which is installed between the low-stage compressor and the high-stage compressor, wherein the high-stage gas-liquid separator is installed on the interstage flow passage.
The heat pump according to claim 1, further comprising high-stage flow passages which are configured to connect between the evaporator and the high-stage compressor without passing through the low-stage compressor, wherein the high-stage gas-liquid separator is installed on the high-stage flow passages.
The heat pump according to any one of claims 1 to 3, wherein a plurality of the evaporators are provided to the heat pump, and
the selector valves are respectively installed to the corresponding evaporators such that the refrigerant are selectively introduced into either the low-stage compressor or the high-stage compressor from the evaporators.