Patent ID: 12222146

DESCRIPTION OF EMBODIMENTS

(1) Configuration of Refrigeration Cycle Apparatus

FIG.1is a schematic configuration diagram of a refrigeration cycle apparatus1.FIG.2is a schematic functional block configuration diagram of the refrigeration cycle apparatus1.

The refrigeration cycle apparatus1is an apparatus used for cooling and heating a room in an office building or the like by performing a vapor compression refrigeration cycle operation.

The refrigeration cycle apparatus1includes a binary refrigerant circuit including a vapor compression primary-side refrigerant circuit5a(corresponding to a first circuit) and a vapor compression secondary-side refrigerant circuit10(corresponding to a second circuit), and performs a binary refrigeration cycle. The primary-side refrigerant circuit5aaccording to the present embodiment encloses, for example, R32, R410A (corresponding to a heat medium), or the like as a refrigerant. The secondary-side refrigerant circuit10encloses, for example, carbon dioxide (corresponding to a refrigerant) as a refrigerant. The primary-side refrigerant circuit5aand the secondary-side refrigerant circuit10are thermally connected via a cascade heat exchanger35described later.

The refrigeration cycle apparatus1is configured by connecting a primary-side unit5, a cascade unit2, a plurality of branch units6a,6b, and6c, and a plurality of utilization units3a,3b, and3cto each other via pipes. The primary-side unit5and the cascade unit2are connected via a primary-side first connection pipe111and a primary-side second connection pipe112. The cascade unit2and the plurality of branch units6a,6b, and6care connected via three connection pipes, namely, a secondary-side second connection pipe9, a secondary-side first connection pipe8, and a secondary-side third connection pipe7. The plurality of branch units6a,6b, and6cand the plurality of utilization units3a,3b, and3care connected via first connecting tubes15a,15b, and15cand second connecting tubes16a,16b, and16c. A single primary-side unit5is provided in the present embodiment. A single cascade unit2is provided in the present embodiment. The plurality of utilization units3a,3b, and3caccording to the present embodiment includes three utilization units, namely, a first utilization unit3a, a second utilization unit3b, and a third utilization unit3c. The plurality of branch units6a,6b, and6caccording to the present embodiment includes three branch units, namely, a first branch unit6a, a second branch unit6b, and a third branch unit6c.

In the refrigeration cycle apparatus1, the utilization units3a,3b, and3ccan individually perform a cooling operation or a heating operation, and heat can be recovered between the utilization units by sending a refrigerant from the utilization unit performing the heating operation to the utilization unit performing the cooling operation. Specifically, heat is recovered in the present embodiment by executing a cooling main operation or a heating main operation of simultaneously executing the cooling operation and the heating operation. In addition, the refrigeration cycle apparatus1is configured to balance thermal loads of the cascade unit2in accordance with entire thermal loads of the plurality of utilization units3a,3b, and3cin consideration of the heat recovery (the cooling main operation or the heating main operation).

(2) Primary-Side Refrigerant Circuit

The primary-side refrigerant circuit5aincludes a primary-side compressor71(corresponding to a first compressor), a primary-side switching mechanism72, a primary-side heat exchanger74(corresponding to a first heat exchanger), a primary-side first expansion valve76, a primary-side subcooling heat exchanger103, a primary-side subcooling circuit104, a primary-side subcooling expansion valve104a, a first liquid shutoff valve108, the primary-side first connection pipe111, a second liquid shutoff valve106, the second refrigerant pipe114, a primary-side second expansion valve102, the cascade heat exchanger35shared with the secondary-side refrigerant circuit10, a first refrigerant pipe113, a second gas shutoff valve107, the primary-side second connection pipe112, a first gas shutoff valve109, and a primary-side accumulator105. The primary-side refrigerant circuit5aspecifically includes a primary-side flow path35bof the cascade heat exchanger35.

The primary-side compressor71is configured to compress a primary-side refrigerant, and includes, for example, a scroll type or another positive-displacement compressor whose operating capacity can be varied by controlling an inverter for a compressor motor71a.

The primary-side accumulator105is provided at a halfway portion of a suction flow path connecting the primary-side switching mechanism72and a suction side of the primary-side compressor71.

In a case where the cascade heat exchanger35functions as an evaporator for the primary-side refrigerant, the primary-side switching mechanism72enters a fifth connecting state of connecting the suction side of the primary-side compressor71and a gas side of the primary-side flow path35bof the cascade heat exchanger35(see the solid lines of the primary-side switching mechanism72inFIG.1). In another case where the cascade heat exchanger35functions as a radiator for the primary-side refrigerant, the primary-side switching mechanism72enters a sixth connecting state of connecting a discharge side of the primary-side compressor71and the gas side of the primary-side flow path35bof the cascade heat exchanger35(see broken lines of the primary-side switching mechanism72inFIG.1). The primary-side switching mechanism72is a device that can switch the flow paths of the refrigerant in the primary-side refrigerant circuit5a, and includes, for example, a four-way switching valve. By changing a switching state of the primary-side switching mechanism72, the cascade heat exchanger35can function as the evaporator or the radiator for the primary-side refrigerant.

The cascade heat exchanger35is configured to cause heat exchange between the primary-side refrigerant such as R32 and a secondary-side refrigerant such as carbon dioxide without mixing the refrigerants. The cascade heat exchanger35includes, for example, a plate heat exchanger. The cascade heat exchanger35includes a secondary-side flow path35abelonging to the secondary-side refrigerant circuit10, and the primary-side flow path35bbelonging to the primary-side refrigerant circuit5a. The secondary-side flow path35ahas a gas side connected to a secondary-side switching mechanism22via a third pipe25, and a liquid side connected to a cascade expansion valve36via a fourth pipe26. The primary-side flow path35bhas a gas side connected to the primary-side compressor71via the first refrigerant pipe113, the second gas shutoff valve107, the primary-side second connection pipe112, the first gas shutoff valve109, and the primary-side switching mechanism72, and a liquid side connected to the second refrigerant pipe114provided with the primary-side second expansion valve102.

The primary-side heat exchanger74is configured to exchange heat between the primary-side refrigerant and outdoor air. The primary-side heat exchanger74has a gas side connected to a pipe extending from the primary-side switching mechanism72. Examples of the primary-side heat exchanger74include a fin-and-tube heat exchanger constituted by large numbers of heat transfer tubes and fins.

The primary-side first expansion valve76is provided on a liquid pipe extending from a liquid side of the primary-side heat exchanger74to the primary-side subcooling heat exchanger103. The primary-side first expansion valve76is an electrically powered expansion valve that has an adjustable opening degree and adjusts a flow rate of the primary-side refrigerant flowing in a portion on a liquid side of the primary-side refrigerant circuit5a.

The primary-side subcooling circuit104branches from a portion between the primary-side first expansion valve76and the primary-side subcooling heat exchanger103, and is connected to a portion between the primary-side switching mechanism72and the primary-side accumulator105on the suction flow path. The primary-side subcooling expansion valve104ais an electrically powered expansion valve that is provided upstream of the primary-side subcooling heat exchanger103in the primary-side subcooling circuit104, has an adjustable opening degree, and adjusts the flow rate of the primary-side refrigerant.

The primary-side subcooling heat exchanger103is a heat exchanger that causes heat exchange between a refrigerant flowing from the primary-side first expansion valve76toward the first liquid shutoff valve108and a refrigerant decompressed at the primary-side subcooling expansion valve104ain the primary-side subcooling circuit104.

The primary-side first connection pipe111is a pipe connecting the first liquid shutoff valve108and the second liquid shutoff valve106, and connects the primary-side unit5and the cascade unit2.

The primary-side second connection pipe112is a pipe connecting the first gas shutoff valve109and the second gas shutoff valve107, and connects the primary-side unit5and the cascade unit2.

The second refrigerant pipe114is a pipe extending from the liquid side of the primary-side flow path35bof the cascade heat exchanger35to the second liquid shutoff valve106.

The primary-side second expansion valve102is provided on the second refrigerant pipe114. The primary-side second expansion valve102is an electric expansion valve that has an adjustable opening degree and adjusts the flow rate of the primary-side refrigerant flowing through the primary-side flow path35bof the cascade heat exchanger35.

The first refrigerant pipe113is a pipe extending from the gas side of the primary-side flow path35bof the cascade heat exchanger35to the second gas shutoff valve107.

The first gas shutoff valve109is provided at a portion between the primary-side second connection pipe112and the primary-side switching mechanism72.

(3) Secondary-Side Refrigerant Circuit

The secondary-side refrigerant circuit10includes the plurality of utilization units3a,3b, and3c, the plurality of branch units6a,6b, and6c, and the cascade unit2, which are connected to each other. Each of the utilization units3a,3b, and3cis connected to a corresponding one of the branch units6a,6b, and6con one-on-one basis. Specifically, the utilization unit3aand the branch unit6aare connected via the first connecting tube15aand the second connecting tube16a, the utilization unit3band the branch unit6bare connected via the first connecting tube15band the second connecting tube16b, and the utilization unit3cand the branch unit6care connected via the first connecting tube15cand the second connecting tube16c. Each of the branch units6a,6b, and6care connected to the cascade unit2via three connection pipes, namely, the secondary-side third connection pipe7, the secondary-side first connection pipe8, and the secondary-side second connection pipe9. Specifically, the secondary-side third connection pipe7, the secondary-side first connection pipe8, and the secondary-side second connection pipe9extending from the cascade unit2are each branched into a plurality of pipes connected to the branch units6a,6b, and6c.

The secondary-side first connection pipe8has a flow of either the refrigerant in a gas-liquid two-phase state or the refrigerant in a gas state in accordance with an operating state. Note that the secondary-side first connection pipe8has a flow of the refrigerant in a supercritical state in accordance with the operating state. The secondary-side second connection pipe9has a flow of either the refrigerant in the gas-liquid two-phase state or the refrigerant in the gas state in accordance with the operating state. The secondary-side third connection pipe7has a flow of either the refrigerant in the gas-liquid two-phase state or the refrigerant in a liquid state in accordance with the operating state. Note that the secondary-side third connection pipe7has a flow of the refrigerant in the supercritical state in accordance with the operating state.

The secondary-side refrigerant circuit10includes a cascade circuit12, branch circuits14a,14b, and14c, and utilization circuits13a,13b, and13c, which are connected to each other.

The cascade circuit12mainly includes a secondary-side compressor21(corresponding to a compressor), the secondary-side switching mechanism22, a first pipe28, a second pipe29, a suction flow path23, a discharge flow path24, the third pipe25, the fourth pipe26, a fifth pipe27, the cascade heat exchanger35, the cascade expansion valve36, a first electric component cooling flow path17, a second electric component cooling flow path18, a third shutoff valve31, a first shutoff valve32, a second shutoff valve33, a secondary-side accumulator30, an oil separator34, an oil return circuit40, a secondary-side receiver45, a bypass circuit46, a bypass expansion valve46a, a secondary-side subcooling heat exchanger47, a secondary-side subcooling circuit48, and a secondary-side subcooling expansion valve48a. The cascade circuit12of the secondary-side refrigerant circuit10specifically includes the secondary-side flow path35aof the cascade heat exchanger35.

The secondary-side compressor21is configured to compress a secondary-side refrigerant, and includes, for example, a scroll type or other positive-displacement compressor whose operating capacity can be varied by controlling an inverter for a compressor motor21a. The secondary-side compressor21is controlled in accordance with an operating load so as to have larger operating capacity as the load increases.

The secondary-side switching mechanism22can switch a connecting state of the secondary-side refrigerant circuit10, specifically, the flow path of the refrigerant in the cascade circuit12. The secondary-side switching mechanism22according to the present embodiment includes a discharge-side connection portion22x, a suction-side connection portion22y, a first switching valve22a, and a second switching valve22b. An end of the discharge flow path24on a side opposite to the secondary-side compressor21is connected to the discharge-side connection portion22x. An end of the suction flow path23on a side opposite to the secondary-side compressor21is connected to the suction-side connection portion22y. The first switching valve22aand the second switching valve22bare provided in parallel to each other between the discharge flow path24and the suction flow path23of the secondary-side compressor21. The first switching valve22ais connected to one end of the discharge-side connection portion22xand one end of the suction-side connection portion22y. The second switching valve22bis connected to the other end of the discharge-side connection portion22xand the other end of the suction-side connection portion22y. In the present embodiment, each of the first switching valve22aand the second switching valve22bincludes the four-way switching valve. Each of the first switching valve22aand the second switching valve22bhas four connection ports, namely, a first connection port, a second connection port, a third connection port, and a fourth connection port. In the first switching valve22aand the second switching valve22baccording to the present embodiment, each of the fourth ports is closed and is a connection port not connected to the flow path of the secondary-side refrigerant circuit10. In the first switching valve22a, the first connection port is connected to the one end of the discharge-side connection portion22x, the second connection port is connected to the third pipe25extending from the secondary-side flow path35aof the cascade heat exchanger35, and the third connection port is connected to the one end of the suction-side connection portion22y. The first switching valve22aswitches between a switching state in which the first connection port and the second connection port are connected and the third connection port and the fourth connection port are connected and a switching state in which the third connection port and the second connection port are connected and the first connection port and the fourth connection port are connected. The second switching valve22bhas the first connection port connected to the other end of the discharge-side connection portion22x, the second connection port connected to the first pipe28, and the third connection port connected to the other end of the suction-side connection portion22y. The second switching valve22bswitches between a switching state in which the first connection port and the second connection port are connected and the third connection port and the fourth connection port are connected and a switching state in which the third connection port and the second connection port are connected and the first connection port and the fourth connection port are connected.

When the secondary-side refrigerant discharged from the secondary-side compressor21is prevented from being sent to the secondary-side first connection pipe8while the cascade heat exchanger35functions as a radiator for the secondary-side refrigerant, the secondary-side switching mechanism22is switched to a first connecting state in which the discharge flow path24and the third pipe25are connected by the first switching valve22aand the first pipe28and the suction flow path23are connected by the second switching valve22b. The first connecting state of the secondary-side switching mechanism22is a connecting state adopted during the cooling operation described later. When the cascade heat exchanger35functions as an evaporator for the secondary-side refrigerant, the secondary-side switching mechanism22is switched to a second connecting state in which the discharge flow path24and the first pipe28are connected by the second switching valve22band the third pipe25and the suction flow path23are connected by the first switching valve22a. The second connecting state of the secondary-side switching mechanism22is a connecting state adopted during the heating operation and during the heating main operation described later. When the secondary-side refrigerant discharged from the secondary-side compressor21is sent to the secondary-side first connection pipe8while the cascade heat exchanger35functions as a radiator for the secondary-side refrigerant, the secondary-side switching mechanism22is switched to a third connecting state in which the discharge flow path24and the third pipe25are connected by the first switching valve22aand the discharge flow path24and the first pipe28are connected by the second switching valve22b. The third connecting state of the secondary-side switching mechanism22is a connecting state adopted during the cooling main operation described later.

As described above, the cascade heat exchanger35is configured to cause heat exchange between the primary-side refrigerant such as R32 and the secondary-side refrigerant such as carbon dioxide without mixing the refrigerants. The cascade heat exchanger35includes the secondary-side flow path35ahaving a flow of the secondary-side refrigerant in the secondary-side refrigerant circuit10and the primary-side flow path35bhaving a flow of the primary-side refrigerant in the primary-side refrigerant circuit5a, so as to be shared between the primary-side unit5and the cascade unit2. Note that in the present embodiment, as shown inFIG.7, the cascade heat exchanger35is disposed inside a cascade casing2xof the cascade unit2. The gas side of the primary-side flow path35bof the cascade heat exchanger35extends to the primary-side second connection pipe112outside the cascade casing2xvia the first refrigerant pipe113and the second gas shutoff valve107. The liquid side of the primary-side flow path35bof the cascade heat exchanger35extends to the primary-side first connection pipe111outside the cascade casing2xvia the second refrigerant pipe114provided with the primary-side second expansion valve102and the second liquid shutoff valve106.

The cascade expansion valve36is an expansion valve for adjusting a flow rate of the secondary-side refrigerant flowing in the cascade heat exchanger35. The cascade expansion valve36is an electric expansion valve connected to the liquid side of the cascade heat exchanger35and has an adjustable opening degree. The cascade expansion valve36is provided on the fourth pipe26.

Each of the third shutoff valve31, the first shutoff valve32, and the second shutoff valve33is provided at a connecting port with an external device or pipe (specifically, the connection pipe7,8, or9). Specifically, the third shutoff valve31is connected to the secondary-side third connection pipe7led out of the cascade unit2. The first shutoff valve32is connected to the secondary-side first connection pipe8led out of the cascade unit2. The second shutoff valve33is connected to the secondary-side second connection pipe9led out of the cascade unit2.

The first pipe28is a refrigerant pipe that connects the first shutoff valve32and the secondary-side switching mechanism22. Specifically, the first pipe28connects the first shutoff valve32and the second connection port of the second switching valve22bof the secondary-side switching mechanism22.

The suction flow path23is a flow path that connects the secondary-side switching mechanism22and the suction side of the secondary-side compressor21. Specifically, the suction flow path23connects the suction-side connection portion22yof the secondary-side switching mechanism22and the suction side of the secondary-side compressor21. The suction flow path23has a halfway portion provided with the secondary-side accumulator30.

The second pipe29is a refrigerant pipe that connects the second shutoff valve33and a halfway portion of the suction flow path23. In the present embodiment, the second pipe29is connected to the suction flow path23at a connection point of the suction flow path23between the suction-side connection portion22yof the secondary-side switching mechanism22and the secondary-side accumulator30.

The discharge flow path24is a refrigerant pipe that connects the discharge side of the secondary-side compressor21and the secondary-side switching mechanism22. Specifically, the discharge flow path24connects the discharge side of the secondary-side compressor21and the discharge-side connection portion22xof the secondary-side switching mechanism22.

The third pipe25is a refrigerant pipe that connects the secondary-side switching mechanism22and a gas side of the cascade heat exchanger35. Specifically, the third pipe25connects the second connection port of the first switching valve22aof the secondary-side switching mechanism22and a gas-side end of the secondary-side flow path35ain the cascade heat exchanger35.

The fourth pipe26is a refrigerant pipe that connects the liquid side (opposite to the gas side, and opposite to the side provided with the secondary-side switching mechanism22) of the cascade heat exchanger35and the secondary-side receiver45. Specifically, the fourth pipe26connects a liquid side end (opposite to the gas side) of the secondary-side flow path35ain the cascade heat exchanger35and the secondary-side receiver45.

The secondary-side receiver45is a refrigerant reservoir that reserves a residue refrigerant in the secondary-side refrigerant circuit10. The secondary-side receiver45is provided with the fourth pipe26, the fifth pipe27, and the bypass circuit46extending outward.

The bypass circuit46is a refrigerant pipe that connects a gas phase region corresponding to an upper region in the secondary-side receiver45and the suction flow path23. Specifically, the bypass circuit46is connected between the secondary-side switching mechanism22and the secondary-side accumulator30on the suction flow path23. The bypass circuit46is provided with the bypass expansion valve46a. The bypass expansion valve46ais an electrically powered expansion valve having an adjustable opening degree to adjust quantity of the refrigerant guided from inside the secondary-side receiver45to the suction side of the secondary-side compressor21.

The fifth pipe27is a refrigerant pipe that connects the secondary-side receiver45and the third shutoff valve31.

The first electric component cooling flow path17is a refrigerant flow path that connects a portion X of the fourth pipe26between the cascade expansion valve36and the secondary-side receiver45and a portion Z of the fifth pipe27between the secondary-side subcooling heat exchanger47and the secondary-side receiver45. The first electric component cooling flow path17includes a first electric component expansion valve17aand a first cooling portion11afor cooling a first electric component91(described later) of the cascade-side control unit20. In the first electric component cooling flow path17, the portion X, the first cooling portion11a, the first electric component expansion valve17a, and the portion Z are arranged in that order. The first electric component expansion valve17ais an electric expansion valve that can adjust the flow rate of the secondary-side refrigerant flowing in the first electric component cooling flow path17.

The second electric component cooling flow path18is a refrigerant flow path that connects a portion Y between the first cooling portion11aand the first electric component expansion valve17aon the first electric component cooling flow path17and a portion W in a halfway portion of the suction flow path23. The second electric component cooling flow path18includes a second cooling portion11bfor cooling a space S2in which a second electric component92(described later) and the first electric component91of the cascade-side control unit20are accommodated, and a second electric component expansion valve18a. In the second electric component cooling flow path18, the portion Y, the second electric component expansion valve18a, the second cooling portion11b, and the portion W are arranged in that order. The second electric component expansion valve18ais an electric expansion valve that can decompress the secondary-side refrigerant after passing through the portion Y and before flowing to the second cooling portion11b.

The secondary-side subcooling circuit48is a refrigerant pipe that connects a part of the fifth pipe27and the suction flow path23. Specifically, the secondary-side subcooling circuit48is connected between the secondary-side switching mechanism22and the secondary-side accumulator30on the suction flow path23. The secondary-side subcooling circuit48according to the present embodiment extends to branch from a portion between the secondary-side receiver45and the secondary-side subcooling heat exchanger47.

The secondary-side subcooling heat exchanger47is configured to cause heat exchange between the refrigerant flowing in a flow path belonging to the fifth pipe27and the refrigerant flowing in a flow path belonging to the secondary-side subcooling circuit48. The secondary-side subcooling heat exchanger47according to the present embodiment is provided between the third shutoff valve31and a portion from where the secondary-side subcooling circuit48branches on the fifth pipe27. The secondary-side subcooling expansion valve48ais provided between a portion branching from the fifth pipe27and the secondary-side subcooling heat exchanger47on the secondary-side subcooling circuit48. The secondary-side subcooling expansion valve48asupplies the secondary-side subcooling heat exchanger47with a decompressed refrigerant, and is an electrically powered expansion valve having an adjustable opening degree.

The secondary-side accumulator30is a reservoir that can reserve the secondary-side refrigerant, and is provided on the suction side of the secondary-side compressor21.

The oil separator34is provided at a halfway portion of the discharge flow path24. The oil separator34is configured to separate, from the secondary-side refrigerant, refrigerating machine oil discharged from the secondary-side compressor21along with the secondary-side refrigerant and return the refrigerating machine oil to the secondary-side compressor21.

The oil return circuit40is provided to connect the oil separator34and the suction flow path23. The oil return circuit40includes an oil return flow path41as a flow path extending from the oil separator34and extending to join a portion between the secondary-side accumulator30and the suction side of the secondary-side compressor21on the suction flow path23. The oil return flow path41has a halfway portion provided with an oil return capillary tube42and an oil return on-off valve44. When the oil return on-off valve44is controlled into an opened state, the refrigerating machine oil separated in the oil separator34passes through the oil return capillary tube42on the oil return flow path41and is returned to the suction side of the secondary-side compressor21. When the secondary-side compressor21is in the operating state on the secondary-side refrigerant circuit10, the oil return on-off valve44according to the present embodiment is kept in the opened state for predetermined time and is kept in a closed state for predetermined time repeatedly, to control returned quantity of the refrigerating machine oil through the oil return circuit40. The oil return on-off valve44according to the present embodiment is an electromagnetic valve controlled to be opened and closed. Alternatively, the oil return on-off valve44may be an electrically powered expansion valve having an adjustable opening degree and not provided with the oil return capillary tube42.

Description is made below to the utilization circuits13a,13b, and13c. Since the utilization circuits13band13care configured similarly to the utilization circuit13a, elements of the utilization circuits13band13cwill not be described repeatedly, assuming that a subscript “b” or “c” will replace a subscript “a” in reference signs denoting elements of the utilization circuit13a.

The utilization circuit13amainly includes a utilization-side heat exchanger52a, a first utilization pipe57a, a second utilization pipe56a, and a utilization-side expansion valve51a.

The utilization-side heat exchanger52ais configured to cause heat exchange between the refrigerant and indoor air, and includes a fin-and-tube heat exchanger constituted by large numbers of heat transfer tubes and fins. A plurality of utilization-side heat exchangers52a,52b, and52care connected in parallel to the secondary-side switching mechanism22, the suction flow path23, and the cascade heat exchanger35.

The second utilization pipe56ahas one end connected to a liquid side (opposite to a gas side) of the utilization-side heat exchanger52ain the first utilization unit3a. The second utilization pipe56ahas the other end connected to the second connecting tube16a. The second utilization pipe56ahas a halfway portion provided with the utilization-side expansion valve51adescribed above.

The utilization-side expansion valve51ais an electrically powered expansion valve that has an adjustable opening degree and adjusts a flow rate of the refrigerant flowing in the utilization-side heat exchanger52a. The utilization-side expansion valve51ais provided on the second utilization pipe56a.

The first utilization pipe57ahas one end connected to the gas side of the utilization-side heat exchanger52ain the first utilization unit3a. The first utilization pipe57aaccording to the present embodiment is connected to a portion opposite to the utilization-side expansion valve51aof the utilization-side heat exchanger52a. The first utilization pipe57ahas the other end connected to the first connecting tube15a.

Description is made below to the branch circuits14a,14b, and14c. Since the branch circuits14band14care configured similarly to the branch circuit14a, elements of the branch circuits14band14cwill not be described repeatedly, assuming that a subscript “b” or “c” will replace a subscript “a” in reference signs denoting elements of the branch circuit14a.

The branch circuit14amainly includes a junction pipe62a, a first branch pipe63a, a second branch pipe64a, a first control valve66a, a second control valve67a, a bypass pipe69a, a check valve68a, and a third branch pipe61a.

The junction pipe62ahas one end connected to the first connecting tube15a. The other end of the junction pipe62ais connected to the first branch pipe63aand the second branch pipe64awhich are branched from the junction pipe.

The first branch pipe63ahas a portion not adjacent to the junction pipe62and connected to the secondary-side first connection pipe8. The first branch pipe63ais provided with the openable and closable first control valve66a.

The second branch pipe64ahas a portion not adjacent to the junction pipe62and connected to the secondary-side second connection pipe9. The second branch pipe64ais provided with the openable and closable second control valve67a.

The bypass pipe69ais a refrigerant pipe that connects a portion of the first branch pipe63acloser to the secondary-side first connection pipe8than the first control valve66aand a portion of the second branch pipe64acloser to the secondary-side second connection pipe9than the second control valve67a. The check valve68ais provided in a halfway portion of the bypass pipe69a. The check valve68aallows only a refrigerant flow from the second branch pipe64atoward the first branch pipe63a, and does not allow a refrigerant flow from the first branch pipe63atoward the second branch pipe64a.

The third branch pipe61ahas one end connected to the second connecting tube16a. The third branch pipe61ahas the other end connected to the secondary-side third connection pipe7.

Then, the first branch unit6acan function as follows by closing the first control valve66aand opening the second control valve67awhen the cooling operation described later is performed. The first branch unit6asends a refrigerant flowing into the third branch pipe61athrough the secondary-side third connection pipe7to the second connecting tube16a. The refrigerant flowing in the second utilization pipe56ain the first utilization unit3avia the second connecting tube16ais sent to the utilization-side heat exchanger52ain the first utilization unit3avia the utilization-side expansion valve51a. Then, the refrigerant sent to the utilization-side heat exchanger52ais evaporated by heat exchange with indoor air, and then flows in the first connecting tube15avia the first utilization pipe57a. The refrigerant having flowed through the first connecting tube15ais sent to the junction pipe62aof the first branch unit6a. The refrigerant having flowed through the junction pipe62adoes not flow toward the first branch pipe63abut flows toward the second branch pipe64a. The refrigerant flowing in the second branch pipe64apasses through the second control valve67a. A part of the refrigerant that has passed through the second control valve67ais sent to the secondary-side second connection pipe9. A remaining part of the refrigerant that has passed through the second control valve67aflows so as to branch into the bypass pipe69aprovided with the check valve68a, passes through a part of the first branch pipe63a, and then is sent to the secondary-side first connection pipe8. As a result, it is possible to increase a total flow path cross-sectional area when the secondary-side gas state refrigerant evaporated in the utilization-side heat exchanger52ais sent to the secondary-side compressor21, so that pressure loss can be reduced.

When the first utilization unit3acools a room at the time of performing the cooling main operation and the heating main operation to be described later, the first branch unit6acan function as follows by closing the first control valve66aand opening the second control valve67a. The first branch unit6asends a refrigerant flowing into the third branch pipe61athrough the secondary-side third connection pipe7to the second connecting tube16a. The refrigerant flowing in the second utilization pipe56ain the first utilization unit3avia the second connecting tube16ais sent to the utilization-side heat exchanger52ain the first utilization unit3avia the utilization-side expansion valve51a. Then, the refrigerant sent to the utilization-side heat exchanger52ais evaporated by heat exchange with indoor air, and then flows in the first connecting tube15avia the first utilization pipe57a. The refrigerant having flowed through the first connecting tube15ais sent to the junction pipe62aof the first branch unit6a. The refrigerant having flowed through the junction pipe62aflows to the second branch pipe64a, passes through the second control valve67a, and then is sent to the secondary-side second connection pipe9.

The first branch unit6acan function as follows by closing the second control valve67aand opening the first control valve66awhen the heating operation described later is performed. In the first branch unit6a, the refrigerant flowing into the first branch pipe63athrough the secondary-side first connection pipe8passes through the first control valve66aand is sent to the junction pipe62a. The refrigerant having flowed through the junction pipe62aflows in the first utilization pipe57ain the utilization unit3avia the first connecting tube15ato be sent to the utilization-side heat exchanger52a. Then, the refrigerant sent to the utilization-side heat exchanger52aradiates heat through heat exchange with indoor air, and then passes through the utilization-side expansion valve51aprovided on the second utilization pipe56a. The refrigerant having passed through the second utilization pipe56aflows through the third branch pipe61aof the first branch unit6avia the second connecting tube16a, and then is sent to the secondary-side third connection pipe7.

When the first utilization unit3aheats a room at the time of performing the cooling main operation and the heating main operation described later, the first branch unit6acan function as follows by closing the second control valve67aand opening the first control valve66a. In the first branch unit6a, the refrigerant flowing into the first branch pipe63athrough the secondary-side first connection pipe8passes through the first control valve66aand is sent to the junction pipe62a. The refrigerant having flowed through the junction pipe62aflows in the first utilization pipe57ain the utilization unit3avia the first connecting tube15ato be sent to the utilization-side heat exchanger52a. Then, the refrigerant sent to the utilization-side heat exchanger52aradiates heat through heat exchange with indoor air, and then passes through the utilization-side expansion valve51aprovided on the second utilization pipe56a. The refrigerant having passed through the second utilization pipe56aflows through the third branch pipe61aof the first branch unit6avia the second connecting tube16a, and then is sent to the secondary-side third connection pipe7.

The first branch unit6a, as well as the second branch unit6band the third branch unit6c, similarly have such a function. Accordingly, the first branch unit6a, the second branch unit6b, and the third branch unit6ccan individually switchably cause the utilization-side heat exchangers52a,52b, and52cto function as a refrigerant evaporator or a refrigerant radiator.

(4) Primary-Side Unit

The primary-side unit5is disposed in a space different from a space provided with the utilization units3a,3b, and3cand the branch units6a,6b, and6c, on a roof, or the like.

The primary-side unit5includes a part of the primary-side refrigerant circuit5adescribed above, a primary-side fan75, various sensors, a primary-side control unit70, and a primary-side casing5xas shown inFIG.7.

The primary-side unit5includes, as a part of the primary-side refrigerant circuit5a, the primary-side compressor71, the primary-side switching mechanism72, the primary-side heat exchanger74, the primary-side first expansion valve76, the primary-side subcooling heat exchanger103, the primary-side subcooling circuit104, the primary-side subcooling expansion valve104a, the first liquid shutoff valve108, the first gas shutoff valve109, and the primary-side accumulator105in the primary-side casing5x.

The primary-side fan75is provided in the primary-side unit5, and generates an air flow of guiding outdoor air into the primary-side heat exchanger74and exhausting, to outdoors, air obtained after heat exchange with the primary-side refrigerant flowing in the primary-side heat exchanger74. The primary-side fan75is driven by a primary-side fan motor75a.

The primary-side unit5is provided with the various sensors. Specifically, there are provided an outdoor air temperature sensor77that detects a temperature of outdoor air before passing through the primary-side heat exchanger74, a primary-side discharge pressure sensor78that detects a pressure of the primary-side refrigerant discharged from the primary-side compressor71, a primary-side suction pressure sensor79that detects a pressure of the primary-side refrigerant sucked into the primary-side compressor71, a primary-side suction temperature sensor81that detects a temperature of the primary-side refrigerant sucked into the primary-side compressor71, and a primary-side heat exchange temperature sensor82that detects a temperature of the refrigerant flowing in the primary-side heat exchanger74.

The primary-side control unit70controls behavior of the elements71(71a),72,75(75a),76, and104aprovided in the primary-side unit5. Then, the primary-side control unit70includes a processor such as a CPU or a microcomputer provided to control the primary-side unit5and a memory, so as to transmit and receive control signals and the like to and from a remote controller (not shown), and to transmit and receive control signals and the like between the cascade-side control unit20in the cascade unit2, branch unit control units60a,60b, and60c, and utilization-side control units50a,50b, and50c.

(5) Cascade Unit

The cascade unit2is disposed in a space different from a space provided with the utilization units3a,3b, and3cand the branch units6a,6b, and6c, on a roof, or the like.

The cascade unit2is connected to the branch units6a,6b, and6cvia the connection pipes7,8, and9, to constitute a part of the secondary-side refrigerant circuit10. The cascade unit2is connected to the primary-side unit5via the primary-side first connection pipe111and the primary-side second connection pipe112, to constitute a part of the primary-side refrigerant circuit5a.

The cascade unit2mainly includes the cascade circuit12described above, various sensors, the cascade-side control unit20, the second liquid shutoff valve106, the second refrigerant pipe114, the primary-side second expansion valve102, the first refrigerant pipe113, and the second gas shutoff valve107that constitute a part of the primary-side refrigerant circuit5a, and the cascade casing2xas shown inFIG.7.

The cascade unit2is provided with a secondary-side suction pressure sensor37that detects a pressure of the secondary-side refrigerant on the suction side of the secondary-side compressor21, a secondary-side discharge pressure sensor38that detects a pressure of the secondary-side refrigerant on the discharge side of the secondary-side compressor21, a secondary-side discharge temperature sensor39that detects a temperature of the secondary-side refrigerant on the discharge side of the secondary-side compressor21, a secondary-side suction temperature sensor88that detects a temperature of the secondary-side refrigerant on the suction side of the secondary-side compressor21, a secondary-side cascade temperature sensor83that detects a temperature of the secondary-side refrigerant flowing between the secondary-side flow path35aof the cascade heat exchanger35and the cascade expansion valve36, a receiver outlet temperature sensor84that detects a temperature of the secondary-side refrigerant flowing between the secondary-side receiver45and the secondary-side subcooling heat exchanger47, a bypass circuit temperature sensor85that detects a temperature of the secondary-side refrigerant flowing downstream of the bypass expansion valve46ain the bypass circuit46, a subcooling outlet temperature sensor86that detects a temperature of the secondary-side refrigerant flowing between the secondary-side subcooling heat exchanger47and the third shutoff valve31, and a subcooling circuit temperature sensor87that detects a temperature of the secondary-side refrigerant flowing through an outlet of the secondary-side subcooling heat exchanger47in the secondary-side subcooling circuit48.

The cascade-side control unit20controls behavior of the elements17a,18a,21(21a),22,36,44,46a,48a, and102provided in the cascade casing2xof the cascade unit2. The cascade-side control unit20includes a processor such as a CPU or a microcomputer provided to control the cascade unit2and a memory, so as to transmit and receive control signals and the like between the primary-side control unit70in the primary-side unit5, the utilization-side control units50a,50b, and50cin the utilization units3a,3b, and3c, and the branch unit control units60a,60b, and60c.

As described above, the cascade-side control unit20can control not only the units constituting the cascade circuit12of the secondary-side refrigerant circuit10but also the primary-side second expansion valve102constituting a part of the primary-side refrigerant circuit5a. Therefore, the cascade-side control unit20controls the valve opening degree of the primary-side second expansion valve102on the basis of a condition of the cascade circuit12controlled by the cascade-side control unit20, so as to bring the condition of the cascade circuit12closer to a desired condition. Specifically, it is possible to control an amount of heat received by the secondary-side refrigerant flowing through the secondary-side flow path35aof the cascade heat exchanger35in the cascade circuit12from the primary-side refrigerant flowing through the primary-side flow path35bof the cascade heat exchanger35or an amount of heat given by the secondary-side refrigerant to the primary-side refrigerant.

(6) Utilization Unit

The utilization units3a,3b, and3care installed by being embedded in or being suspended from a ceiling in an indoor space of an office building or the like, or by being hung on a wall surface in the indoor space, or the like.

The utilization units3a,3b, and3care connected to the cascade unit2via the connection pipes7,8, and9.

The utilization units3a,3b, and3crespectively include the utilization circuits13a,13b, and13cconstituting a part of the secondary-side refrigerant circuit10.

Hereinafter, configurations of the utilization units3a,3b, and3care described. The second utilization unit3band the third utilization unit3care configured similarly to the first utilization unit3a. The configuration of only the first utilization unit3awill thus be described here. As for the configuration of each of the second utilization unit3band the third utilization unit3c, elements will be denoted by reference signs obtained by replacing a subscript “a” in reference signs of elements of the first utilization unit3awith a subscript “b” or “c”, and these elements will not be described repeatedly.

The first utilization unit3amainly includes the utilization circuit13adescribed above, an indoor fan53a, the utilization-side control unit50a, and various sensors. Note that the indoor fan53aincludes an indoor fan motor54a.

The indoor fan53agenerates an air flow of sucking indoor air into the unit and supplying the indoor space with supply air obtained after heat exchange with the refrigerant flowing in the utilization-side heat exchanger52a. The indoor fan53ais driven by the indoor fan motor54a.

The utilization unit3ais provided with a liquid-side temperature sensor58athat detects a temperature of a refrigerant on the liquid side of the utilization-side heat exchanger52a. The utilization unit3ais further provided with an indoor temperature sensor55athat detects an indoor temperature as a temperature of air introduced from the indoor space before passing through the utilization-side heat exchanger52a.

The utilization-side control unit50acontrols behavior of the elements51aand53a(54a) of the utilization unit3a. Then, the utilization-side control unit50aincludes a processor such as a CPU or a microcomputer provided to control the utilization unit3aand a memory, so as to transmit and receive control signals and the like to and from the remote controller (not shown), and to transmit and receive control signals and the like among the cascade-side control unit20in the cascade unit2, the branch unit control units60a,60b, and60c, and the primary-side control unit70in the primary-side unit5.

Note that the second utilization unit3bincludes the utilization circuit13b, an indoor fan53b, the utilization-side control unit50b, and an indoor fan motor54b. The third utilization unit3cincludes the utilization circuit13c, an indoor fan53c, the utilization-side control unit50c, and an indoor fan motor54c.

(7) Branch Unit

The branch units6a,6b, and6care installed in a space behind the ceiling of the indoor space of an office building or the like.

Each of the branch units6a,6b, and6cis connected to a corresponding one of the utilization units3a,3b, and3con one-on-one basis. The branch units6a,6b, and6care connected to the cascade unit2via the connection pipes7,8, and9.

Next, configurations of the branch units6a,6b, and6cwill be described. The second branch unit6band the third branch unit6care configured similarly to the first branch unit6a. The configuration of only the first branch unit6awill thus be described here. As for the configuration of each of the second branch unit6band the third branch unit6c, elements will be denoted by reference signs obtained by replacing a subscript “a” in reference signs of elements of the first branch unit6awith a subscript “b” or “c”, and these elements will not be described repeatedly.

The first branch unit6amainly includes the branch circuit14aand the branch unit control unit60adescribed above.

The branch unit control unit60acontrols behavior of the elements66aand67aof the branch unit6a. Then, the branch unit control unit60aincludes a processor such as a CPU or a microcomputer provided to control the branch unit6aand a memory, so as to transmit and receive control signals and the like to and from the remote controller (not shown), and to transmit and receive control signals and the like between the cascade-side control unit20in the cascade unit2, the utilization units3a,3b, and3c, and the primary-side control unit70in the primary-side unit5.

Note that the second branch unit6bincludes the branch circuit14band the branch unit control unit60b. The third branch unit6cincludes the branch circuit14cand the branch unit control unit60c.

(8) Control Unit

In the refrigeration cycle apparatus1, the cascade-side control unit20, the utilization-side control units50a,50b, and50c, the branch unit control units60a,60b, and60c, and the primary-side control unit70described above are communicably connected to each other in a wired or wireless manner to constitute a control unit80. Therefore, the control unit80controls behavior of the units21(21a),22,36,44,46a,48a,51a,51b,51c,53a,53b,53c(54a,54b,54c),66a,66b,66c,67a,67b,67c,71(71a),72,75(75a),76,104aon the basis of detection information of the various sensors37,38,39,83,84,85,86,87,88,77,78,79,81,82,58a,58b,58c, and the like, and instruction information received from a remote controller (not shown) and the like.

(9) Behavior of Refrigeration Cycle Apparatus

Next, behavior of the refrigeration cycle apparatus1will be described with reference toFIGS.3to6.

Refrigeration cycle operation of the refrigeration cycle apparatus1can be mainly divided into the cooling operation, the heating operation, the cooling main operation, and the heating main operation.

Here, the cooling operation is refrigeration cycle operation in which only the utilization unit in which the utilization-side heat exchanger functions as a refrigerant evaporator exists, and the cascade heat exchanger35functions as a radiator for the secondary-side refrigerant for an evaporation load of the entire utilization unit.

The heating operation corresponds to refrigeration cycle operation in a case where only the utilization units in which the utilization-side heat exchanger functions as a refrigerant radiator exists, and the cascade heat exchanger35functions as an evaporator for the secondary-side refrigerant for a radiation load of the entire utilization unit.

The cooling main operation is operation in which the utilization unit in which the utilization-side heat exchanger functions as a refrigerant evaporator and the utilization unit in which the utilization-side heat exchanger functions as a refrigerant radiator are mixed. The cooling main operation is refrigeration cycle operation in which, when an evaporation load is a main thermal load of the entire utilization unit, the cascade heat exchanger35functions as a radiator for the secondary-side refrigerant in order to process the evaporation load of the entire utilization unit.

The heating main operation is operation in which the utilization unit in which the utilization-side heat exchanger functions as a refrigerant evaporator and the utilization unit in which the utilization-side heat exchanger functions as a refrigerant radiator are mixed. The heating main operation is refrigeration cycle operation in which, when a radiation load is a main heat load of the entire utilization unit, the cascade heat exchanger35functions as an evaporator for the secondary-side refrigerant in order to process the radiation load of the entire utilization unit.

Note that the behavior of the refrigeration cycle apparatus1including the refrigeration cycle operation is performed by the control unit80described above.

(9-1) Cooling Operation

In the cooling operation, for example, each of the utilization-side heat exchangers52a,52b, and52cin the utilization units3a,3b, and3cfunctions as a refrigerant evaporator, and the cascade heat exchanger35functions as a radiator for the secondary-side refrigerant. In this cooling operation, the primary-side refrigerant circuit5aand the secondary-side refrigerant circuit10of the refrigeration cycle apparatus1are configured as shown inFIG.3. Note that arrows attached to the primary-side refrigerant circuit5aand arrows attached to the secondary-side refrigerant circuit10inFIG.3indicate flows of the refrigerant during the cooling operation.

Specifically, in the primary-side unit5, the primary-side switching mechanism72is switched to the fifth connecting state to cause the cascade heat exchanger35to function as an evaporator for the primary-side refrigerant. The fifth connecting state of the primary-side switching mechanism72is depicted by the solid lines of the primary-side switching mechanism72inFIG.3. Accordingly, in the primary-side unit5, the primary-side refrigerant discharged from the primary-side compressor71passes through the primary-side switching mechanism72and exchanges heat with outdoor air supplied from the primary-side fan75in the primary-side heat exchanger74to be condensed. The primary-side refrigerant condensed in the primary-side heat exchanger74passes through the primary-side first expansion valve76controlled into a fully opened state, and a part of the refrigerant flows toward the first liquid shutoff valve108via the primary-side subcooling heat exchanger103, and another part of the refrigerant branches into the primary-side subcooling circuit104. The refrigerant flowing in the primary-side subcooling circuit104is decompressed while passing through the primary-side subcooling expansion valve104a. The refrigerant flowing from the primary-side first expansion valve76toward the first liquid shutoff valve108exchanges heat with the refrigerant decompressed by the primary-side subcooling expansion valve104aand flowing in the primary-side subcooling circuit104in the primary-side subcooling heat exchanger103, and is cooled until reaching a subcooled state. The refrigerant in the subcooled state flows through the primary-side first connection pipe111, the second liquid shutoff valve106, and the second refrigerant pipe114in that order, and is decompressed while passing through the primary-side second expansion valve102. Here, a valve opening degree of the primary-side second expansion valve102is controlled such that a degree of superheating of the primary-side refrigerant sucked into the primary-side compressor71satisfies a predetermined condition. When flowing through the primary-side flow path35bof the cascade heat exchanger35, the primary-side refrigerant decompressed by the primary-side second expansion valve102evaporates by exchanging heat with the secondary-side refrigerant flowing through the secondary-side flow path35a, and flows toward the second gas shutoff valve107through the first refrigerant pipe113. The refrigerant having passed through the second gas shutoff valve107passes through the primary-side second connection pipe112and the first gas shutoff valve109, and then reaches the primary-side switching mechanism72. The refrigerant having passed through the primary-side switching mechanism72joins the refrigerant having flowed in the primary-side subcooling circuit104, and is then sucked into the primary-side compressor71via the primary-side accumulator105.

In the cascade unit2, by switching the secondary-side switching mechanism22to the first connecting state, the cascade heat exchanger35functions as a radiator for the secondary-side refrigerant. In the first connecting state of the secondary-side switching mechanism22, the discharge flow path24and the third pipe25are connected by the first switching valve22a, and the first pipe28and the suction flow path23are connected by the second switching valve22b. In the first to third utilization units3a,3b, and3c, the second control valves67a,67b, and67care controlled into the opened state. Accordingly, each of the utilization-side heat exchangers52a,52b, and52cin the utilization units3a,3b, and3cfunctions as a refrigerant evaporator. All of the utilization-side heat exchangers52a,52b, and52cof the utilization units3a,3b, and3cand the suction side of the secondary-side compressor21of the cascade unit2are connected via the first utilization pipes57a,57b, and57c, the first connecting tubes15a,15b, and15c, the junction pipes62a,62b, and62c, the second branch pipes64a,64b, and64c, the bypass pipes69a,69b, and69c, some of the first branch pipes63a,63b, and63c, the secondary-side first connection pipe8, and the secondary-side second connection pipe9. The opening degree of the secondary-side subcooling expansion valve48ais controlled such that a degree of subcooling of the secondary-side refrigerant flowing through the outlet of the secondary-side subcooling heat exchanger47toward the secondary-side third connection pipe7satisfies a predetermined condition. The bypass expansion valve46ais controlled into the closed state. In the utilization units3a,3b, and3c, the opening degrees of the utilization-side expansion valves51a,51b, and51care adjusted.

In the cooling operation, the secondary-side refrigerant circuit10controls capacity, for example, by controlling a frequency of the secondary-side compressor21such that evaporation temperature of the secondary-side refrigerant in the utilization-side heat exchangers52a,52b, and52cbecomes predetermined secondary-side evaporation target temperature. The opening degree of the cascade expansion valve36is adjusted such that the secondary-side refrigerant flowing through the cascade heat exchanger35has a critical pressure or less. The primary-side refrigerant circuit5acontrols capacity, for example, by controlling a frequency of the primary-side compressor71such that evaporation temperature of the primary-side refrigerant in the primary-side flow path35bof the cascade heat exchanger35becomes predetermined primary-side evaporation target temperature. As described above, in the cooling operation, by executing either or both of the control for increasing the valve opening degree of the cascade expansion valve36and the control for increasing the frequency of the primary-side compressor71in the primary-side refrigerant circuit5a, the carbon dioxide refrigerant flowing through the cascade heat exchanger35is controlled so as not to exceed a critical point.

The opening degree of the first electric component expansion valve17aprovided in the first electric component cooling flow path17is adjusted so as to be in the fully opened state or a predetermined opening degree. The second electric component expansion valve18aprovided in the second electric component cooling flow path18is adjusted to have a predetermined opening degree with which the secondary-side refrigerant passing through the second electric component expansion valve18acan be decompressed. The valve opening degree of the second electric component expansion valve18amay be controlled to satisfy such a condition that the secondary-side refrigerant after passing through the second cooling portion11bhas a predetermined degree of superheating or more, for example. In this case, for example, a temperature sensor of the secondary-side refrigerant flowing through a portion downstream of the second cooling portion11bin the second electric component cooling flow path18may be used.

In such a secondary-side refrigerant circuit10, a high-pressure secondary-side refrigerant compressed and discharged by the secondary-side compressor21is sent to the secondary-side flow path35aof the cascade heat exchanger35through the first switching valve22aof the secondary-side switching mechanism22. The high-pressure secondary-side refrigerant flowing in the secondary-side flow path35aof the cascade heat exchanger35radiates heat, and the primary-side refrigerant flowing in the primary-side flow path35bof the cascade heat exchanger35evaporates. The secondary-side refrigerant having radiated heat in the cascade heat exchanger35passes through the cascade expansion valve36whose opening degree is adjusted, and then most of the refrigerant flows into the secondary-side receiver45, and a remaining part of the refrigerant branches from the portion X toward the first electric component cooling flow path17and flows. The refrigerant flowing through the first electric component cooling flow path17and not in the critical state cools the first electric component91of the cascade-side control unit20when passing through the first cooling portion11a. The refrigerant that has branched and flowed from the portion Y of the first electric component cooling flow path17to the second electric component cooling flow path18is decompressed when passing through the second electric component expansion valve18a, becomes a refrigerant having a lower temperature, and is sent to the second cooling portion11b. The refrigerant passing through the second cooling portion11bcools the space S2in which the second electric component92and the first electric component91of the cascade-side control unit20are provided. A part of the refrigerant having flowed out of the secondary-side receiver45branches into the secondary-side subcooling circuit48, is decompressed at the secondary-side subcooling expansion valve48a, and then joins into the suction flow path23. In the secondary-side subcooling heat exchanger47, another part of the refrigerant having flowed out of the secondary-side receiver45is cooled by the refrigerant flowing in the secondary-side subcooling circuit48, and is then sent to the secondary-side third connection pipe7via the third shutoff valve31.

Then, the refrigerant sent to the secondary-side third connection pipe7is branched into three portions to pass through the third branch pipes61a,61b, and61cof the first to third branch units6a,6b, and6c. Thereafter, the refrigerant having flowed through the second connecting tubes16a,16b, and16cis sent to the second utilization pipes56a,56b, and56cof the first to third utilization units3a,3b, and3c. The refrigerant sent to the second utilization pipes56a,56b, and56cis sent to the utilization-side expansion valves51a,51b, and51cin the utilization units3a,3b, and3c.

Then, the refrigerant having passed the utilization-side expansion valves51a,51b, and51cwhose opening degrees are adjusted exchanges heat with indoor air supplied by the indoor fans53a,53b, and53cin the utilization-side heat exchangers52a,52b, and52c. The refrigerant flowing in the utilization-side heat exchangers52a,52b, and52cis thus evaporated into a low-pressure gas refrigerant. Indoor air is cooled and is supplied into the indoor space. The indoor space is thus cooled. The low-pressure gas refrigerant evaporated in the utilization-side heat exchangers52a,52b, and52cflows through the first utilization pipes57a,57b, and57c, flows through the first connecting tubes15a,15b, and15c, and then is sent to the junction pipes62a,62b, and62cof the first to third branch units6a,6b, and6c.

Then, the low-pressure gas refrigerant sent to the junction pipes62a,62b, and62cflows to the second branch pipes64a,64b, and64c. A part of the refrigerant that has passed through the second control valves67a,67b, and67cin the second branch pipes64a,64b, and64cis sent to the secondary-side second connection pipe9. A remaining part of the refrigerant that has passed through the second control valves67a,67b, and67cpasses through the bypass pipes69a,69b, and69c, flows through a part of the first branch pipes63a,63b, and63c, and then is sent to the secondary-side first connection pipe8.

Then, the low-pressure gas refrigerant sent to the secondary-side first connection pipe8and the secondary-side second connection pipe9is returned to the suction side of the secondary-side compressor21through the first shutoff valve32, the second shutoff valve33, the first pipe28, the second pipe29, the second switching valve22bof the secondary-side switching mechanism22, the suction flow path23, and the secondary-side accumulator30.

Behavior during the cooling operation is executed in this manner.

(9-2) Heating Operation

In the heating operation, each of the utilization-side heat exchangers52a,52b, and52cin the utilization units3a,3b, and3cfunctions as a refrigerant radiator. In the heating operation, the cascade heat exchanger35operates to function as an evaporator for the secondary-side refrigerant. In the heating operation, the primary-side refrigerant circuit5aand the secondary-side refrigerant circuit10of the refrigeration cycle apparatus1are configured as shown inFIG.4. Arrows attached to the primary-side refrigerant circuit5aand arrows attached to the secondary-side refrigerant circuit10inFIG.4indicate flows of the refrigerant during the heating operation.

Specifically, in the primary-side unit5, the primary-side switching mechanism72is switched to a sixth operating state to cause the cascade heat exchanger35to function as a radiator for the primary-side refrigerant. The sixth operating state of the primary-side switching mechanism72corresponds to a connecting state depicted by broken lines in the primary-side switching mechanism72inFIG.4. Accordingly, in the primary-side unit5, the primary-side refrigerant discharged from the primary-side compressor71, having passed the primary-side switching mechanism72and the first gas shutoff valve109, passes through the primary-side second connection pipe112and the second gas shutoff valve107to be sent to the primary-side flow path35bof the cascade heat exchanger35. The refrigerant flowing in the primary-side flow path35bof the cascade heat exchanger35is condensed by exchanging heat with the secondary-side refrigerant flowing in the secondary-side flow path35a. When flowing through the second refrigerant pipe114, the primary-side refrigerant condensed in the cascade heat exchanger35passes through the primary-side second expansion valve102controlled into the fully opened state. The refrigerant that has passed through the primary-side second expansion valve102flows through the second liquid shutoff valve106, the primary-side first connection pipe111, the first liquid shutoff valve108, and the primary-side subcooling heat exchanger103in that order, and is decompressed by the primary-side first expansion valve76. During the heating operation, the primary-side subcooling expansion valve104ais controlled into the closed state, so that the refrigerant does not flow into the primary-side subcooling circuit104. Therefore, no heat is exchanged in the primary-side subcooling heat exchanger103. The valve opening degree of the primary-side first expansion valve76is controlled such that, for example, a degree of superheating of the refrigerant sucked into the primary-side compressor71satisfies a predetermined condition. The refrigerant decompressed at the primary-side first expansion valve76exchanges heat with outdoor air supplied from the primary-side fan75in the primary-side heat exchanger74to be evaporated, and is sucked into the primary-side compressor71via the primary-side switching mechanism72and the primary-side accumulator105.

In the cascade unit2, the secondary-side switching mechanism22is switched to the second connecting state. The cascade heat exchanger35thus functions as an evaporator for the secondary-side refrigerant. In the second connecting state of the secondary-side switching mechanism22, the discharge flow path24and the first pipe28are connected by the second switching valve22b, and the third pipe25and the suction flow path23are connected by the first switching valve22a. The opening degree of the cascade expansion valve36is adjusted. In the first to third branch units6a,6b, and6c, the first control valves66a,66b, and66care controlled into the opened state, and the second control valves67a,67b, and67care controlled into the closed state. Accordingly, each of the utilization-side heat exchangers52a,52b, and52cin the utilization units3a,3b, and3cfunctions as a refrigerant radiator. Then, the utilization-side heat exchangers52a,52b, and52cin the utilization units3a,3b, and3cand the discharge side of the secondary-side compressor21in the cascade unit2are connected via the discharge flow path24, the first pipe28, the secondary-side first connection pipe8, the first branch pipes63a,63b, and63c, the junction pipes62a,62b, and62c, the first connecting tubes15a,15b, and15c, and the first utilization pipes57a,57b, and57c. The secondary-side subcooling expansion valve48aand the bypass expansion valve46aare controlled into the closed state. In the utilization units3a,3b, and3c, the opening degrees of the utilization-side expansion valves51a,51b, and51care adjusted.

In the heating operation, the secondary-side refrigerant circuit10controls capacity of the secondary-side compressor21so as to achieve a frequency at which the loads in the utilization-side heat exchangers52a,52b, and52ccan be processed. As a result, in the heating operation, control is performed such that the secondary-side refrigerant discharged from the secondary-side compressor21can be in the critical state exceeding the critical pressure. The primary-side refrigerant circuit5acontrols capacity, for example, by controlling the frequency of the primary-side compressor71so that condensation temperature of the primary-side refrigerant in the primary-side flow path35bof the cascade heat exchanger35becomes predetermined primary-side condensation target temperature.

The opening degree of the first electric component expansion valve17aprovided in the first electric component cooling flow path17is adjusted so as to be in the fully opened state or a predetermined opening degree. The second electric component expansion valve18aprovided in the second electric component cooling flow path18is adjusted to have a predetermined opening degree with which the secondary-side refrigerant passing through the second electric component expansion valve18acan be decompressed. The valve opening degree of the second electric component expansion valve18amay be controlled to satisfy such a condition that the secondary-side refrigerant after passing through the second cooling portion11bhas a predetermined degree of superheating or more, for example.

In such a secondary-side refrigerant circuit10, the high-pressure refrigerant compressed and discharged by the secondary-side compressor21is sent to the first pipe28through the second switching valve22bof the secondary-side switching mechanism22. The refrigerant sent to the first pipe28is sent to the secondary-side first connection pipe8via the first shutoff valve32.

Then, the high-pressure refrigerant sent to the secondary-side first connection pipe8is branched into three portions to be sent to the first branch pipes63a,63b, and63cin the utilization units3a,3b, and3cin operation. The high-pressure refrigerant sent to the first branch pipes63a,63b, and63cpasses through the first control valves66a,66b, and66c, and flows in the junction pipes62a,62b, and62c. The refrigerant having flowed in the first connecting tubes15a,15b, and15cand the first utilization pipes57a,57b, and57cis then sent to the utilization-side heat exchangers52a,52b, and52c.

Then, the high-pressure refrigerant sent to the utilization-side heat exchangers52a,52b, and52cexchanges heat with indoor air supplied by the indoor fans53a,53b, and53cin the utilization-side heat exchangers52a,52b, and52c. The refrigerant flowing in the utilization-side heat exchangers52a,52b, and52cthus radiates heat. Indoor air is heated and is supplied into the indoor space. The indoor space is thus heated. The refrigerant having radiated heat in the utilization-side heat exchangers52a,52b, and52cflows in the second utilization pipes56a,56b, and56cand passes the utilization-side expansion valves51a,51b, and51cwhose opening degrees are adjusted. The secondary-side refrigerant having passed through the utilization-side expansion valves51a,51b, and51chas the critical pressure or less. Thereafter, the refrigerant having flowed through the second connecting tubes16a,16b, and16cflows in the third branch pipes61a,61b, and61cof the branch units6a,6b, and6c.

Then, the refrigerant sent to the third branch pipes61a,61b, and61cis sent to the secondary-side third connection pipe7to join.

Then, most of the refrigerant sent to the secondary-side third connection pipe7passes through the third shutoff valve31and then is sent to the cascade expansion valve36, and a remaining part of the refrigerant branches from the portion Z toward the first electric component cooling flow path17and flows. The refrigerant flowing through the first electric component cooling flow path17and not in the critical state passes through the first cooling portion11aafter passing through the first electric component expansion valve17a, and cools the first electric component91of the cascade-side control unit20at that time. The refrigerant that has branched and flowed from the portion Y of the first electric component cooling flow path17to the second electric component cooling flow path18is decompressed when passing through the second electric component expansion valve18a, becomes a refrigerant having a lower temperature, and is sent to the second cooling portion11b. The refrigerant passing through the second cooling portion11bcools the space S2in which the second electric component92and the first electric component91of the cascade-side control unit20are provided. The flow rate of the refrigerant sent to the cascade expansion valve36is adjusted by the cascade expansion valve36, and then the refrigerant is sent to the cascade heat exchanger35. In the cascade heat exchanger35, the secondary-side refrigerant flowing in the secondary-side flow path35ais evaporated into a low-pressure gas refrigerant and is sent to the secondary-side switching mechanism22, and the primary-side refrigerant flowing in the primary-side flow path35bof the cascade heat exchanger35is condensed. Then, the secondary-side low-pressure gas refrigerant sent to the first switching valve22aof the secondary-side switching mechanism22is returned to the suction side of the secondary-side compressor21through the suction flow path23and the secondary-side accumulator30.

Behavior during the heating operation is executed in this manner.

(9-3) Cooling Main Operation

In the cooling main operation, for example, the utilization-side heat exchangers52aand52bin the utilization units3aand3beach function as a refrigerant evaporator, and the utilization-side heat exchanger52cin the utilization unit3cfunctions as a refrigerant radiator. In the cooling main operation, the cascade heat exchanger35functions as a radiator for the secondary-side refrigerant. In the cooling main operation, the primary-side refrigerant circuit5aand the secondary-side refrigerant circuit10of the refrigeration cycle apparatus1are configured as shown inFIG.5. Arrows attached to the primary-side refrigerant circuit5aand arrows attached to the secondary-side refrigerant circuit10inFIG.5indicate flows of the refrigerant during the cooling main operation.

Specifically, in the primary-side unit5, the primary-side switching mechanism72is switched to the fifth connecting state (the state depicted by solid lines in the primary-side switching mechanism72inFIG.5) to cause the cascade heat exchanger35to function as an evaporator for the primary-side refrigerant. Accordingly, in the primary-side unit5, the primary-side refrigerant discharged from the primary-side compressor71passes through the primary-side switching mechanism72and exchanges heat with outdoor air supplied from the primary-side fan75in the primary-side heat exchanger74to be condensed. The primary-side refrigerant condensed in the primary-side heat exchanger74passes through the primary-side first expansion valve76controlled into a fully opened state, and a part of the refrigerant flows toward the first liquid shutoff valve108via the primary-side subcooling heat exchanger103, and another part of the refrigerant branches into the primary-side subcooling circuit104. The refrigerant flowing in the primary-side subcooling circuit104is decompressed while passing through the primary-side subcooling expansion valve104a. The refrigerant flowing from the primary-side first expansion valve76toward the first liquid shutoff valve108exchanges heat with the refrigerant decompressed by the primary-side subcooling expansion valve104aand flowing in the primary-side subcooling circuit104in the primary-side subcooling heat exchanger103, and is cooled until reaching a subcooled state. The refrigerant in the subcooled state flows through the primary-side first connection pipe111, the second liquid shutoff valve106, and the second refrigerant pipe114in that order, and is decompressed by the primary-side second expansion valve102. At this time, for example, the valve opening degree of the primary-side second expansion valve102is controlled such that a degree of superheating of the refrigerant sucked into the primary-side compressor71satisfies a predetermined condition. When flowing through the primary-side flow path35bof the cascade heat exchanger35, the primary-side refrigerant decompressed by the primary-side second expansion valve102evaporates by exchanging heat with the secondary-side refrigerant flowing through the secondary-side flow path35a, and flows toward the second gas shutoff valve107through the first refrigerant pipe113. The refrigerant having passed through the second gas shutoff valve107passes through the primary-side second connection pipe112and the first gas shutoff valve109, and then reaches the primary-side switching mechanism72. The refrigerant having passed through the primary-side switching mechanism72joins the refrigerant having flowed in the primary-side subcooling circuit104, and is then sucked into the primary-side compressor71via the primary-side accumulator105.

In the cascade unit2, the secondary-side switching mechanism22is switched to the third connecting state in which the discharge flow path24and the third pipe25are connected by the first switching valve22aand the discharge flow path24and the first pipe28are connected by the second switching valve22bto cause the cascade heat exchanger35to function as a radiator for the secondary-side refrigerant. The opening degree of the cascade expansion valve36is adjusted. In the first to third branch units6a,6b, and6c, the first control valve66cand the second control valves67aand67bare controlled into the opened state, and the first control valves66aand66band the second control valve67care controlled into the closed state. Accordingly, the utilization-side heat exchangers52aand52bin the utilization units3aand3beach function as a refrigerant evaporator, and the utilization-side heat exchanger52cin the utilization unit3cfunctions as a refrigerant radiator. The utilization-side heat exchangers52aand52bin the utilization units3aand3band the suction side of the secondary-side compressor21in the cascade unit2are connected via the secondary-side second connection pipe9, and the utilization-side heat exchanger52cin the utilization unit3cand the discharge side of the secondary-side compressor21in the cascade unit2are connected via the secondary-side first connection pipe8. The opening degree of the secondary-side subcooling expansion valve48ais controlled such that a degree of subcooling of the secondary-side refrigerant flowing through the outlet of the secondary-side subcooling heat exchanger47toward the secondary-side third connection pipe7satisfies a predetermined condition. The bypass expansion valve46ais controlled into the closed state. In the utilization units3a,3b, and3c, the opening degrees of the utilization-side expansion valves51a,51b, and51care adjusted.

In the cooling main operation, the secondary-side refrigerant circuit10controls capacity, for example, by controlling the frequency of the secondary-side compressor21such that evaporation temperature in a heat exchanger functioning as an evaporator for the secondary-side refrigerant among the utilization-side heat exchanger52a,52b, and52cbecomes predetermined secondary-side evaporation target temperature. The opening degree of the cascade expansion valve36is adjusted such that the secondary-side refrigerant flowing through the cascade heat exchanger35has a critical pressure or less. The primary-side refrigerant circuit5acontrols capacity, for example, by controlling a frequency of the primary-side compressor71such that evaporation temperature of the primary-side refrigerant in the primary-side flow path35bof the cascade heat exchanger35becomes predetermined primary-side evaporation target temperature. As described above, in the cooling operation, by executing either or both of the control for increasing the valve opening degree of the cascade expansion valve36and the control for increasing the frequency of the primary-side compressor71in the primary-side refrigerant circuit5a, the carbon dioxide refrigerant flowing through the cascade heat exchanger35is controlled so as not to exceed a critical point.

The opening degree of the first electric component expansion valve17aprovided in the first electric component cooling flow path17is adjusted so as to be in the fully opened state or a predetermined opening degree. The second electric component expansion valve18aprovided in the second electric component cooling flow path18is adjusted to have a predetermined opening degree with which the secondary-side refrigerant passing through the second electric component expansion valve18acan be decompressed. The valve opening degree of the second electric component expansion valve18amay be controlled to satisfy such a condition that the secondary-side refrigerant after passing through the second cooling portion11bhas a predetermined degree of superheating or more, for example.

In such a secondary-side refrigerant circuit10, a part of the secondary-side high-pressure refrigerant compressed and discharged by the secondary-side compressor21is sent to the secondary-side first connection pipe8through the second switching valve22bof the secondary-side switching mechanism22, the first pipe28, and the first shutoff valve32, and the rest is sent to the secondary-side flow path35aof the cascade heat exchanger35through the first switching valve22aof the secondary-side switching mechanism22and the third pipe25.

Then, the high-pressure refrigerant sent to the secondary-side first connection pipe8is sent to the first branch pipe63c. The high-pressure refrigerant sent to the first branch pipe63cis sent to the utilization-side heat exchanger52cin the utilization unit3cvia the first control valve66cand the junction pipe62c.

Then, the high-pressure refrigerant sent to the utilization-side heat exchanger52cexchanges heat with indoor air supplied by the indoor fan53cin the utilization-side heat exchanger52c. The refrigerant flowing in the utilization-side heat exchanger52cthus radiates heat. Indoor air is heated and is supplied into the indoor space, and the utilization unit3cexecutes heating operation. The refrigerant having radiated heat in the utilization-side heat exchanger52cflows in the second utilization pipe56c, and the flow rate of the refrigerant is adjusted at the utilization-side expansion valve51c. The refrigerant having flowed through the second connecting tube16cis sent to the third branch pipe61cin the branch unit6c.

Then, the refrigerant sent to the third branch pipe61cis sent to the secondary-side third connection pipe7.

The high-pressure refrigerant sent to the secondary-side flow path35aof the cascade heat exchanger35exchanges heat with the primary-side refrigerant flowing in the primary-side flow path35bin the cascade heat exchanger35to radiate heat. The flow rate of the secondary-side refrigerant having radiated heat in the cascade heat exchanger35at the cascade expansion valve36, and then most of the refrigerant flows into the secondary-side receiver45, and a remaining part of the refrigerant branches from the portion X toward the first electric component cooling flow path17and flows. The refrigerant flowing through the first electric component cooling flow path17and not in the critical state cools the first electric component91of the cascade-side control unit20when passing through the first cooling portion11a. The refrigerant that has branched and flowed from the portion Y of the first electric component cooling flow path17to the second electric component cooling flow path18is decompressed when passing through the second electric component expansion valve18a, becomes a refrigerant having a lower temperature, and is sent to the second cooling portion11b. The refrigerant passing through the second cooling portion11bcools the space S2in which the second electric component92and the first electric component91of the cascade-side control unit20are provided. A part of the refrigerant having flowed out of the secondary-side receiver45branches into the secondary-side subcooling circuit48, is decompressed at the secondary-side subcooling expansion valve48a, and then joins into the suction flow path23. In the secondary-side subcooling heat exchanger47, another part of the refrigerant having flowed out of the secondary-side receiver45is cooled by the refrigerant flowing in the secondary-side subcooling circuit48, is then sent to the secondary-side third connection pipe7via the third shutoff valve31, and joins the refrigerant having radiated heat in the utilization-side heat exchanger52c.

Then, the refrigerant having joined in the secondary-side third connection pipe7is branched into two portions to be sent to the third branch pipes61aand61bof the branch units6aand6b. Thereafter, the refrigerant having flowed through the second connecting tubes16aand16bis sent to the second utilization pipes56aand56bof the first and second utilization units3aand3b. The refrigerant flowing in the second utilization pipes56aand56bpasses the utilization-side expansion valves51aand51bin the utilization units3aand3b.

Then, the refrigerant having passed the utilization-side expansion valves51aand51bwhose opening degrees are adjusted exchanges heat with indoor air supplied by the indoor fans53aand53bin the utilization-side heat exchangers52aand52b. The refrigerant flowing in the utilization-side heat exchangers52aand52bis thus evaporated into a low-pressure gas refrigerant. Indoor air is cooled and is supplied into the indoor space. The indoor space is thus cooled. The low-pressure gas refrigerant evaporated in the utilization-side heat exchangers52aand52bis sent to the junction pipes62aand62bof the first and second branch units6aand6b.

Then, the low-pressure gas refrigerant sent to the junction pipes62aand62bis sent to the secondary-side second connection pipe9via the second control valves67aand67band the second branch pipes64aand64b, to join.

Then, the low-pressure gas refrigerant sent to the secondary-side second connection pipe9is returned to the suction side of the secondary-side compressor21via the second shutoff valve33, the second pipe29, the suction flow path23, and the secondary-side accumulator30.

Behavior during the cooling main operation is executed in this manner.

(9-4) Heating Main Operation

In the heating main operation, for example, the utilization-side heat exchangers52aand52bin the utilization units3aand3beach function as a refrigerant radiator, and the utilization-side heat exchanger52cfunctions as a refrigerant evaporator. In the heating main operation, the cascade heat exchanger35functions as an evaporator for the secondary-side refrigerant. In the heating main operation, the primary-side refrigerant circuit5aand the secondary-side refrigerant circuit10of the refrigeration cycle apparatus1are configured as shown inFIG.6. Arrows attached to the primary-side refrigerant circuit5aand arrows attached to the secondary-side refrigerant circuit10inFIG.6indicate flows of the refrigerant during the heating main operation.

Specifically, in the primary-side unit5, the primary-side switching mechanism72is switched to a sixth operating state to cause the cascade heat exchanger35to function as a radiator for the primary-side refrigerant. The sixth operating state of the primary-side switching mechanism72corresponds to a connecting state depicted by broken lines in the primary-side switching mechanism72inFIG.6. Accordingly, in the primary-side unit5, the primary-side refrigerant discharged from the primary-side compressor71, having passed the primary-side switching mechanism72and the first gas shutoff valve109, passes through the primary-side second connection pipe112and the second gas shutoff valve107to be sent to the primary-side flow path35bof the cascade heat exchanger35. The refrigerant flowing in the primary-side flow path35bof the cascade heat exchanger35is condensed by exchanging heat with the secondary-side refrigerant flowing in the secondary-side flow path35a. When flowing through the second refrigerant pipe114, the primary-side refrigerant condensed in the cascade heat exchanger35passes through the primary-side second expansion valve102controlled into the fully opened state. Then, the primary-side refrigerant flows through the second liquid shutoff valve106, the primary-side first connection pipe111, the first liquid shutoff valve108, and the primary-side subcooling heat exchanger103in that order, and is decompressed by the primary-side first expansion valve76. During the heating main operation, the primary-side subcooling expansion valve104ais controlled into the closed state, so that the refrigerant does not flow into the primary-side subcooling circuit104. Therefore, no heat is exchanged in the primary-side subcooling heat exchanger103. The valve opening degree of the primary-side first expansion valve76is controlled such that, for example, a degree of superheating of the refrigerant sucked into the primary-side compressor71satisfies a predetermined condition. The refrigerant decompressed at the primary-side first expansion valve76exchanges heat with outdoor air supplied from the primary-side fan75in the primary-side heat exchanger74to be evaporated, and is sucked into the primary-side compressor71via the primary-side switching mechanism72and the primary-side accumulator105.

In the cascade unit2, the secondary-side switching mechanism22is switched to the second connecting state. In the second connecting state of the secondary-side switching mechanism22, the discharge flow path24and the first pipe28are connected by the second switching valve22b, and the third pipe25and the suction flow path23are connected by the first switching valve22a. The cascade heat exchanger35thus functions as an evaporator for the secondary-side refrigerant. The opening degree of the cascade expansion valve36is adjusted. In the first to third branch units6a,6b, and6c, the first control valves66aand66band the second control valve67care controlled into the opened state, and the first control valve66cand the second control valves67aand67bare controlled into the closed state. Accordingly, the utilization-side heat exchangers52aand52bin the utilization units3aand3beach function as a refrigerant radiator, and the utilization-side heat exchanger52cin the utilization unit3cfunctions as a refrigerant evaporator. Then, the utilization-side heat exchanger52cin the utilization unit3cand the suction side of the secondary-side compressor21in the cascade unit2are connected via the first utilization pipe57c, the first connecting tube15c, the junction pipe62c, the second branch pipe64c, and the secondary-side second connection pipe9. The utilization-side heat exchangers52aand52bin the utilization units3aand3band the discharge side of the secondary-side compressor21in the cascade unit2are connected via the discharge flow path24, the first pipe28, the secondary-side first connection pipe8, the first branch pipes63aand63b, the junction pipes62aand62b, the first connecting tubes15aand15b, and the first utilization pipes57aand57b. The secondary-side subcooling expansion valve48aand the bypass expansion valve46aare controlled into the closed state. In the utilization units3a,3b, and3c, the opening degrees of the utilization-side expansion valves51a,51b, and51care adjusted.

In the heating main operation, the secondary-side refrigerant circuit10controls capacity, for example, by controlling the frequency of the secondary-side compressor21so as to process a load in a heat exchanger functioning as a radiator for the secondary-side refrigerant among the utilization-side heat exchangers52a,52b, and52c. As a result, in the heating main operation, control is performed such that the secondary-side refrigerant discharged from the secondary-side compressor21can be in the critical state exceeding the critical pressure. The primary-side refrigerant circuit5acontrols capacity, for example, by controlling the frequency of the primary-side compressor71such that condensation temperature of the primary-side refrigerant in the primary-side flow path35bof the cascade heat exchanger35becomes predetermined primary-side condensation target temperature.

The opening degree of the first electric component expansion valve17aprovided in the first electric component cooling flow path17is adjusted so as to be in the fully opened state or a predetermined opening degree. The second electric component expansion valve18aprovided in the second electric component cooling flow path18is adjusted to have a predetermined opening degree with which the secondary-side refrigerant passing through the second electric component expansion valve18acan be decompressed. The valve opening degree of the second electric component expansion valve18amay be controlled to satisfy such a condition that the secondary-side refrigerant after passing through the second cooling portion11bhas a predetermined degree of superheating or more, for example.

In such a secondary-side refrigerant circuit10, the high-pressure secondary-side refrigerant compressed and discharged by the secondary-side compressor21is sent to the secondary-side first connection pipe8through the second switching valve22bof the secondary-side switching mechanism22, the first pipe28, and the first shutoff valve32.

Then, the high-pressure refrigerant sent to the secondary-side first connection pipe8is branched into two portions to be sent to the first branch pipes63aand63bof the first branch unit6aand the second branch unit6bconnected to the first utilization unit3aand the second utilization unit3bin operation. The high-pressure refrigerant sent to the first branch pipes63aand63bis sent to the utilization-side heat exchangers52aand52bin the first utilization unit3aand the second utilization unit3bvia the first control valves66aand66b, the junction pipes62aand62b, and the first connecting tubes15aand15b.

Then, the high-pressure refrigerant sent to the utilization-side heat exchangers52aand52bexchanges heat with indoor air supplied by the indoor fans53aand53bin the utilization-side heat exchangers52aand52b. The refrigerant flowing in the utilization-side heat exchangers52aand52bthus radiates heat. Indoor air is heated and is supplied into the indoor space. The indoor space is thus heated. The refrigerant having radiated heat in the utilization-side heat exchangers52aand52bflows in the second utilization pipes56aand56b, and passes the utilization-side expansion valves51aand51bwhose opening degrees are adjusted. The secondary-side refrigerant having passed through the utilization-side expansion valves51aand51bhas the critical pressure or less. Thereafter, the refrigerant having flowed through the second connecting tubes16aand16bis sent to the secondary-side third connection pipe7via the third branch pipes61aand61bof the branch units6aand6b.

Then, a part of the refrigerant sent to the secondary-side third connection pipe7is sent to the third branch pipe61cof the branch unit6c, and the remaining flows toward the third shutoff valve31.

Then, the refrigerant sent to the third branch pipe61cflows in the second utilization pipe56cof the utilization unit3cvia the second connecting tube16c, and is sent to the utilization-side expansion valve51c.

Then, the refrigerant having passed the utilization-side expansion valve51cwhose opening degree is adjusted exchanges heat with indoor air supplied by the indoor fan53cin the utilization-side heat exchanger52c. The refrigerant flowing in the utilization-side heat exchanger52cis thus evaporated into a low-pressure gas refrigerant. Indoor air is cooled and is supplied into the indoor space. The indoor space is thus cooled. The low-pressure gas refrigerant evaporated in the utilization-side heat exchanger52cpasses through the first utilization pipe57cand the first connecting tube15cto be sent to the junction pipe62c.

Then, the low-pressure gas refrigerant sent to the junction pipe62cis sent to the secondary-side second connection pipe9via the second control valve67cand the second branch pipe64c.

Then, the low-pressure gas refrigerant sent to the secondary-side second connection pipe9is returned to the suction side of the secondary-side compressor21via the second shutoff valve33, the second pipe29, the suction flow path23, and the secondary-side accumulator30.

Most of the refrigerant having flowed toward the third shutoff valve31is sent to the cascade expansion valve36, and a remaining part of the refrigerant branches from the portion Z toward the first electric component cooling flow path17and flows. The refrigerant flowing through the first electric component cooling flow path17and not in the critical state passes through the first cooling portion11aafter passing through the first electric component expansion valve17a, and cools the first electric component91of the cascade-side control unit20at that time. The refrigerant that has branched and flowed from the portion Y of the first electric component cooling flow path17to the second electric component cooling flow path18is decompressed when passing through the second electric component expansion valve18a, becomes a refrigerant having a lower temperature, and is sent to the second cooling portion11b. The refrigerant passing through the second cooling portion11bcools the space S2in which the second electric component92and the first electric component91of the cascade-side control unit20are provided. The refrigerant sent to the cascade expansion valve36passes through the cascade expansion valve36controlled in opening degree, and then exchanges heat with the primary-side refrigerant flowing in the primary-side flow path35bin the secondary-side flow path35aof the cascade heat exchanger35. As a result, the refrigerant flowing in the secondary-side flow path35aof the cascade heat exchanger35is evaporated into a low-pressure gas refrigerant, and is sent to the first switching valve22aof the secondary-side switching mechanism22. The low-pressure gas refrigerant sent to the first switching valve22aof the secondary-side switching mechanism22joins the low-pressure gas refrigerant evaporated in the utilization-side heat exchanger52cin the suction flow path23. The refrigerant thus joined is returned to the suction side of the secondary-side compressor21via the secondary-side accumulator30.

Behavior during the heating main operation is executed in this manner.

(10) Connection Configuration Between Primary-Side Unit and Cascade Unit

FIG.7is a schematic outer appearance view illustrating connection between the primary-side unit5and the cascade unit2.

The primary-side unit5includes the primary-side casing5xhaving a plurality of surfaces and a substantially rectangular parallelepiped shape. The primary-side casing5xinternally accommodates, as a part of the primary-side refrigerant circuit5a, the primary-side compressor71, the primary-side switching mechanism72, the primary-side heat exchanger74, the primary-side first expansion valve76, the primary-side subcooling heat exchanger103, the primary-side subcooling circuit104, the primary-side subcooling expansion valve104a, the first liquid shutoff valve108, the first gas shutoff valve109, and the primary-side accumulator105. The primary-side first connection pipe111and the primary-side second connection pipe112as a part of the primary-side refrigerant circuit5aextend from the primary-side casing5x.

The cascade unit2includes the cascade casing2xhaving a substantially rectangular parallelepiped shape. The cascade casing2xaccommodates a part of the secondary-side refrigerant circuit10and a part of the primary-side refrigerant circuit5a. A part of the secondary-side refrigerant circuit10accommodated in the cascade casing2xincludes the cascade circuit12including the secondary-side compressor21, the secondary-side switching mechanism22, the first pipe28, the second pipe29, the suction flow path23, the discharge flow path24, the third pipe25, the fourth pipe26, the fifth pipe27, the secondary-side flow path35aof the cascade heat exchanger35, the cascade expansion valve36, the third shutoff valve31, the first shutoff valve32, the second shutoff valve33, the secondary-side accumulator30, the oil separator34, the oil return circuit40, the secondary-side receiver45, the bypass circuit46, the bypass expansion valve46a, the secondary-side subcooling heat exchanger47, the secondary-side subcooling circuit48, and the secondary-side subcooling expansion valve48a. A part of the primary-side refrigerant circuit5aaccommodated in the cascade casing2xincludes the second liquid shutoff valve106, the second refrigerant pipe114, the primary-side second expansion valve102, the primary-side flow path35bof the cascade heat exchanger35, the first refrigerant pipe113, and the second gas shutoff valve107. The secondary-side third connection pipe7, the secondary-side first connection pipe8, and the secondary-side second connection pipe9as a part of the secondary-side refrigerant circuit10extend from the cascade casing2x. The primary-side first connection pipe111and the primary-side second connection pipe112as a part of the primary-side refrigerant circuit5aextend from the cascade casing2x.

The cascade casing2xhas a plurality of surfaces including a top surface120a, a right side surface120b, a front surface120c, a left side surface120d, a back surface120e, and a bottom surface120f. Among the plurality of surfaces, the front surface120cis provided with a connection opening120x. The primary-side first connection pipe111, the primary-side second connection pipe112, the secondary-side third connection pipe7, the secondary-side first connection pipe8, and the secondary-side second connection pipe9pass through the connection opening120x. The cascade heat exchanger35is placed on the bottom surface120f.

The second liquid shutoff valve106to which the primary-side first connection pipe111is connected and the second gas shutoff valve107to which the primary-side second connection pipe112is connected are located in the connection opening120xof the cascade casing2x. Similarly, the third shutoff valve31to which the secondary-side third connection pipe7is connected, the first shutoff valve32to which the secondary-side first connection pipe8is connected, and the second shutoff valve33to which the secondary-side second connection pipe9is connected are located inside the connection opening120xin the cascade casing2x.

(11) Cascade-Side Control Unit

As shown inFIG.7, the cascade-side control unit20is provided near an upper front side in the cascade casing2xof the cascade unit2so as to face the back side of the front surface120c.

FIG.8is a schematic configuration diagram of the cascade-side control unit20as viewed from a side.

The cascade-side control unit20includes an electric component casing90, an electric component attachment plate94, the first electric component91, the second electric component92, a third electric component93, and the like.

The electric component casing90has a substantially rectangular parallelepiped shape including a top surface90a, a bottom surface90f, a front surface90c, a back surface90e, and a left side surface and a right side surface (not shown), and is formed by sheet metal. The electric component casing90internally accommodates the electric component attachment plate94, the first electric component91, the second electric component92, the third electric component93, a heat transfer member95, and the first cooling portion11a. On the back surface of the electric component casing90, a second cooling portion11bextending so as to be folded back in a left-right direction is fixed from behind via a heat transfer member96formed by metal.

The electric component attachment plate94is provided so as to partition the inside of the electric component casing90into a front space S1and a rear space S2in an orientation in which a thickness direction is a front-rear direction. The electric component attachment plate94has a front surface94xto which the third electric component93is attached and a back surface94yto which the first electric component91and the second electric component92are attached.

The first electric component91, the second electric component92, and the third electric component93are electric parts constituting the cascade-side control unit20.

The first electric component91is an electric component for an inverter of the secondary-side compressor21and is an intelligent power module (IPM) which is a heat-generating part. The first electric component91is provided near a lower part of the back surface94yof the electric component attachment plate94.

The second electric component92is an electric component including a noise filter which is a heat-generating part. The second electric component92is provided near an upper part of the back surface94yof the electric component attachment plate94and above the first electric component91.

The third electric component93is an electric component including a main control board. The third electric component93is provided near an upper part of the front surface94xof the electric component attachment plate94and above the heat transfer member95.

The first cooling portion11aextends so as to be folded back in the left-right direction in front view. The first cooling portion11ais fixed to a portion near the lower part of the front surface94xof the electric component attachment plate94and below the third electric component93via the heat transfer member95formed by metal. The first cooling portion11a, the heat transfer member95, and the first electric component91are disposed so as to have an overlapping portion in front view.

In the above configuration, a cooling energy of the secondary-side refrigerant flowing through the first cooling portion11ais transferred to the first electric component91via the heat transfer member95, and a temperature rise of the first electric component91can be suppressed.

A cooling energy of the secondary-side refrigerant flowing through the second cooling portion11bcauses circulation of air in the space S2on the back side of the electric component attachment plate94in an internal space of the electric component casing90. Specifically, air near an upper part on the back side of the electric component casing90is cooled by the cooling energy from the second cooling portion11b, and becomes cold air and descends downward. Then, the air that has descended downward reaches the first electric component91and is heated by heat generated from the first electric component91to rise. The downward air flow and the upward air flow form a circulating flow of air as indicated by a two-dot chain line arrow inFIG.8. It is therefore possible to suppress a temperature rise of the first electric component91and the second electric component92provided in the space S2on the back side of the electric component attachment plate94in the internal space of the electric component casing90.

Since the temperature of the secondary-side refrigerant flowing through the second cooling portion11bis reduced by the second electric component expansion valve18a, the temperature of the secondary-side refrigerant flowing through the second cooling portion11bis lower than the temperature of the secondary-side refrigerant flowing through the first cooling portion11a, which may cause dew condensation on a back surface portion of the electric component casing90. However, since none of the first electric component91, the second electric component92, and the third electric component93is in contact with the back surface portion of the electric component casing90, dew condensation water is prevented from reaching the first electric component91, the second electric component92, and the third electric component93. Since the secondary-side refrigerant flowing through the first cooling portion11ais the refrigerant before being decompressed by the second electric component expansion valve18a, a decrease in temperature is suppressed. Therefore, generation of dew condensation in the first cooling portion11ais suppressed.

(12) Characteristics of Embodiment

In the refrigeration cycle apparatus1according to the present embodiment, the cascade unit2is provided with the cascade heat exchanger35that exchanges heat between the primary-side refrigerant flowing through the primary-side refrigerant circuit5aand the secondary-side refrigerant flowing through the secondary-side refrigerant circuit10, and is not provided with a heat exchanger that exchanges heat with air. Accordingly, the cascade unit2is not provided with a fan that supplies an air flow to the heat exchanger. Therefore, in order to cool the first electric component91and the second electric component92which are heat-generating parts in the cascade-side control unit20, an air flow toward the heat exchanger cannot be used. However, in the refrigeration cycle apparatus1according to the present embodiment, the first electric component91and the second electric component92can be cooled by causing the secondary-side refrigerant flowing through the secondary-side refrigerant circuit10to flow in the first cooling portion11aand the second cooling portion11battached to the cascade-side control unit20. The first electric component91and the second electric component92provided in the electric component casing90of the cascade-side control unit20can be cooled by the first cooling portion11aand the second cooling portion11b, and there is no need to supply an air flow into the electric component casing90. Therefore, a structure with high sealability can be adopted as the electric component casing90. As a result, dust and the like are prevented from entering the electric component casing90, and reliability of the electric components can be enhanced.

In the secondary-side refrigerant circuit10, a carbon dioxide refrigerant that can be in the supercritical state where the behavior becomes unstable is used as the refrigerant. However, the carbon dioxide refrigerant flowing through the cascade heat exchanger35does not exchange heat with outdoor air whose temperature naturally changes due to weather change, but exchanges heat with the primary-side refrigerant flowing in the primary-side refrigerant circuit5a. When the cascade heat exchanger35functions as a radiator for the secondary-side refrigerant, the temperature and flow rate of the primary-side refrigerant flowing through the cascade heat exchanger35are controlled. As a result, it is possible to prevent the secondary-side refrigerant, which is sent to the first cooling portion11aand the second cooling portion11bafter passing through the cascade heat exchanger35, from being in the supercritical state, and it is possible to avoid a situation in which the temperature of the secondary-side refrigerant is likely to change greatly. Therefore, the temperature of the secondary-side refrigerant flowing through the first cooling portion11aand the second cooling portion11bcan be stabilized, and the temperature of the first electric component91and the second electric component92can be prevented from being abnormally increased. When the cascade heat exchanger35functions as a radiator for the secondary-side refrigerant, the pressure of the secondary-side refrigerant to be sent to the first cooling portion11aand the second cooling portion11bcan be made equal to or lower than the critical pressure by performing control to increase the valve opening degree of the cascade expansion valve36. This configuration can also stabilize the temperature of the secondary-side refrigerant flowing through the first cooling portion11aand the second cooling portion11b.

In the refrigeration cycle apparatus1according to the present embodiment, the first cooling portion11aand the second cooling portion11bthrough which the secondary-side refrigerant having a temperature lower than the temperature of the first cooling portion11aflows can be used to cool the plurality of electric components included in the cascade-side control unit20in different temperature ranges. Here, the first cooling portion11ais in thermal contact with the first electric component91via the heat transfer member95, so that the first electric component91can be efficiently cooled without interposing an air space. In addition, the first cooling portion11ais different from the second cooling portion11bthrough which the low-temperature refrigerant decompressed by the second electric component expansion valve18aflows, and the refrigerant having a relatively high temperature flows through the first cooling portion11a. Thus, generation of dew condensation is suppressed in the first cooling portion11a. Therefore, in the first cooling portion11a, it is possible to efficiently cool the first electric component91and to prevent the first electric component91from getting wet with dew condensation water. On the other hand, since the refrigerant having a low temperature and decompressed by the second electric component expansion valve18aflows through the second cooling portion11b, the refrigerant can sufficiently cool the space S2on the back side of the electric component casing90. As a result, although the second cooling portion11band the second electric component92are not disposed in direct contact with each other, the second electric component92can be sufficiently cooled. Even if dew condensation water is generated in the second cooling portion11b, there is no electric component in direct contact with the second cooling portion11b, and no electric component is disposed below the second cooling portion11b. It is therefore possible to prevent the electric components from getting wet with the dew condensation water.

In the refrigeration cycle apparatus1according to the present embodiment, the primary-side compressor71and the like can control capacity in the primary-side refrigerant circuit5a. Therefore, even if the temperature of the outdoor air changes, the capacity is controlled in the primary-side refrigerant circuit5a, so that it is easy to secure an amount of heat exchange required in the secondary-side flow path35aof the cascade heat exchanger35of the secondary-side refrigerant circuit10. As a result, even if the temperature of the outdoor air changes, the amount of heat exchange in the secondary-side flow path35aof the cascade heat exchanger35can be controlled so as to cope with load processing required in the secondary-side refrigerant circuit10.

In the refrigeration cycle apparatus1according to the present embodiment, since the binary refrigeration cycle is adopted, the secondary-side refrigerant circuit10can provide more sufficient capacity than in a single refrigerant cycle. In the refrigeration cycle apparatus1according to the present embodiment adopting the binary refrigeration cycle, since heat can be received from the primary-side refrigerant circuit5a, the capacity of the secondary-side compressor21can be reduced more than in the single refrigeration cycle. Therefore, a heat generation amount can be suppressed to be small even in the first electric component91which is the IPM for the inverter of the secondary-side compressor21. As a result, abnormal heat generation can be sufficiently suppressed only by cooling by the first cooling portion11a.

(13) Other Embodiments

(13-1) Another Embodiment A

In the above embodiment, a case has been described as an example where the first electric component91and the second electric component92are cooled by causing the secondary-side refrigerant flowing through the secondary-side refrigerant circuit10to flow into the first cooling portion11aand the second cooling portion11b.

However, for example, as shown inFIG.9, the first electric component91may be cooled by causing the secondary-side refrigerant flowing through the secondary-side refrigerant circuit10to flow into the first cooling portion11a, and the first electric component91, the second electric component92, and the third electric component may be cooled by using an electric component fan97. The electric component fan97is controlled to be driven by the cascade-side control unit20during each of the cooling operation, the heating operation, the cooling main operation, and the heating main operation. In this case, the second electric component cooling flow path18provided with the second cooling portion11band the second electric component expansion valve18ain the above embodiment can be omitted.

In another embodiment A, the electric component casing90of the cascade-side control unit20is provided with a top surface opening90zthat is opened to allow air to flow in the up-down direction in an upper part of the space S2on the back side in the top surface90a. The electric component casing90is also provided with a front surface opening90ythat is opened to allow air to flow in the front-rear direction in a lower part of the space S1on the front side which is a place far from the top surface opening90zin the front surface90c. The electric component casing90has no opening in the back surface90eand the bottom surface90f. Therefore, air near the secondary-side compressor21hardly flows into the electric component casing90.

The cascade casing2xof the cascade unit2is provided with a top surface opening120zthat is opened to allow air to flow in the up-down direction in the top surface120a. The top surface opening120zof the cascade casing2xand the top surface opening90zof the electric component casing90are disposed so as to overlap each other in plan view. The cascade casing2xis provided with a front surface opening120ythat is opened to allow air to flow in the front-rear direction in the front surface120c. The front surface opening120yof the cascade casing2xand the front surface opening90yof the electric component casing90are disposed so as to overlap each other in front view.

The electric component attachment plate94is provided with ventilation openings94athat are opened in the front-rear thickness direction in a lower part, near a center, and in an upper part.

The second electric component92of the cascade-side control unit20is provided with a heat sink98constituting a heat radiation fin for promoting heat release from the electric component. The heat sink98is configured so that a plurality of heat radiation fins extends toward the back side of the second electric component92. The heat radiation fins are arranged side by side at predetermined intervals in the left-right direction so that the thickness direction is in the left-right direction.

The cascade-side control unit20is provided with the electric component fan97at a position in an upper part of the space S2on the back side in the electric component casing90and facing the top surface opening90z. The electric component fan97is disposed closer to the top surface opening90zthan the electric components disposed in the electric component casing90. The electric component fan97is driven to form an air flow in the up-down direction.

As a result, when the electric component fan97is driven, an air flow for cooling the first electric component91, the second electric component92, and the third electric component93is generated in the electric component casing90as indicated by arrows inFIG.9. Specifically, the outdoor air is taken into the electric component casing90by sequentially passing through the front surface opening120yof the cascade casing2xand the front surface opening90yof the electric component casing90. In the electric component casing90, the air passes through the ventilation openings94aof the electric component attachment plate94while ascending in the space S1on the front side, and is sent to the space S2on the back side. The air having ascended in the space S1on the front side passes around the third electric component93to cool the third electric component93. The air having reached the space S2on the back side passes around the first electric component91to cool the first electric component91and ascend in the space S2. The air flow ascending in the space S2passes through the heat sink98to efficiently cool the second electric component92. As in the above embodiment, the first electric component91is also cooled by the first cooling portion11a.

The air that has ascended in the space S2on the back side as described above passes through the top surface opening90zof the electric component casing90and the top surface opening120zof the cascade casing2xin that order by the electric component fan97and is discharged to outdoors.

In the above configuration, the electric components of the cascade-side control unit20can be also sufficiently cooled.

(13-2) Another Embodiment B

In the another embodiment A, description has been given by exemplifying a case in which the electric component fan97is disposed in the electric component casing90, the top surface opening120zof the cascade casing2xand the top surface opening90zof the electric component casing90are disposed so as to overlap each other in plan view, and the front surface opening120yof the cascade casing2xand the front surface opening90yof the electric component casing90are disposed so as to overlap each other in front view.

However, for example, as shown inFIG.10, the top surface opening90zof the electric component casing90may be disposed so as to have a portion not overlapping with the top surface opening120zof the cascade casing2xin plan view, or may be disposed so as not to overlap with the top surface opening120zof the cascade casing2xat all. Furthermore, the front surface opening90yof the electric component casing90may be disposed so as to have a portion not overlapping the front surface opening120yof the cascade casing2xwhen viewed in front view or from a periphery. In this case, for example, an upper end of the front surface opening90yof the electric component casing90is preferably disposed at a position higher than an upper end of the front surface opening120yof the cascade casing2x, and a lower end of the front surface opening90yof the electric component casing90is more preferably disposed at a position higher than the upper end of the front surface opening120yof the cascade casing2x.

By adopting such a water shielding structure, rainwater is prevented from reaching the inside of the electric component casing90even when the cascade unit2is disposed outdoors.

(13-3) Another Embodiment C

In the another embodiments A and B, description has been given by exemplifying a structure in which the electric component fan97is disposed in the electric component casing90, the first electric component91is provided on one surface of the electric component attachment plate94, and the second electric component92and the third electric component93are provided on the other surface of the electric component attachment plate94in the cascade-side control unit20.

However, for example, as shown inFIG.11, the cascade-side control unit20may have a structure in which all the electric components, namely, the first electric component91, the second electric component92, and the third electric component93are provided on one side surface of the electric component attachment plate94.

As in the another embodiment B, the front surface opening90yof the electric component casing90may be disposed so as to have a portion not overlapping the front surface opening120yof the cascade casing2xwhen viewed in front view or from the periphery. In this case, for example, an upper end of the front surface opening90yof the electric component casing90is preferably disposed at a position higher than an upper end of the front surface opening120yof the cascade casing2x, and a lower end of the front surface opening90yof the electric component casing90is more preferably disposed at a position higher than the upper end of the front surface opening120yof the cascade casing2x. The front surface opening90yof the electric component casing90is preferably located below a center of the electric component casing90in a height direction.

The electric component casing90may have an exhaust opening90wfor guiding an air flow exhausted from the electric component fan97to the outside of the electric component casing90. The exhaust opening90wis preferably provided on the front surface of the electric component casing90and at a position away from the front surface opening90y. When the front surface opening90yis located below, the exhaust opening90wis preferably located above the center in the height direction of the electric component casing90.

Similarly, the cascade casing2xmay have an exhaust opening120wfor guiding an air flow exhausted from the electric component fan97to outdoors. The exhaust opening120wis preferably provided on the front surface of the cascade casing2xand at a position away from the front surface opening120y. The exhaust opening120wof the cascade casing2xmay have a portion overlapping with the exhaust opening90wof the electric component casing90in front view.

As a result, in the air flow formed by the electric component fan97, it is possible to suppress a short circuit in which the air exhausted to outdoors from the exhaust opening120wof the cascade casing2xis directly taken into the front surface opening120yof the cascade casing2x.

(13-4) Another Embodiment D

In the another embodiments A, B, and C, description has been given by exemplifying a case in which the electric component fan97is disposed in the electric component casing90to actively form an air flow in the electric component casing90.

However, the electric component fan97in the another embodiments A, B, and C may be omitted, for example, when heat in a space in the electric component casing90can be exhausted from the top surface opening90zor the like by natural convection even if there is no source of forming an air flow, such as the electric component fan97.

(13-5) Another Embodiment E

In the above embodiment, description has been given by exemplifying a case in which the second electric component cooling flow path18is a refrigerant flow path that connects the portion Y between the first cooling portion11aand the first electric component expansion valve17aon the first electric component cooling flow path17and the portion W at a halfway portion of the suction flow path23.

However, for example, as shown inFIG.12, the second electric component cooling flow path18may be a refrigerant flow path that connects a portion Y1between the portion X of the fourth pipe26between the cascade expansion valve36and the secondary-side receiver45and the first cooling portion11aof the first electric component cooling flow path17and the portion W at a halfway portion of the suction flow path23.

In this case, the second electric component expansion valve18acan decompress not the refrigerant after the heat is radiated in the first cooling portion11abut the refrigerant before the refrigerant is sent to the first cooling portion11a. Accordingly, the electric components can be cooled in the second cooling portion11bby using the sufficiently cooled refrigerant.

(13-6) Another Embodiment F

In the above embodiment, description has been given by exemplifying a case in which the second electric component cooling flow path18is a refrigerant flow path that connects the portion Y between the first cooling portion11aand the first electric component expansion valve17aon the first electric component cooling flow path17and the portion W at a halfway portion of the suction flow path23.

However, for example, as shown inFIG.13, the second electric component cooling flow path18may be a refrigerant flow path that connects a portion Y2between the portion X of the fourth pipe26between the cascade expansion valve36and the secondary-side receiver45and the secondary-side receiver45and the portion W at a halfway portion of the suction flow path23.

In this case, as in the another embodiment E, the second electric component expansion valve18acan decompress not the refrigerant after the heat is radiated in the first cooling portion11abut the refrigerant before the refrigerant is sent to the first cooling portion11a. Accordingly, the electric components can be cooled in the second cooling portion11bby using the sufficiently cooled refrigerant.

(13-7) Another Embodiment G

In the above embodiment, description has been given by exemplifying a case in which the refrigeration cycle apparatus1in which one cascade unit2is connected to one primary-side unit5.

However, as shown inFIG.14, for example, by connecting a first cascade unit2a, a second cascade unit2b, and a third cascade unit2c, which are a plurality of cascade units, in parallel to one primary-side unit5, the refrigeration cycle apparatus1may include a first secondary-side refrigerant circuit10aincluding a first cascade circuit12a, a second secondary-side refrigerant circuit10bincluding a second cascade circuit12b, and a third secondary-side refrigerant circuit10cincluding a third cascade circuit12c. Note that, inFIG.14, an internal structure of each of the first cascade unit2a, the second cascade unit2b, and the third cascade unit2cis similar to that of the cascade unit2according to the above embodiment, and thus only a part of each cascade unit is illustrated.

Although not shown, each of the first cascade unit2a, the second cascade unit2b, and the third cascade unit2cis connected with the plurality of branch units6a,6b, and6cand the plurality of utilization units3a,3b, and3cas in the above embodiment. Specifically, the first cascade unit2ais connected to a plurality of branch units and utilization units via a secondary-side third connection pipe7a, a secondary-side first connection pipe8a, and a secondary-side second connection pipe9a. The second cascade unit2bis connected, via a secondary-side third connection pipe7b, a secondary-side first connection pipe8b, and a secondary-side second connection pipe9b, with a plurality of branch units and utilization units different from those connected with the first cascade unit2a. The third cascade unit2cis connected, via a secondary-side third connection pipe7c, a secondary-side first connection pipe8c, and a secondary-side second connection pipe9c, with another plurality of branch units and utilization units different from those connected to the first cascade unit2aand different from those connected to the second cascade unit2b.

Here, the primary-side unit5and the first cascade unit2aare connected via a primary-side first connection pipe111aand a primary-side second connection pipe112a. The primary-side unit5and the second cascade unit2bare connected via a primary-side first connection pipe111bbranched from the primary-side first connection pipe111aand a primary-side second connection pipe112bbranched from the primary-side second connection pipe112a. The primary-side unit5and the third cascade unit2care connected via a primary-side first connection pipe111cbranched from the primary-side first connection pipe111aand a primary-side second connection pipe112cbranched from the primary-side second connection pipe112a.

Here, each of the first cascade unit2a, the second cascade unit2b, and the third cascade unit2cincludes a primary-side second expansion valve102whose opening degree is controlled by the first cascade unit2a, the second cascade unit2b, and the third cascade unit2c. A first cascade-side control unit20aincluded in the first cascade unit2a, a second cascade-side control unit20bincluded in the second cascade unit2b, and a third cascade-side control unit20cincluded in the third cascade unit2ccontrol the opening degree of the corresponding primary-side second expansion valve102. As in the above embodiment, each of the first cascade-side control unit20a, the second cascade-side control unit20b, and the third cascade-side control unit20ccontrols the valve opening degree of the corresponding primary-side second expansion valve102on the basis of conditions of the first cascade circuit12a, the second cascade circuit12b, and the third cascade circuit12ccontrolled by the first cascade-side control unit20a, the second cascade-side control unit20b, and the third cascade-side control unit20c. As a result, the primary-side refrigerant flowing through the primary-side refrigerant circuit5ais controlled to have a flow rate of the primary-side refrigerant in the primary-side first connection pipe111aand the primary-side second connection pipe112a, a flow rate of the primary-side refrigerant in the primary-side first connection pipe111band the primary-side second connection pipe112b, and a flow rate of the primary-side refrigerant in the primary-side first connection pipe111cand the primary-side second connection pipe112cso as to correspond to a difference in loads in the first secondary-side refrigerant circuit10a, the second secondary-side refrigerant circuit10b, and the third secondary-side refrigerant circuit10c.

(13-8) Another Embodiment H

In the above embodiment, R32 or R410A is exemplified as the refrigerant used in the primary-side refrigerant circuit5a, and carbon dioxide is exemplified as the refrigerant used in the secondary-side refrigerant circuit10.

However, the refrigerant used in the primary-side refrigerant circuit5ais not limited, and an HFC-32, an HFO refrigerant, a mixed refrigerant of the HFC-32 and the HFO refrigerant, carbon dioxide, ammonia, propane, or the like can be used.

Furthermore, instead of the primary-side refrigerant circuit5athrough which the refrigerant flows, a heat medium circuit through which a heat medium such as water or brine flows may be used. In this case, the heat medium circuit may include a heat source that functions as a heating source or a cooling source, and a pump for circulating the heat medium. In this case, the flow rate can be adjusted by the pump, and the amount of heat can be controlled by the heating source or the cooling source.

The refrigerant used in the secondary-side refrigerant circuit10is not limited, and an HFC-32, an HFO refrigerant, a mixed refrigerant of the HFC-32 and the HFO refrigerant, carbon dioxide, ammonia, propane, or the like can be used.

Examples of the HFO refrigerant include HFO-1234yf and HFO-1234ze.

The same refrigerant or different refrigerants may be used in the primary-side refrigerant circuit5aand the secondary-side refrigerant circuit10. Preferably, the refrigerant used in the secondary-side refrigerant circuit10has at least one of lower global warming potential (GWP), lower ozone depletion potential (ODP), lower flammability, or lower toxicity than the refrigerant used in the primary-side refrigerant circuit5a. The flammability can be compared in accordance with classifications related to ASHRAE 34 flammability, for example. The toxicity can be compared, for example, in accordance with classifications related to ASHRAE 34 safety grade. In particular, when an overall content volume of the secondary-side refrigerant circuit10is larger than an overall content volume of the primary-side refrigerant circuit5a, by using the refrigerant lower than the refrigerant in the primary-side refrigerant circuit5ain at least one of the global warming potential (GWP), the ozone depletion potential (ODP), the flammability, or the toxicity in the secondary-side refrigerant circuit10, adverse effects when a leak occurs can be reduced.

(13-9) Others

Note that the electric component may drive the compressor.

The control unit may be included in the cascade unit, or may be included in a unit such as a heat source unit other than the cascade unit in the refrigeration cycle apparatus.

The second circuit may include a decompression mechanism capable of decompressing the refrigerant that has passed through the cascade heat exchanger. The refrigerant flowing between the cascade heat exchanger and the decompression mechanism may flow to the first cooling portion, and the refrigerant decompressed by the decompression mechanism may flow to the second cooling portion.

The second circuit may include a first decompression mechanism capable of decompressing the refrigerant that has passed through the cascade heat exchanger, and may include a refrigerant flow path branched from a branch point between the cascade heat exchanger and the first decompression mechanism and provided with a second decompression mechanism. In this case, the refrigerant flowing between the cascade heat exchanger and the branch point may flow to the first cooling portion, and the refrigerant decompressed by the second decompression mechanism in the refrigerant flow path may flow to the second cooling portion.

It is preferable that the electric component casing is not provided with an opening through which an air flow passes.

When the first electric part can be cooled by exhaust heat from the exhaust heat opening, an electric component fan is not required to be provided in the electric component casing.

Note that a first refrigerant may flow through the first circuit, and a second refrigerant different from the first refrigerant may flow through the second circuit.

Supplementary Note

Although the embodiments of the present disclosure have been described above, it will be understood that various changes in form and details can be made without departing from the gist and scope of the present disclosure described in the claims.

REFERENCE SIGNS LIST

1: refrigeration cycle apparatus2: cascade unit2x: cascade casing3a: first utilization unit3b: second utilization unit3c: third utilization unit5: primary-side unit5a: primary-side refrigerant circuit (first circuit)5x: primary-side casing (first casing)10: secondary-side refrigerant circuit (second circuit)11a: first cooling portion (cooling portion)11b: second cooling portion (cooling portion)12: cascade circuit13a,13b,13c: utilization circuit17: first electric component cooling flow path17a: first electric component expansion valve18: second electric component cooling flow path18a: second electric component expansion valve (decompression mechanism)20: cascade-side control unit (control unit)21: secondary-side compressor (compressor)21a: compressor motor22: secondary-side switching mechanism22a: first switching valve22b: second switching valve22x: discharge-side connection portion22y: suction-side connection portion23: suction flow path24: discharge flow path25: third pipe26: fourth pipe27: fifth pipe28: first pipe29: second pipe30: secondary-side accumulator34: oil separator35: cascade heat exchanger35a: secondary-side flow path35b: primary-side flow path36: cascade expansion valve37: secondary-side suction pressure sensor38: secondary-side discharge pressure sensor39: secondary-side discharge temperature sensor45: secondary-side receiver46: bypass circuit46a: bypass expansion valve47: secondary-side subcooling heat exchanger48: secondary-side subcooling circuit48a: secondary-side subcooling expansion valve50a-c: utilization-side control unit51a-c: utilization-side expansion valve52a-c: utilization-side heat exchanger (second heat exchanger)53a-c: indoor fan58a,58b,58c: liquid-side temperature sensor60a,60b,60c: branch unit control unit66a,66b,66c: first control valve67a,67b,67c: second control valve68a,68b,68c: check valve69a,69b,69c: bypass pipe70: primary-side control unit71: primary-side compressor (first compressor)72: primary-side switching mechanism74: primary-side heat exchanger (first heat exchanger)76: primary-side first expansion valve77: outdoor air temperature sensor78: primary-side discharge pressure sensor79: primary-side suction pressure sensor80: control unit81: primary-side suction temperature sensor82: primary-side heat exchange temperature sensor83: secondary-side cascade temperature sensor84: receiver outlet temperature sensor85: bypass circuit temperature sensor86: subcooling outlet temperature sensor87: subcooling circuit temperature sensor88: secondary-side suction temperature sensor90: electric component casing90w: exhaust opening (exhaust heat opening)90y: front surface opening90z: top surface opening (exhaust heat opening)91: first electric component (inverter part)92: second electric component (first electric part)93: third electric component (first electric part)94: electric component attachment plate94a: ventilation opening97: electric component fan98: heat sink102: primary-side second expansion valve103: primary-side subcooling heat exchanger104: primary-side subcooling circuit104a: primary-side subcooling expansion valve105: primary-side accumulator111: primary-side first connection pipe112: primary-side second connection pipe113: first refrigerant pipe114: second refrigerant pipe120w: exhaust opening120x: connection opening120y: front surface opening120z: top surface opening

CITATION LIST

Patent Literature

Patent Literature 1: JP 2020-180709 A