Heat pump device

Abstract

Provided is a heat pump device capable of achieving both suppression of refrigerant leakage and comfort. A heat pump device (1, 1a) executes an air conditioning operation of an air conditioning target space (R). The heat pump device comprises a utilization heat exchanger (300, 300a), a heat source heat exchanger (102), a first expansion mechanism (108a), a compressor (101), a refrigerant circuit (100), a shut-off valve (110a, 110b), a refrigerant sensor (400), and a control unit (600, 600a). The control unit closes the shut-off valve when, during the air conditioning operation, the refrigerant concentration is higher than a predetermined first concentration (d1). Further, the control unit executes first control for reducing the circulation amount of refrigerant in the refrigerant circuit when, during the air conditioning operation, the refrigerant concentration is lower than the first concentration and higher than a predetermined second concentration (d2) lower than the first concentration.

Description

Heat pump device

[0001] It relates to a heat pump device.

[0002] Patent Document 1 (Japanese Patent Application Laid-Open No. 2002-228281) discloses a technique of performing a pump-down operation by stopping the air-conditioning operation and controlling the compressor and each valve when detecting refrigerant leakage, and recovering the refrigerant in the heat source heat exchanger. The air conditioner (heat pump device) of Patent Document 1 can reduce the amount of refrigerant leakage in the space where the utilization heat exchanger is installed.

[0003] Depending on the type of refrigerant, in order to quickly detect refrigerant leakage and reduce the amount of refrigerant leakage, the detectable refrigerant concentration (detection concentration) may be set lower than that of other refrigerants. However, if the detection concentration is set low, false detection is likely to occur. For this reason, the heat pump device disclosed in Patent Document 1 has a problem that the air-conditioning operation stops every time false detection occurs, and the comfort is impaired.

[0004] An object of the present disclosure is to provide a heat pump device that can achieve both suppression of refrigerant leakage and comfort.

[0005] The heat pump device of the first aspect executes an air-conditioning operation on the air-conditioning target space. The heat pump device includes a utilization heat exchanger, a heat source heat exchanger, a first expansion mechanism, a compressor, a refrigerant circuit, a shut-off valve, a refrigerant sensor, and a control unit.

[0006] The utilization heat exchanger causes the refrigerant to exchange heat with a heat medium. The heat source heat exchanger causes the refrigerant to exchange heat with a heat source outside the air-conditioning target space. The refrigerant circuit is filled with refrigerant in which the utilization heat exchanger, the heat source heat exchanger, the first expansion mechanism, and the compressor are connected by refrigerant pipes. The shut-off valve blocks the refrigerant flowing between the first expansion mechanism and the liquid-side end of the utilization heat exchanger or the refrigerant flowing between the compressor and the gas-side end of the utilization heat exchanger. The refrigerant sensor detects the refrigerant concentration in the air-conditioning target space.

[0007] The control unit closes the shut-off valve if the refrigerant concentration is higher than a predetermined first concentration during air conditioning operation. Furthermore, if the refrigerant concentration is lower than the first concentration but higher than a predetermined second concentration lower than the first concentration during air conditioning operation, the control unit performs a first control to reduce the amount of refrigerant circulating in the refrigerant circuit.

[0008] This heat pump system closes a shut-off valve when the refrigerant concentration is higher than the first concentration, thus suppressing further refrigerant leakage even if a leak occurs. Furthermore, when the refrigerant concentration is higher than the second concentration (which is lower than the first concentration), the first control is executed to reduce the amount of refrigerant circulating in the refrigerant circuit. In this way, this heat pump system can monitor the refrigerant concentration changes during the first control without stopping the air conditioning operation, and determine whether the detection result was not a false detection, thus achieving both refrigerant leakage suppression and comfort.

[0009] The heat pump device in the second aspect is the heat pump device in the first aspect, wherein the control unit controls the first expansion mechanism in the first control so that the opening degree becomes smaller.

[0010] This heat pump device reduces the amount of refrigerant circulating in the refrigerant circuit by controlling the opening of the first expansion mechanism to a smaller degree.

[0011] The heat pump device of the third aspect is a heat pump device of the first or second aspect, wherein the refrigerant circuit further includes branch piping and a second expansion mechanism. The branch piping allows a portion of the refrigerant flowing between the heat source heat exchanger and the first expansion mechanism to merge with the intermediate pressure generated by the compressor. The second expansion mechanism reduces the pressure of the refrigerant flowing through the branch piping. When the air conditioning operation is a heating operation, the control unit controls the second expansion mechanism in the first control to reduce its opening degree.

[0012] This heat pump system reduces the amount of refrigerant circulating in the refrigerant circuit by controlling the opening of the second expansion mechanism to a smaller degree when the air conditioning is in heating mode.

[0013] The heat pump device of the fourth perspective is a heat pump device of any of the first, third, or fourth perspectives, wherein the control unit controls the compressor to reduce its rotational speed in the first control.

[0014] This heat pump system reduces the amount of refrigerant circulating in the refrigerant circuit by controlling the compressor's rotational speed to decrease.

[0015] The fifth aspect of the heat pump device is a heat pump device according to any of the first or fourth aspects, further comprising a circulation pump that supplies water, which is a heat transfer medium, to the heat exchanger. The control unit causes the circulation pump to increase its discharge rate in the first control.

[0016] This heat pump system reduces the amount of refrigerant circulating in the refrigerant circuit by controlling the circulation pump to increase its discharge rate.

[0017] The heat pump device of the sixth aspect is a heat pump device of any of the first to fifth aspects, further comprising a fan that supplies air, which is a heat transfer medium, to the heat exchanger. The control unit controls the fan to increase its rotational speed in the first control.

[0018] This heat pump device reduces the amount of refrigerant circulating in the refrigerant circuit by controlling the fan to increase its rotation speed.

[0019] The heat pump device of the seventh aspect is a heat pump device of any of the first or sixth aspects, wherein the control unit closes the shut-off valve if the refrigerant concentration after a predetermined first time from the start of the first control is equal to or greater than the first concentration.

[0020] This heat pump system detects a high probability of refrigerant leakage if the refrigerant concentration rises above the initial concentration one hour after the start of the first control cycle. In this case, the heat pump system can suppress further refrigerant leakage by closing the shut-off valve. Thus, during the first control cycle, this heat pump system can monitor the refrigerant concentration trend without stopping the air conditioning operation and determine whether the detection result was a false positive (in other words, whether a refrigerant leak is actually occurring), thus achieving both refrigerant leakage suppression and comfort.

[0021] The heat pump device of the eighth aspect is the heat pump device of the seventh aspect, wherein the control unit terminates the first control if the refrigerant concentration after a predetermined second time from the start of the first control is less than or equal to the second concentration.

[0022] This heat pump system terminates the first control if, two hours after the start of the first control, the refrigerant concentration decreases to a level lower than the second concentration, indicating a low probability of refrigerant leakage. In this way, the heat pump system can monitor the refrigerant concentration trend during the first control without stopping the air conditioning operation, and determine whether the detection result was a false detection. This allows for both suppression of refrigerant leakage and comfort.

[0023] The heat pump device of the ninth aspect is the heat pump device of the eighth aspect, further comprising a notification unit. The control unit causes the notification unit to notify if the refrigerant concentration a predetermined third time after the start of the first control is lower than the first concentration and higher than the second concentration.

[0024] This heat pump system will issue a notification if, three hours after the start of the first control, the refrigerant concentration is lower than the first concentration but higher than the second concentration, indicating a possible refrigerant leak. Based on this notification, the user of this heat pump system can consider whether maintenance is necessary. In this way, this heat pump system can monitor the refrigerant concentration changes during the first control without stopping the air conditioning operation and determine whether the detection result was a false positive, thus achieving both refrigerant leak suppression and comfort.

[0025] The heat pump device of the tenth aspect is a heat pump device of any of the first to ninth aspects, wherein the refrigerant is flammable or toxic.

[0026] In heat pump systems using flammable or toxic refrigerants, the detectable refrigerant concentration (detectable concentration) is sometimes set lower than that of other refrigerants in order to quickly detect refrigerant leaks and reduce the amount of leaked refrigerant. However, setting the detectable concentration too low can easily lead to false detections. Therefore, heat pump systems using flammable or toxic refrigerants have the problem of having to stop the air conditioning operation every time a false detection occurs, compromising comfort.

[0027] This heat pump system can monitor the refrigerant concentration changes during the first control phase without stopping the air conditioning operation, and determine whether the detection result was a false detection. Therefore, even when the detection concentration is set low, it can achieve both suppression of refrigerant leakage and comfort.

[0028] The heat pump device of the 11th aspect is a heat pump device of any of the 1st to 9th aspects, wherein the refrigerant is carbon dioxide or a mixed refrigerant containing carbon dioxide.

[0029] Carbon dioxide or carbon dioxide-containing refrigerants are typically filled into the refrigerant circuit at high pressure, so if a refrigerant leak occurs, the leakage rate tends to be higher than with other refrigerants. For this reason, in heat pump systems using carbon dioxide or carbon dioxide-containing refrigerants, it is necessary to set the detection concentration low in order to quickly detect refrigerant leaks. However, setting the detection concentration too low can easily lead to false detections. As a result, heat pump systems using carbon dioxide or carbon dioxide-containing refrigerants have the problem of having to stop the air conditioning operation every time a false detection occurs, compromising comfort. This heat pump system can determine whether the detection result was a false detection by observing the change in refrigerant concentration during the first control without stopping the air conditioning operation, thus achieving both refrigerant leak suppression and comfort even when the detection concentration is set low.

[0030] This is a schematic diagram of the heat pump device 1. This is a schematic diagram showing the connection relationship between the control unit 600 and each part. This is a flowchart showing the control flow of the leak monitoring control. This is a diagram showing an example of the change in refrigerant concentration d after the start of circulation amount suppression control. This is a schematic diagram of the heat pump device 1a. This is a schematic diagram showing the connection relationship between the control unit 600a and each part.

[0031] <First Embodiment> (1) Overall Configuration Diagram 1 is a schematic diagram of a heat pump device 1 according to the first embodiment of the present disclosure. The heat pump device 1 is a refrigeration cycle device that performs heating and cooling operations, which are air conditioning operations, for an air-conditioned space R such as the interior of a building by executing a vapor compression type refrigeration cycle.

[0032] The heat pump device 1 heats or cools water and uses this water to perform heating and cooling operations in the space R to be air-conditioned. The heat pump device 1 includes a refrigerant circuit 100, a heat transfer medium circuit 200, a first heat exchanger 300, a refrigerant sensor 400, a notification unit 500, and a control unit 600.

[0033] The refrigerant circuit 100 is configured by connecting each of the devices described later with refrigerant piping. The refrigerant circuit 100 is filled with refrigerant. The heat transfer medium circuit 200 is filled with heat transfer medium.

[0034] A portion of the refrigerant circuit 100 is housed in the first casing 2 and installed outside the air-conditioned space R (e.g., outdoors). The remaining portion of the refrigerant circuit 100, the heat transfer medium circuit 200, the first heat exchanger 300, the refrigerant sensor 400, and the notification unit 500 are installed, for example, indoors. The first heat exchanger 300 is housed in the second casing 3.

[0035] In this embodiment, the refrigerant is flammable R290 (propane), and the heat transfer medium is water. A flammable refrigerant refers to a refrigerant classified as 2L or more in the US ANSI / ASHRAE 34 standard.

[0036] As will be explained in more detail later, the heat pump device 1 performs leak monitoring control to monitor refrigerant leakage and signs of refrigerant leakage during air conditioning operation.

[0037] (2) Detailed Configuration (2-1) First Heat Exchanger 300 The first heat exchanger 300 causes the refrigerant filled in the refrigerant circuit 100 to exchange heat with the heat transfer medium filled in the heat transfer medium circuit 200. The first heat exchanger 300 has a first flow path 301 and a second flow path 302. The first heat exchanger 300 is an example of a heat exchanger in use.

[0038] The first flow path 301 includes a liquid-side end 301a and a gas-side end 301b. The second flow path 302 includes one end 302a and the other end 302b.

[0039] The first flow path 301 is a flow path through which the refrigerant flows. Although details will be described later, the first flow path 301 forms part of the refrigerant circuit 100. The second flow path 302 is a flow path through which the heat medium flows. Although details will be described later, the second flow path 302 forms part of the heat medium circuit 200.

[0040] (2-2) Refrigerant Circuit 100 The refrigerant circuit 100 includes a first compressor 101, a second heat exchanger 102, a four-way switching valve 103, a receiver tank 104, a bridge circuit 105, a third heat exchanger 106, connecting pipes 107a, 107b, expansion valves 108a, 108b, 108c, a solenoid valve 109, shutoff valves 110a, 110b, and the first flow path 301 of the first heat exchanger 300.

[0041] (2-2-1) First Compressor 101 The first compressor 101 compresses the low-pressure refrigerant in the refrigerant circuit 100 and the intermediate-pressure refrigerant in the refrigerant circuit 100, and then discharges it as the high-pressure refrigerant in the refrigerant circuit 100. The first compressor 101 has a first suction part 101a, a second suction part 101b, a discharge part 101c, a first compression part 101d, and a second compression part 101e. The first compressor 101 is controlled by the control unit 600. The first compressor 101 is an example of a compressor.

[0042] The first compression part 101d compresses the low-pressure refrigerant sucked from the first suction part 101a and discharges it as the intermediate-pressure refrigerant to the second compression part 101e.

[0043] The second compression part 101e compresses the intermediate-pressure refrigerant in the second suction part 101b and / or the intermediate-pressure refrigerant discharged from the first compression part 101d, and discharges it as the high-pressure refrigerant from the discharge part 101c.

[0044] (2-2-2) Second Heat Exchanger 102 The second heat exchanger 102 causes the refrigerant circulating in the refrigerant circuit 100 to exchange heat with a heat source (for example, outdoor air). The second heat exchanger 102 has a gas-side end 102a and a liquid-side end 102b. The second heat exchanger 102 is an example of a heat source heat exchanger.

[0045] (2-2-3) Four-way switching valve 103 The four-way switching valve 103 has a first port 103a, a second port 103b, a third port 103c, and a fourth port 103d. The four-way switching valve 103 switches between a first state and a second state in which the communication states of the first port 103a, the second port 103b, the third port 103c, and the fourth port 103d are different based on an instruction from the control unit 600. In the first state, the first port 103a and the second port 103b communicate with each other, and the third port 103c and the fourth port 103d communicate with each other. In the second state, the first port 103a and the fourth port 103d communicate with each other, and the second port 103b and the third port 103c communicate with each other.

[0046] The first port 103a is connected to the discharge part 101c of the first compressor 101. The second port 103b is connected to the connecting pipe 107b. The third port 103c is connected to the first suction part 101a of the first compressor 101. The fourth port 103d is connected to the gas-side end 102a of the second heat exchanger 102.

[0047] (2-2-4) Receiver tank 104 The receiver tank 104 stores surplus refrigerant to circulate an appropriate amount of refrigerant in the refrigerant circuit 100. The receiver tank 104 has an inflow part 104a, a first outflow part 104b, and a second outflow part 104c. Refrigerant flows into the receiver tank 104 from the inflow part 104a. The refrigerant that has flowed into the receiver tank 104 flows out from the first outflow part 104b and the second outflow part 104c.

[0048] The second outflow part 104c of the receiver tank 104 is connected to a refrigerant pipe that connects the first suction part 101a of the first compressor 101 and the third port 103c of the four-way switching valve 103.

[0049] (2-2-5) Bridge circuit 105 The bridge circuit 105 has a first connection point 105ab, a second connection point 105bc, a third connection point 105cd, and a fourth connection point 105da.

[0050] A second check valve 105b is provided between the first connection point 105ab and the second connection point 105bc to restrict the flow of refrigerant from the first connection point 105ab to the second connection point 105bc and to allow the flow of refrigerant in the reverse direction. A third check valve 105c is provided between the second connection point 105bc and the third connection point 105cd to allow the flow of refrigerant from the second connection point 105bc to the third connection point 105cd and to restrict the flow of refrigerant in the reverse direction. A fourth check valve 105d is provided between the third connection point 105cd and the fourth connection point 105da to allow the flow of refrigerant from the third connection point 105cd to the fourth connection point 105da and to restrict the flow of refrigerant in the reverse direction. A first check valve 105a is provided between the fourth connection point 105da and the first connection point 105ab, which restricts the flow of refrigerant from the fourth connection point 105da to the first connection point 105ab and allows the flow of refrigerant in the reverse direction.

[0051] The first connection point 105ab is connected to the connecting pipe 107a. The second connection point 105bc is connected to the first outlet 104b of the receiver tank 104. The third connection point 105cd is connected to the liquid side end 102b of the second heat exchanger 102. The fourth connection point 105da is connected to the first flow path 106a of the third heat exchanger 106.

[0052] (2-2-6) Third heat exchanger 106 The third heat exchanger 106 has a first flow path 106a and a second flow path 106b. The third heat exchanger 106 performs heat exchange between the refrigerant passing through the first flow path 106a and the refrigerant passing through the second flow path 106b. The third heat exchanger 106 is an economizer heat exchanger.

[0053] One end 106aa of the first channel 106a is connected to the fourth connection point 105da of the bridge circuit 105. The other end 106ab of the first channel 106a is connected to the inlet 104a of the receiver tank 104.

[0054] The second flow path 106b has one end 106ba connected to a refrigerant pipe that connects the fourth connection point 105da of the bridge circuit 105 to one end 106aa of the first flow path 106a. The other end 106bb of the second flow path 106b is connected to the second suction section 101b of the first compressor 101.

[0055] (2-2-7) Connecting pipes 107a and 107b Connecting pipes 107a and 107b are pipes that connect the portion of the refrigerant circuit 100 housed in the first casing 2 to the portion housed in the second casing 3.

[0056] One end 107aa of the connecting pipe 107a is connected to the liquid side end 301a of the first flow path 301 of the first heat exchanger 300 via refrigerant piping. The other end 107ab of the connecting pipe 107a is connected to the first connection point 105ab of the bridge circuit 105 via refrigerant piping.

[0057] One end 107ba of the connecting pipe 107b is connected to the gas side end 301b of the first flow path 301 of the first heat exchanger 300 via refrigerant piping. The other end 107bb of the connecting pipe 107b is connected to the second port 103b of the four-way switching valve 103 via refrigerant piping.

[0058] (2-2-8) Expansion valves 108a, 108b, 108c The expansion valves 108a, 108b, and 108c adjust the flow rate of the refrigerant passing through them and reduce the pressure by changing the opening degree based on the instructions of the control unit 600.

[0059] The expansion valve 108a is provided in the refrigerant piping connecting the first outlet 104b of the receiver tank 104 and the second connection point 105bc of the bridge circuit 105. The expansion valve 108a is an example of the first expansion mechanism.

[0060] The expansion valve 108b is provided in the refrigerant piping that connects the inlet 104a of the receiver tank 104 to the first flow path 106a of the third heat exchanger 106.

[0061] The expansion valve 108c is provided in the branch pipe 100a, which is a refrigerant pipe connecting the refrigerant piping that connects the fourth connection point 105da of the bridge circuit 105 and the first flow path 106a of the third heat exchanger 106, and the second flow path 106b of the third heat exchanger 106. The branch pipe 100a allows a portion of the refrigerant flowing between the second heat exchanger 102 and the expansion valve 108a to merge with the intermediate pressure generated by the first compressor 101. The expansion valve 108c is an example of a second expansion mechanism.

[0062] (2-2-9) Solenoid valve 109 The solenoid valve 109 switches between an open state and a closed state based on instructions from the control unit 600.

[0063] The solenoid valve 109 is installed in the refrigerant piping that connects the first suction port 101a of the first compressor 101 and the third port 103c of the four-way switching valve 103 to the second outlet port 104c of the receiver tank 104. The solenoid valve 109 is a gas vent valve that removes gaseous refrigerant from the receiver tank 104.

[0064] (2-2-10) Shut-off valves 110a, 110b The shut-off valves 110a, 110b switch between an open state and a closed state based on instructions from the control unit 600.

[0065] The shut-off valve 110a is provided in the connecting pipe 107a. This allows the shut-off valve 110a to shut off the refrigerant flowing between the expansion valve 108a and the liquid-side end 301a of the first heat exchanger 300.

[0066] The shut-off valve 110b is installed in the connecting pipe 107b. This allows the shut-off valve 110b to shut off the refrigerant flowing between the first compressor 101 and the gas side end 301b of the first heat exchanger 300.

[0067] (2-2-11) First flow path 301 of the first heat exchanger 300 The liquid-side end 301a of the first flow path 301 of the first heat exchanger 300 is connected to the bridge circuit 105 via a connecting pipe 107a.

[0068] The first flow path 301 of the first heat exchanger 300 has its gas-side end 301b connected to a four-way switching valve 103 via a connecting pipe 107b.

[0069] (2-3) Heat transfer medium circuit 200 The heat transfer medium circuit 200 includes a circulation pump 201, a fourth heat exchanger 202, and a second flow path 302 of the first heat exchanger 300.

[0070] (2-3-1) Circulation pump 201 The circulation pump 201 circulates the heat transfer medium within the heat transfer medium circuit 200 and supplies the heat transfer medium to the first heat exchanger 300. The circulation pump 201 draws in the heat transfer medium filled in the heat transfer medium circuit 200 from the suction section 201a and discharges it from the discharge section 201b. The discharge amount of the circulation pump 201 is controlled by the control unit 600.

[0071] (2-3-2) Fourth heat exchanger 202 The fourth heat exchanger 202 causes the heat transfer medium circulating in the heat transfer medium circuit 200 to exchange heat with the air in the space to be air-conditioned R. One end 202a of the fourth heat exchanger 202 is connected to the second flow path 302 of the first heat exchanger 300. The other end 202b of the fourth heat exchanger 202 is connected to the suction part 201a of the circulation pump 201. Multiple fourth heat exchangers 202 may be provided.

[0072] (2-3-3) Second flow path 302 of the first heat exchanger 300 The second flow path 302 of the first heat exchanger 300 has one end 302a connected to one end 202a of the fourth heat exchanger 202.

[0073] The second flow path 302 of the first heat exchanger 300 is connected to the discharge section 201b of the circulation pump 201.

[0074] (2-4) Refrigerant sensor 400 The refrigerant sensor 400 detects the refrigerant concentration d in the air-conditioned space R. The control unit 600 acquires the detection result of the refrigerant sensor 400.

[0075] (2-5) Notification Unit 500 The notification unit 500 notifies the detection result based on the instructions of the control unit 600 when signs of refrigerant leakage are detected in the leak monitoring control. The notification unit 500 notifies the detection result, for example, by sound, light, or a message displayed on the remote control display (not shown).

[0076] (2-6) Control Unit 600 The control unit 600 controls the operation of each component of the heat pump system 1 and realizes heating and cooling operation and leakage monitoring control.

[0077] The control unit 600 is electrically connected to the first compressor 101, the four-way switching valve 103, the expansion valves 108a, 108b, 108c, the solenoid valve 109, the shut-off valves 110a, 110b, the circulation pump 201, the refrigerant sensor 400, and the notification unit 500 so as to be able to send and receive control signals and the like. Figure 2 is a schematic diagram showing the connection relationship between the control unit 600 and each of the parts.

[0078] The control unit 600 is implemented by a computer. The control unit 600 includes a control arithmetic unit and a memory device (neither of which are shown in the figure). The control arithmetic unit is a processor such as a CPU or GPU. The control arithmetic unit reads a program stored in the memory device and performs predetermined image processing and arithmetic processing according to this program. Furthermore, the control arithmetic unit writes the calculation results to the memory device and reads information stored in the memory device according to the program.

[0079] (3) Overall Operation (3-1) Heating Operation During heating operation, the control unit 600 drives the first compressor 101 and the circulation pump 201, controls the four-way switching valve 103 to the first state, and controls the shut-off valves 110a and 110b to the open state. The control unit 600 also controls the opening degree of the expansion valves 108a, 108b and 108c to an appropriate opening degree according to the operating state. Furthermore, the control unit 600 controls the solenoid valve 109 to the open or closed state according to the pressure of the receiver tank 104.

[0080] (Refrigerant Circuit 100) The first compressor 101 draws in the low-pressure gas phase refrigerant from the refrigerant circuit 100 through the first suction port 101a and the intermediate-pressure refrigerant from the refrigerant circuit 100 through the second suction port 101b, and discharges it as high-pressure gas phase refrigerant from the discharge port 101c. The high-pressure gas phase refrigerant flows into the connecting pipe 107b through the four-way switching valve 103 in the order of the first port 103a and the second port 103b. The refrigerant that has flowed out of the connecting pipe 107b flows into the first flow path 301 of the first heat exchanger 300. In the first flow path 301, the high-pressure gas phase refrigerant condenses to become high-pressure liquid phase refrigerant. At this time, the refrigerant releases heat to the heat transfer medium passing through the second flow path 302.

[0081] The high-pressure liquid-phase refrigerant that flows out from the first flow path 301 flows into the bridge circuit 105 from the first connection point 105ab through the connecting pipe 107a, and flows out from the fourth connection point 105da through the first check valve 105a.

[0082] A portion of the refrigerant that flows out of the bridge circuit 105 from the fourth connection point 105da passes through the first flow path 106a of the third heat exchanger 106, the expansion valve 108b, the receiver tank 104, and the expansion valve 108a in that order. The expansion valves 108b and 108a, set to an appropriate opening degree, reduce the pressure of the high-pressure liquid phase refrigerant to convert it into a low-pressure gas-liquid two-phase refrigerant.

[0083] A portion of the remaining refrigerant that has flowed out of the bridge circuit 105 from the fourth connection point 105da flows into the refrigerant piping connected to the second flow path 106b upstream of the first flow path 106a of the third heat exchanger 106, and passes through the expansion valve 108c and the second flow path 106b of the third heat exchanger 106 in that order. The expansion valve 108c, set to an appropriate opening, reduces the pressure of the high-pressure liquid phase refrigerant to an intermediate pressure refrigerant. The intermediate pressure refrigerant absorbs heat from the refrigerant passing through the first flow path 106a in the second flow path 106b of the third heat exchanger 106, and is then drawn into the first compressor 101 from the second suction section 101b. The low-pressure gas-liquid two-phase refrigerant flows back into the bridge circuit 105 from the second connection point 105bc, passes through the third check valve 105c, and flows out from the third connection point 105cd. The refrigerant that flows out of the bridge circuit 105 from the third connection point 105cd evaporates in the second heat exchanger 102 and becomes a low-pressure gaseous refrigerant. At this time, the refrigerant absorbs heat from the heat source. The low-pressure gaseous refrigerant that flows out of the second heat exchanger 102 passes through the four-way switching valve 103 in the order of the fourth port 103d and the third port 103c, and is then drawn into the first compressor 101 from the first suction port 101a.

[0084] (Heat transfer medium circuit 200) The circulation pump 201 draws in the heat transfer medium circulating in the heat transfer medium circuit 200 from the suction part 201a and discharges it from the discharge part 201b. The discharged heat transfer medium flows into the second flow path 302 of the first heat exchanger 300 from one end 202a. The heat transfer medium that flows into the second flow path 302 absorbs heat from the refrigerant passing through the first flow path 301. The heat transfer medium that flows out of the second flow path 302 flows into the fourth heat exchanger 202. The heat transfer medium that flows into the fourth heat exchanger 202 releases heat into the air in the space to be air-conditioned R. In other words, the heat transfer medium that flows into the fourth heat exchanger 202 heats the air in the space to be air-conditioned R. The heat transfer medium that flows out of the fourth heat exchanger 202 is drawn back into the circulation pump 201 from the suction part 201a.

[0085] (3-2) Cooling Operation In cooling operation, the control unit 600 drives the first compressor 101 and the circulation pump 201, controls the four-way switching valve 103 to the second state, and controls the shut-off valves 110a and 110b to the open state. The control unit 600 also controls the opening degree of the expansion valves 108a, 108b and 108c to an appropriate opening degree according to the operating state. Furthermore, the control unit 600 controls the solenoid valve 109 to the open or closed state according to the pressure of the receiver tank 104.

[0086] (Refrigerant Circuit 100) The first compressor 101 draws in the low-pressure gas phase refrigerant from the refrigerant circuit 100 through the first suction port 101a and the intermediate-pressure refrigerant from the refrigerant circuit 100 through the second suction port 101b, and discharges it as high-pressure gas phase refrigerant from the discharge port 101c. The high-pressure gas phase refrigerant flows into the second heat exchanger 102 through the four-way switching valve 103 in the order of the first port 103a and the fourth port 103d. The high-pressure gas phase refrigerant condenses in the second heat exchanger 102 to become high-pressure liquid phase refrigerant. At this time, the refrigerant releases heat to the heat source. The high-pressure liquid phase refrigerant that has flowed out of the second heat exchanger 102 flows into the bridge circuit 105 from the third connection point 105cd and flows out from the fourth connection point 105da through the fourth check valve 105d.

[0087] A portion of the refrigerant that flows out of the bridge circuit 105 from the fourth connection point 105da passes through the first flow path 106a of the third heat exchanger 106, the expansion valve 108b, the receiver tank 104, and the expansion valve 108a in that order. The expansion valves 108b and 108a, set to an appropriate opening degree, reduce the pressure of the high-pressure liquid phase refrigerant to convert it into a low-pressure gas-liquid two-phase refrigerant.

[0088] A portion of the remaining refrigerant that has flowed out of the bridge circuit 105 from the fourth connection point 105da flows into the refrigerant piping connected to the second flow path 106b upstream of the first flow path 106a of the third heat exchanger 106, and passes through the expansion valve 108c and the second flow path 106b of the third heat exchanger 106 in that order. The expansion valve 108c, set to an appropriate opening, reduces the pressure of the high-pressure liquid phase refrigerant to an intermediate pressure refrigerant. The intermediate pressure refrigerant absorbs heat from the refrigerant passing through the first flow path 106a in the second flow path 106b of the third heat exchanger 106, and is then drawn into the first compressor 101 from the second suction section 101b. The low-pressure gas-liquid two-phase refrigerant flows back into the bridge circuit 105 from the second connection point 105bc, passes through the second check valve 105b, and flows out from the first connection point 105ab.

[0089] The refrigerant that flows out of the bridge circuit 105 from the first connection point 105ab flows into the first flow path 301 of the first heat exchanger 300 through the connecting pipe 107a. In the first flow path 301, the refrigerant evaporates and becomes a low-pressure gaseous refrigerant. At this time, the refrigerant absorbs heat from the heat transfer medium passing through the second flow path 302. The refrigerant that flows out of the second flow path 302 flows into the four-way switching valve 103 through the connecting pipe 107b, passes through the fourth port 103d and the third port 103c in that order, and is then drawn back into the first compressor 101 from the first suction port 101a.

[0090] (Heat transfer medium circuit 200) The circulation pump 201 draws in the heat transfer medium circulating in the heat transfer medium circuit 200 from the suction port 201a and discharges it from the discharge port 201b. The discharged heat transfer medium flows into the second flow path 302 of the first heat exchanger 300 from the other end 302b. The heat transfer medium that flows into the second flow path 302 releases heat to the refrigerant passing through the first flow path 301. The heat transfer medium that flows out of the second flow path 302 flows into the fourth heat exchanger 202. The heat transfer medium that flows into the fourth heat exchanger 202 absorbs heat from the air in the space to be air-conditioned R. In other words, the heat transfer medium that flows into the fourth heat exchanger 202 cools the air in the space to be air-conditioned R. The heat transfer medium that flows out of the fourth heat exchanger 202 is drawn back into the circulation pump 201 from the suction port 201a.

[0091] (3-3) Leakage Monitoring and Control (3-3-1) Overview of Control The heat pump device 1 monitors refrigerant leakage and signs of refrigerant leakage during air conditioning operation in the leakage monitoring and control system.

[0092] In leak monitoring control, the control unit 600 closes the shut-off valve 110a if the refrigerant concentration d in the air-conditioned space R is higher than a predetermined first concentration d1 during air conditioning operation. Also in leak monitoring control, if the refrigerant concentration d in the air-conditioned space R is lower than the first concentration d1 and higher than a predetermined second concentration d2 which is lower than the first concentration d1, the control unit 600 performs circulation rate suppression control to reduce the amount of refrigerant circulating in the refrigerant circuit 10.

[0093] In leak monitoring control, if the refrigerant concentration d after a predetermined first time t1 from the start of circulation rate suppression control is higher than a first concentration d1, the control unit 600 closes at least one of the shut-off valves 110a and 110b.

[0094] In leak monitoring control, the control unit 600 terminates leak monitoring control if the refrigerant concentration d after a predetermined second time t2 from the start of circulation rate suppression control is lower than the second concentration d2.

[0095] In leak monitoring control, the control unit 600 causes the notification unit 500 to notify if, after a predetermined third time t3 from the start of circulation rate suppression control, the refrigerant concentration d is lower than the first concentration d1 and higher than the second concentration d2.

[0096] The first concentration d1 is the concentration at which there is a high possibility of refrigerant leakage from the refrigerant circuit 10, and the shut-off valve 110a should be closed immediately to suppress refrigerant leakage into the air-conditioned space R. The second concentration d2 is the concentration at which there is a possibility of refrigerant leakage from the refrigerant circuit 10, but there is also a possibility of false detection, and the change in refrigerant concentration d in the air-conditioned space R should be observed without closing the shut-off valve 110a. Specifically, the first concentration d1 and the second concentration d2 are set according to Annex E of the European standard EN378-1.

[0097] In this embodiment, for example, the first time t1, the second time t2, and the third time t3 are all 5 minutes. Hereafter, the first time t1, the second time t2, and the third time t3 will be collectively referred to as time t.

[0098] (3-3-2) Control Flow Diagram 3 is a flowchart showing the control flow of leak monitoring control. When heating or cooling operation is started, the control unit 600 starts leak monitoring control (start) and proceeds to step S100.

[0099] In step S100, the control unit 600 compares the refrigerant concentration d of the air-conditioned space R with a first concentration d1 and proceeds to step S110 or step S150.

[0100] Specifically, the control unit 600 acquires the refrigerant concentration d detected by the refrigerant sensor 400. If the refrigerant concentration d is greater than or equal to the first concentration d1 (d ≥ d1), the control unit 600 proceeds to step S150. If the refrigerant concentration d is lower than the first concentration d1 (d < d1), the control unit 600 proceeds to step S110.

[0101] In step S110, the control unit 600 compares the refrigerant concentration d with the second concentration d2 and proceeds to step S120 or step S100.

[0102] Specifically, the control unit 600 acquires the refrigerant concentration d detected by the refrigerant sensor 400. If the refrigerant concentration d is higher than the second concentration d2 (d > d2), the process proceeds to step S120. If the refrigerant concentration d is less than or equal to the second concentration d2 (d ≤ d2), the control unit 600 proceeds to step S100.

[0103] In step S120, the control unit 600 starts a process to reduce the amount of refrigerant circulating in the refrigerant circuit 10 (hereinafter referred to as circulation amount suppression control), and proceeds to step S130. Circulation amount suppression control is an example of the first control.

[0104] Specifically, in the circulation volume suppression control, the control unit 600 controls the expansion valve 108a so that its opening degree becomes smaller than normal.

[0105] In step S130, the control unit 600 waits until a predetermined time t has elapsed, and then proceeds to step S140.

[0106] In step S140, the control unit 600 compares the refrigerant concentration d with the first concentration d1 and the second concentration d2, and proceeds to step S150, step S160, or step S170.

[0107] Specifically, the control unit 600 acquires the refrigerant concentration d detected by the refrigerant sensor 400. If the refrigerant concentration d is greater than or equal to the first concentration d1 (d ≥ d1), the control unit 600 proceeds to step S150. If the refrigerant concentration d is lower than the first concentration d1 and higher than the second concentration d2 (d1 > d > d2), the control unit 600 proceeds to step S160. Furthermore, if the refrigerant concentration d is less than or equal to the second concentration d2 (d ≤ d2), the control unit 600 proceeds to step S170.

[0108] In step S150, the control unit 600 closes at least one of the shut-off valves 110a and 110b to terminate the leak monitoring control (termination).

[0109] In step S160, the control unit 600 continues the circulation rate reduction process and notifies the notification unit 500 of the detection result indicating that signs of refrigerant leakage have been detected, and proceeds to step S130.

[0110] In step S170, the control unit 600 terminates the circulation volume suppression control and proceeds to step S100.

[0111] The control unit 600 terminates the leak monitoring control when the heating or cooling operation is completed.

[0112] (3-3-3) Control Details Next, we will explain the details of the leak monitoring control. Figure 4 shows an example of the change in refrigerant concentration d after the start of circulation rate suppression control. In Figure 4, time 0 indicates the time when the circulation rate suppression control was started.

[0113] After starting leak monitoring control, the control unit 600, if the refrigerant concentration d is greater than or equal to a first concentration d1 (in step S100 (d≧d1)), has a high probability of refrigerant leakage occurring, and therefore closes at least one of the shut-off valves 110a and 110b to terminate leak monitoring control (step S150). As a result, the circulation of refrigerant in the refrigerant circuit 100 is stopped, and further refrigerant leakage in the air-conditioned space R is suppressed even if refrigerant leakage is occurring.

[0114] If the refrigerant concentration d is lower than the first concentration d1 (in step S100, (d < d1)), the control unit 600 compares the refrigerant concentration d with the second concentration d2 (step S110). If the refrigerant concentration d is less than or equal to the second concentration d2 (in step S110, (d ≤ d2)), the possibility of refrigerant leakage is low, so the control unit 600 proceeds to step S100. In other words, if the refrigerant concentration d is lower than the first concentration d1 and less than or equal to the second concentration d2, the control unit 600 repeats steps S100 and S110. If the refrigerant concentration d is higher than the second concentration d2 (in step S110, (d > d2)), signs of refrigerant leakage are observed, so the control unit 600 starts executing circulation rate suppression control (step S120). In circulation rate suppression control, the control unit 600 reduces the amount of refrigerant circulating in the refrigerant circuit 100. During the circulation rate suppression control, the control unit 600 monitors the change in refrigerant concentration d without stopping the air conditioning operation and determines whether the detection result was a false detection.

[0115] The control unit 600 compares the refrigerant concentration d with a first concentration d1 and a second concentration d2 after a time t has elapsed since the start of circulation rate suppression control. At this point, as shown in L1 of Figure 4, if the refrigerant concentration d is greater than or equal to the first concentration d1 (d≧d1 in step S140), there is a high possibility that refrigerant leakage is occurring, so the control unit 600 closes at least one of the shut-off valves 110a and 110b and terminates the leakage monitoring control (step S150). Also, at this point, as shown in L2 of Figure 4, if the refrigerant concentration d is lower than the first concentration d1 and higher than the second concentration d2 (d1>d>d2 in step S140), there is a continuing indication of refrigerant leakage, so the control unit 600 causes the notification unit 500 to notify it of the detection result indicating that an indication of refrigerant leakage has been detected (step S160), and continues to monitor the trend of the refrigerant concentration d.

[0116] Furthermore, at this point, as shown in L3 in Figure 4, if the refrigerant concentration d is less than or equal to the second concentration d2 (step S140) (d < d2), the possibility of refrigerant leakage is low, so the control unit 600 terminates the circulation amount suppression control (step S170) and restarts the process from step S100 again.

[0117] (4) Features (4-1) The heat pump device 1 performs air conditioning operation of the space R to be air-conditioned. The heat pump device 1 comprises a first heat exchanger 300, a second heat exchanger 102, an expansion valve 108a, a first compressor 101, a refrigerant circuit 100, a shut-off valve 110a, a refrigerant sensor 400, and a control unit 600.

[0118] The first heat exchanger 300 causes the refrigerant to exchange heat with a heat transfer medium. The second heat exchanger 102 causes the refrigerant to exchange heat with a heat source outside the air-conditioned space R. The refrigerant circuit 100 is connected by refrigerant piping to the first heat exchanger 300, the second heat exchanger 102, the expansion valve 108a, and the first compressor 101, and is filled with refrigerant. The shut-off valve 110a shuts off the refrigerant flowing between the expansion valve 108a and the liquid side end of the first heat exchanger 300, or the refrigerant flowing between the first compressor 101 and the gas side end of the first heat exchanger 300. The refrigerant sensor 400 detects the refrigerant concentration d in the air-conditioned space R.

[0119] During air conditioning operation, the control unit 600 closes the shut-off valve 110a if the refrigerant concentration d is higher than a predetermined first concentration d1. Furthermore, during air conditioning operation, if the refrigerant concentration d is lower than the first concentration d1 and higher than a predetermined second concentration d2 which is lower than the first concentration d1, the control unit 600 performs circulation rate suppression control to reduce the amount of refrigerant circulating in the refrigerant circuit 100.

[0120] The heat pump device 1 closes the shut-off valve 110a when the refrigerant concentration d is higher than the first concentration d1, thus suppressing further refrigerant leakage even if a refrigerant leak occurs. Furthermore, when the refrigerant concentration d is higher than the second concentration d2, which is lower than the first concentration d1, the circulation rate is reduced in the refrigerant circuit 100 by performing circulation rate reduction control. In this way, the heat pump device 1 can monitor the change in refrigerant concentration d during circulation rate reduction control without stopping the air conditioning operation and can determine whether the detection result was not a false detection, thus achieving both refrigerant leakage suppression and comfort.

[0121] (4-2) The control unit 600 controls the expansion valve 108a to open to a smaller degree in the circulation volume suppression control.

[0122] The heat pump device 1 reduces the amount of refrigerant circulating in the refrigerant circuit 100 by controlling the expansion valve 108a to a smaller opening.

[0123] (4-3) The control unit 600 closes the shut-off valve 110a if the refrigerant concentration d after a predetermined time t from the start of circulation amount suppression control is equal to or greater than the first concentration d1.

[0124] If the refrigerant concentration d rises to a first concentration d1 or higher after time t has elapsed since the start of circulation rate reduction control in the heat pump device 1, there is a high probability of refrigerant leakage. In this case, the heat pump device 1 can prevent further refrigerant leakage by closing the shut-off valve 110a. In this way, the heat pump device 1 can observe the change in refrigerant concentration d during circulation rate reduction control without stopping the air conditioning operation and determine whether the detection result was a false detection (in other words, whether refrigerant leakage is actually occurring), thus achieving both refrigerant leakage suppression and comfort.

[0125] (4-4) The control unit 600 terminates the circulation amount suppression control if the refrigerant concentration d after a predetermined time t from the start of the circulation amount suppression control is less than or equal to the second concentration d2.

[0126] The heat pump device 1 terminates the circulation rate reduction control if, after time t from the start of circulation rate reduction control, the refrigerant concentration d decreases to a second concentration d2 or lower, because the possibility of refrigerant leakage is low. In this way, the heat pump device 1 can monitor the change in refrigerant concentration d during circulation rate reduction control without stopping the air conditioning operation and can determine whether the detection result was not a false detection, thus achieving both refrigerant leakage suppression and comfort.

[0127] (4-5) The heat pump device 1 further includes a notification unit 500. The control unit 600 causes the notification unit 500 to notify if the refrigerant concentration d after a certain time t from the start of circulation rate suppression control is lower than the first concentration d1 and higher than the second concentration d2.

[0128] If, three hours t3 after starting circulation rate reduction control, the heat pump device 1 detects that the refrigerant concentration d is lower than the first concentration d1 and higher than the second concentration d2, it indicates a refrigerant leak and triggers a notification from the notification unit 500. Based on this notification, the user of the heat pump device 1 can consider whether maintenance is necessary. In this way, the heat pump device 1 can monitor the refrigerant concentration d during circulation rate reduction control without stopping the air conditioning operation and determine whether the detection result was a false detection, thus achieving both refrigerant leak suppression and comfort.

[0129] (4-6) The heat pump device 1 has a flammable refrigerant.

[0130] In heat pump systems using flammable refrigerants, the detectable refrigerant concentration (detection concentration) is sometimes set lower compared to other refrigerants in order to quickly detect refrigerant leaks and reduce the amount of leaked refrigerant. However, setting the detection concentration too low can easily lead to false detections. As a result, heat pump systems using flammable refrigerants have the problem of having to stop the air conditioning operation every time a false detection occurs, compromising comfort.

[0131] The heat pump device 1 can monitor the trend of the refrigerant concentration d without stopping the air conditioning operation during circulation rate suppression control, and determine whether the detection result was not a false detection. Therefore, even when the detected concentration is set low, it is possible to achieve both suppression of refrigerant leakage and comfort.

[0132] (5) Modified Examples (5-1) Modified Example 1 In circulation volume suppression control, the method for reducing the amount of refrigerant circulating in the refrigerant circuit 10 is not limited to the above-described embodiment. When the air conditioning operation is heating operation, the control unit 600 may control the expansion valve 108c to open to a smaller degree in circulation volume suppression control.

[0133] In the modified example 1, the heat pump device 1 reduces the amount of refrigerant circulating in the refrigerant circuit 100 by controlling the expansion valve 108c to a smaller opening when the air conditioning operation is in heating operation.

[0134] (5-2) Modification 2 The control unit 600 may control the first compressor 101 to reduce its rotational speed in the circulation volume suppression control.

[0135] The heat pump device 1 according to the modified example 2 reduces the amount of refrigerant circulating in the refrigerant circuit 100 by controlling the rotational speed of the first compressor 101 to decrease.

[0136] (5-3) Modification 3 The control unit 600 may control the circulation pump 201 to increase its discharge rate in the circulation volume suppression control.

[0137] The heat pump device 1 according to the modified example 3 reduces the amount of refrigerant circulating in the refrigerant circuit 100 by controlling the circulation pump 201 to increase its discharge rate.

[0138] (5-4) Modification 4 The refrigerant may be toxic. A toxic refrigerant refers to a refrigerant classified as B in the US ANSI / ASHRAE 34 standard.

[0139] In the case of heat pump systems that use toxic refrigerants, just like with flammable refrigerants, it is necessary to set the detection concentration low. This presents a problem where the air conditioning operation is stopped every time a false detection occurs, compromising comfort. Therefore, the heat pump system 1 according to Modification 4, which uses a toxic refrigerant, can also achieve both suppression of refrigerant leakage and comfort.

[0140] (5-5) Modification 5 The refrigerant may be carbon dioxide or a mixed refrigerant containing carbon dioxide.

[0141] Carbon dioxide or carbon dioxide-containing refrigerants are typically filled into the refrigerant circuit at high pressure, so if a refrigerant leak occurs, the leakage rate tends to be higher than with other refrigerants. For this reason, in heat pump systems using carbon dioxide or carbon dioxide-containing refrigerants, it is necessary to set the detection concentration low in order to quickly detect refrigerant leaks. However, setting the detection concentration too low can easily lead to false detections. As a result, heat pump systems using carbon dioxide or carbon dioxide-containing refrigerants also have the problem of air conditioning operation being stopped each time a false detection occurs, compromising comfort. Therefore, the heat pump system 1 according to Modification 5, which uses carbon dioxide or carbon dioxide-containing refrigerants, can achieve both refrigerant leak suppression and comfort.

[0142] (5-6) Modification 6 The first time t1, the second time t2, and the third time t3 may be different from each other.

[0143] <Second Embodiment> (1) Overall Configuration Next, the heat pump device 1a according to the second embodiment will be described. Figure 5 is a schematic diagram of the heat pump device 1a. In the following, the differences between the heat pump device 1 and the heat pump device 1a will be described in detail, and descriptions of identical or corresponding features or well-known technologies may be omitted.

[0144] The heat pump device 1a includes a first heat exchanger 300a in place of the first heat exchanger 300. The heat pump device 1a does not have a heat transfer medium circuit 200. The heat pump device 1a includes a control unit 600a in place of the control unit 600. The heat pump device 1a further includes a fan 700.

[0145] (2) Detailed Configuration (2-1) First Heat Exchanger 300a The first heat exchanger 300a causes the refrigerant filled in the refrigerant circuit 100 to exchange heat with the air in the air-conditioned space R, which is the heat transfer medium. The first heat exchanger 300a is an example of a heat exchanger used.

[0146] One end 107aa of the connecting pipe 107a is connected to the liquid side end 300aa of the first heat exchanger 300a via refrigerant piping. One end 107ba of the connecting pipe 107b is connected to the gas side end 300ab of the first heat exchanger 300a via refrigerant piping.

[0147] (2-2) Fan 700 The fan 700 supplies air from the space R to be air-conditioned to the first heat exchanger 300a. The rotation speed of the fan 700 is controlled by the control unit 600a.

[0148] (2-3) Control Unit 600a The difference between the control unit 600 and the control unit 600a is that the control unit 600a is not connected to the circulation pump 201 and is electrically connected to the fan 700 so that it can send and receive control signals, etc. Figure 6 is a schematic diagram showing the connection relationship between the control unit 600a and each part.

[0149] (3) Overall operation (3-1) Leak monitoring operation The difference between the leak monitoring operation performed by heat pump device 1 and the leak monitoring operation performed by heat pump device 1a is the method of reducing the amount of refrigerant circulated in the refrigerant circuit 10 in the circulation amount suppression control.

[0150] Specifically, in the leak monitoring operation performed by the heat pump device 1, the control unit 600a controls the fan 700 to increase its rotational speed in the circulation volume suppression control.

[0151] (4) Features The heat pump device 1a reduces the amount of refrigerant circulating in the refrigerant circuit 100 by controlling the fan 700 to increase its rotation speed. Similar to the heat pump device 1, the heat pump device 1a can also observe the change in refrigerant concentration d during the circulation rate suppression control without stopping the air conditioning operation, and determine whether the detection result was not a false detection, thus achieving both suppression of refrigerant leakage and comfort.

[0152] <Conclusion> The embodiments of this disclosure have been described above, but it should be understood that various modifications to the form and details are possible without departing from the spirit and scope of this disclosure as described in the claims.

[0153] 1, 1a: Heat pump device 10: Refrigerant circuit 70: Control unit 100: Refrigerant circuit 101: First compressor (compressor) 100a: Branch piping 102: Heat source heat exchanger 108a: Expansion valve (first expansion mechanism) 108c: Expansion valve (second expansion mechanism) 110a, 110b: Shut-off valve 201: Circulation pump 300, 300a: Utilizing heat exchanger 301a: Liquid side end 300aa: Liquid side end 301b: Gas side end 300ba: Gas side end 400: Refrigerant sensor 500: Notification unit 600, 600a: Control unit 700: Fan d: Refrigerant concentration d1: First concentration d2: Second concentration t1: First time t2: Second time t3: Third hour R: Air-conditioned space

[0154] Patent No. 2002-228281

Claims

1. A heat pump device (1, 1a) for performing air conditioning operation of an air-conditioned space (R), comprising: a utilization heat exchanger (300, 300a) for causing a refrigerant to exchange heat with a heat transfer medium; a heat source heat exchanger (102) outside the air-conditioned space for causing the refrigerant to exchange heat with a heat source; a first expansion mechanism (108a); a compressor (101); a refrigerant circuit (100) in which the utilization heat exchanger, the heat source heat exchanger, the first expansion mechanism, and the compressor are connected by refrigerant piping and filled with the refrigerant; and shut-off valves (110a, 110b) for shutting off the refrigerant flowing between the first expansion mechanism and the liquid side end (301a, 300aa) of the utilization heat exchanger or the refrigerant flowing between the compressor and the gas side end (301b, 300ba) of the utilization heat exchanger. A heat pump device comprising a refrigerant sensor (400) for detecting the refrigerant concentration (d) in the space to be air-conditioned, and a control unit (600, 600a), wherein the control unit closes the shut-off valve when the refrigerant concentration is higher than a predetermined first concentration (d1) during air conditioning operation, and performs a first control to reduce the amount of refrigerant circulating in the refrigerant circuit when the refrigerant concentration is lower than the first concentration and higher than a predetermined second concentration (d2) which is lower than the first concentration during air conditioning operation.

2. The heat pump device according to claim 1, wherein the control unit controls the first expansion mechanism in the first control to reduce its opening degree.

3. The refrigerant circuit further comprises a branch pipe (100a) that merges a portion of the refrigerant flowing between the heat source heat exchanger and the first expansion mechanism with the intermediate pressure generated by the compressor, and a second expansion mechanism (108c) that reduces the pressure of the refrigerant flowing through the branch pipe, wherein the control unit controls the second expansion mechanism to open less in the first control when the air conditioning operation is a heating operation, according to claim 1 or 2.

4. The heat pump device according to any one of claims 1 to 3, wherein the control unit controls the compressor to reduce its rotational speed in the first control.

5. The heat pump device according to any one of claims 1 to 4, further comprising a circulation pump (201) that supplies water, which is the heat transfer medium, to the heat exchanger, wherein the control unit controls the circulation pump to increase its discharge rate in the first control.

6. The heat pump device according to any one of claims 1 to 5, further comprising a fan (700) that supplies air, which is the heat transfer medium, to the heat exchanger, wherein the control unit controls the fan to increase its rotational speed in the first control.

7. If the refrigerant concentration after a predetermined first time (t1) from the start of the first control is equal to or greater than the first concentration, the control unit closes the shut-off valve, the heat pump device according to any one of claims 1 to 6.

8. If the refrigerant concentration after a predetermined second time (t2) from the start of the first control is less than or equal to the second concentration, the control unit terminates the first control, as described in claim 7.

9. The heat pump device according to claim 8, further comprising a notification unit, wherein if the refrigerant concentration after a predetermined third time (t3) from the start of the first control is lower than the first concentration and higher than the second concentration, the control unit causes the notification unit to notify.

10. The heat pump device according to any one of claims 1 to 9, wherein the refrigerant is flammable or toxic.

11. The heat pump device according to any one of claims 1 to 9, wherein the refrigerant is carbon dioxide or a mixed refrigerant containing carbon dioxide.

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