Fuel cell cooling system

Abstract

The invention provides a fuel cell cooling system. A fuel cell cooling system is provided with a first cooling flow path, a fuel cell, a second cooling flow path, a radiator, an intercooler, an intermediate heat exchanger, and a bypass flow path, and in power generation by the fuel cell, when the temperature of a refrigerant in the first cooling flow path is lower than a first reference value, the temperature of the refrigerant in the second cooling flow path is lower than the first reference value. When the temperature of the refrigerant in the first cooling flow path is higher than a first reference value, a first operation for circulating the refrigerant in the second cooling flow path through a path passing through the intermediate heat exchanger, the intermediate cooler, and the bypass flow path is performed. A second operation is performed in which the refrigerant is circulated in a second cooling flow path through a path that passes through the intermediate heat exchanger, the intermediate cooler, and the radiator.

Description

Technical Field

[0001] The technology disclosed in this specification relates to a fuel cell cooling system. Background Art

[0002] The fuel cell system disclosed in Japanese Patent Application Laid-Open No. 2002-33108 includes a first cooling flow path and a second cooling flow path through which a refrigerant circulates. A fuel cell is provided in the first cooling flow path. A radiator is provided in the second cooling flow path. An intermediate heat exchanger is provided across the first and second cooling flow paths. The intermediate heat exchanger performs heat exchange between the first and second cooling flow paths.

[0003] In a fuel cell system, an intercooler is provided to cool the compressed air supplied to the fuel cell. In the technology of Japanese Patent Application Laid-Open No. 2002-33108, if an intercooler is provided in the second cooling flow path, the refrigerant cooled by the radiator can be supplied to the intercooler and the intermediate heat exchanger. During power generation by the fuel cell, the refrigerant can be circulated in the first cooling flow path and then in the second cooling flow path by passing through the radiator, the intermediate heat exchanger, and the intercooler. The heat generated by the fuel cell is transferred to the intermediate heat exchanger via the refrigerant flowing in the first cooling flow path. The intermediate heat exchanger cools the refrigerant in the first cooling flow path by exchanging heat with the refrigerant in the second cooling flow path (i.e., the refrigerant cooled by the radiator). Therefore, the fuel cell can be efficiently cooled by the refrigerant in the first cooling flow path. In addition, the intercooler cools the compressed air by exchanging heat with the refrigerant in the second cooling flow path (i.e., the refrigerant cooled by the radiator). Therefore, the compressed air can be efficiently cooled. Summary of the Invention

[0004] When the fuel cell is started in a low-temperature environment, the temperature of the fuel cell is low immediately after the start-up, and the power generation efficiency is low. In addition, if the fuel cell is started, it is necessary to supply refrigerant to the intercooler. In the above-mentioned fuel cell system, if refrigerant is supplied to the intercooler, refrigerant is also supplied to the intermediate heat exchanger. As a result, the fuel cell is cooled by the refrigerant in the intermediate heat exchanger and the first cooling flow path, and the temperature of the fuel cell is difficult to increase. Therefore, the power generation efficiency of the fuel cell is difficult to increase. In this way, if an intercooler is provided in the second cooling flow path, there is a problem that the temperature of the fuel cell is difficult to increase in a low-temperature environment. In this specification, a technology is proposed that can increase the temperature of the fuel cell while supplying refrigerant to the intercooler.

[0005] Method 1

[0006] The fuel cell cooling system disclosed in this specification includes:

[0007] a first cooling flow path for circulating a refrigerant;

[0008] A fuel cell disposed in the first cooling flow path;

[0009] a second cooling flow path for circulating a refrigerant;

[0010] a radiator disposed in the second cooling flow path;

[0011] an intercooler provided in the second cooling flow path; and

[0012] an intermediate heat exchanger for performing heat exchange between the first cooling flow path and the second cooling flow path;

[0013] The second cooling flow path includes a bypass flow path provided in parallel with the radiator.

[0014] During power generation by the fuel cell, when the temperature of the refrigerant in the first cooling flow path is lower than a first reference value, a first operation is performed in which the refrigerant circulates in the first cooling flow path via a path passing through the fuel cell and the intermediate heat exchanger, and circulates in the second cooling flow path via a path passing through the intermediate heat exchanger, the intermediate cooler, and the bypass flow path.

[0015] During power generation by the fuel cell, when the temperature of the refrigerant in the first cooling flow path is higher than the first reference value, a second action is performed in which the refrigerant circulates in the first cooling flow path through the fuel cell and the intermediate heat exchanger and in the second cooling flow path through the intermediate heat exchanger, the intermediate cooler and the radiator.

[0016] In the above-mentioned fuel cell cooling system, when the temperature of the refrigerant in the first cooling flow path falls below a first reference value during power generation by the fuel cell, a first action is performed. In the first action, the refrigerant circulates in the second cooling flow path via a path passing through the intermediate heat exchanger, the intermediate cooler, and the bypass flow path. Because the refrigerant circulates in a path that bypasses the radiator, the temperature of the refrigerant in the second cooling flow path is difficult to drop. Therefore, the amount of heat transfer between the first cooling flow path and the second cooling flow path in the intermediate heat exchanger is small. As a result, the temperature of the refrigerant in the first cooling flow path is difficult to drop, and the temperature of the fuel cell can be efficiently increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Features, advantages, and technical and industrial significance of embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals represent like elements, wherein:

[0018] Figure 1is a block diagram of the fuel cell cooling system.

[0019] Figure 2 This is an explanatory diagram of the first circulation flow path.

[0020] Figure 3 It is an explanatory diagram of the second circulation flow path.

[0021] Figure 4 This is a flowchart of the operation selection process of the fuel cell cooling system. DETAILED DESCRIPTION

[0022] Following the above-mentioned embodiment 1, the additional configuration of the fuel cell cooling system disclosed in this specification will be described below.

[0023] Method 2

[0024] According to the fuel cell cooling system described in embodiment 1,

[0025] In the first operation and the second operation, in the second cooling flow path, the refrigerant flows in parallel through the intermediate heat exchanger and the intercooler.

[0026] Method 3

[0027] According to the fuel cell cooling system described in embodiment 1 or 2,

[0028] In the first action, when the temperature of the refrigerant in the first cooling flow path is lower than a second reference value, the circulation speed of the refrigerant in the first cooling flow path is slowed down compared to when the temperature of the refrigerant in the first cooling flow path is higher than the second reference value.

[0029] Method 4

[0030] The fuel cell cooling system according to any one of aspects 1 to 3,

[0031] In the first action, when the temperature of the refrigerant in the first cooling flow path is lower than the second reference value, the circulation speed of the refrigerant in the second cooling flow path is slowed down compared to when the temperature of the refrigerant in the first cooling flow path is higher than the second reference value.

[0032] According to aspect 2, the refrigerant flowing in the second cooling flow path flows into the intermediate heat exchanger and then flows into the intercooler. That is, the intermediate heat exchanger exchanges heat between the first cooling flow path and the second cooling flow path and cools the intercooler.

[0033] Figure 1The fuel cell cooling system 100 shown is mounted on a device (eg, a fuel cell electric vehicle) that uses a fuel cell as a power source. The fuel cell cooling system 100 includes a first cooling system 10 , a second cooling system 20 , and an intermediate heat exchanger 30 .

[0034] Refrigerant circulates in the first cooling system 10. Refrigerant circulates in the second cooling system 20. The intermediate heat exchanger 30 includes a first heat exchange path 30a and a second heat exchange path 30b. The first heat exchange path 30a is part of the first cooling system 10, and the second heat exchange path 30b is part of the second cooling system 20. The intermediate heat exchanger 30 exchanges heat between the first heat exchange path 30a and the second heat exchange path 30b.

[0035] The first cooling system 10 includes a fuel cell 14 and a first cooling flow path 12. The fuel cell 14 is provided in the first cooling flow path 12. Compressed air is supplied to the fuel cell 14 from an air compressor (not shown), and hydrogen is supplied from a tank (not shown). The fuel cell 14 generates electricity by reacting oxygen and hydrogen, which is then supplied to a motor (not shown).

[0036] The first cooling flow path 12 includes a flow path 12a and a flow path 12b. Flow path 12a connects the downstream end of the first heat exchange flow path 30a and the upstream end of the refrigerant flow path within the fuel cell 14. Flow path 12b connects the downstream end of the refrigerant flow path within the fuel cell 14 and the upstream end of the first heat exchange flow path 30a. The first cooling flow path 12 is composed of the flow path 12a, the refrigerant flow path provided within the fuel cell 14, the flow path 12b, and the first heat exchange flow path 30a. In other words, the first cooling flow path 12 is an annular flow path through which the refrigerant circulates.

[0037] The first cooling system 10 includes a pump 16 and temperature sensors 18a and 18b. Pump 16 is installed in flow path 12b. Pump 16 delivers refrigerant from its installation location toward the intermediate heat exchanger 30. When pump 16 is activated, the refrigerant circulates through the first cooling flow path 12 in the order of the intermediate heat exchanger 30, flow path 12a, fuel cell 14, and flow path 12b.

[0038] Temperature sensor 18a is provided in flow path 12a. Temperature sensor 18a detects the temperature of the coolant flowing into fuel cell 14. Temperature sensor 18b is provided in flow path 12b. Temperature sensor 18b detects the temperature of the coolant discharged from fuel cell 14 (hereinafter referred to as FC outlet temperature).

[0039] The second cooling system 20 includes a radiator 24 , a second cooling flow path 22 , an intercooler 32 , and a three-way valve 38 .

[0040] The radiator 24 is provided in the second cooling flow path 22. The radiator 24 cools the refrigerant flowing in the second cooling flow path 22 by exchanging heat with the outside air.

[0041] The second cooling flow path 22 includes a flow path 22a, a flow path 22b, a flow path 22c, an intercooler flow path 34, and a bypass flow path 36. Flow path 22a is connected to the upstream end of the second heat exchange flow path 30b and the downstream end of the refrigerant flow path within the radiator 24. Flow path 22b is connected to a three-way valve 38 and the downstream end of the second heat exchange flow path 30b. Flow path 22c is connected to the three-way valve 38 and the upstream end of the refrigerant flow path within the radiator 24. The upstream end of the intercooler flow path 34 is connected to flow path 22a. The downstream end of the intercooler flow path 34 is connected to flow path 22b. The intercooler flow path 34 is a flow path provided in parallel with the intermediate heat exchanger 30 for the flow of refrigerant. The upstream end of the bypass flow path 36 is connected to the three-way valve 38. The downstream end of the bypass flow path 36 is connected to flow path 22a upstream of the intercooler flow path 34. The second cooling flow path 22 is composed of flow path 22b, flow path 22c, the refrigerant flow path in the radiator 24, flow path 22a, the intercooler flow path 34, the bypass flow path 36, and the second heat exchange flow path 30b. The second cooling flow path 22 is an annular flow path in which the refrigerant circulates.

[0042] The intercooler 32 is provided in the intercooler flow path 34 . The intercooler 32 cools the compressed air supplied to the fuel cell 14 by exchanging heat with the refrigerant flowing in the intercooler flow path 34 .

[0043] The three-way valve 38 switches between a state in which the flow path 22 b is connected to the flow path 22 c and a state in which the flow path 22 b is connected to the bypass flow path 36 .

[0044] The second cooling system 20 includes a pump 26. Pump 26 is provided in flow path 22a. Pump 26 is located downstream of the connection between flow path 22a and bypass flow path 36 and upstream of the connection between flow path 22a and intercooler flow path 34. Pump 26 delivers refrigerant from its location toward the intermediate heat exchanger 30 and intercooler 32.

[0045] The second cooling system 20 includes a temperature sensor 28a and a temperature sensor 28b. The temperature sensor 28a is provided in the flow path 22a. The temperature sensor 28a detects the temperature of the refrigerant discharged from the radiator 24. The temperature sensor 28b is provided in the flow path 22c. The temperature sensor 28b detects the temperature of the refrigerant flowing into the radiator 24.

[0046] The fuel cell cooling system 100 includes a control device 40 . The control device 40 controls the pumps 16 and 26 and the three-way valve 38 based on the temperature of the coolant in the first cooling flow path 12 .

[0047] Compressed air is supplied from an air compressor (not shown) and hydrogen is supplied from a tank (not shown) to the fuel cell 14. The fuel cell 14 generates electricity by reacting oxygen and hydrogen. While the fuel cell 14 is generating electricity, the fuel cell cooling system 100 can execute warm-up control and normal control as described below.

[0048] Warm-up control is executed when the temperature of the fuel cell 14 is low. During warm-up control, the controller 40 operates the pump 16. When the pump 16 operates, the refrigerant circulates through the first cooling flow path 12 in the order of the intermediate heat exchanger 30, the flow path 12a, the fuel cell 14, and the flow path 12b. Therefore, the heat generated by power generation by the fuel cell 14 is transferred to the intermediate heat exchanger 30 (i.e., the first heat exchange flow path 30a) via the refrigerant in the first cooling flow path 12. The intermediate heat exchanger 30 transfers the heat generated by power generation by the fuel cell 14 from the first heat exchange flow path 30a to the second heat exchange flow path 30b.

[0049] In the warm-up control, the controller 40 operates the pump 26. In addition, the controller 40 connects the flow path 22b to the bypass flow path 36 via the three-way valve 38. Figure 2 circulates in the first circulation flow path 101 indicated by the arrow. That is, the refrigerant sent by the pump 26 flows in parallel in the intermediate heat exchanger 30 and the intermediate cooler 32. The refrigerant that has passed through the intermediate heat exchanger 30 and the intermediate cooler 32 then flows to the bypass flow path 36 via the three-way valve 38. Therefore, the refrigerant does not flow in the radiator 24. The intermediate heat exchanger 30 cools the refrigerant in the first cooling flow path 12 by heat exchange between the first cooling flow path 12 and the second cooling flow path 22. In addition, the intermediate cooler 32 cools the compressed air supplied to the fuel cell 14 by heat exchange with the refrigerant flowing in the intermediate cooler flow path 34.

[0050] As described above, during warm-up control, the fuel cell 14 is cooled, and the compressed air supplied to the fuel cell 14 is also cooled by the intercooler 32. Furthermore, during warm-up control, since refrigerant does not flow through the radiator 24, it is difficult to cool the refrigerant in the second cooling flow path 22. Consequently, heat exchange by the intermediate heat exchanger 30 is difficult, and cooling of the refrigerant in the first cooling flow path 12 is also difficult. Consequently, the temperature of the fuel cell 14 tends to rise.

[0051] Normal control is executed when the temperature of the fuel cell 14 is higher than a reference value. During normal control, the controller 40 operates the pump 16. Thus, as in warm-up control, the refrigerant circulates through the first cooling flow path 12. Therefore, the heat generated by power generation by the fuel cell 14 is transferred to the intermediate heat exchanger 30 (i.e., the first heat exchange flow path 30a) via the refrigerant in the first cooling flow path 12. The intermediate heat exchanger 30 transfers the heat generated by power generation by the fuel cell 14 from the first heat exchange flow path 30a to the second heat exchange flow path 30b.

[0052] In addition, in normal control, the control device 40 operates the pump 26. In addition, the control device 40 connects the flow path 22b and the flow path 22c via the three-way valve 38. Therefore, the refrigerant Figure 3 circulates in the second circulation flow path 102 indicated by the arrow. That is, the refrigerant sent by the pump 26 flows in parallel in the intermediate heat exchanger 30 and the intercooler 32. The refrigerant that has passed through the intermediate heat exchanger 30 and the intercooler 32 then flows to the radiator 24 via the three-way valve 38. Therefore, no refrigerant flows in the bypass flow path 36. The radiator 24 cools the refrigerant in the second cooling flow path 22 by heat exchange with the outside air. Therefore, the refrigerant cooled by the radiator 24 flows to the intermediate heat exchanger 30 and the intercooler 32. The intermediate heat exchanger 30 cools the refrigerant in the first cooling flow path 12 by heat exchange between the first cooling flow path 12 and the second cooling flow path 22. Since the refrigerant in the second cooling flow path 22 is cooled by the radiator 24, the intermediate heat exchanger 30 can efficiently cool the refrigerant in the first cooling flow path 12. Furthermore, the intercooler 32 cools the compressed air supplied to the fuel cell 14 by exchanging heat with the refrigerant flowing in the intercooler flow path 34 .

[0053] As described above, during normal control, the fuel cell 14 is cooled, and the compressed air supplied to the fuel cell 14 via the intercooler 32 is also cooled. Furthermore, during normal control, the refrigerant in the second cooling flow path 22 is cooled by the radiator 24. Therefore, the refrigerant in the first cooling flow path 12 can be efficiently cooled by the intermediate heat exchanger 30. Consequently, the fuel cell 14 can be efficiently cooled.

[0054] The control device 40 executes Figure 4 The processing is shown in the flowchart.

[0055] In S2, the control device 40 measures the outside air temperature using a temperature sensor (not shown). The control device 40 determines whether the outside air temperature is below the cold determination temperature T1 (e.g., 0°C). When the vehicle is parked, the refrigerant temperature is roughly the same as the outside air temperature. Therefore, the process in S2 is equivalent to determining whether the temperature of the refrigerant flowing through the first cooling flow path 12 is below the cold determination temperature T1.

[0056] When the outside air temperature is below the cold determination temperature T1 (if the answer is yes in S2), the control device 40 performs cold warm-up control in S4. During cold warm-up control, the control device 40 performs the warm-up control described above. During cold warm-up control, the control device 40 controls the output current of the fuel cell 14 to a high value. In addition, during cold warm-up control, the control device 40 controls the discharge flow rate of the pumps 16 and 26 to a low value. As described above, the temperature of the fuel cell 14 tends to rise during warm-up control. In particular, during cold warm-up control, heat is easily generated in the fuel cell 14 due to the high output current of the fuel cell 14. In addition, since the discharge flow rate of the pumps 16 and 26 is low, heat is difficult to transfer from the fuel cell 14 to the refrigerant. Therefore, the temperature of the fuel cell 14 tends to rise particularly easily. In this way, by implementing cold warm-up control when the air temperature is below the cold determination temperature T1, the temperature of the fuel cell 14 rises rapidly. As a result, the power generation efficiency of the fuel cell 14 increases.

[0057] If the FC outlet temperature is lower than the cooling and warming control end temperature T2, the control device 40 performs cooling and warming control until the vehicle power is turned off (i.e., YES in S6 and NO in S8). If the FC outlet temperature exceeds the cooling and warming control end temperature T2 (NO in S6), the control device 40 performs S12.

[0058] If the outside air temperature is higher than the cold determination temperature T1 in S2, the control device 40 determines in S10 whether the FC outlet temperature is lower than the warm-up control end temperature T3. In other words, the control device 40 determines whether the temperature of the refrigerant flowing in the first cooling flow path 12 is lower than the warm-up control end temperature T3. The warm-up control end temperature T3 is a temperature higher than the cold determination temperature T1.

[0059] If the FC outlet temperature is lower than the warm-up control end temperature T3 (if YES in S10), the controller 40 performs normal warm-up control in S12. During normal warm-up control, the controller 40 performs the warm-up control described above. During normal warm-up control, the controller 40 controls the output current of the fuel cell 14 to a low value (i.e., lower than the value in S4). Furthermore, during normal warm-up control, the controller 40 controls the discharge flow rates of the pumps 16 and 26 to a high value (i.e., higher than the value in S4). As described above, the temperature of the fuel cell 14 tends to rise during warm-up control. However, during normal warm-up control, the fuel cell 14 temperature rises less rapidly than during cold warm-up control due to the low output current of the fuel cell 14 and the high discharge flow rates of the pumps 16 and 26. Thus, when the temperature of the fuel cell 14 rises to a certain level, the temperature gradient within the fuel cell 14 is mitigated by reducing the power generation of the fuel cell 14 compared to cold warm-up control and increasing the refrigerant flow rate.

[0060] If the FC outlet temperature is lower than the warm-up control end temperature T3, the control device 40 performs normal warm-up control until the vehicle power is turned off (i.e., YES in S10 and NO in S14). If the FC outlet temperature exceeds the warm-up control end temperature T3 (NO in S10), the control device 40 performs S16.

[0061] In S16 , the control device 40 performs the above-described normal control. Therefore, the fuel cell 14 can be efficiently cooled, and the compressed air can be efficiently cooled by the intercooler 32 .

[0062] If the FC outlet temperature is higher than the warm-up control restart temperature T4, the control device 40 performs normal control until the vehicle power is turned off (i.e., NO in S18 and NO in S20). Warm-up control restart temperature T4 is a temperature lower than warm-up control end temperature T3. If the FC outlet temperature falls below the warm-up control restart temperature T4 (YES in S18), the control device 40 performs normal warm-up control in S12.

[0063] In the embodiment, the intercooler 32 is provided in the intercooler flow path 34. However, the intercooler 32 may also be provided in the flow path 22b. Alternatively, the intercooler 32 may be provided between the pump 26 and the intermediate heat exchanger 30. In other words, the refrigerant may flow in series through the intermediate heat exchanger 30 and the intercooler 32.

[0064] The cold warm-up control and the normal warm-up control of the embodiment are examples of the first operation. The normal control of the embodiment is an example of the second operation.

[0065] The warm-up control end temperature T3 of the embodiment is an example of the first reference value. The cold determination temperature T1 of the embodiment is an example of the second reference value.

[0066] In the embodiment, the three-way valve 38 constitutes the flow path changing device that changes the refrigerant flow path within the second cooling flow path 22. However, the flow path changing device may also be constituted by another device. Furthermore, in the embodiment, the three-way valve 38 is a solenoid valve, but the flow path changing device may also be constituted by a device that does not use electricity. For example, the flow path changing device may also be constituted by a device that switches the flow path based on the thermal expansion of a material, such as a thermostat.

[0067] In the embodiment, the temperature sensor 18a detects the temperature of the refrigerant flowing into the fuel cell 14. However, the temperature sensor 18a may also be provided near the outlet or inlet of the intermediate heat exchanger 30.

[0068] The temperature sensor 18b detects the temperature of the refrigerant discharged from the fuel cell 14. However, the temperature sensor 18b may be provided near the outlet or inlet of the intermediate heat exchanger 30.

[0069] In the embodiment, the temperature sensor 28a detects the temperature of the refrigerant discharged from the radiator 24. However, the temperature sensor 28a may also be provided near the outlet or inlet of the intermediate heat exchanger 30.

[0070] In the embodiment, the temperature sensor 28 b is provided in the flow path 22 c . However, the temperature sensor 28 b may also be provided near the outlet or inlet of the intermediate heat exchanger 30 .

[0071] The above detailed descriptions of the embodiments are intended to be illustrative only and do not limit the technical solutions. The technologies described in the technical solutions include various variations and modifications of the specific examples exemplified above. The technical elements described in this specification or the accompanying drawings demonstrate their technical usefulness individually or in various combinations, and are not limited to the combinations described in the technical solutions at the time of application. Furthermore, the technologies exemplified in this specification or the accompanying drawings are technologies that achieve multiple objectives simultaneously, and achieving even one of these objectives alone is technically useful.

Claims

1. A fuel cell cooling system, wherein: have: a first cooling flow path for circulating a refrigerant; a fuel cell disposed in the first cooling flow path; a second cooling flow path for circulating a refrigerant; a radiator provided in the second cooling flow path; an intercooler provided in the second cooling flow path; and an intermediate heat exchanger for performing heat exchange between the first cooling flow path and the second cooling flow path, The second cooling flow path includes a bypass flow path provided in parallel with the radiator. During power generation by the fuel cell, when the temperature of the refrigerant in the first cooling flow path is lower than a first reference value, a first action is performed in which the refrigerant circulates in the first cooling flow path via a path passing through the fuel cell and the intermediate heat exchanger, and circulates in the second cooling flow path via a path passing through the intermediate heat exchanger, the intercooler, and the bypass flow path. During power generation by the fuel cell, when the temperature of the refrigerant in the first cooling flow path is higher than the first reference value, a second action is performed in which the refrigerant circulates in the first cooling flow path through a path passing through the fuel cell and the intermediate heat exchanger and in a path passing through the intermediate heat exchanger, the intermediate cooler, and the radiator.

2. The fuel cell cooling system according to claim 1, wherein: In the first operation and the second operation, the refrigerant flows in parallel in the intermediate heat exchanger and the intercooler in the second cooling flow path.

3. The fuel cell cooling system according to claim 1 or 2, wherein: In the first operation, when the temperature of the refrigerant in the first cooling flow path is lower than a second reference value, the circulation speed of the refrigerant in the first cooling flow path is slowed down compared to a case where the temperature of the refrigerant in the first cooling flow path is higher than the second reference value.

4. The fuel cell cooling system according to claim 3, wherein: In the first action, when the temperature of the refrigerant in the first cooling flow path is lower than the second reference value, the circulation speed of the refrigerant in the second cooling flow path is slowed down compared to the case where the temperature of the refrigerant in the first cooling flow path is higher than the second reference value.

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