Refrigeration Cycle Apparatus

The present application claims priority to Japanese patent application 2023-023078, filed Feb. 17, 2023, and PCT/JP2024/000755, filed Jan. 15, 2024, the entire contents of each of which being incorporated herein by reference.

The present disclosure relates to a refrigeration cycle apparatus.

A refrigeration cycle apparatus using carbon dioxide as a refrigerant has been considered. Patent Literature 1 (JP 2008-045769 A) discloses a method of heating a refrigerant to be filled by using a heater in order to prevent the refrigerant flowing into a refrigerant circuit due to a rapid pressure decrease at the time of filling a refrigeration cycle apparatus from entering a solid state (dry ice state).

A refrigeration cycle apparatus according to a first aspect includes a refrigerant circuit, a heat source, a utilizer, a detector, and a processor. The refrigerant circuit includes a compressor, and a carbon dioxide refrigerant flows through the refrigerant circuit. The heat source accommodates the compressor. The utilizer is connected to the heat source via a connecting pipe. The detector detects a pressure of the refrigerant in a low pressure flow path of the refrigerant circuit. The processor is configured to execute a refrigerant filling operation of moving the refrigerant from a refrigerant storage container to the refrigerant circuit. In the refrigerant filling operation, the processor is configured to control the number of rotations of the compressor on the basis of a detection value of the detector.

is a schematic configuration diagram of an air conditioneraccording to a first embodiment. The air conditionerperforms a vapor compression refrigeration cycle operation and executes an air conditioning operation (a cooling operation and a heating operation) in an air conditioning target space such as an indoor space. The air conditionerincludes one heat source unit or heat source, one or more utilization units or utilizers, a control unit or processor, and a first connecting pipeand a second connecting pipethat connect the heat source unitand the utilization units. The heat source unit, the utilization unit, and the connecting pipesandconnected to each other constitute a refrigerant circuit. A refrigerant filled in the refrigerant circuitis carbon dioxide. Hereinafter, the first connecting pipeand the second connecting pipeare also collectively referred to as connecting pipesand. The air conditioneris an example of a refrigeration cycle apparatus.

Although details will be described later, in the air conditioner, an inside of a heat source refrigerant flow path(described later) of the heat source unitis not filled with a sufficient amount of refrigerant to execute an air conditioning operation at a time of shipment from a manufacturing factory. The air conditionerperforms a refrigerant filling operation of filling the refrigerant circuitwith the refrigerant filled in a first refrigerant storage containerin an installation work of installation at a predetermined installation site.

The utilization unitis installed in the air conditioning target space. The utilization unitincludes a utilization refrigerant flow pathconstituting a part of the refrigerant circuit. The utilization refrigerant flow pathincludes a utilization heat exchanger.

The utilization heat exchangerexchanges heat between the refrigerant flowing inside and air in the air conditioning target space. One end of the utilization heat exchangeris connected to the first connecting pipe. The other end of the utilization heat exchangeris connected to the second connecting pipe.

The heat source unitis installed outside the air conditioning target space (outdoor space or the like). The heat source unitincludes a heat source refrigerant flow pathconstituting a part of the refrigerant circuit. The heat source refrigerant flow pathincludes a compressor, a flow path switching mechanism, a heat source heat exchanger, a heat source expansion mechanism, a first shutoff valve, a second shutoff valve, and a detector. The compressor, the flow path switching mechanism, the heat source heat exchanger, the heat source expansion mechanism, the first shutoff valve, and the second shutoff valveare connected to each other via a refrigerant pipe

The compressorsucks a low-pressure refrigerant in a refrigeration cycle from a suction pipe, compresses the refrigerant by a compression mechanism, and discharges the compressed refrigerant as a high-pressure refrigerant to a discharge pipe. The compressoris a positive displacement compressor. The compressoris driven by a motor whose number of rotations is controlled via an inverter. In the present embodiment, the heat source unitincludes only one compressor, or the number of compressorsmay be plural. The control unitcontrols start, stop, and the number of rotations of the motor included in the compressor.

The flow path switching mechanismswitches a flow direction of the refrigerant and changes a state of the refrigerant circuitbetween a first state and a second state. When the refrigerant circuitis in the first state, the heat source heat exchangerfunctions as a radiator for the refrigerant, and the utilization heat exchangerfunctions as an evaporator for the refrigerant. When the refrigerant circuitis in the second state, the heat source heat exchangerfunctions as an evaporator for the refrigerant, and the utilization heat exchangerfunctions as a radiator for the refrigerant. The state of the flow path switching mechanismis changed by the control unit.

In the present embodiment, the flow path switching mechanismis a four-way switching valve having four ports P, P, P, and P. The port Pis connected to one end of the heat source heat exchanger. The port Pis connected to the discharge pipeof the compressor. The port Pis connected to the suction pipeof the compressor. The port Pis connected to the second shutoff valve. In the first state, the port Pcommunicates with the port P, and the port Pcommunicates with the port P. In the second state, the port Pcommunicates with the port P, and the port Pcommunicates with the port P.

The flow path switching mechanismis not required to be a four-way switching valve. For example, the flow path switching mechanismmay be configured by combining a plurality of electromagnetic valves and refrigerant pipes so that the flow direction of the refrigerant can be switched as described above.

The heat source heat exchangercauses heat exchange between a refrigerant flowing inside and air at an installation site of the heat source unit(heat source air). One end of the heat source heat exchangeris connected to the port Pof the flow path switching mechanism. The other end of the heat source heat exchangeris connected to the heat source expansion mechanism.

The heat source expansion mechanismadjusts a flow rate of the refrigerant flowing through the heat source refrigerant flow pathand decompresses the refrigerant by controlling an opening degree. One end of the heat source expansion mechanismis connected to the heat source heat exchanger. The other end of the heat source expansion mechanismis connected to the first shutoff valve. The opening degree of the heat source expansion mechanismis controlled by the control unit. The heat source expansion mechanismis an example of an expansion mechanism.

The first shutoff valveis a valve provided at a connecting portion between the heat source unit(heat source refrigerant flow path) and the first connecting pipe. When the first shutoff valveis closed, a flow of the refrigerant between the heat source refrigerant flow pathand the first connecting pipeis restricted. The first shutoff valveis, for example, a manually operated valve.

The second shutoff valveis a valve provided at a connecting portion between the heat source unit(heat source refrigerant flow path) and the second connecting pipe. When the second shutoff valveis closed, a flow of the refrigerant between the heat source refrigerant flow pathand the second connecting pipeis restricted. The second shutoff valveis, for example, a manually operated valve. In the present embodiment, the second shutoff valveis a three-way valve provided with a service port communicable with the outside of the refrigerant circuit. The service port of the second shutoff valvefunctions as a filling port that detachably connects the first refrigerant storage containerin the refrigerant filling operation.

The first shutoff valveand the second shutoff valveare closed at a time of shipment at a manufacturing factory, and are opened at the time of installation work of the air conditioner. After completion of the installation work, the first shutoff valveand the second shutoff valveare normally maintained in an open state.

The detectordetects a pressure of the refrigerant in a low pressure flow path. The detectoris a pressure sensor. The low pressure flow pathis a flow path included in the refrigerant circuitthrough which the low-pressure refrigerant in the refrigeration cycle flows. Specifically, the low pressure flow pathis a flow path that connects the suction pipeof the compressorand the second shutoff valvethat is a connecting point between the heat source unitand the second connecting pipe. In the present embodiment, the detectordetects the pressure of the refrigerant in the refrigerant pipeconnecting the suction pipeof the compressorand the flow path switching mechanism. The detectormay detect the pressure of the refrigerant in another refrigerant pipe(the refrigerant pipeconnecting the port Pand the second shutoff valve, or the refrigerant pipeconnecting the port Pand the suction pipeof the compressor) included in the low pressure flow path. The detectoroutputs the detected pressure of the refrigerant to the control unit.

The control unitcontrols operation of electrically connected components constituting the heat source unit. The control unitcontrols the components of the heat source unitto achieve the cooling operation, the heating operation, and the refrigerant filling operation described later.is a block diagram of the control unit. The control unitis electrically connected to the compressor, the flow path switching mechanism, the heat source expansion mechanism, and the detectorso as to be able to exchange control signals and information.

The control unit, e.g., processor,is implemented by a computer. The control unitincludes a control calculator and a storage. A processor such as a CPU or a GPU can be used for the control calculator. The control calculator reads a program stored in the storage and performs predetermined calculation processing in accordance with the program. Furthermore, the control calculator can write a calculation result to the storage and read information stored in the storage in accordance with the program. The configuration of the control unitdescribed here is merely an example, and the function of the control unitmay be implemented by software, hardware, or a combination of software and hardware.

The connecting pipesandare connection pipes connecting the heat source refrigerant flow pathand the utilization refrigerant flow path(in other words, the heat source unitand the utilization unit). The heat source refrigerant flow path, the utilization refrigerant flow path, the first connecting pipe, and the second connecting pipeare connected to constitute the refrigerant circuit.

The first refrigerant storage containeris a container (cylinder) filled with a refrigerant to be filled in the refrigerant circuitin the refrigerant filling operation.is a schematic configuration diagram of the air conditionerto which the first refrigerant storage containeris connected.

The first refrigerant storage containerincludes a storage portionand a third shutoff valve. The first refrigerant storage containeris connected to the second shutoff valvevia a pipe. The storage portionstores the refrigerant. The third shutoff valveis a valve to which one end of the pipeis connected. When the third shutoff valveis closed, the flow of the refrigerant between the storage portionand the pipeis restricted. The third shutoff valveis, for example, a manually operated valve.

Next, a description will be given of operations of components of the air conditioner.

In the cooling operation, the control unitcontrols the flow path switching mechanismto the first state. In addition, the control unitcontrols the opening degree of the heat source expansion mechanismin accordance with a load.

In this state, when the control unitactivates the compressor, the low-pressure refrigerant in the refrigeration cycle is sucked from the suction pipeof the compressor, compressed, and discharged from the discharge pipeas a high-pressure refrigerant. The high-pressure refrigerant discharged from the compressoris sent to the heat source heat exchangervia the flow path switching mechanism, exchanges heat with the heat source air, and is cooled. In other words, the heat source heat exchangerfunctions as a radiator. The high-pressure refrigerant cooled in the heat source heat exchangeris decompressed when passing through the heat source expansion mechanismto become a low-pressure refrigerant in a gas-liquid two-phase state. The low-pressure refrigerant in the gas-liquid two-phase state is sent to the utilization unitvia the first shutoff valveand the first connecting pipe. The refrigerant sent to the utilization unitexchanges heat with air in the air conditioning target space to be heated, and evaporates to become a low-pressure refrigerant. In other words, the utilization heat exchangerfunctions as an evaporator. The low-pressure refrigerant heated in the utilization heat exchangeris sent to the heat source unitvia the second connecting pipe, and again sucked into the compressorvia the second shutoff valveand the flow path switching mechanism.

In the heating operation, the control unitcontrols the flow path switching mechanismto the second state. In addition, the control unitcontrols the opening degree of the heat source expansion mechanismin accordance with a load.

In this state, when the control unitactivates the compressor, the low-pressure refrigerant in the refrigeration cycle is sucked from the suction pipeof the compressor, compressed, and discharged from the discharge pipeas a high-pressure refrigerant. The high-pressure refrigerant discharged from the compressoris sent to the utilization unitvia the flow path switching mechanism, the second shutoff valve, and the second connecting pipe. The high-pressure refrigerant sent to the utilization unitexchanges heat with air in the air conditioning target space in the utilization heat exchangerto be cooled. In other words, the utilization heat exchangerfunctions as a radiator. The high-pressure refrigerant cooled in the utilization heat exchangeris sent to the heat source unitvia the first connecting pipe. The refrigerant sent to the heat source unitis decompressed when passing through the first shutoff valveand the heat source expansion mechanismto become a low-pressure refrigerant in a gas-liquid two-phase state. The low-pressure refrigerant in the gas-liquid two-phase state flows into the heat source heat exchanger. The low-pressure refrigerant in the gas-liquid two-phase state that has flowed into the heat source heat exchangerexchanges heat with the heat source air and is heated to evaporate and become a low-pressure refrigerant. In other words, the heat source heat exchangerfunctions as an evaporator. The low-pressure refrigerant heated by the heat source heat exchangeris again sucked into the compressorvia the flow path switching mechanism.

The refrigerant filling operation is an operation of moving (filling) the refrigerant from the first refrigerant storage containerto the entire refrigerant circuit. The refrigerant filling operation is typically an operation executed by the air conditionerin the refrigerant filling operation performed after the installation work in which the air conditioneris installed at a predetermined installation site. The installation work includes a step of installing each of the heat source unitand the utilization unitat an installation site and a step of connecting the heat source unitand the utilization unitvia the connecting pipesandto form the refrigerant circuit.is a flowchart of processing in the refrigerant filling operation.

In the refrigerant filling operation, the control unitcontrols the number of rotations of the compressoron the basis of a detection value of the detector. Hereinafter, the refrigerant filling operation will be described in detail.

In the filling operation, an operator or the like performing the installation work connects the first refrigerant storage containervia the pipeto the refrigerant circuitof the air conditioner, which is installed at a predetermined installation site and in which the first shutoff valveand the second shutoff valveare opened, as a preparation before starting the refrigerant filling operation. Specifically, the pipeconnected to the first refrigerant storage containeris connected to the service port of the second shutoff valvefunctioning as a filling port. Thereafter, when the third shutoff valveis opened, the refrigerant filled in the first refrigerant storage containerflows into the refrigerant circuitvia the service port of the second shutoff valve. Thereafter, the refrigerant filling operation is started when the operator or the like instructs the control unit(start).

In step S, the control unitactivates the compressor, sets the flow path switching mechanismto the first state or the second state, and proceeds to step S.

In step S, the control unitacquires the detection value of the detector, and proceeds to step S.

In step S, the control unitcontrols the number of rotations of the compressoron the basis of the detection value of the detectorso that the refrigerant flowing into refrigerant circuitdoes not enter a solid state (dry ice state). Specifically, the control unitcontrols the number of rotations of the compressorso that the detection value (in other words, the pressure of the refrigerant in the low pressure flow path) of the detectordoes not become equal to or less than 0.52 MPa, which is a pressure at a triple point of carbon dioxide. For example, when the detection value of the detectorchanges from a value larger than a first threshold value, which is a pressure higher than 0.52 MPa by a predetermined value, to a value equal to or less than the first threshold value, the number of rotations of the compressoris only required to be made smaller than the number of rotations before the detection value of the detectorbecomes equal to or less than the first threshold value. Thereafter, the control unitproceeds to step S. The flow of the refrigerant sucked from the suction pipeof the compressoris similar to that in the cooling operation or the heating operation described above, and will not be described. When the detection value of the detectorbecomes equal to or less than the first threshold value and the number of rotations of the compressoris decreased, and then the detection value of the detectorbecomes equal to or more than a second threshold value higher than the first threshold value, the number of rotations of the compressormay be increased again in order to secure a pressure difference between the first refrigerant storage containerand the refrigerant circuit.

In step S, the control unitdetermines whether the refrigerant circuithas been filled with a sufficient amount of refrigerant for executing the air conditioning operation. If the refrigerant circuit has been filled with a sufficient amount of refrigerant (Yes), the control unitproceeds to step S. If the refrigerant circuit has not been filled with a sufficient amount of refrigerant (No), the control unitproceeds to step S. Specifically, the determination as to whether a sufficient amount of refrigerant for executing the air conditioning operation has been filled is made on the basis of whether the pressure of the refrigerant in the radiator and the temperature of the refrigerant at an outlet of the radiator have reached predetermined thresholds values.

The operator or the like may determine whether the refrigerant circuitis filled with a sufficient amount of refrigerant for executing the air conditioning operation. For example, when the weight of the first refrigerant storage containeris less than a predetermined value, the operator or the like determines that a sufficient amount of refrigerant has been filled, and can instruct the control unitto that effect.

In step S, the control unitstops the compressorand ends the refrigerant filling operation (end).

When the refrigerant filling operation is finished, the first refrigerant storage containerand the pipeare removed from the air conditioner. Accordingly, the filling operation ends.

(4-1)

The air conditionerincludes the refrigerant circuit, the heat source unit, the utilization unit, the detector, and the control unit.

The refrigerant circuitincludes the compressor, and a carbon dioxide refrigerant flows through the refrigerant circuit. The heat source unitaccommodates the compressor. The utilization unitis connected to the heat source unitvia the second connecting pipe. The detectordetects the pressure of the refrigerant in the low pressure flow pathof the refrigerant circuit. The control unitexecutes the refrigerant filling operation of moving the refrigerant from the first refrigerant storage containerto the refrigerant circuit. In the refrigerant filling operation, the control unitcontrols the number of rotations of the compressoron the basis of a detection value of the detector.

In the filling operation of filling the refrigerant circuit with the refrigerant from the refrigerant storage container, there is a case where the compressor is activated during the filling operation to suck the refrigerant into the refrigerant circuit in order to avoid a situation where the refrigerant cannot be filled or the filling takes time due to an insufficient pressure difference between the refrigerant storage container and the refrigerant circuit. On the other hand, in a case where the carbon dioxide refrigerant has a specific enthalpy of less than 430 kJ/kg, the carbon dioxide refrigerant is in the solid state (dry ice state) when the pressure decreases to a triple point pressure (about 0.52 MPa) of carbon dioxide or less. Therefore, when the compressor is activated in the filling operation of the carbon dioxide refrigerant, there is a possibility that the pressure of the low pressure flow pathdecreases to the triple point pressure of carbon dioxide or less, and the carbon dioxide refrigerant enters the solid state. A description will be given by using a simplified diagram illustrating a state of pressure-enthalpy of carbon dioxide illustrated in.

For example, a refrigerant filled in a cylinder or the like and having a temperature of 30° C. and a pressure of 12 MPa (see point Qin) changes its phase to the solid state at point Qwhere the temperature and the pressure are lower than those of the carbon dioxide triple point (triple point temperature: −56.56° C., triple point pressure: 0.52 MPa) when the pressure of the low pressure flow pathbecomes lower than the carbon dioxide triple point due to activation of the compressor. There is a possibility that the refrigerant thus having entered the solid state flows through the refrigerant circuit, and damages components constituting the refrigerant circuit.

In the air conditioner, in the refrigerant filling operation, the control unitcontrols the number of rotations of the compressorso that the detection value (in other words, the pressure of the refrigerant in the low pressure flow path) of the detectordoes not become equal to or less than 0.52 MPa, which is the triple point pressure of carbon dioxide. Therefore, the pressure of the refrigerant filled from the first refrigerant storage containerinto the refrigerant circuitis prevented from becoming lower than the triple point pressure of carbon dioxide, and the refrigerant is prevented from entering the solid state in the refrigerant circuit.

As described above, the air conditionercan easily suppress solidification of the filled carbon dioxide refrigerant by a simple method of controlling the number of rotations of the compressorin the filling operation of filling the refrigerant while activating the compressor.

(4-2)

The low pressure flow pathis a flow path that connects the suction pipeof the compressorand the second shutoff valvethat is a connecting point between the heat source unitand the second connecting pipe.

(4-3)

The refrigerant circuitincludes the second shutoff valvefunctioning as a filling port that detachably connects the first refrigerant storage container.