Cascade Refrigeration Cycle Apparatus

The present application is a continuation of International Application No. PCT/JP2024/000492, filed Jan. 11, 2024, which claims priority to Japanese Patent Application No. 2023-013948, filed Feb. 1, 2023, the entire contents of each are incorporated herein by reference.

The present disclosure relates to a cascade refrigeration cycle apparatus.

From the viewpoint of environmental conservation, a technique using carbon dioxide (CO) having a small global warming potential as a refrigerant has attracted attention.

In a case where COis used as a refrigerant in a refrigeration cycle apparatus and heat is exchanged between heat source air and COin a radiator, due to characteristics of CO, when a temperature of the heat source air is high, the refrigerant does not change in phase in the radiator, an enthalpy difference due to the heat exchange decreases, and efficiency deteriorates.

Therefore, for example, as in Patent Literature 1 (WO 2014/181399 A), there is known a cascade refrigeration cycle apparatus in which a cycle using COas a refrigerant and a supercooling cycle for exchanging heat with COare combined to expand a supercooling region of a cycle using COand improve efficiency.

A cascade refrigeration cycle apparatus according to a first aspect comprises a fan, a first cycle, a second cycle, and a heat exchanger. In the first cycle, a first refrigerant having a critical point of 40° C. or higher circulates. The first cycle includes a condenser in which air supplied by the fan and the first refrigerant exchange heat. In the second cycle, carbon dioxide as a second refrigerant circulates. The second cycle includes a radiator in which air supplied by the fan and the second refrigerant exchange heat. In the heat exchanger, the first refrigerant and the second refrigerant exchange heat. The condenser is disposed on a windward side of the radiator in a first direction that is a direction of an airflow generated by the fan.

A cascade refrigeration cycle apparatus according to an embodiment of the present disclosure will be described hereinafter with reference to the drawings.

An outline of a cascade refrigeration cycle apparatusof the present disclosure will be described hereinafter with reference to.is a schematic configuration diagram of the cascade refrigeration cycle apparatus.

The cascade refrigeration cycle apparatusis an apparatus that performs vapor compression refrigeration cycle operation to cool or heat a temperature adjustment target. In the present embodiment, the cascade refrigeration cycle apparatuscools or heats air in a room of an office building or the like as a temperature adjustment target to perform cooling or heating of the room of the office building or the like.

In the present embodiment, the temperature adjustment target of the cascade refrigeration cycle apparatusis air. Alternatively, the cascade refrigeration cycle apparatus of the present disclosure may be a device that cools or heats water, a heat medium, or the like that is the temperature adjustment target. In the present embodiment, the cascade refrigeration cycle apparatuscools and heats a room in an office building or the like, but the cascade refrigeration cycle apparatus may be an apparatus dedicated to cooling.

As illustrated in, the cascade refrigeration cycle apparatusmainly includes a vapor compression first cycle, a vapor compression second cycle, a fan, and a control device.

The first cycleis a refrigerant circuit in which a first refrigerant having a higher critical point than a second refrigerant used in the second cyclecirculates.

The first refrigerant is a refrigerant having a critical point of 40° C. or higher. The first refrigerant is preferably a refrigerant having a critical point of 50° C. or higher. The first refrigerant preferably has a relatively low global warming potential. Although the type of the refrigerant is not limited, the first refrigerant is, for example, any single refrigerant of R290 (critical point 370° C.), R1234yf (critical point 95° C.), R1234ze (critical point 154° C.), or R32 (critical point 72° C.), or a mixed refrigerant including the above refrigerants.

The second cycleis a refrigerant circuit through which a refrigerant including carbon dioxide (CO) circulates as the second refrigerant. The critical point of COis 31.1° C. In the present embodiment, the refrigerant circulating in the second cycleis a single refrigerant of CO.

The first cycleand the second cycleare thermally connected via a cascade heat exchanger. In the cascade heat exchanger, the first refrigerant circulating in the first cycleand the second refrigerant circulating in the second cycleexchange heat.

The cascade refrigeration cycle apparatusincludes the first cyclein addition to the second cyclefor the following reasons.

At present, from the viewpoint of environmental conservation, use of COas a refrigerant attracts attention. COhas an excellent characteristic of having a small global warming potential but has a characteristic of having a low critical point. Therefore, in a case where only the second cycle using COas the second refrigerant is used in the refrigeration cycle apparatus, if a cooling operation is performed by using the heat exchanger on a heat source side as a radiator under a condition where the temperature of heat source air is high (a condition where the temperature of the heat source air exceeds the critical point of CO), the COdoes not change in phase, and thus the cycle becomes a cycle as indicated by a broken line in. In such a cycle, since an enthalpy difference due to heat exchange is small, the obtained cooling capacity becomes relatively small as indicated by a double-headed arrow of a broken line in, and the efficiency is deteriorated.

On the other hand, in the cascade refrigeration cycle apparatusof the present disclosure, the first cycle having a relatively high critical point is used for subcooling the second refrigerant in addition to the second cycle using COas the second refrigerant. Therefore, the cycle can be improved as indicated by a one-dot chain line in the Mollier diagram of, and the obtained cooling capacity can be expanded as indicated by a double-headed arrow of a one-dot chain line in.

The fanis a device that generates an airflow in order to supply air as a heat source (heat source air) to a condenserin the first cycleand a first heat exchangerin the second cycle.

As illustrated in, the cascade refrigeration cycle apparatusis divided into a heat source unitand a utilization unit. The heat source unitand the utilization unitare connected via connection pipesandconstituting the second cycle.

The heat source unitincludes a housing. The housingaccommodates various devices constituting the first cycle, some of various devices constituting the second cycle, the fan, and the like. The heat source unitis installed on, but not limited to, a rooftop of a building such as an office building in which the cascade refrigeration cycle apparatusis installed, near a wall of a building, or the like.

The utilization unitincludes a housing. The housingaccommodates a second heat exchangerof the second cycle, a fan (not illustrated) that supplies air to the second heat exchanger, and the like. The utilization unitis installed, for example, in an air conditioning target space or near the air conditioning target space (for example, a ceiling space or the like of the air conditioning target space). Although only one utilization unithaving the second heat exchangeris depicted in the example of, the cascade refrigeration cycle apparatusmay include a plurality of utilization unitshaving the second heat exchangersconnected in parallel to each other.

The control deviceis electrically connected to various devices constituting the second cycle, various devices constituting the first cycle, and the fanand controls operations of the devices electrically connected to the control device.

The first cycle, the second cycle, the fan, the control device, and the heat source unitwill be described in detail.

In the first cycle (first refrigerant circuit), the first refrigerant circulates. The first cycleis mainly used for subcooling the second refrigerant flowing in the second cycle during the cooling operation.

The first cyclemainly includes a compressor, the condenser, an expansion mechanism, and the cascade heat exchangerwhich are connected by pipes. In the first cycle, the first refrigerant discharged from the compressorflows through the condenser, the expansion mechanism, and the cascade heat exchangerin this order, and returns to a suction side of the compressor.

The compressorcompresses the first refrigerant. For example, the compressoris a variable operating capacity compressor including an inverter-controlled motor. Alternatively, the compressormay be a compressor having a constant operating capacity. The compressoris, for example, a scroll compressor or a rotary compressor. However, the type of the compressoris not limited to the above examples, and may be appropriately selected.

In the condenser, the air (heat source air) supplied by the fanand the first refrigerant exchange heat. In the condenser, the first refrigerant obtains cold energy from the heat source air. The condenseris, for example, a fin-and-tube heat exchanger having a large number of heat transfer tubes and fins.

The expansion mechanismdecompresses the first refrigerant. The expansion mechanismis, for example, an electronic expansion valve having a variable opening degree. However, the expansion mechanismis not limited to this example, and may be an automatic temperature expansion valve having a temperature sensitive cylinder or a capillary tube.

The cascade heat exchangercauses the first refrigerant and the second refrigerant to exchange heat with each other without mixing the first refrigerant and the second refrigerant. The cascade heat exchangeris, for example, a plate heat exchanger. The cascade heat exchangerincludes a first flow pathconstituting a part of the first cycleand a second flow pathconstituting a part of the second cycle. In the cascade heat exchanger, the first refrigerant flowing through first flow pathand a second fluid flowing through second flow pathexchange heat, and the second fluid is cooled by the first fluid. One end of the first flow pathis connected to the expansion mechanismvia a refrigerant pipe, and the other end is connected to the suction side of the compressorvia a refrigerant pipe.

In the second cycle (second refrigerant circuit), the second refrigerant circulates. The second refrigerant circulating in the second cycleis used for cooling and heating the air in a space as the temperature adjustment target.

The second cyclemainly includes a compressor, a switching mechanism, the first heat exchanger, the cascade heat exchanger, an expansion mechanism, and the second heat exchanger.

The compressorcompresses the second refrigerant. For example, the compressoris a variable operating capacity compressor including an inverter-controlled motor. Alternatively, the compressormay be a compressor having a constant operating capacity. The compressoris, for example, a scroll compressor or a rotary compressor. However, the type of the compressoris not limited to the above examples, and may be appropriately selected.

The switching mechanismis a mechanism that switches a state of the second cyclebetween a first state and a second state. When the second cycleis in the first state (see the solid line of the switching mechanismin), the first heat exchangerfunctions as a radiator for the second refrigerant, and the second heat exchangerfunctions as an evaporator for the second refrigerant. When the second cycleis in the second state (see the broken line of the switching mechanismin), the first heat exchangerfunctions as an evaporator for the second refrigerant, and the second heat exchangerfunctions as a radiator for the second refrigerant.

The switching mechanismis, for example, a four-way switching valve. When the state of the second cycleis set to the first state, the switching mechanismconnects a discharge pipeand a first pipe, and connects a suction pipeand a third pipe. When the state of the second cycleis set to the second state, the switching mechanismconnects the discharge pipeand the third pipe, and connects the suction pipeand the first pipe. Here, the discharge pipeis a pipe that connects a discharge side of the compressorand the switching mechanism. The first pipeis a pipe that connects the switching mechanismand the first heat exchanger. Here, the suction pipeis a pipe that connects the suction side of the compressorand the switching mechanism. Third pipeis a pipe that connects the switching mechanismand the connection pipe.

In the first heat exchanger, the air (heat source air) supplied by the fanand the second refrigerant exchange heat. When the state of the second cycleis the first state, the first heat exchangerfunctions as a radiator, and the second refrigerant obtains cold energy from the heat source air in the first heat exchanger. When the state of the second cycleis the second state, the first heat exchangerfunctions as an evaporator, and the second refrigerant obtains thermal energy from the heat source air in the first heat exchanger. The first heat exchangeris, for example, a fin-and-tube heat exchanger having a large number of heat transfer tubes and fins.

As described above, the cascade heat exchangeris a heat exchanger that causes the first refrigerant and the second refrigerant to exchange heat without mixing with each other, and the second flow pathof the cascade heat exchangerconstitutes a part of the second cycle. The cascade heat exchangeris disposed in the second pipe. The second pipeis a pipe that connects the first heat exchangerand the connection pipein the second cycle.

The expansion mechanismdecompresses the second refrigerant. The expansion mechanismis disposed on the second pipebetween the cascade heat exchangerand a connecting portion between the second pipeand the connection pipe. The expansion mechanismis, for example, an electronic expansion valve having a variable opening degree. However, the expansion mechanismis not limited to this example, and may be an automatic temperature expansion valve having a temperature sensitive cylinder or a capillary tube.

In the second heat exchanger, the second refrigerant and air in the air conditioning target space exchange heat. The second heat exchangeris accommodated in the housing. The air in the air conditioning target space is supplied to the second heat exchangerby a fan (not illustrated) disposed in the housing. In the second heat exchanger, the air in the air conditioning target space supplied by the fan and the second refrigerant exchange heat. When the state of the second cycleis the first state, the second heat exchangerfunctions as an evaporator, and the air in the air conditioning target space is cooled by the second refrigerant in the second heat exchanger. When the state of the second cycleis the second state, the second heat exchangerfunctions as a radiator, and the air in the air conditioning target space is heated by the second refrigerant in the second heat exchanger. The second heat exchangeris, for example, a fin-and-tube heat exchanger having a large number of heat transfer tubes and fins.

The fanis accommodated in the housingof the heat source unit. The fanrotates an impellerabout an axis O by a motor (not illustrated) to supply the heat source air to the condenserin the first cycleand the first heat exchangerin the second cycleaccommodated in the housingof the heat source unit. Thus, heat exchange between the first refrigerant and the second refrigerant and the heat source air are promoted. The fanis, for example, an axial flow fan, although the type is not limited. In the present embodiment, in particular, the fanis, for example, a propeller fan.

The control deviceis a device that controls the operation of the cascade refrigeration cycle apparatus.

The control deviceis electrically connected to the compressorand the expansion mechanismin the first cycle, the compressor, the switching mechanismand the expansion mechanismin the second cycle, and the fan(see the broken lines in). The control devicecontrols the operation of the cascade refrigeration cycle apparatusby controlling the operation of these electrically connected devices.

In the present embodiment, an electric circuit and a control board (not illustrated) mounted on the heat source unitand an electric circuit and a control board (not illustrated) mounted on the utilization unitare communicably connected to each other, and function as the control devicein cooperation with each other.illustrates the control device, for convenience, at a position away from the heat source unit, the utilization unit, and the like.

In the present embodiment, the control deviceincludes an arithmetic and control unit and a storage. As the arithmetic and control unit, a processor such as a CPU can be used. The arithmetic and control unit reads a program stored in the storage, and controls the operation of the cascade refrigeration cycle apparatusin accordance with this program.

Specifically, when causing the cascade refrigeration cycle apparatusto perform a heating operation, the control devicecontrols the operation of the switching mechanismto set the state of the second cycleto the second state and operate the compressor. The control devicecontrols an operating capacity of the motor of the compressoron the basis of a measurement result of a sensor (a sensor that measures a temperature and a pressure of the second refrigerant at an appropriate location in the second cycle, or a sensor that measures a temperature of the heat source air, the sensor is referred to as a first sensor hereinafter), not illustrated, disposed at an appropriate location. The control deviceoperates the motors of the fanand a fan of the utilization unitat a predetermined number of rotations. Furthermore, the control devicecontrols the opening degree of the electronic expansion valve as the expansion mechanismon the basis of the measurement result of the first sensor.

When causing the cascade refrigeration cycle apparatusto perform the cooling operation, the control devicecontrols the operation of the switching mechanismto set the state of the second cycleto the first state and operate the compressor. The control devicecontrols the operating capacity of the motor of the compressoron the basis of the measurement result of the first sensor. The control deviceoperates the motors of the fanand a fan of the utilization unitat a predetermined number of rotations. Furthermore, the control devicecontrols the opening degree of the electronic expansion valve as the expansion mechanismon the basis of the measurement result of the first sensor.

Furthermore, the control deviceoperates the compressorwhen causing the cascade refrigeration cycle apparatusto perform the cooling operation. The control devicemay operate the compressorwhenever causing the cascade refrigeration cycle apparatusto perform the cooling operation. Alternatively, the control devicemay operate the compressor, for example, when the temperature of the heat source air (outside air) is higher than a predetermined temperature. The control devicecontrols an operating capacity of the motor of the compressoron the basis of a measurement result of a sensor (a sensor that measures a temperature and a pressure of the first refrigerant at an appropriate location in the first cycle, or a sensor that measures a temperature of the heat source air, the sensor is referred to as a second sensor hereinafter), not illustrated, disposed at an appropriate location.

The control devicecontrols the opening degree of the electronic expansion valve as the expansion mechanismon the basis of the measurement result of the second sensor.

The heat source unitwill be described mainly with reference toin addition to.is a plan view of an inside of the heat source unitof the cascade refrigeration cycle apparatus, the plan view schematically illustrating an arrangement of the first heat exchanger, the condenser, and the fanin the heat source unit.is a side view of the first heat exchanger, the condenser, and the fanwhen viewed in a direction of arrows A-A in.is a schematic rear view of the first heat exchangerand the condenseraccording to a first example inwhen viewed from a rear.

In the following description, expressions indicating directions such as “upper”, “lower”, “front (front face)”, “rear (rear face)” “left”, and “right” are used for convenience in order to represent directions and positions. Unless otherwise specified, expressions such as “upper”, “lower”, “front (front face)”, “rear (rear face)”, “left”, and “right” follow directions of arrows in the drawings. Note that, unless otherwise specified, these expressions are not intended to limit the disclosure of the present application.