Air conditioning device

Abstract

This air conditioning device comprises: a refrigerant circuit in which a compressor, a flow path switching device, a plurality of heat source-side heat exchangers arranged in parallel, an expansion unit, and a utilization-side heat exchanger are connected by means of refrigerant piping, and in which a refrigerant flows; a plurality of heat source-side pipes respectively provided with the plurality of heat source-side heat exchangers; a heat source-side solenoid valve provided to each of the plurality of heat source-side pipes; a heat source-side expansion unit provided to each of the plurality of heat source-side pipes; a plurality of bypass pipes connecting the discharge side of the compressor and the respective heat source-side pipes; and a plurality of bypass solenoid valves respectively provided to the plurality of bypass pipes.

Description

air conditioning equipment

[0001] The present disclosure relates to an air conditioner including a refrigerant circuit.

[0002] Conventionally, heat pump type air conditioners are known that are equipped with a heat source side heat exchanger that exchanges heat between air and a refrigerant and a user side heat exchanger that exchanges heat between water and a refrigerant, and that perform hot water supply or heating operation. Generally, air conditioners perform a defrosting operation to remove frost that forms on the heat source side heat exchanger during hot water supply or heating operation. In recent years, techniques have been proposed to suppress the freezing of water that occurs during the reverse cycle defrosting operation.

[0003] Patent Document 1 discloses an air conditioning apparatus including a heat source unit, a first usage unit, and a second usage unit. The heat source unit includes a compressor, a four-way valve, and a heat source-side heat exchanger that exchanges heat between a refrigerant and outdoor air. The first usage unit includes a usage-side heat exchanger that exchanges heat between the refrigerant and indoor air. The second usage unit includes a water heat exchanger that exchanges heat between water and the refrigerant. Patent Document 1 controls the flow of refrigerant to the second usage unit during defrosting operation, and allows the refrigerant to flow only through the first usage unit.

[0004] JP 2017-36882 A

[0005] However, although the air conditioner disclosed in Patent Document 1 can suppress water freezing, the energy input to melt the frost is only the electrical input from the compressor and the heat capacity of the refrigerant piping. Therefore, compared to defrosting methods that remove heat energy from water, the time required for defrosting, i.e., the time that hot water supply and heating are stopped, is significantly longer, reducing user comfort.

[0006] The present disclosure has been made to solve the above-mentioned problems, and provides an air conditioner that performs a defrosting operation without impairing the comfort of the user.

[0007] The air conditioning apparatus of the present disclosure includes a compressor, a flow path switching device, a refrigerant circuit in which a refrigerant flows, in which a plurality of heat source side heat exchangers arranged in parallel, an expansion section, and a user side heat exchanger are connected by refrigerant piping, a plurality of heat source side pipes in which a plurality of the heat source side heat exchangers are respectively provided, a heat source side solenoid valve provided in each of the plurality of heat source side pipes, a heat source side expansion section provided in each of the plurality of heat source side pipes, a plurality of bypass pipes connecting the discharge side of the compressor to each of the heat source side pipes, and a plurality of bypass solenoid valves provided in each of the plurality of bypass pipes.

[0008] According to the present disclosure, one heat source-side heat exchanger can function as a condenser, while the other heat source-side heat exchanger functions as an evaporator. This allows the heat source-side heat exchangers to be defrosted alternately, while preventing refrigerant from flowing to the user-side heat exchangers. Therefore, thermal energy removed from the air or the like can be used for defrosting, and a drop in temperature on the user side can be suppressed. This allows defrosting operation to be performed without compromising user comfort.

[0009] 1 is a schematic diagram showing an air conditioner according to embodiment 1. FIG. 2 is a schematic diagram showing a heat source machine according to embodiment 1. FIG. 3 is a circuit diagram showing an air conditioner according to embodiment 1. FIG. 4 is a circuit diagram showing the flow of refrigerant during cooling operation of an air conditioner according to embodiment 1. FIG. 5 is a circuit diagram showing the flow of refrigerant during heating operation of an air conditioner according to embodiment 1. FIG. 6 is a circuit diagram showing the flow of refrigerant during a first defrosting operation of an air conditioner according to embodiment 1. FIG. 7 is a circuit diagram showing the flow of refrigerant during a second defrosting operation of an air conditioner according to embodiment 1. FIG. 8 is a circuit diagram showing the flow of refrigerant during a first defrosting operation of an air conditioner according to embodiment 2. FIG. 9 is a circuit diagram showing the flow of refrigerant during a second defrosting operation of an air conditioner according to embodiment 2. FIG. 10 is a circuit diagram showing the flow of refrigerant during a first defrosting operation of an air conditioner according to embodiment 3.

[0010] Hereinafter, an embodiment of an air conditioning apparatus according to the present disclosure will be described with reference to the drawings. Note that the present disclosure is not limited to the embodiment described below. Furthermore, in the following drawings, including FIG. 2, the size relationships between the components may differ from the actual size relationships. Furthermore, in the following description, terms indicating directions are used as appropriate to facilitate understanding of the present disclosure, but these terms are for the purpose of explaining the present disclosure and do not limit the present disclosure. Examples of terms indicating directions include "up," "down," "right," "left," "front," and "rear."

[0011] Embodiment 1. FIG. 1 is a schematic diagram showing an air conditioning apparatus 1 according to embodiment 1. The air conditioning apparatus 1 conditions the air in, for example, a space to be air-conditioned, and as shown in FIG. 1 , includes multiple heat source units 2 and multiple load-side units 3. The air conditioning apparatus 1 is, for example, a top-flow modular chiller system. The air conditioning apparatus 1 performs heating and cooling operations using a heat pump-type heat source unit 2. The heating operation is an operation in which hot water is supplied to the load-side units 3 by removing heat from a medium such as air or water, which serves as a heat source. The cooling operation is an operation in which cold water is supplied to the load-side units 3 by releasing heat into a medium such as air or water, which serves as a heat source. The load-side units 3 include devices tailored to user needs, such as a heat exchanger that uses cold water or hot water to cool or heat indoor air, or a radiator that heats by circulating hot water.

[0012] FIG. 2 is a schematic diagram showing a heat source unit 2 according to the first embodiment. As shown in FIG. 2, the heat source unit 2 has a heat source-side heat exchanger 22 disposed on the side of a housing 2a, and a heat source-side blower 23 disposed in the upper part of the housing 2a. Outdoor air drawn in from the side undergoes heat exchange in the heat source-side heat exchanger 22, passes through the heat source-side blower 23, and is blown out from the upper part of the housing 2a. A representative unit 1a (see FIG. 1) is provided among the multiple heat source units 2, and the representative unit is provided with a pump 4. Headers 5 are connected to both ends of the pump 4. A header 5 is connected to both ends of a load-side unit 3 including a load-side heat exchanger 6 and a load-side valve 7. A bypass valve 8 is connected between the headers 5, and a differential pressure sensor 9 detects the differential pressure in each header 5. The air conditioning device 1 allows the user to freely set the water temperature, water flow rate, and differential pressure required, and the control unit 19 controls the heat source unit 2, pump 4, and bypass valve 8 based on the water temperature, water flow rate, and differential pressure required by the user. Note that there may be only one heat source unit 2, and there may also be only one load-side unit 3.

[0013] FIG. 3 is a circuit diagram showing an air conditioner 1 according to the first embodiment. As shown in FIG. 3, one heat source unit 2 has four modules, including four refrigerant circuits 10 and two water circuits 12. Four heat source-side fans 23 are installed on the top of the heat source unit 2. The pump 4 may be built into the heat source unit 2 (see FIG. 2) or installed externally to the heat source unit 2 (see FIG. 3). The cushion tank 15 mixes the water supplied from the heat source unit 2 with the water in the cushion tank 15 to reduce the temperature fluctuation range when the water temperature fluctuates significantly. As described below, this first embodiment can suppress a decrease in water temperature, thereby enabling the cushion tank 15 to be made smaller. This reduces costs and installation space. The air conditioner 1 can be applied to all chiller products that perform both cooling and heating operations.

[0014] As shown in FIG. 3 , the refrigerant circuit 10 includes a compressor 20, a flow switching device 21, a heat-source-side heat exchanger 22, a heat-source-side expansion section 32, an expansion section 24, and a user-side heat exchanger 25, all connected by refrigerant piping 11. The compressor 20 draws in low-temperature, low-pressure refrigerant, compresses the drawn refrigerant, and discharges it into high-temperature, high-pressure refrigerant. The compressor 20 is, for example, a capacity-controllable inverter compressor. The heat-source-side heat exchanger 22 exchanges heat between, for example, outdoor air and the refrigerant. The heat-source-side heat exchanger 22 functions as a condenser during cooling operation and as an evaporator during heating operation. The heat-source-side blower 23 sends outdoor air to the heat-source-side heat exchanger 22. The heat-source-side expansion section 32 is a pressure-reducing valve or an expansion valve that reduces the pressure of the refrigerant and expands it.

[0015] The expansion section 24 is a pressure-reducing valve or expansion valve that reduces the pressure of the refrigerant to expand it. The user-side heat exchanger 25 exchanges heat between the refrigerant flowing in the refrigerant circuit 10 and the water flowing in the water circuit 12. The user-side heat exchanger 25 functions as an evaporator during cooling operation and as a condenser during heating operation. The injection circuit 13 is located between the heat-source-side expansion section 32 and the expansion section 24 and the suction side of the compressor 20, and the refrigerant is injected via an injection adjustment valve 18. The parallel circuit 14, which is parallel to the expansion section 24, is provided with an REC 16 and a check valve 17.

[0016] The control unit 19 is configured by dedicated hardware or a CPU (also referred to as a central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, or processor) that executes a program stored in a storage device. When the control unit 19 is dedicated hardware, the control unit 19 corresponds to, for example, a single circuit, a composite circuit, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof. Each functional unit realized by the control unit 19 may be realized by separate hardware, or each functional unit may be realized by a single piece of hardware.

[0017] When the control unit 19 is a CPU, each function executed by the control unit 19 is realized by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in a storage device. The CPU realizes each function by reading and executing the programs stored in the storage device. Note that some of the functions of the control unit 19 may be realized by dedicated hardware, and some may be realized by software or firmware. The storage device may be configured as a hard disk, or as a volatile storage device such as random access memory (RAM) that can temporarily store data. The storage device may also be configured as a non-volatile storage device such as flash memory that can store data long-term.

[0018] FIG. 4 is a circuit diagram showing the flow of refrigerant during cooling operation of the air conditioning apparatus 1 according to the first embodiment. Next, the refrigerant circuit 10 will be described in detail. FIG. 4 illustrates a case where the heat source-side heat exchanger 22 includes two heat source-side heat exchangers 22, a first heat source-side heat exchanger 22a and a second heat source-side heat exchanger 22b. FIG. 4 also illustrates a case where the heat source-side expansion section 32 includes two heat source-side expansion sections 32, a first heat source-side expansion section 32a and a second heat source-side expansion section 32b. As shown in FIG. 4 , two parallel heat source-side pipes 30, a first heat source-side pipe 30a and a second heat source-side pipe 30b, are connected between the flow path switching device 21 and the expansion section 24.

[0019] The first heat source side piping 30a is provided with a first heat source side heat exchanger 22a and a first heat source side expansion section 32a, and the second heat source side piping 30b is provided with a second heat source side heat exchanger 22b and a second heat source side expansion section 32b. The refrigerant circuit 10 is provided with two heat source side solenoid valves 31 that block the flow of refrigerant. The first heat source side piping 30a is provided with a first heat source side solenoid valve 31a, and the second heat source side piping 30b is provided with a second heat source side solenoid valve 31b. It is noted that three or more heat source side heat exchangers 22, heat source side piping 30, heat source side solenoid valves 31, and heat source side expansion sections 32 may be provided.

[0020] The refrigerant circuit 10 is provided with two bypass pipes 33 connecting the discharge side of the compressor 20 to each of the heat source side pipes 30. The bypass pipes 33 include a first bypass pipe 33a connected to the first heat source side pipe 30a and a second bypass pipe 33b connected to the second heat source side pipe 30b. The refrigerant circuit 10 is provided with two bypass solenoid valves 34 that block the flow of refrigerant. The first bypass pipe 33a is provided with a first bypass solenoid valve 34a, and the second bypass pipe 33b is provided with a second bypass solenoid valve 34b. Three or more bypass pipes and bypass solenoid valves 34 may be provided.

[0021] Here, the heat source-side blower 23 sends air to the second heat source-side heat exchanger 22b and then to the first heat source-side heat exchanger 22a in this order. In this way, one heat source-side heat exchanger 22 is disposed downstream of the other heat source-side heat exchanger 22 in the air flow direction.

[0022] (Cooling Operation) Next, the flow of refrigerant during cooling operation will be described. As shown in Fig. 4, during cooling operation, the first heat source side solenoid valve 31a, the second heat source side solenoid valve 31b, the expansion section 24, the first heat source side expansion section 32a, and the second heat source side expansion section 32b are open, and the first bypass solenoid valve 34a and the second bypass solenoid valve 34b are closed.

[0023] In cooling operation, the refrigerant drawn into the compressor 20 is compressed by the compressor 20 and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the compressor 20 passes through the high-pressure side of the flow switching device 21 and flows into the heat-source-side heat exchanger 22, which functions as a condenser. In the heat-source-side heat exchanger 22, the refrigerant exchanges heat with outdoor air sent by the heat-source-side blower 23, condensing and liquefying. Specifically, the refrigerant branches into the first heat-source-side piping 30a and the second heat-source-side piping 30b and flows into the first heat-source-side heat exchanger 22a and the second heat-source-side heat exchanger 22b, respectively. In the first heat-source-side heat exchanger 22a and the second heat-source-side heat exchanger 22b, the refrigerant exchanges heat with outdoor air sent by the heat-source-side blower 23, condensing and liquefying. The condensed liquid refrigerant is decompressed in the first heat source side expansion section 32a and the second heat source side expansion section 32b, respectively, and then merges and flows into the expansion section 24. In the expansion section 24, the refrigerant is expanded and decompressed to become low-temperature, low-pressure, two-phase gas-liquid refrigerant. The two-phase gas-liquid refrigerant then flows into the user-side heat exchanger 25, which functions as an evaporator, where it exchanges heat with water flowing in the water circuit 12 and evaporates and gasifies. At this time, the water flowing in the water circuit 12 is cooled, and chilled water is supplied. The evaporated low-temperature, low-pressure gas refrigerant passes through the low-pressure side of the flow path switching device 21 and is drawn into the compressor 20.

[0024] Because the second heat source-side heat exchanger 22b is located upwind of the first heat source-side heat exchanger 22a, air warmed by the second heat source-side heat exchanger 22b flows through the first heat source-side heat exchanger 22a. Generally, during cooling operation in which the user-side heat exchanger 25 functions as an evaporator, the refrigerant and water flow in parallel, forming a parallel flow. Because the refrigerant is in a two-phase state within the evaporator, its temperature remains nearly constant. Therefore, there is no difference in performance between parallel flow and counterflow.

[0025] (Heating operation) Figure 5 is a circuit diagram showing the flow of refrigerant during heating operation of the air conditioning apparatus 1 according to Embodiment 1. Next, the flow of refrigerant during heating operation will be described. As shown in Figure 5, during heating operation, the first heat source side solenoid valve 31a, the second heat source side solenoid valve 31b, the expansion section 24, the first heat source side expansion section 32a, and the second heat source side expansion section 32b are open, and the first bypass solenoid valve 34a and the second bypass solenoid valve 34b are closed.

[0026] During heating operation, the refrigerant drawn into the compressor 20 is compressed by the compressor 20 and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the compressor 20 passes through the high-pressure side of the flow path switching device 21 and flows into the user-side heat exchanger 25, which functions as a condenser. In the user-side heat exchanger 25, the refrigerant exchanges heat with water flowing in the water circuit 12 and condenses to become a liquid. At this time, the water flowing in the water circuit 12 is heated, and hot water is supplied. The condensed liquid refrigerant flows into the expansion section 24, where it is decompressed and branches into the first heat-source-side piping 30a and the second heat-source-side piping 30b. The refrigerant flows into the first heat-source-side expansion section 32a and the second heat-source-side expansion section 32b, respectively, where it expands and decompresses to become a low-temperature, low-pressure, two-phase gas-liquid refrigerant. The refrigerant in the gas-liquid two-phase state then flows into the first heat source side heat exchanger 22 a and the second heat source side heat exchanger 22 b, respectively. Thereafter, the refrigerant is evaporated and gasified through heat exchange with the outdoor air sent by the heat source side blower 23 in the first heat source side heat exchanger 22 a and the second heat source side heat exchanger 22 b. The evaporated and gasified refrigerant then merges with the outside air, passes through the low-pressure side of the flow path switching device 21, and is drawn into the compressor 20.

[0027] During heating operation, the air is cooled by the refrigerant in the heat source-side heat exchanger 22. When the air temperature drops below the dew point, condensation forms on the heat transfer surfaces of the heat transfer tubes and fins of the heat source-side heat exchanger 22. At this time, if the heat transfer surface is below 0°C, frost forms on the heat transfer surface. The air temperature is higher on the windward side, resulting in a larger temperature difference between the air and the refrigerant, which tends to increase the heat exchange rate. Therefore, the amount of frost tends to be greater in the second heat source-side heat exchanger 22b on the windward side. The control unit 19 adjusts the opening ratio between the first heat source-side expansion section 32a and the second heat source-side expansion section 32b, thereby changing the refrigerant flow rate. Since frost is less likely to form in the heat source-side heat exchanger 22 with a lower refrigerant flow rate, the ratio of the amount of frost formation can be adjusted.

[0028] As heating operation continues, frost grows and obstructs airflow, reducing the heat transfer performance of the heat source-side heat exchanger 22. To maintain the heat exchange rate with reduced heat transfer performance, it is necessary to increase the temperature difference between the refrigerant and the air. If the first heat source-side expansion section 32a and the second heat source-side expansion section 32b are throttled to increase the temperature difference between the refrigerant and the air, the evaporator pressure decreases. The reduced evaporator pressure reduces the pressure on the suction side of the compressor 20, reducing the refrigerant suction density. Because the refrigerant circulation volume is proportional to the suction density and the compressor 20 rotation speed, the compressor 20 rotation speed is controlled to increase in order to maintain heating capacity. When the upper limit of the compressor 20 rotation speed due to mechanical limitations is reached, heating capacity decreases. Therefore, although it depends on the frost growth rate and the compressor 20 rotation speed, there is a limit to the operation duration when the heat transfer surface of the heat source-side heat exchanger 22 is below 0°C. Therefore, after a certain period of operation, it becomes necessary to melt the frost. For example, frosting almost always occurs when the outside air temperature is below 0°C, and frosting can occur even when the outside air temperature is between 0°C and 7°C.

[0029] (Defrosting Operation) The control unit 19 switches from heating operation to defrosting operation using thresholds such as the outside air temperature, the refrigerant temperature, the suction pressure, and the duration of the heating operation. In defrosting operation, high-temperature refrigerant is circulated through the heat-source-side heat exchanger 22 to melt frost. In the first embodiment, the heat-source-side heat exchangers 22 are alternately defrosted. While one heat-source-side heat exchanger 22 is being defrosted, the other heat-source-side heat exchanger 22 functions as an evaporator, and thus a defrosting operation is performed quickly and without a decrease in water temperature using heat recovered from the air. The control unit 19 controls the multiple heat-source-side solenoid valves 31, the multiple bypass solenoid valves 34, the multiple heat-source-side expansion sections 32, and the expansion section 24 so that the refrigerant flows as follows. As a result, the refrigerant discharged from the compressor 20 flows through one heat-source-side heat exchanger 22, passes through the multiple heat-source-side expansion sections 32, flows through the other heat-source-side heat exchanger 22, and is drawn into the compressor 20.

[0030] (First defrosting operation) Fig. 6 is a circuit diagram showing the flow of refrigerant during the first defrosting operation of the air conditioning apparatus 1 according to Embodiment 1. Next, the flow of refrigerant during the first defrosting operation will be described. As shown in Fig. 6, during the first defrosting operation, the second heat source side solenoid valve 31b, the first bypass solenoid valve 34a, the first heat source side expansion section 32a, and the second heat source side expansion section 32b are open, and the first heat source side solenoid valve 31a, the second bypass solenoid valve 34b, and the expansion section 24 are closed. During the first defrosting operation, the first heat source side heat exchanger 22a is defrosted.

[0031] In the first defrosting operation, the refrigerant drawn into the compressor 20 is compressed by the compressor 20 and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the compressor 20 passes through the first bypass solenoid valve 34a and flows into the first heat-source-side heat exchanger 22a, which functions as a condenser. In the first heat-source-side heat exchanger 22a, the refrigerant exchanges heat with outdoor air sent by the heat-source-side blower 23, condensing and liquefying. At this time, the high-temperature refrigerant flows into the first heat-source-side heat exchanger 22a, thereby defrosting the first heat-source-side heat exchanger 22a. The condensed liquid refrigerant expands and decompresses in the first heat-source-side expansion section 32a and the second heat-source-side expansion section 32b, becoming low-temperature, low-pressure, two-phase gas-liquid refrigerant. The refrigerant in the gas-liquid two-phase state then flows into the second heat source-side heat exchanger 22b, which functions as an evaporator, where it evaporates and gasifies through heat exchange with the outdoor air sent by the heat source-side blower 23. The evaporated refrigerant in a low-temperature, low-pressure gas state passes through the second heat source-side solenoid valve 31b and the low-pressure side of the flow path switching device 21, and is drawn into the compressor 20.

[0032] In the first defrosting operation, the switching direction of the flow path switching device 21 is the same as the switching direction in the heating operation. To suppress noise generated when the refrigerant in a gas-liquid two-phase state passes through, the refrigerant is preferably decompressed by the second heat-source-side expansion section 32b downstream of the first heat-source-side expansion section 32a. The second heat-source-side expansion section 32b may be controlled using a target value for the superheat of the refrigerant on the suction side of the compressor 20 to prevent liquid refrigerant from returning to the compressor 20, or an appropriate opening degree may be determined in advance through testing and fixed.

[0033] In the first defrosting operation, the second heat source-side heat exchanger 22b acts as an evaporator, and therefore, unlike the reverse defrosting method, the heat source-side blower 23 does not stop. However, to avoid heat radiation loss in the section where defrosting has been completed, it is preferable to operate the heat source-side blower 23 at a low airflow rate. Because air cooled in the second heat source-side heat exchanger 22b flows to the first heat source-side heat exchanger 22a, heat radiation loss is more likely to occur than in the second defrosting operation described below. In the first defrosting operation, there is a possibility that frost adhering to the second heat source-side heat exchanger 22b will grow, albeit slightly.

[0034] (Second defrosting operation) Fig. 7 is a circuit diagram showing the flow of refrigerant during the second defrosting operation of the air conditioning apparatus 1 according to Embodiment 1. Next, the flow of refrigerant during the second defrosting operation will be described. As shown in Fig. 7, during the first defrosting operation, the first heat source side solenoid valve 31a, the second bypass solenoid valve 34b, the first heat source side expansion section 32a, and the second heat source side expansion section 32b are open, and the second heat source side solenoid valve 31b, the first bypass solenoid valve 34a, and the expansion section 24 are closed. During the second defrosting operation, the second heat source side heat exchanger 22b is defrosted.

[0035] In the second defrosting operation, the refrigerant drawn into the compressor 20 is compressed by the compressor 20 and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the compressor 20 passes through the second bypass solenoid valve 34b and flows into the second heat-source-side heat exchanger 22b, which functions as a condenser. In the second heat-source-side heat exchanger 22b, the refrigerant exchanges heat with outdoor air sent by the heat-source-side blower 23, condensing and liquefying. At this time, the high-temperature refrigerant flows into the second heat-source-side heat exchanger 22b, thereby defrosting the second heat-source-side heat exchanger 22b. The condensed liquid refrigerant expands and decompresses in the second heat-source-side expansion section 32b and the first heat-source-side expansion section 32a, becoming low-temperature, low-pressure, two-phase gas-liquid refrigerant. The refrigerant in the gas-liquid two-phase state then flows into the first heat source-side heat exchanger 22a, which functions as an evaporator, where it evaporates and gasifies through heat exchange with the outdoor air sent by the heat source-side blower 23. The evaporated refrigerant in a low-temperature, low-pressure gas state passes through the first heat source-side solenoid valve 31a and the low-pressure side of the flow path switching device 21, and is drawn into the compressor 20.

[0036] In the second defrosting operation, the switching direction of the flow path switching device 21 is the same as the switching direction in the heating operation. To suppress noise generated when the refrigerant in a gas-liquid two-phase state passes through, the refrigerant is preferably decompressed by the first heat-source-side expansion section 32a downstream of the second heat-source-side expansion section 32b. The first heat-source-side expansion section 32a may be controlled using a target value for the degree of superheat of the refrigerant on the suction side of the compressor 20 to prevent liquid refrigerant from returning to the compressor 20, or an appropriate opening degree may be determined in advance through testing and fixed.

[0037] In the second defrosting operation, the first heat source-side heat exchanger 22a functions as an evaporator, so unlike the reverse defrosting method, the heat source-side blower 23 does not stop. Air warmed in the second heat source-side heat exchanger 22b flows to the first heat source-side heat exchanger 22a, making frost formation less likely. However, if melted frost remains on the surface of the first heat source-side heat exchanger 22a, the melted frost may refreeze. Therefore, it is preferable to continue the first defrosting operation for a certain period of time after the frost has melted, before switching to the second defrosting operation. By continuing the first defrosting operation for a certain period of time, water droplets remaining after the frost has melted easily flow down and are easily drained, and are also easily heated by the refrigerant and evaporated.

[0038] Note that a reverse defrost operation may be performed instead of the second defrost operation. In the reverse frost operation, the heat source side heat exchanger 22 does not become cold, so the possibility of frost formation and refreezing is low. However, even in this case, it is preferable to continue the reverse defrost operation for a certain period of time so that water droplets after melting frost can easily flow down and be drained, and can also be easily heated by the refrigerant and evaporated. This may cause some concern about a drop in water temperature.

[0039] According to the first embodiment, it is possible to operate the system such that one heat source-side heat exchanger 22 functions as a condenser and the other heat source-side heat exchanger 22 functions as an evaporator. This allows the heat source-side heat exchangers 22 to be defrosted alternately, while preventing refrigerant from flowing to the user-side heat exchangers 25. This allows thermal energy removed from the air, etc., to be used for defrosting, and also prevents a temperature drop on the user side. This allows the defrosting operation to be performed without impairing user comfort.

[0040] Conventionally, there is known an air conditioner 1 that uses a reverse defrosting operation, in which the flow direction is switched to the same as that of the cooling operation after heating operation. Because this system recovers heat and defrosts the refrigerant itself, defrosting is completed in a short time, but there is a risk of the temperature of the water supplied to the user-side units dropping. In reverse defrosting operation, the heat source-side blower 23 is stopped to avoid heat loss in the section where the frost on the heat source-side heat exchanger 22 has melted.

[0041] In contrast, in the present embodiment 1, the heat source side heat exchangers 22 are alternately defrosted. While one heat source side heat exchanger 22 is being defrosted, the other heat source side heat exchanger 22 acts as an evaporator, and therefore, a defrosting operation can be performed quickly and without a decrease in water temperature using heat recovered from the air.

[0042] Embodiment 2. Fig. 8 is a circuit diagram showing the flow of refrigerant during a first defrosting operation of an air conditioning apparatus 1 according to embodiment 2, and Fig. 9 is a circuit diagram showing the flow of refrigerant during a second defrosting operation of an air conditioning apparatus 1 according to embodiment 2. Embodiment 2 differs from embodiment 1 in that the heat source side blower 23 has a function of switching the blowing direction to the reverse direction. In embodiment 2, parts common to embodiment 1 are assigned the same reference numerals and description thereof will be omitted, and the description will focus on the differences from embodiment 1.

[0043] As shown in FIG. 8 , in the first defrosting operation, air flows in the opposite direction to that of the first embodiment, so that the first heat source-side heat exchanger 22a is located upstream of the second heat source-side heat exchanger 22b. As a result, air heated in the first heat source-side heat exchanger 22a flows to the second heat source-side heat exchanger 22b. Thus, the frost adhering to the second heat source-side heat exchanger 22b is melted by the heated outdoor air. In the frosted section of the first heat source-side heat exchanger 22a, the heat of the refrigerant is transferred to the frost, so the outdoor air is not heated, and warm air is generated in the defrosted section. Therefore, immediately after defrosting begins, the outdoor air directly hits the second heat source-side heat exchanger 22b, and as defrosting progresses, the warm air begins to hit the second heat source-side heat exchanger 22b. Note that FIG. 9 is similar to FIG. 6 of the first embodiment.

[0044] Embodiment 3. Figure 10 is a circuit diagram showing the flow of refrigerant during the first defrosting operation of an air conditioning apparatus 1 according to embodiment 3. Embodiment 3 differs from embodiments 1 and 2 in that a plurality of heat source units 2 are arranged close together. In embodiment 3, parts that are common to embodiments 1 and 2 are given the same reference numerals and description thereof is omitted, and the description will focus on the differences from embodiments 1 and 2.

[0045] As shown in FIG. 10 , multiple heat source units 2 are arranged closely together. It is assumed that multiple modular heat pump chillers are arranged adjacent to each other. If all heat source units 2 simultaneously perform defrosting operation, hot water cannot be supplied. Therefore, some heat source units 2 often perform defrosting operation while other heat source units 2 continue heating operation. In this state, if the heat-source-side blower 23 rotates in reverse, the air blown out from the heat source unit 2 in heating operation is sucked in by the heat source unit 2 in defrosting operation. The air blown out from the heat source unit 2 in heating operation has already been cooled by the heat-source-side heat exchanger 22, and the absolute humidity has decreased due to condensation or frost formation. This makes it possible to prevent frost from forming on the heat source unit 2 in defrosting operation.

[0046] 1 Air conditioning apparatus, 1a Representative unit, 2 Heat source unit, 2a Housing, 3 Load side unit, 4 Pump, 5 Header, 6 Load side heat exchanger, 7 Load side valve, 8 Bypass valve, 9 Differential pressure sensor, 10 Refrigerant circuit, 11 Refrigerant piping, 12 Water circuit, 13 Injection circuit, 14 Parallel circuit, 15 Cushion tank, 16 REC, 17 Check valve, 18 Injection adjustment valve, 19 Control unit, 20 Compressor, 21 Flow path switching device, 22 Heat source side heat exchanger, 22a First heat source side heat exchanger, 22b Second heat source side heat exchanger, 23 Heat source side blower, 24 Expansion section, 25 Use side heat exchanger, 30 Heat source side piping, 30a First heat source side piping, 30b Second heat source side piping, 31 Heat source side solenoid valve, 31a First heat source side solenoid valve, 31b Second heat source side solenoid valve, 32 Heat source side expansion section, 32a First heat source side expansion section, 32b Second heat source side expansion section, 33 Bypass piping, 33a First bypass piping, 33b Second bypass piping, 34 Bypass solenoid valve, 34a First bypass solenoid valve, 34b Second bypass solenoid valve.

Claims

1. An air conditioning apparatus comprising: a refrigerant circuit in which a refrigerant flows, in which a compressor, a flow switching device, a plurality of heat source side heat exchangers arranged in parallel, an expansion section, and a user side heat exchanger are connected by refrigerant piping; a plurality of heat source side pipes in which a plurality of the heat source side heat exchangers are respectively provided; a heat source side solenoid valve provided in each of the plurality of heat source side pipes; a plurality of heat source side expansion sections provided in each of the plurality of heat source side pipes; a plurality of bypass pipes connecting the discharge side of the compressor to each of the heat source side pipes; and a plurality of bypass solenoid valves provided in each of the plurality of bypass pipes.

2. An air conditioning apparatus as described in claim 1, further comprising a control unit that controls operation, wherein the control unit controls the plurality of heat source side solenoid valves, the plurality of bypass solenoid valves, the plurality of heat source side expansion units and the expansion units so that refrigerant discharged from the compressor flows to one of the heat source side heat exchangers, passes through the plurality of heat source side expansion units, then flows to the other heat source side heat exchanger and is sucked into the compressor.

3. The air conditioning apparatus according to claim 2, wherein one of the heat source side heat exchangers is disposed downstream of the other heat source side heat exchanger in the air flow direction.

4. An air conditioning apparatus according to claim 3, further comprising a heat source side blower that sends air to the plurality of heat source side heat exchangers, the heat source side blower having a function of switching the blowing direction to the reverse direction.

5. An air conditioning apparatus according to any one of claims 1 to 4, wherein a plurality of heat source units each having a plurality of heat source-side heat exchangers are arranged.

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