REFRIGERANT VESSEL AND REFRIGERATION CYCLE APPARATUS

Provided are a refrigerant vessel and a refrigeration cycle apparatus capable of suppressing accumulation of a refrigerating machine oil inside. A secondary-side receiver reserves a refrigerant in a secondary-side refrigerant circuit in which a refrigerant and a refrigerating machine oil circulate, the secondary-side receiver including a vessel body, a first refrigerant pipe connected to the vessel body, and a second refrigerant pipe connected to the vessel body, in which the refrigerating machine oil is incompatible with the refrigerant and has a higher density than the refrigerant, and the second refrigerant pipe extends downward from a bottom part of the vessel body.

TECHNICAL FIELD

BACKGROUND ART

Conventionally, a receiver for reserving a refrigerant has been used in a refrigerant circuit included in a refrigeration cycle apparatus.

As such a refrigeration cycle apparatus, for example, a refrigeration cycle apparatus described in Patent Literature 1 (JP 2008-164225 A) uses a carbon dioxide refrigerant as a refrigerant and uses incompatible PAG oil as a refrigerating machine oil. With this refrigeration cycle apparatus, in order to avoid accumulation of refrigerating machine oil at a bottom of a refrigerant vessel such as a receiver, it is proposed that an outlet pipe connected to a side peripheral surface of the refrigerant vessel is disposed so that a vicinity of a distal end located inside the refrigerant vessel is obliquely cut and the distal end is in contact with a bottom part of the refrigerant vessel.

SUMMARY

A refrigerant vessel according to a first aspect is a refrigerant vessel that reserves a refrigerant in a refrigerant circuit. In the refrigerant circuit, the refrigerant and the refrigerating machine oil circulate. The refrigerant vessel includes a vessel body, a first refrigerant pipe, and a second refrigerant pipe. The first refrigerant pipe is connected to the vessel body. The second refrigerant pipe is connected to the vessel body. The refrigerating machine oil is incompatible with the refrigerant. The refrigerating machine oil has a higher density than the refrigerant. The second refrigerant pipe extends downward from a bottom part of the vessel body.

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 of an indoor space in a building or the like by performing 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 refrigerant circuit) and a vapor compression secondary-side refrigerant circuit10(corresponding to a refrigerant circuit, a second refrigerant circuit), and performs a binary refrigeration cycle. In the present embodiment, for example, R32 or R410A is sealed as a refrigerant in the primary-side refrigerant circuit5a.In the secondary-side refrigerant circuit10, for example, carbon dioxide is sealed as a refrigerant. In the secondary-side refrigerant circuit10, a refrigerating machine oil incompatible with the refrigerant is used as a refrigerating machine oil that circulates in the circuit together with the refrigerant to improve lubricity of a sliding portion and the like. The refrigerating machine oil has a higher density and a higher specific gravity than the refrigerant in a use state, and thus tends to be located below the refrigerant. In the present embodiment, a polyalkylene glycol oil (PAG oil) that is incompatible with carbon dioxide as a refrigerant and has a higher density than the carbon dioxide refrigerant is used.

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. The present embodiment provides the single primary-side unit5. The present embodiment provides the single cascade unit2. The plurality of utilization units3a,3b,and3caccording to the present embodiment includes three utilization units, namely, the first utilization unit3a, the second utilization unit3b,and the third utilization unit3c.In the present embodiment, the plurality of branch units6a,6b,and6cis three branch units of the first branch unit6a,the second branch unit6b,and the third branch unit6c.

In the refrigeration cycle apparatus1, the utilization units3a,3b,and3ccan individually perform cooling operation or 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 performing cooling main operation or heating main operation of simultaneously performing cooling operation and heating operation. In addition, the refrigeration cycle apparatus1is configured to balance heat loads of the cascade unit2in accordance with entire heat loads of the plurality of utilization units3a,3b,and3calso in consideration of the heat recovery (the cooling main operation or the heating main operation).

The primary-side refrigerant circuit5aincludes a primary-side compressor71, a primary-side switching mechanism72, a primary-side heat exchanger74, 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. This primary-side refrigerant circuit5aspecifically includes a primary-side flow path35bof the cascade heat exchanger35.

The primary-side compressor71is a device for compressing a primary-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 motor71a.

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

When the cascade heat exchanger35functions as an evaporator for the primary-side refrigerant, the primary-side switching mechanism72enters a fifth connection state of connecting the suction side of the primary-side compressor71and a gas side of a primary-side flow path35bof the cascade heat exchanger35(see solid lines in the primary-side switching mechanism72inFIG.1). In addition, when the cascade heat exchanger35functions as a radiator for the primary-side refrigerant, the primary-side switching mechanism72enters a sixth connection 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 in the primary-side switching mechanism72inFIG.1). In such a manner, the primary-side switching mechanism72is a device that can switch the flow path of the refrigerant in the primary-side refrigerant circuit5a,and includes, for example, a four-way switching valve. Then, 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 a device for causing heat exchange between a refrigerant such as R32 which is a primary-side refrigerant and a refrigerant such as carbon dioxide which is a secondary-side refrigerant without mixing the refrigerants with each other. The cascade heat exchanger35is, for example, a plate-type heat exchanger. The cascade heat exchanger35includes a secondary-side flow path35abelonging to the secondary-side refrigerant circuit10and 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 has a liquid side connected to the second refrigerant pipe114provided with the primary-side second expansion valve102.

The primary-side heat exchanger74is a device for exchanging 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. The primary-side heat exchanger74includes, for example, a fin-and-tube heat exchanger including a large number 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 for adjusting 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 circuit104and has an adjustable opening degree for adjusting the flow rate of the primary-side refrigerant.

The primary-side subcooling heat exchanger103causes 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 a 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 for adjusting a flow rate of the primary-side refrigerant flowing in 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 between the primary-side second connection pipe112and the primary-side switching mechanism72.

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,and6cone on one. 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.

In accordance with an operating state, either the refrigerant in a gas-liquid two-phase state or the refrigerant in a gas state flows in the secondary-side first connection pipe8. Note that, in accordance with the operating state, the refrigerant in a supercritical state flows in the secondary-side first connection pipe8. In accordance with the operating state, either the refrigerant in the gas-liquid two-phase state or the refrigerant in the gas state flows in the secondary-side second connection pipe9. In accordance with the operating state, either the refrigerant in the gas-liquid two-phase state or the refrigerant in a liquid state flows in the secondary-side third connection pipe7. Note that, in accordance with the operating state, the refrigerant in a supercritical state flows in the secondary-side third connection pipe7.

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 circuit12principally includes a secondary-side compressor21, 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 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(corresponding to a refrigerant vessel), 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 a device for compressing the secondary-side refrigerant, and is exemplarily constituted by 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 mechanism22is a mechanism that can switch a connection state of the secondary-side refrigerant circuit10, specifically, the flow path of the refrigerant in the cascade circuit12. In the present embodiment, the secondary-side switching mechanism22includes 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 a 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 a closed 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 connection 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 connection state of the secondary-side switching mechanism22is a connection 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 connection 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 connection state of the secondary-side switching mechanism22is a connection 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 connection 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 connection state of the secondary-side switching mechanism22is a connection state adopted during the cooling main operation described later.

As described above, the cascade heat exchanger35is a device for causing heat exchange between the refrigerant such as R32 which is the primary-side refrigerant and the refrigerant such as carbon dioxide which is the secondary-side refrigerant without mixing the refrigerants with each other. The cascade heat exchanger35includes the secondary-side flow path35ain which the secondary-side refrigerant in the secondary-side refrigerant circuit10flows and the primary-side flow path35bin which the primary-side refrigerant in the primary-side refrigerant circuit5aflows, so as to be shared between the primary-side unit5and the cascade unit2. Note that, in the present embodiment, the cascade heat exchanger35is disposed inside a cascade casing (not illustrated) of 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 casing via 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 casing via 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 that is connected to a 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 connecting 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 path23connects the secondary-side switching mechanism22and a 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 secondary-side accumulator30is provided at a halfway portion of the suction flow path23.

The second pipe29is a refrigerant pipe that connects the second shutoff valve33to 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 connecting a 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 connecting 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 connecting 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 vessel that reserves a residue refrigerant in the secondary-side refrigerant circuit10. Extended from the secondary-side receiver45are the fourth pipe26, the fifth pipe27, and the bypass circuit46.

The bypass circuit46is a refrigerant pipe connecting a gas phase region which is 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 that can adjust a quantity of the refrigerant guided from inside the secondary-side receiver45to the suction side of the secondary-side compressor21by adjusting an opening degree.

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

The secondary-side subcooling circuit48is a refrigerant pipe connecting 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. In the present embodiment, the secondary-side subcooling circuit48extends to branch from a portion between the secondary-side receiver45and the secondary-side subcooling heat exchanger47.

The secondary-side subcooling heat exchanger47is a heat exchanger that causes 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. In the present embodiment, the secondary-side subcooling heat exchanger47is provided between a portion from where the secondary-side subcooling circuit48branches and the third shutoff valve31on 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 valve48ais an electrically powered expansion valve that has an adjustable opening degree and supplies the secondary-side subcooling heat exchanger47with a decompressed refrigerant.

The secondary-side accumulator30is a vessel 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 a device for separating refrigerating machine oil discharged from the secondary-side compressor21along with the secondary-side refrigerant from 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 path41which is 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. An oil return capillary tube42and an oil return on-off valve44are provided at a halfway portion of the oil return flow path41. 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. In the present embodiment, when the secondary-side compressor21is in an operating state on the secondary-side refrigerant circuit10, the oil return on-off valve44is kept in the opened state for predetermined time and is kept in a closed state for predetermined time repetitively, to control a returned quantity of the refrigerating machine oil through the oil return circuit40. In the present embodiment, the oil return on-off valve44is 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.

Hereinafter, the utilization circuits13a,13b,and13cwill be described. 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 circuit13aprincipally 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 a device for causing heat exchange between a refrigerant and indoor air, and includes, for example, a fin-and-tube heat exchanger including a large number of heat transfer tubes and fins. The 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 other end of the second utilization pipe56ais connected to the second connecting tube16a.The utilization-side expansion valve51adescribed above is provided at a halfway portion of the second utilization pipe56a.

The utilization-side expansion valve51ais an electrically powered expansion valve that has an adjustable opening degree for adjusting 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.In the present embodiment, the first utilization pipe57ais 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.

Hereinafter, the branch circuits14a,14b,and14cwill be described. 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 regulating valve66a,a second regulating valve67a,a bypass pipe69a,a check valve68a,and a third branch pipe61a.

The junction pipe62ahas one end connected to the first connecting tube15a.The junction pipe62ahas the other end branched to be connected with the first branch pipe63aand the second branch pipe64a.

The first branch pipe63ahas a portion opposite to the junction pipe62and connected to the secondary-side first connection pipe8. The first branch pipe63ais provided with the openable and closable first regulating valve66a.

The second branch pipe64ahas a portion opposite to the junction pipe62and connected to the secondary-side second connection pipe9. The second branch pipe64ais provided with the openable and closable second regulating 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 regulating valve66aand a portion of the second branch pipe64acloser to the secondary-side second connection pipe9than the second regulating valve67a.The check valve68ais provided at 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 other end of the third branch pipe61ais connected to the secondary-side third connection pipe7.

The first branch unit6acan function as follows by closing the first regulating valve66aand opening the second regulating 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 unit3athrough the second connecting tube16ais sent to the utilization-side heat exchanger52ain the first utilization unit3athrough the utilization-side expansion valve51a.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 regulating valve67a.A part of the refrigerant that has passed through the second regulating valve67ais sent to the secondary-side second connection pipe9. The remaining part of the refrigerant that has passed through the second regulating 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 sectional area when the secondary-side refrigerant in a gas state evaporated in the utilization-side heat exchanger52ais sent to the secondary-side compressor21, so that a pressure loss can be reduced.

When the first utilization unit3acools an indoor space 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 first regulating valve66aand opening the second regulating 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 unit3athrough the second connecting tube16ais sent to the utilization-side heat exchanger52ain the first utilization unit3athrough the utilization-side expansion valve51a.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 regulating valve67a,and then is sent to the secondary-side second connection pipe9.

The first branch unit6acan function as follows by closing the second regulating valve67aand opening the first regulating 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 regulating 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 tube15aand is sent to the utilization-side heat exchanger52a.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 an indoor space 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 regulating valve67aand opening the first regulating valve66a.In the first branch unit6a,the refrigerant flowing into the first branch pipe63athrough the secondary-side first connection pipe8passes through the first regulating 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 tube15aand is sent to the utilization-side heat exchanger52a.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.

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, and a primary-side control unit70, and a primary-side casing (not illustrated).

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 casing.

The primary-side fan75is provided in the primary-side unit5, and generates an air flow of guiding outdoor air into the primary-side heat exchanger74, and 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 motion of the elements71(71a),72,75(75a),76, and104aprovided in the primary-side unit5. 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 illustrated), and to transmit and receive control signals and the like between a cascade-side control unit20in a 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,the cascade casing (not illustrated), and the like.

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 at an outlet of the secondary-side subcooling heat exchanger47in the secondary-side subcooling circuit48.

The cascade-side control unit20controls motion of the elements21(21a),22,36,44,46a,48a,and102provided in the cascade casing of 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.

In such a manner, the cascade-side control unit20can control not only the elements 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 a 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 in the secondary-side flow path35aof the cascade heat exchanger35in the cascade circuit12from the primary-side refrigerant flowing in 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 on an indoor space of a 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, the utilization units3a,3b,and3cwill be described in terms of their configurations. 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 by 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 temperature of air introduced from the indoor space before passing through the utilization-side heat exchanger52a.

The utilization-side control unit50acontrols motion of the elements51aand53a(54a) constituting the utilization unit3a.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 illustrated), and to transmit and receive control signals and the like between 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 above a ceiling of an indoor space of a building or the like.

Each of the branch units6a,6b,and6cis connected to a corresponding one of the utilization units3a,3b,and3cone by one. The branch units6a,6b,and6care connected to the cascade unit2via the connection pipes7,8, and9.

Next, the branch units6a,6b,and6cwill be described next in terms of their configurations. 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 circuit14adescribed above and the branch unit control unit60a.

The branch unit control unit60acontrols motion of the elements66aand67aconstituting the branch unit6a.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 depicted), 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 heat 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 motion of the elements21(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 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 illustrated) and the like.

(9) Motion of Refrigeration Cycle Apparatus

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

The refrigeration cycle operation of the refrigeration cycle apparatus1can be mainly divided into cooling operation, heating operation, cooling main operation, and 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 with respect to an evaporation load of the entire utilization unit.

Here, the heating operation is refrigeration cycle operation in which only the utilization unit 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 with respect to 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 heat 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 motion of the refrigeration cycle apparatus1including the refrigeration cycle operation is performed by the control unit80described above.

(9-1) Cooling Operation

During the cooling operation, for example, all 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 the cooling operation, the primary-side refrigerant circuit5aand the secondary-side refrigerant circuit10of the refrigeration cycle apparatus1are configured as illustrated 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 connection state to cause the cascade heat exchanger35to function as an evaporator for the primary-side refrigerant. The fifth connection state of the primary-side switching mechanism72is depicted by solid lines in 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 valve108through 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 when 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 when 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 in 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 in 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 through 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 connection state, the cascade heat exchanger35functions as a radiator for the secondary-side refrigerant. In the first connection 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,3c,the second regulating valves67a,67b,67care controlled to the opened state. Accordingly, all of the utilization-side heat exchangers52a,52b,and52cin the utilization units3a,3b,and3cfunction as refrigerant evaporators. 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,a part of the first branch pipes63a,63b,and63c,the secondary-side first connection pipe8, and the secondary-side second connection pipe9. In addition, an 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 to 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 compressor21so that evaporation temperature of the secondary-side refrigerant in the utilization-side heat exchangers52a,52b,and52cbecomes a predetermined secondary-side evaporation target temperature. The opening degree of the cascade expansion valve36is adjusted such that the secondary-side refrigerant flowing in 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 a predetermined primary-side evaporation target temperature. In such a manner, in the cooling operation, 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 circuit5aare executed, and thus, the carbon dioxide refrigerant flowing in the cascade heat exchanger35is controlled so as not to exceed a critical point.

In such a secondary-side refrigerant circuit10, a secondary-side high-pressure 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 secondary-side high-pressure 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 exchanger35is evaporated. The secondary-side refrigerant having radiated heat in the cascade heat exchanger35passes through the cascade expansion valve36whose opening degree is adjusted, and then flows into the secondary-side receiver45. A part of the refrigerant flowing out of the secondary-side receiver45branches and flows into the secondary-side subcooling circuit48, is decompressed in the secondary-side subcooling expansion valve48a,and then joins 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 pipe7through 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 through 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. The 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 in 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 regulating valves67a,67b,and67cin the second branch pipes64a,64b, and64cis sent to the secondary-side second connection pipe9. The remaining part of the refrigerant that has passed through the second regulating 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.

Motion during the cooling operation is performed in such a manner.

(9-2) Heating Operation

During 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 illustrated 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 mechanism72is a connection 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 through the primary-side switching mechanism72and the first gas shutoff valve109passes through the primary-side second connection pipe112and the second gas shutoff valve107and is 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 in the second refrigerant pipe114, the primary-side refrigerant condensed in the cascade heat exchanger35passes through the primary-side second expansion valve102controlled to 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 heating operation, the primary-side subcooling expansion valve104ais controlled to the closed state. Accordingly, the refrigerant does not flow to the primary-side subcooling circuit104and does not exchange heat in the primary-side subcooling heat exchanger103. The valve opening degree of the primary-side first expansion valve76is controlled such that, for example, the degree of superheating of the refrigerant sucked into the primary-side compressor71satisfies a predetermined condition. The refrigerant decompressed by the primary-side first expansion valve76evaporates by exchanging heat with outdoor air supplied from the primary-side fan75in the primary-side heat exchanger74, passes through the primary-side switching mechanism72and the primary-side accumulator105, and is sucked into the primary-side compressor71.

In the cascade unit2, the secondary-side switching mechanism22is switched to the second connection state. The cascade heat exchanger35thus functions as an evaporator for the secondary-side refrigerant. In the second connection 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 regulating valves66a,66b,and66care controlled to the opened state, and the second regulating valves67a,67b,and67care controlled to the closed state. Accordingly, all of the utilization-side heat exchangers52a,52b,and52cin the utilization units3a,3b,and3cfunction as refrigerant radiators. 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 to the closed state. In the utilization units3a,3b,and3c,the opening degrees of the utilization-side expansion valves51a,51b,and51care adjusted.

During the heating operation, the secondary-side refrigerant circuit10controls capacity on 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, the secondary-side refrigerant discharged from the secondary-side compressor21is controlled to be in a 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 a predetermined primary-side condensation target temperature.

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 pipe8through 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,and3cwhich are utilization units in operation. The high-pressure refrigerant sent to the first branch pipes63a,63b,and63cpasses through the first regulating valves66a,66b,and66c,and flows in the junction pipes62a,62b,and62c.Thereafter, the refrigerant having flowed in the first connecting tubes15a,15b,and15cand the first utilization pipes57a,57b,and57cis 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. The indoor air is heated and 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 through the utilization-side expansion valves51a,51b,and51cwhose opening degrees are adjusted. The secondary-side refrigerant that has 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.

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

The refrigerant sent to the secondary-side third connection pipe7passes through the third shutoff valve31and then is sent to the cascade expansion valve36. The flow rate of the refrigerant sent to the cascade expansion valve36is adjusted at 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.

Motion during the heating operation is performed in such a manner.

(9-3) Cooling Main Operation

During the cooling main operation, for example, the utilization-side heat exchangers52aand52bin the utilization units3aand3bfunction as refrigerant evaporators, 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 illustrated 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 connection 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 valve108through 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 when 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, a valve opening degree of the primary-side second expansion valve102is controlled such that the degree of superheating of the refrigerant sucked into the primary-side compressor71satisfies a predetermined condition. When flowing in 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 in 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 through 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 connection 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 regulating valve66cand the second regulating valves67aand67bare controlled to the opened state, and the first regulating valves66aand66band the second regulating valve67care controlled to the closed state. Accordingly, the utilization-side heat exchangers52aand52bin the utilization units3aand3bfunction as refrigerant evaporators, 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. In addition, an 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 to 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 between the utilization-side heat exchanger52a,52b,and52cbecomes a predetermined secondary-side evaporation target temperature. The opening degree of the cascade expansion valve36is adjusted such that the secondary-side refrigerant flowing in 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 a predetermined primary-side evaporation target temperature. In such a manner, in the cooling operation, 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 circuit5aare executed, and thus, the carbon dioxide refrigerant flowing in the cascade heat exchanger35is controlled so as not to exceed a critical point.

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 unit3cthrough the first regulating 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. The indoor air is heated and is supplied into the indoor space, and the utilization unit3cperforms the 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.After that, 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 exchanger35is adjusted at the cascade expansion valve36, and then the secondary-side refrigerant flows into the secondary-side receiver45. 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 pipe7through 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 in the second connecting tubes16aand16bis sent to the second utilization pipes56aand56bof the first and second utilization units3aand3b.The refrigerant flowing in the second utilization pipes56aand56bpasses through the utilization-side expansion valves51aand51bin the utilization units3aand3b.

The refrigerant having passed through 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. The 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.

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

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.

Motion during the cooling main operation is performed in such a manner.

(9-4) Heating Main Operation

During the heating main operation, for example, the utilization-side heat exchangers52aand52bin the utilization units3aand3bfunction as refrigerant radiators, 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 illustrated 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 connection 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 through the primary-side switching mechanism72and the first gas shutoff valve109passes through the primary-side second connection pipe112and the second gas shutoff valve107and is 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 in the second refrigerant pipe114, the primary-side refrigerant condensed in the cascade heat exchanger35passes through the primary-side second expansion valve102controlled to 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 to the closed state. Accordingly, the refrigerant does not flow into the primary-side subcooling circuit104and does not exchange heat in the primary-side subcooling heat exchanger103. The valve opening degree of the primary-side first expansion valve76is controlled such that, for example, the degree of superheating of the refrigerant sucked into the primary-side compressor71satisfies a predetermined condition. The refrigerant decompressed by the primary-side first expansion valve76evaporates by exchanging heat with outdoor air supplied from the primary-side fan75in the primary-side heat exchanger74, passes through the primary-side switching mechanism72and the primary-side accumulator105, and is sucked into the primary-side compressor71.

In the cascade unit2, the secondary-side switching mechanism22is switched to the second connection state. In the second connection 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 regulating valves66aand66band the second regulating valve67care controlled to the opened state, and the first regulating valve66cand the second regulating valves67aand67bare controlled to the closed state. Accordingly, the utilization-side heat exchangers52aand52bin the utilization units3aand3bfunction as refrigerant radiators, and the utilization-side heat exchanger52cin the utilization unit3cfunctions as a refrigerant evaporator. 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 to 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 between the utilization-side heat exchangers52a,52b,and52c.As a result, in the heating main operation, the secondary-side refrigerant discharged from the secondary-side compressor21is controlled to 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 a predetermined primary-side condensation target temperature.

In such a secondary-side refrigerant circuit10, 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.

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 unit3bwhich are utilization units in 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 regulating valves66aand66b,the junction pipes62aand62b,and the first connecting tubes15aand15b.

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. The indoor air is heated and 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 through the utilization-side expansion valves51aand51bwhose opening degree is adjusted. The secondary-side refrigerant that has 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.

A part of the refrigerant sent to the secondary-side third connection pipe7is sent to the third branch pipe61cof the branch unit6c,and the rest 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.

The refrigerant having passed through 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. The 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.

The low-pressure gas refrigerant sent to the junction pipe62cis sent to the secondary-side second connection pipe9through the second regulating valve67cand the second branch pipe64c.

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.

The refrigerant flowing toward the third shutoff valve31is sent to the cascade expansion valve36. The refrigerant sent to the cascade expansion valve36passes through the cascade expansion valve36whose opening degree is adjusted, 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 exchanger35evaporates to become 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.

Motion during the heating main operation is performed in such a manner.

(9-5) Oil Return Operation

When a predetermined oil return condition is satisfied during the heating operation and the heating main operation, the operation is performed with the connection state of the secondary-side refrigerant circuit10temporarily set as the connection state during the cooling operation to perform the oil return operation. As a result, the refrigerating machine oil retained at a lower end of the vessel body90of the secondary-side receiver45can be extracted from the secondary-side receiver45through the second refrigerant pipe97of the fifth pipe27extending from a lower end of the secondary-side receiver45.

The predetermined oil return condition is not limited, and for example, the heating operation and the heating main operation may be performed for a predetermined time. An end of the oil return operation is not limited, and for example, the oil return operation may be performed for a predetermined time.

FIG.7is a schematic configuration diagram of the secondary-side receiver45.

The secondary-side receiver45includes the vessel body90, a first refrigerant pipe96, a second refrigerant pipe97, and a third refrigerant pipe98.

The vessel body90is a substantially cylindrical vessel having an internal volume corresponding to the amount of refrigerant filled in the secondary-side refrigerant circuit10, and temporarily reserves the refrigerant flowing in the secondary-side refrigerant circuit10. The vessel body90includes an upper part91, a lower peripheral surface part92, and a bottom part93, which are welded and fixed to each other. The upper part91has a cylindrical shape in which an internal space is formed so as to open downward. The lower peripheral surface part92is disposed under the upper part91and has a cylindrical shape penetrating in an up-down direction. The bottom part93is a columnar member whose thickness direction is the up-down direction. The bottom part93has an upper surface93afacing upward, toward a space inside the secondary-side receiver45, and a lower surface93bfacing downward, toward a space outside the secondary-side receiver45. In the present embodiment, both the upper surface93aand the lower surface93bextend in a horizontal plane. The bottom part93has a portion penetrating in the up-down direction at a center in plan view, and an end of the second refrigerant pipe97on a side connected to the secondary-side receiver45is inserted from below. The bottom part93and the second refrigerant pipe97are welded to each other.

In the present embodiment, the first refrigerant pipe96is, for example, a pipe extending laterally from a part of a peripheral surface of the vessel body90, and constitutes a part of the fourth pipe26in the secondary-side refrigerant circuit10. The first refrigerant pipe96is welded to the upper part91of the vessel body90. The first refrigerant pipe96has a portion extending downward inside the secondary-side receiver45, and an end located inside the secondary-side receiver45has an opening96aformed to be inclined with respect to an axial direction in which the pipe extends. The end of the first refrigerant pipe96in the secondary-side receiver45is in contact with the upper surface93aof the bottom part93or extends to a position in front of the upper surface93aof the bottom part93.

The second refrigerant pipe97is a pipe extending downward from the bottom part93of the vessel body90, and constitutes a part of the fifth pipe27in the secondary-side refrigerant circuit10. The second refrigerant pipe97is welded to the bottom part93in a state of being inserted into a penetrating portion in the up-down direction formed in the bottom part93. In the present embodiment, the upper end97aof the second refrigerant pipe97is disposed at a height position equal to or lower than a height position of a portion of the upper surface93aof the bottom part93where the second refrigerant pipe97is connected. Specifically, in the present embodiment, the upper end97aof the second refrigerant pipe97is disposed on the same horizontal plane as the upper surface93aof the bottom part93.

The third refrigerant pipe98is a pipe extending laterally from a part of the peripheral surface of the vessel body90, and constitutes a part of the bypass circuit46in the secondary-side refrigerant circuit10. The third refrigerant pipe98is welded to the upper part91of the vessel body90.

(11) Characteristics of Embodiment

In the secondary-side refrigerant circuit10of the refrigeration cycle apparatus1according to the present embodiment, the carbon dioxide refrigerant and the PAG oil which are incompatible with each other are used. Here, the PAG oil has a higher density than the carbon dioxide refrigerant in a use condition in the secondary-side refrigerant circuit10. Therefore, in the secondary-side receiver45, the PAG oil is likely to be located below the carbon dioxide refrigerant.

In the secondary-side receiver45according to the present embodiment, the second refrigerant pipe97is provided so as to penetrate the bottom part93in the up-down direction. The upper end97aof the second refrigerant pipe97is disposed at the same height position as the upper surface93aof the bottom part93or at a height position lower than the upper surface93aof the bottom part93. As a result, the PAG oil flowing into the secondary-side receiver45via the first refrigerant pipe96and located below carbon dioxide refrigerant passes through the second refrigerant pipe97and is efficiently sent out of the secondary-side receiver45. Therefore, the refrigerating machine oil is prevented from being continuously reserved in the secondary-side receiver45.

In the refrigeration cycle apparatus1according to the present embodiment, the carbon dioxide refrigerant discharged from the secondary-side compressor21of the secondary-side refrigerant circuit10is not in the supercritical state by exchanging heat with the primary-side refrigerant flowing in the primary-side refrigerant circuit5ain the cascade heat exchanger35or by controlling the valve opening degree of the cascade expansion valve36, and is sent to the secondary-side receiver45. Therefore, even if the carbon dioxide refrigerant and the refrigerating machine oil are phase-separated in the secondary-side receiver45, it is possible to prevent the refrigerating machine oil from continuously accumulating in the secondary-side receiver45while avoiding the supercritical state in which the behavior tends to be unstable.

(12) Other Embodiments

(12-1) Another Embodiment A

In the above embodiment, as an example, a case has been described where the upper surface93aof the bottom part93of the secondary-side receiver45is a horizontal plane.

Alternatively, for example, as illustrated inFIG.8, the bottom part93of the secondary-side receiver45may have an upper curved surface193athat is curved so as to gently protrude downward and constitutes an inner bottom surface of the secondary-side receiver45, instead of the upper surface93aaccording to the above embodiment. The upper curved surface193ahas a curved shape that gradually descends toward the upper end97aof the second refrigerant pipe97. The upper end97aof the second refrigerant pipe97is located at a lowermost end of the upper curved surface193a.

In this case, since the refrigerating machine oil located on the upper curved surface193ais guided to the upper end97aof the second refrigerant pipe97by a weight of the refrigerating machine oil, the refrigerating machine oil can be efficiently discharged from the secondary-side receiver45.

(12-2) Another Embodiment B

In the another embodiment A, as an example, a case has been described where the bottom part93of the secondary-side receiver45has the upper curved surface193a.

Alternatively, for example, as illustrated inFIG.9, the bottom part93of the secondary-side receiver45may have a lower curved surface193bthat is curved so as to protrude downward similarly to the upper curved surface193aand constitutes an outer bottom surface of the secondary-side receiver45, instead of the lower surface93b.

In this case, not only the effects of the above embodiment and the another embodiment A can be obtained, but also the thickness of the bottom part93in the up-down direction can be made constant, and a pressure resistance strength of the secondary-side receiver45can be easily secured.

(12-3) Another Embodiment C

In the above embodiment, as an example, a case has been described where the height position of the upper end97aof the second refrigerant pipe97is equal to or lower than the height position of the portion of the upper surface93aof the bottom part93where the second refrigerant pipe97is connected.

However, the height position of the upper end97aof the second refrigerant pipe97is not limited to the height position as described above.

For example, as illustrated inFIG.10, the upper end197aof the second refrigerant pipe197may be located slightly above a portion of the upper surface93aof the bottom part93where the second refrigerant pipe197is connected. For example, the height position of the upper end197aof the second refrigerant pipe197may be higher than the portion of the upper surface93aof the bottom part93where the second refrigerant pipe197is connected, and may be lower than a height position 15 mm higher than the portion. The height position of the upper end197aof the second refrigerant pipe197may be equal to or lower than a height position 10 mm higher than the portion of the upper surface93aof the bottom part93where the second refrigerant pipe197is connected. A difference in a height direction between the upper end197aof the second refrigerant pipe197and the portion of the upper surface93aof the bottom part93where the second refrigerant pipe197is connected may be 1/100 or less of a height of the vessel body90of the secondary-side receiver45. Since the upper end197aof the second refrigerant pipe197protrudes further upward than the upper surface93aof the bottom part93as described above, a pipe protruding margin can be secured to facilitate manufacturing.

A portion above the upper surface93aof the bottom part93near the upper end197aof the second refrigerant pipe197may be flared such that a flow path area increases upward.

(12-4) Another Embodiment D

In the above embodiment, as an example, a case has been described where the first refrigerant pipe96is provided so as to extend laterally from a part of a peripheral surface of the secondary-side receiver45.

However, a connection form of the first refrigerant pipe96with the secondary-side receiver45is not limited to the above case.

For example, as illustrated inFIG.11, the first refrigerant pipe196may be provided so as to extend downward from the bottom part93of the secondary-side receiver45. In this case, the upper end196aof the first refrigerant pipe196may be configured similarly to the upper end97aof the second refrigerant pipe97according to the above embodiment, or similarly to the upper end197aof the second refrigerant pipe197of the another embodiment C.

(12-5) Another Embodiment E

In the above embodiment, as an example, a case has been described where the second refrigerant pipe97is provided so as to penetrate the bottom part93in the up-down direction in the secondary-side receiver45as a high-pressure receiver provided at a portion in which the high-pressure refrigerant flows in the secondary-side refrigerant circuit10.

Alternatively, for example, as an intermediate-pressure receiver18in a refrigerant circuit210of an air conditioner201illustrated inFIG.12, a second refrigerant pipe19may be provided so as to penetrate the bottom part in the up-down direction.

The air conditioner201is a device that performs a vapor compression refrigeration cycle to condition air in a target space. The air conditioner201mainly includes an outdoor unit202, an indoor unit203, a liquid-side connection pipe207and a gas-side connection pipe208that connect the outdoor unit202and the indoor unit203, and a controller4that controls motion of the air conditioner201. The air conditioner201performs a refrigeration cycle in which a refrigerant sealed in the refrigerant circuit210is compressed, radiates heat, is decompressed, evaporated, and then compressed again. The air conditioner201is filled with a refrigerant and a refrigerating machine oil that is incompatible with the refrigerant and has a higher density than the refrigerant. Specifically, the refrigerant is a carbon dioxide refrigerant, and the refrigerating machine oil is PAG oil.

The outdoor unit202is connected to the indoor unit203via the liquid-side connection pipe207and the gas-side connection pipe208, and constitutes a part of the refrigerant circuit210. The outdoor unit202mainly includes a compressor221, a four-way switching valve222, an outdoor heat exchanger235, a first refrigerant pipe17, a first outdoor expansion valve17a,the intermediate-pressure receiver18, the second refrigerant pipe19, a second outdoor expansion valve19a,an outdoor fan11, a liquid-side shutoff valve231, and a gas-side shutoff valve232.

The compressor221is a device that compresses a low-pressure refrigerant in the refrigeration cycle to a high pressure. The compressor221used herein is a closed compressor in which a rotary type, scroll type, or other positive-displacement compression element is driven to rotate by a compressor motor. The compressor motor is for changing a capacity, and an operating frequency can be controlled by an inverter.

By switching the connection state, the four-way switching valve222can switch between a connection state in which a cooling operation is performed by connecting a suction side of the compressor221and the gas-side shutoff valve232while connecting a discharge side of the compressor221and the outdoor heat exchanger235, and a connection state in which a heating operation is performed by connecting the suction side of the compressor221and the outdoor heat exchanger235while connecting the discharge side of the compressor221and the gas-side shutoff valve232.

The outdoor heat exchanger235functions as a radiator for the high-pressure refrigerant in the refrigeration cycle during the cooling operation, and functions as an evaporator for the low-pressure refrigerant in the refrigeration cycle during the heating operation. The outdoor heat exchanger235includes a plurality of heat transfer fins and a plurality of heat transfer tubes penetrated through and fixed to the plurality of heat transfer fins. The outdoor heat exchanger235is an air heat exchanger that causes heat exchange between the refrigerant and air flowing outside.

The outdoor fan11sucks outdoor air into the outdoor unit202, causes the outdoor air to exchange heat with the refrigerant in the outdoor heat exchanger235, and then generates an air flow to be discharged to the outside. The outdoor fan11is driven to rotate by an outdoor fan motor.

The first refrigerant pipe17connects an end of the outdoor heat exchanger235on an opposite side of the compressor221and the intermediate-pressure receiver18. The first refrigerant pipe17is provided with a first outdoor expansion valve17awhose valve opening degree is controllable. During the cooling operation, the opening degree of the first outdoor expansion valve17ais controlled in order to send the intermediate-pressure refrigerant obtained by decompressing the high-pressure refrigerant to the intermediate-pressure receiver18. During the heating operation, the opening degree of the first outdoor expansion valve17ais controlled in order to send the low-pressure refrigerant obtained by decompressing the intermediate-pressure refrigerant to the outdoor heat exchanger235.

The intermediate-pressure receiver18is provided between the first outdoor expansion valve17aand the second outdoor expansion valve19ain the refrigerant circuit210. Note that the details of the specific structure of the intermediate-pressure receiver18are similar to those of the secondary-side receiver45according to the above embodiment.

The second refrigerant pipe19connects the bottom part of the intermediate-pressure receiver18and the liquid-side shutoff valve231. The second refrigerant pipe19is provided with a second outdoor expansion valve19awhose valve opening degree is controllable. During the heating operation, the opening degree of the second outdoor expansion valve19ais controlled in order to send the intermediate-pressure refrigerant obtained by decompressing the high-pressure refrigerant to the intermediate-pressure receiver18. During the cooling operation, the opening degree of the second outdoor expansion valve19ais controlled in order to send the low-pressure refrigerant obtained by decompressing the intermediate-pressure refrigerant to the indoor heat exchanger252.

The liquid-side shutoff valve231is a manual valve disposed at a connecting part of the outdoor unit202with the liquid-side connection pipe207. The gas-side shutoff valve232is a manual valve disposed at a connecting part of the outdoor unit202with the gas-side connection pipe208.

The outdoor unit202includes an outdoor unit control unit4athat controls motion of each element constituting the outdoor unit202. The indoor unit203is installed on, for example, an indoor wall surface as a target space. The indoor unit203is connected to the outdoor unit202via the liquid-side connection pipe207and the gas-side connection pipe208, and constitutes a part of the refrigerant circuit210. The indoor unit203includes the indoor heat exchanger252, an indoor fan253, and the like.

The indoor heat exchanger252has a liquid side connected to the liquid-side connection pipe207and a gas side end connected to the gas-side connection pipe208. The indoor heat exchanger252functions as an evaporator for the low-pressure refrigerant in the refrigeration cycle during the cooling operation, and functions as a condenser for the high-pressure refrigerant in the refrigeration cycle during the heating operation. The indoor heat exchanger252includes a plurality of heat transfer fins and a plurality of heat transfer tubes penetrated through and fixed to the plurality of heat transfer fins.

The indoor fan253sucks indoor air into the indoor unit203, causes the indoor air to exchange heat with the refrigerant in the indoor heat exchanger252, and then generates an air flow to be discharged to the outside.

The indoor unit203includes an indoor unit control unit4bthat controls motion of each element constituting the indoor unit203.

As in the above embodiment, the intermediate-pressure receiver18described above can efficiently discharge the refrigerating machine oil which is incompatible with the carbon dioxide refrigerant, has a higher density than the carbon dioxide refrigerant, and tends to be located below the carbon dioxide refrigerant through the second refrigerant pipe19.

(12-6) Another Embodiment F

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

Alternatively, as illustrated inFIG.13, for example, by connecting are a plurality of cascade units, namely, a first cascade unit2a,a second cascade unit2b,and a third cascade unit2c,in parallel to each other 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.13, 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 illustrated, each of the first cascade unit2a,the second cascade unit2b, and the third cascade unit2cis connected to 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,to a plurality of branch units and utilization units different from those connected to 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,to 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.Furthermore, 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. Similarly to 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.

(12-7) Another Embodiment G

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.

Alternatively, the refrigerant provided in the primary-side refrigerant circuit5ashould not be limited, and examples of the refrigerant include HFC-32, an HFO refrigerant, a refrigerant obtained by mixing HFC-32 and the HFO refrigerant, carbon dioxide, ammonia, and propane.

Furthermore, instead of the primary-side refrigerant circuit5ain which the refrigerant flows, a heat medium circuit in 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 heat source or a cold 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 heat source or the cold source.

The refrigerant provided in the secondary-side refrigerant circuit10should not be limited, and examples of the refrigerant include HFC-32, an HFO refrigerant, a refrigerant obtained by mixing HFC-32 and the HFO refrigerant, carbon dioxide, ammonia, and propane.

Note that 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.Here, the flammability can be compared in accordance with classifications related to ASHRAE 34 flammability, for example. Note that 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.

In some embodiments, the first refrigerant pipe may introduce the refrigerant into the vessel body, and the second refrigerant pipe may derive the refrigerant from the vessel body.

That the refrigerating machine oil is incompatible with the refrigerant means that the refrigerant and the refrigerating machine oil are separated from each other without becoming a uniform layer of liquid in the refrigerant vessel under a use environment of the refrigerant and the refrigerating machine oil.

That the density of the refrigerating machine oil is higher than the density of the refrigerant means that the density of the refrigerating machine oil is higher than the density of the refrigerant in a liquid state under the use environment of the refrigerant and the refrigerating machine oil.

The height position of the upper end of the second refrigerant pipe is preferably equal to or lower than a position 10 mm higher than the lowermost end of the inner peripheral surface of the bottom part of the vessel body.

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.

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CITATION LIST

Patent Literature

Patent Literature 1: JP 2008-164225 A