JP7617464B1 - Air Conditioning Equipment - Google Patents

Abstract

An air conditioner adjusts the temperature difference between an indoor temperature and a target indoor temperature during heating operation in which a refrigerant is compressed to or above its critical pressure to heat the room.
[Solution] The air conditioner (1) includes a refrigerant circuit (6) and a control device (130). The refrigerant circuit (6) includes a compressor (23), a radiator (64), an expansion valve (63), and an evaporator (24), and performs a refrigeration cycle for performing a heating operation for heating a room by compressing the refrigerant to a critical pressure (Pc) or higher. The control device (130) controls the refrigerant circuit (6). The control device (130) controls the expansion valve (63) to adjust the refrigerant temperature (TE) at the outlet (E) of the radiator (64), and controls the high pressure (Ph) of the refrigerant circuit (6) based on the temperature difference (ΔTR) between the room temperature (TR) and a target room temperature (TR0).
[Selected Figure] Figure 1

Description

This disclosure relates to air conditioning devices.

For example, as shown in Patent Document 1, various technologies have been disclosed for air conditioners. The air conditioner disclosed in Patent Document 1 includes a refrigerant circuit. The refrigerant circuit has a compressor, a radiator, an expansion valve, and an evaporator, and performs a refrigeration cycle to perform a heating operation to heat the room.

JP 2021-055874 A

When a refrigerant with a low critical pressure is used for heating operation, the refrigerant is compressed above its critical pressure. When the refrigerant is compressed above its critical pressure, the condensation temperature of the refrigerant no longer exists in the region above the critical pressure, making it difficult to control the refrigerant temperature. For this reason, in supercritical operation in which the refrigerant is compressed above its critical pressure, it becomes difficult to adjust the indoor temperature, and it becomes difficult to adjust the temperature difference between the indoor temperature and the target indoor temperature.

The objective of this disclosure is to adjust the temperature difference between the indoor temperature and the target indoor temperature during heating operation in an air conditioning system, in which the refrigerant is compressed to above the critical pressure to heat the room.

The first aspect of the present disclosure is directed to an air conditioner (1). The air conditioner (1) includes a refrigerant circuit (6) having a compressor (23), a radiator (64), an expansion valve (63), and an evaporator (24), which performs a refrigeration cycle to perform a heating operation for heating a room by compressing the refrigerant to a critical pressure (Pc) or higher, and a control device (130) that controls the refrigerant circuit (6), and the control device (130) controls the expansion valve (63) to adjust the refrigerant temperature (TE) at the outlet (E) of the radiator (64), and controls the high pressure (Ph) of the refrigerant circuit (6) based on the temperature difference (ΔTR) between the room temperature (TR) and the target room temperature (TR0).

In the first aspect, in the air conditioning device (1), during heating operation in which the refrigerant is compressed to a critical pressure (Pc) or higher to heat the room, the temperature difference (ΔTR) between the room temperature (TR) and the target room temperature (TR0) can be adjusted.

In a second aspect of the present disclosure, in the first aspect, the control device (130) controls the compressor (23) to increase the high pressure (Ph) of the refrigerant circuit (6) when the temperature difference (ΔTR) becomes greater than a first value.

According to the second aspect, when the temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0) is greater than the first value, the indoor temperature (TR) can be increased by increasing the high pressure (Ph) of the refrigerant circuit (6). The temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0) can be reduced.

In a third aspect of the present disclosure, in the first or second aspect, the control device (130) controls the compressor (23) to lower the high pressure (Ph) of the refrigerant circuit (6) when the temperature difference (ΔTR) becomes smaller than a second value.

According to the third aspect, when the temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0) is smaller than the second value, the high pressure (Ph) of the refrigerant circuit (6) is lowered, thereby reducing the load on the compressor (23).

In a fourth aspect of the present disclosure, in any one of the first to third aspects, the control device (130) controls the compressor (23) so that the high pressure (Ph) of the refrigerant circuit (6) is set to the lower limit (Ph1) of the control range when the temperature difference (ΔTR) becomes smaller than a third value.

According to the fourth aspect, when the temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0) is smaller than the third value, the high pressure (Ph) of the refrigerant circuit (6) is set to the lower limit value (Ph1), which is advantageous in reducing the load on the compressor (23).

In a fifth aspect of the present disclosure, in any one of the first to fourth aspects, the refrigerant circuit (6) includes a gas-liquid separator (25) connected downstream of the radiator (64) and separating the refrigerant into a gas refrigerant and a liquid refrigerant, a gas vent passage (41) connecting a gas storage section (25a) of the gas-liquid separator (25) and a suction side (23i) of the compressor (23), and an on-off valve (42) provided in the gas vent passage (41), and the control device (130) opens the on-off valve (42) when the temperature difference (ΔTR) becomes greater than a fourth value.

According to the fifth aspect, when the temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0) is greater than the fourth value, the indoor temperature (TR) can be further increased by promoting the flow of refrigerant from the gas storage section (25a) of the gas-liquid separator (25) to the suction side (23i) of the compressor (23). This is advantageous in reducing the temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0).

In a sixth aspect of the present disclosure, in any one of the first to fifth aspects, the refrigerant circuit (6) has a gas-liquid separator (25) connected downstream of the radiator (64) and separating the refrigerant into a gas refrigerant and a liquid refrigerant, and the specific enthalpy (he) of the refrigerant at the outlet (E) of the radiator (64) is smaller than the specific enthalpy (hc) of the refrigerant at the critical point (C).

According to the sixth aspect, the gas-liquid separation effect of the gas-liquid separator (25) can be increased by increasing the amount of liquid refrigerant flowing into the gas-liquid separator (25).

In a seventh aspect of the present disclosure, in any one of the first to sixth aspects, the radiator (64) includes a first radiator (64A) and a second radiator (64B) connected in parallel to each other, the expansion valve (63) includes a first expansion valve (63A) corresponding to the first radiator (64A) and a second expansion valve (63B) corresponding to the second radiator (64B), and the control device (130) controls the high pressure (Ph) of the refrigerant circuit (6) based on either or both of a first temperature difference (ΔTRA) that is a temperature difference between an indoor temperature (TRA) corresponding to the first radiator (64A) and a target indoor temperature (TR0A) and a second temperature difference (ΔTRB) that is a temperature difference between an indoor temperature (TRB) corresponding to the second radiator (64B) and a target indoor temperature (TR0B).

According to the seventh aspect, even if there are two or more radiators (64), the temperature difference (ΔTR) between the room temperature (TR) and the target room temperature (TR0) can be adjusted during heating operation in which the refrigerant is compressed to or above the critical pressure (Pc) to heat the room.

In the eighth aspect of the present disclosure, in the seventh aspect, the control device (130) controls the high pressure (Ph) of the refrigerant circuit (6) based on the larger of the first temperature difference (ΔTRA) and the second temperature difference (ΔTRB).

According to the eighth aspect, by adopting the worse condition (larger temperature difference) between the first temperature difference (ΔTRA) and the second temperature difference (ΔTRB), it is advantageous to reduce the temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0).

In a ninth aspect of the present disclosure, in any one of the first to eighth aspects, the refrigerant is carbon dioxide.

According to the ninth aspect, the use of carbon dioxide as a refrigerant is advantageous from the standpoint of environmental protection.

FIG. 1 is a piping diagram of an air conditioner (1) according to an embodiment. FIG. 2 is a diagram showing a piping system in the vicinity of the air conditioning unit (60). FIG. 3 is a block diagram showing the connections between the controller (130) and peripheral devices. FIG. 4 is a graph showing the relationship between specific enthalpy (h) and pressure (P) of a refrigerant. FIG. 5 is a control flowchart of the air conditioner (1) during heating operation.

Embodiments of the present disclosure will be described in detail below with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below, and various modifications are possible without departing from the technical spirit of the present disclosure. The drawings are intended to conceptually explain the present disclosure, and therefore may exaggerate or simplify dimensions, ratios, or numbers as necessary to facilitate understanding.

The air conditioner (1) according to this embodiment performs a refrigeration cycle. The air conditioner (1) is also called a refrigeration device. The air conditioner (1) performs air conditioning for the room. The air conditioner (1) cools an object to be cooled. The object to be cooled here includes the air inside equipment such as a refrigerator, a freezer, or a showcase. Hereinafter, such equipment will be referred to as a refrigeration facility.

(1) Overall Configuration Fig. 1 is a piping diagram of an air conditioner (1). As shown in Fig. 1, the air conditioner (1) includes a heat source unit (10) installed outdoors, an air conditioning unit (60) that conditions the air inside the room, and a cold storage unit (70) that cools the air inside the room. The air conditioning unit (60) includes a first air conditioning unit (60A) and a second air conditioning unit (60B) that are connected in parallel to each other.

The air conditioner (1) includes four interconnecting pipes (2, 3, 4, 5) that connect the heat source unit (10), the air conditioning unit (60), and the cooling unit (70). In the air conditioner (1), the heat source unit (10), the air conditioning unit (60), and the cooling unit (70) are connected by these interconnecting pipes (2, 3, 4, 5) to form a refrigerant circuit (6). In other words, the air conditioner (1) includes a refrigerant circuit (6).

The refrigerant circuit (6) contains a filled refrigerant. The refrigerant circuit (6) circulates the refrigerant to perform a refrigeration cycle. In this embodiment, the refrigerant is carbon dioxide. The refrigerant circuit (6) performs a refrigeration cycle in which the refrigerant is compressed to or above its critical pressure.

(1-1) Interconnecting Pipes The four interconnecting pipes (2, 3, 4, 5) consist of a first liquid interconnecting pipe (2), a first gas interconnecting pipe (3), a second liquid interconnecting pipe (4), and a second gas interconnecting pipe (5). The first liquid interconnecting pipe (2) and the first gas interconnecting pipe (3) correspond to the air conditioning unit (60). The second liquid interconnecting pipe (4) and the second gas interconnecting pipe (5) correspond to the cooling unit (70).

(2) Heat Source Unit The heat source unit (10) has a heat source circuit (11) and an outdoor fan (12). The heat source circuit (11) has a compression element (20), an outdoor heat exchanger (24), and a gas-liquid separator (25). The heat source circuit (11) has a first outdoor expansion valve (26) and a second outdoor expansion valve (27). The heat source circuit (11) further has a subcooling heat exchanger (28) and an intercooler (29).

The heat source circuit (11) has four shutoff valves (13, 14, 15, 16). The four shutoff valves (13, 14, 15, 16) are composed of a first gas shutoff valve (13), a first liquid shutoff valve (14), a second gas shutoff valve (15), and a second liquid shutoff valve (16).

The first gas stop valve (13) is connected to the first gas connection pipe (3). The first liquid stop valve (14) is connected to the first liquid connection pipe (2). The second gas stop valve (15) is connected to the second gas connection pipe (5). The second liquid stop valve (16) is connected to the second liquid connection pipe (4).

The heat source unit (10) has a flow path switching mechanism (30). In the piping system diagram of the refrigerant circuit (6) in FIG. 1 and the like, the details of the flow path switching mechanism (30) are omitted. The flow path switching mechanism (30) switches the flow path of the refrigerant in the refrigerant circuit (6).

(2-1) Compression Element The compression element (20) compresses the refrigerant. The compression element (20) has a first compressor (21), a second compressor (22), and a third compressor (23). The compression element (20) performs an operation in which the refrigerant is compressed in a single stage and an operation in which the refrigerant is compressed in two stages. The third compressor (23) is an example of a compressor in this embodiment.

The first compressor (21) is a cold-conditioning compressor corresponding to the cold-conditioning unit (70). The second compressor (22) is an air-conditioning compressor corresponding to the air-conditioning unit (60). The first compressor (21) and the second compressor (22) are low-stage compression sections. The first compressor (21) and the second compressor (22) are connected in parallel.

The third compressor (23) is a high-stage compression section. The third compressor (23) is connected in series with the first compressor (21) or in series with the second compressor (22).

The first compressor (21), the second compressor (22), and the third compressor (23) are rotary compressors whose compression mechanisms are driven by a motor. The first compressor (21), the second compressor (22), and the third compressor (23) are of a variable capacity type. The rotation speed of the motor of the first compressor (21), the second compressor (22), and the third compressor (23) is adjusted by an inverter device. In other words, the first compressor (21), the second compressor (22), and the third compressor (23) are configured so that their operating capacities are adjustable.

A first suction pipe (21a) is connected to the suction section of the first compressor (21). A first discharge pipe (21b) is connected to the discharge section of the first compressor (21). A second suction pipe (22a) is connected to the suction section of the second compressor (22). A second discharge pipe (22b) is connected to the discharge section of the second compressor (22). A third suction pipe (23a) is connected to the suction section of the third compressor (23). A third discharge pipe (23b) is connected to the discharge section of the third compressor (23).

(2-2) Intermediate Flow Passage The heat source circuit (11) includes an intermediate flow passage (18). The intermediate flow passage (18) connects the discharge portion of the first compressor (21) and the discharge portion of the second compressor (22) to the suction portion of the third compressor (23). The intermediate flow passage (18) includes a first discharge pipe (21b), a second discharge pipe (22b), and a third suction pipe (23a).

(2-3) Outdoor Heat Exchanger and Outdoor Fan The outdoor heat exchanger (24) is an example of an evaporator. The outdoor heat exchanger (24) is a fin-and-tube type air heat exchanger. The outdoor fan (12) is disposed near the outdoor heat exchanger (24). The outdoor fan (12) transports outdoor air. The outdoor heat exchanger exchanges heat between the refrigerant flowing therethrough and the outdoor air transported by the outdoor fan (12).

(2-4) Liquid Side Flow Path The heat source circuit (11) includes a liquid side flow path (40). The liquid side flow path (40) is provided between the liquid side end of the outdoor heat exchanger (24) and the two liquid stop valves (14, 16). The liquid side flow path (40) includes first to fifth pipes (40a, 40b, 40c, 40d, 40e).

One end of the first pipe (40a) is connected to the liquid side end of the outdoor heat exchanger (24). The other end of the first pipe (40a) is connected to the top of the gas-liquid separator (25). One end of the second pipe (40b) is connected to the bottom of the gas-liquid separator (25). The other end of the second pipe (40b) is connected to the second liquid shutoff valve (16). One end of the third pipe (40c) is connected to the middle of the second pipe (40b). The other end of the third pipe (40c) is connected to the first liquid shutoff valve (14). One end of the fourth pipe (40d) is connected to the first pipe (40a) between the first outdoor expansion valve (26) and the gas-liquid separator (25). The other end of the fourth pipe (40d) is connected to the middle of the third pipe (40c). One end of the fifth pipe (40e) is connected to the first pipe (40a) between the outdoor heat exchanger (24) and the first outdoor expansion valve (26). The other end of the fifth pipe (40e) is connected to the second pipe (40b) between the gas-liquid separator (25) and the junction of the third pipe (40c).

(2-5) Outdoor Expansion Valve The first outdoor expansion valve (26) is provided in the first pipe (40a). The first outdoor expansion valve (26) is provided in the first pipe (40a) between the liquid side end of the outdoor heat exchanger (24) and the connection portion with the fourth pipe (40d). The second outdoor expansion valve (27) is provided in the fifth pipe (40e). The first outdoor expansion valve (26) and the second outdoor expansion valve (27) are expansion valves whose opening degrees are adjustable. The first outdoor expansion valve (26) and the second outdoor expansion valve (27) are electronic expansion valves whose opening degrees are adjusted based on a pulse signal.

(2-6) Gas-Liquid Separator The gas-liquid separator (25) is a sealed container that stores a refrigerant. The gas-liquid separator (25) separates the refrigerant into a gas refrigerant and a liquid refrigerant. A gas storage section (25a) and a liquid storage section (25b) are formed inside the gas-liquid separator (25). The gas storage section (25a) is formed on the top side of the gas-liquid separator (25). The liquid storage section (25b) is formed on the bottom side of the gas-liquid separator (25).

(2-7) Gas Vent Pipe The heat source circuit (11) has a gas vent pipe (41) as a gas vent passage. One end of the gas vent pipe (41) is connected to the gas storage section (25a) at the top of the gas-liquid separator (25). The other end of the gas vent pipe (41) is connected to the intermediate flow path (18). The gas vent pipe (41) sends gas refrigerant in the gas-liquid separator (25) to the intermediate flow path (18). The gas vent pipe (41) is an example of a gas vent passage that connects the gas storage section (25a) of the gas-liquid separator (25) to the suction side (23i) of the third compressor (23), which is a high-stage compression section.

The gas vent pipe (41) is provided with a gas vent valve (42) as an on-off valve. The gas vent valve (42) is an expansion valve whose opening is adjustable. The gas vent valve (42) is an electronic expansion valve whose opening is adjusted based on a pulse signal. The gas vent valve (42) may be an electric valve or an electromagnetic on-off valve. The gas vent valve (42) is an example of an on-off valve provided in the gas vent pipe (41) as a gas vent passage.

(2-8) Subcooling Heat Exchanger The subcooling heat exchanger (28) has a first flow path (28a) which is a high-pressure side flow path and a second flow path (28b) which is a low-pressure side flow path. The subcooling heat exchanger (28) exchanges heat between the refrigerant in the first flow path (28a) and the refrigerant in the second flow path (28b). In other words, the subcooling heat exchanger (28) cools the refrigerant flowing in the first flow path (28a) by the refrigerant flowing in the second flow path (28b).

The second flow path (28b) constitutes a part of the injection flow path (43). The injection flow path (43) includes an upstream flow path (44) and a downstream flow path (45).

One end of the upstream flow path (44) is connected to the third pipe (40c) upstream of the connection portion of the fourth pipe (40d). The other end of the upstream flow path (44) is connected to the inlet end of the second flow path (28b). The upstream flow path (44) is provided with an injection valve (46) which is a subcooling side pressure reducing valve. The injection valve (46) is an expansion valve whose opening is adjustable. The injection valve (46) is an electronic expansion valve whose opening is adjusted based on a pulse signal.

One end of the downstream flow path (45) is connected to the outlet end of the second flow path (28b). The other end of the downstream flow path (45) is connected to the intermediate flow path (18).

(2-9) Intercooler The intercooler (29) is provided in the intermediate flow path (18). The intercooler (29) is a fin-and-tube type air heat exchanger. A cooling fan (29a) is disposed in the vicinity of the intercooler (29). The intercooler (29) exchanges heat between the refrigerant flowing therethrough and the outdoor air transported by the cooling fan (29a).

(2-10) Oil Separation Circuit The heat source circuit (11) includes an oil separation circuit. The oil separation circuit has an oil separator (50), a first oil return pipe (51), and a second oil return pipe (52).

The oil separator (50) is connected to the third discharge pipe (23b). The oil separator (50) separates oil from the refrigerant discharged from the compression element (20). The inlet ends of the first oil return pipe (51) and the second oil return pipe (52) communicate with the oil separator (50). The outlet end of the first oil return pipe (51) is connected to the intermediate flow path (18). The first oil return pipe (51) is provided with a first oil amount control valve (53).

The outlet side of the second oil return pipe (52) is separated into a first branch pipe (52a) and a second branch pipe (52b). The first branch pipe (52a) is connected to the oil reservoir of the first compressor (21). The second branch pipe (52b) is connected to the oil reservoir of the second compressor (22). The first branch pipe (52a) is provided with a second oil amount control valve (54). The second branch pipe (52b) is provided with a third oil amount control valve (55).

(2-11) Bypass Pipe The heat source circuit (11) has a first bypass pipe (56), a second bypass pipe (57), and a third bypass pipe (58). The first bypass pipe (56) corresponds to the first compressor (21). The second bypass pipe (57) corresponds to the second compressor (22). The third bypass pipe (58) corresponds to the third compressor (23).

Specifically, the first bypass pipe (56) directly connects the first suction pipe (21a) and the first discharge pipe (21b). The second bypass pipe (57) directly connects the second suction pipe (22a) and the second discharge pipe (22b). The third bypass pipe (58) directly connects the third suction pipe (23a) and the third discharge pipe (23b).

(2-12) Check Valve The heat source circuit (11) has a plurality of check valves. The plurality of check valves includes first to twelfth check valves (CV1 to CV12). These check valves (CV1 to CV12) allow the flow of refrigerant in the direction of the arrow in FIG. 1 and prohibit the flow of refrigerant in the opposite direction.

The first check valve (CV1) and the second check valve (CV2) are provided in the flow path switching mechanism (30).

The third check valve (CV3) is provided in the third discharge pipe (23b). The fourth check valve (CV4) is provided in the first pipe (40a). The fifth check valve (CV5) is provided in the third pipe (40c). The sixth check valve (CV6) is provided in the fourth pipe (40d). The seventh check valve (CV7) is provided in the fifth pipe (40e). The eighth check valve (CV8) is provided in the first bypass pipe (56). The ninth check valve (CV9) is provided in the second bypass pipe (57). The tenth check valve (CV10) is provided in the third bypass pipe (58). The eleventh check valve (CV11) is provided in the first discharge pipe (21b). The twelfth check valve (CV12) is provided in the second discharge pipe (22b).

(3) Air Conditioning Unit Fig. 2 is a piping diagram in the vicinity of an air conditioning unit (60). The air conditioning unit (60) is a utilization unit installed indoors. The air conditioning unit (60) has an indoor circuit (61) and an indoor fan (62). A first liquid connection pipe (2) is connected to a liquid side end of the indoor circuit (61). A first gas connection pipe (3) is connected to a gas side end of the indoor circuit (61).

As shown in FIG. 2, the indoor circuit (61) has, in order from the liquid side end to the gas side end, an indoor expansion valve (63) and an indoor heat exchanger (64). The indoor expansion valve (63) is an example of an expansion valve. The indoor expansion valve (63) is an expansion valve whose opening is adjustable. The indoor expansion valve (63) is an electronic expansion valve whose opening is adjusted based on a pulse signal.

The indoor heat exchanger (64) is a fin-and-tube type air heat exchanger. The indoor heat exchanger (64) is an example of a radiator. The indoor fan (62) is disposed near the indoor heat exchanger (64). The indoor fan (62) transports indoor air. The indoor heat exchanger (64) exchanges heat between the refrigerant flowing therethrough and the indoor air transported by the indoor fan (62).

The air conditioning unit (60) includes a first air conditioning unit (60A) and a second air conditioning unit (60B) connected in parallel to each other. The indoor circuit (61) includes a first indoor circuit (61A) and a second indoor circuit (61B) connected in parallel to each other. The first indoor circuit (61A) corresponds to the first air conditioning unit (60A). The second indoor circuit (61B) corresponds to the second air conditioning unit (60B).

The indoor heat exchanger (64) includes a first indoor heat exchanger (64A) and a second indoor heat exchanger (64B) connected in parallel to each other. The first indoor heat exchanger (64A) is an example of a first radiator. The second indoor heat exchanger (64B) is an example of a second radiator.

The indoor expansion valve (63) includes a first indoor expansion valve (63A) corresponding to the first indoor heat exchanger (64A) and a second indoor expansion valve (63B) corresponding to the second indoor heat exchanger (64B). The first indoor expansion valve (63A) is an example of a first expansion valve. The second indoor expansion valve (63B) is an example of a second expansion valve. The indoor fan (62) includes a first indoor fan (62A) corresponding to the first indoor heat exchanger (64A) and a second indoor fan (62B) corresponding to the second indoor heat exchanger (64B).

(4) Chilling Unit The chilling unit (70) is a utilization unit that cools the interior of the refrigerator. The chilling unit (70) has a chilling circuit (71) and a chilling fan (72). The second liquid connection pipe (4) is connected to the liquid side end of the chilling circuit (71). The second gas connection pipe (5) is connected to the gas side end of the chilling circuit (71).

The cold-setting circuit (71) has, in order from the liquid side end to the gas side end, a cold-setting expansion valve (73) and a cold-setting heat exchanger (74). The cold-setting expansion valve (73) is an expansion valve whose opening is adjustable. The cold-setting expansion valve (73) is an electronic expansion valve whose opening is adjusted based on a pulse signal.

The cold-air heat exchanger (74) is a fin-and-tube type air heat exchanger. The cold-air fan (72) is disposed near the cold-air heat exchanger (74). The cold-air fan (72) transports the air inside the storage compartment. The cold-air heat exchanger (74) exchanges heat between the refrigerant flowing therethrough and the air inside the storage compartment transported by the cold-air fan (72).

(5) Flow path switching mechanism The flow path switching mechanism (30) is provided in the heat source circuit (11). The flow path switching mechanism (30) switches the flow path of the refrigerant circuit (6) so as to switch at least between a first refrigeration cycle and a second refrigeration cycle. The first refrigeration cycle is a refrigeration cycle in which the outdoor heat exchanger (24) functions as a radiator, and the indoor heat exchanger (64) and the cold-setting heat exchanger (74) function as evaporators. The second refrigeration cycle is a refrigeration cycle in which the outdoor heat exchanger (24) functions as an evaporator, and the indoor heat exchanger (64) and the cold-setting heat exchanger (74) function as radiators.

The flow path switching mechanism (30) has a first port (P1), a second port (P2), a third port (P3), a fourth port (P4), a first switching flow path (31), a second switching flow path (32), a third switching flow path (33), and a fourth switching flow path (34). An opening and closing mechanism (not shown) is provided in each of the switching flow paths (31-34). Each opening and closing mechanism includes an opening and closing valve and an expansion valve.

The first port (P1) is connected to the discharge portion of the third compressor (23). The second port (P2) is connected to the suction portion of the second compressor (22). The third port (P3) is connected to the gas end of the indoor heat exchanger (64). The fourth port (P4) is connected to the gas end of the outdoor heat exchanger (24).

The first switching flow path (31), the second switching flow path (32), the third switching flow path (33), and the fourth switching flow path (34) are connected in a bridge shape. The first switching flow path (31) connects the first port (P1) to the third port (P3). The second switching flow path (32) connects the first port (P1) to the fourth port (P4). The third switching flow path (33) connects the second port (P2) to the third port (P3). The fourth switching flow path (34) connects the second port (P2) to the fourth port (P4).

The fourth switching flow path (34) is provided with a first check valve (CV1). The first switching flow path (31) is provided with a second check valve (CV2). The first check valve (CV1) allows the flow of refrigerant from the fourth port (P4) to the second port (P2) in the fourth switching flow path (34) and prohibits the flow of refrigerant from the second port (P2) to the fourth port (P4). The second check valve (CV2) allows the flow of refrigerant from the first port (P1) to the third port (P3) in the first switching flow path (31) and prohibits the flow of refrigerant from the third port (P3) to the first port (P1).

(6) Sensors The air conditioner (1) has a plurality of sensors, including a refrigerant pressure sensor that detects the pressure of the refrigerant, a refrigerant temperature sensor that detects the temperature of the refrigerant, and an air temperature sensor that detects the temperature of the air.

The refrigerant pressure sensors include a high-pressure pressure sensor (101), an intermediate pressure sensor (102), a first suction pressure sensor (103), a second suction pressure sensor (104), and a liquid-side pressure sensor (105). The high-pressure pressure sensor (101) is provided in the third discharge pipe (23b). The high-pressure pressure sensor (101) detects the pressure of the refrigerant on the discharge side of the compression element (20), in other words, the high-pressure pressure of the refrigerant circuit (6).

The intermediate pressure sensor (102) is provided in the third suction pipe (23a). The intermediate pressure sensor (102) detects the pressure of the refrigerant between the low-stage compressor and the high-stage compressor, in other words, the intermediate pressure of the refrigerant circuit (6). The first suction pressure sensor (103) is provided in the first suction pipe (21a). The first suction pressure sensor (103) detects the pressure of the refrigerant on the suction side of the first compressor (21). The second suction pressure sensor (104) is provided in the second suction pipe (22a). The second suction pressure sensor (104) detects the pressure of the refrigerant on the suction side of the second compressor (22).

The liquid side pressure sensor (105) is provided in the liquid side flow path (40). Specifically, the liquid side pressure sensor (105) is provided in the second pipe (40b). The liquid side pressure sensor (105) detects a pressure equivalent to the internal pressure of the gas-liquid separator (25). The liquid side pressure sensor (105) detects a pressure equivalent to the pressure of the refrigerant in the first flow path (28a).

The refrigerant temperature sensors include a first discharge temperature sensor (111), a first intake temperature sensor (112), a second discharge temperature sensor (113), a second intake temperature sensor (114), a third discharge temperature sensor (115), a third intake temperature sensor (116), a liquid side temperature sensor (117), an injection side temperature sensor (118), an outdoor heat exchanger temperature sensor (119), and an indoor heat exchanger temperature sensor (120).

The first discharge temperature sensor (111) is provided in the first discharge pipe (21b) and detects the temperature of the refrigerant discharged from the first compressor (21). The first intake temperature sensor (112) is provided in the first intake pipe (21a) and detects the temperature of the refrigerant sucked into the first compressor (21). The second discharge temperature sensor (113) is provided in the second discharge pipe (22b) and detects the temperature of the refrigerant discharged from the second compressor (22). The second intake temperature sensor (114) is provided in the second intake pipe (22a) and detects the temperature of the refrigerant sucked into the second compressor (22). The third discharge temperature sensor (115) is provided in the third discharge pipe (23b) and detects the temperature of the refrigerant discharged from the third compressor (23). The third intake temperature sensor (116) is provided in the third intake pipe (23a) and detects the temperature of the refrigerant sucked into the third compressor (23).

The liquid-side temperature sensor (117) is provided in the liquid-side flow path (40). Specifically, the liquid-side temperature sensor (117) is provided on the outflow side of the first flow path (28a) of the subcooling heat exchanger (28) in the liquid-side flow path (40). The liquid-side temperature sensor (117) detects the temperature of the refrigerant that has flowed out of the first flow path (28a).

The injection side temperature sensor (118) is provided in the downstream flow path (45) of the injection flow path (43). In other words, the injection side temperature sensor (118) is provided on the outflow side of the second flow path (28b) of the subcooling heat exchanger (28). The injection side temperature sensor (118) detects the temperature of the refrigerant that has flowed out of the second flow path (28b).

The outdoor heat exchanger temperature sensor (119) is provided on a heat transfer tube of the outdoor heat exchanger (24). The outdoor heat exchanger temperature sensor (119) is provided on the liquid side end of the outdoor heat exchanger (24). The outdoor heat exchanger temperature sensor (119) detects the temperature of the refrigerant at the liquid side end of the outdoor heat exchanger (24).

The indoor heat exchanger temperature sensor (120) is provided on the heat transfer tube of the indoor heat exchanger (64). The indoor heat exchanger temperature sensor (120) is provided on the liquid side end of the indoor heat exchanger (64). The indoor heat exchanger temperature sensor (120) detects the temperature of the refrigerant at the liquid side end of the indoor heat exchanger (64). The indoor heat exchanger temperature sensor (120) includes a first indoor heat exchanger temperature sensor (120A) and a second indoor heat exchanger temperature sensor (120B).

The first indoor heat exchanger temperature sensor (120A) corresponds to the first indoor heat exchanger (64A). The first indoor heat exchanger temperature sensor (120A) is provided on a heat transfer tube of the first indoor heat exchanger (64A). The first indoor heat exchanger temperature sensor (120A) is provided on the liquid side end of the first indoor heat exchanger (64A). The first indoor heat exchanger temperature sensor (120A) detects the temperature of the refrigerant at the liquid side end of the first indoor heat exchanger (64A).

The second indoor heat exchanger temperature sensor (120B) corresponds to the second indoor heat exchanger (64B). The second indoor heat exchanger temperature sensor (120B) is provided on a heat transfer tube of the second indoor heat exchanger (64B). The second indoor heat exchanger temperature sensor (120B) is provided on the liquid side end of the second indoor heat exchanger (64B). The second indoor heat exchanger temperature sensor (120B) detects the temperature of the refrigerant at the liquid side end of the second indoor heat exchanger (64B).

The air temperature sensor includes an outdoor air temperature sensor (121) and an indoor air temperature sensor (122). The outdoor air temperature sensor (121) detects the temperature of the outdoor air.

The indoor temperature sensor (122) detects the indoor temperature in the room in which the air conditioning unit (60) (indoor heat exchanger (64)) is installed. The indoor temperature sensor (122) includes a first indoor temperature sensor (122A) and a second indoor temperature sensor (122B).

The first indoor temperature sensor (122A) detects the indoor temperature in the room where the first air conditioning unit (60A) (first indoor heat exchanger (64A)) is installed. The second indoor temperature sensor (122B) detects the indoor temperature in the room where the second air conditioning unit (60B) (second indoor heat exchanger (64B)) is installed.

(7) Controller Fig. 3 is a block diagram showing the connection relationship between the controller (130) as a control device and peripheral devices. The air conditioner (1) includes a controller (130). The controller (130) is an example of a control device. The controller (130) controls the refrigerant circuit (6). The controller (130) includes a microcomputer mounted on a control board and a memory device (specifically, a semiconductor memory) that stores software for operating the microcomputer.

As shown in FIG. 3, the controller (130) has an outdoor controller (131), an indoor controller (132), and a cold-conditioning controller (133). As shown in FIG. 1, the outdoor controller (131) is provided in the heat source unit (10). The indoor controller (132) is provided in the air conditioning unit (60). The cold-conditioning controller (133) is provided in the cold-conditioning unit (70). The outdoor controller (131) can communicate with the indoor controller (132) and the cold-conditioning controller (133).

The indoor controller (132) includes a first indoor controller (132A) and a second indoor controller (132B) connected in parallel to each other. The first indoor controller (132A) corresponds to the first air conditioning unit (60A). The second indoor controller (132B) corresponds to the second air conditioning unit (60B).

The controller (130) receives control commands from the user and detection signals from each sensor. The controller (130) controls each device of the air conditioner (1). Specifically, the controller (130) controls the ON/OFF of the first compressor (21), the second compressor (22), and the third compressor (23). The controller (130) adjusts the capacity (strictly speaking, the motor rotation speed) of the first compressor (21), the second compressor (22), and the third compressor (23). The controller (130) controls the ON/OFF of each fan. The controller (130) adjusts the opening degree of each expansion valve. The controller (130) switches each valve between open and closed.

(8) Heating Operation (8-1) Operation of the Air Conditioning Apparatus During Heating Operation of the air conditioning apparatus (1) will be described. The operation of the air conditioning apparatus (1) includes cooling operation, cooling operation, cooling and cooling operation, heating operation, heating and cooling operation, and defrost operation. In this example, only the heating operation will be described. In heating operation, the cooling unit (70) stops, and the air conditioning unit (60) heats the room. The flow of refrigerant during heating operation is shown by the thick line in FIG. 1.

As shown in FIG. 1, in the heating operation, the controller (130) controls the on-off valves provided in the switching paths (31-34) to close the second switching path (32) and the third switching path (33) and open the first switching path (31) and the fourth switching path (34).

The controller (130) stops the first compressor (21) and operates the second compressor (22) and the third compressor (23). The controller (130) opens the second outdoor expansion valve (27) and the injection valve (46) to a predetermined opening degree and closes the first outdoor expansion valve (26). The controller (130) closes the cold-unit expansion valve (73) and opens the indoor expansion valve (63). The controller (130) operates the outdoor fan (12) and the indoor fan (62) and stops the cold-unit fan (72).

During heating operation, a refrigeration cycle is performed in which the indoor heat exchanger (64) functions as a radiator, the outdoor heat exchanger (24) functions as an evaporator, and the function of the cooling heat exchanger (74) is essentially stopped.

Specifically, the refrigerant compressed by the second compressor (22) is cooled in the intercooler (29) and then sucked into the third compressor (23). The refrigerant compressed by the third compressor (23) is sent to the air conditioning unit (60).

The refrigerant sent to the air conditioning unit (60) dissipates heat in the indoor heat exchanger (64). As a result, the air in the room is heated. The refrigerant that has dissipated heat in the indoor heat exchanger (64) flows into the gas-liquid separator (25). In the gas-liquid separator (25), the refrigerant is separated into gas refrigerant and liquid refrigerant.

The liquid refrigerant separated in the gas-liquid separator (25) is cooled in the subcooling heat exchanger (28) by the refrigerant flowing through the injection flow path (43). The refrigerant in the injection flow path (43) is sent to the intermediate flow path (18).

The refrigerant cooled by the subcooling heat exchanger (28) is decompressed by the second outdoor expansion valve (27) and then evaporates in the outdoor heat exchanger (24). The refrigerant evaporated in the outdoor heat exchanger (24) is sucked into the second compressor (22) and compressed again.

(8-2) Components of the air conditioner during heating In heating operation, the refrigerant circuit (6) has a second compressor (22) as a compressor, a third compressor (23) as a compressor, an indoor heat exchanger (64) as a radiator, an indoor expansion valve (63) as an expansion valve, and an outdoor heat exchanger (24) as an evaporator.

The air conditioning unit (60) includes a first air conditioning unit (60A) and a second air conditioning unit (60B) connected in parallel to each other.

The indoor heat exchanger (64) as a radiator includes a first indoor heat exchanger (64A) as a first radiator and a second indoor heat exchanger (64B) as a second radiator. The first indoor heat exchanger (64A) and the second indoor heat exchanger (64B) are connected in parallel to each other.

The indoor expansion valve (63) as an expansion valve includes a first indoor expansion valve (63A) as a first expansion valve corresponding to the first indoor heat exchanger (64A) and a second indoor expansion valve (63B) as a second expansion valve corresponding to the second indoor heat exchanger (64B).

The indoor fans (62) include a first indoor fan (62A) corresponding to the first indoor heat exchanger (64A) and a second indoor fan (62B) corresponding to the second indoor heat exchanger (64B).

The refrigerant circuit (6) has a gas-liquid separator (25), a gas vent pipe (41) as a gas vent passage, and a gas vent valve (42) as an on-off valve.

In heating operation, the gas-liquid separator (25) is connected downstream of the indoor heat exchanger (64). The gas-liquid separator (25) separates the refrigerant into gas refrigerant and liquid refrigerant. A gas storage section (25a) and a liquid storage section (25b) are formed inside the gas-liquid separator (25). The gas storage section (25a) is disposed at the top of the gas-liquid separator (25) and stores gas refrigerant. The liquid storage section (25b) is disposed at the bottom of the gas-liquid separator (25) and stores liquid refrigerant.

One end of the gas vent pipe (41) is connected to the gas storage section (25a) of the gas-liquid separator (25). The other end of the gas vent pipe (41) is connected to the intermediate flow path (18). The intermediate flow path (18) is connected to the third suction pipe (23a) on the suction side (23i) of the third compressor (23).

The gas vent pipe (41) connects the gas storage section (25a) of the gas-liquid separator (25) to the third suction pipe (23a) on the suction side (23i) of the third compressor (23) via the intermediate flow path (18).

The high-pressure sensor (101) detects the high-pressure pressure (Ph) as the high pressure in the refrigerant circuit (6). The high-pressure pressure (Ph) is an example of the high pressure in this embodiment. The high-pressure pressure (Ph) in the refrigerant circuit (6) is also the pressure of the refrigerant on the discharge side of the third compressor (23).

The indoor heat exchanger temperature sensor (120) detects the temperature of the refrigerant at the liquid side end of the indoor heat exchanger (64). During heating operation, the indoor heat exchanger temperature sensor (120) detects the outlet refrigerant temperature (TE) as the refrigerant temperature at the outlet (E) of the indoor heat exchanger (64). The indoor heat exchanger temperature sensor (120) includes a first indoor heat exchanger temperature sensor (120A) and a second indoor heat exchanger temperature sensor (120B).

The first indoor heat exchanger temperature sensor (120A) detects the temperature of the refrigerant at the liquid side end of the first indoor heat exchanger (64A). The first indoor heat exchanger temperature sensor (120A) detects the first outlet refrigerant temperature (TEA) as the refrigerant temperature at the first outlet (EA) of the first indoor heat exchanger (64A) during heating operation. The first outlet refrigerant temperature (TEA) corresponds to the first indoor heat exchanger (64A). The second indoor heat exchanger temperature sensor (120B) detects the temperature of the refrigerant at the liquid side end of the second indoor heat exchanger (64B). The second indoor heat exchanger temperature sensor (120B) detects the second outlet refrigerant temperature (TEB) as the refrigerant temperature at the second outlet (EB) of the second indoor heat exchanger (64B) during heating operation. The second outlet refrigerant temperature (TEB) corresponds to the second indoor heat exchanger (64B).

The indoor temperature sensor (122) detects the indoor temperature (TR) in the room where the air conditioning unit (60) (indoor heat exchanger (64)) is installed. The indoor temperature sensor (122) includes a first indoor temperature sensor (122A) and a second indoor temperature sensor (122B).

The first indoor temperature sensor (122A) detects a first indoor temperature (TRA) in the room where the first air conditioning unit (60A) (first indoor heat exchanger (64A)) is installed. The first indoor temperature (TRA) corresponds to the first indoor heat exchanger (64A). The second indoor temperature sensor (122B) detects a second indoor temperature (TRB) in the room where the second air conditioning unit (60B) (second indoor heat exchanger (64B)) is installed. The second indoor temperature (TRB) corresponds to the second indoor heat exchanger (64B).

(8-3) Function of the Air Conditioner Controller During Heating The outdoor controller (131) of the controller (130) sets a target high pressure (Ph0) that is a target value of the high pressure (Ph) of the refrigerant circuit (6). The outdoor controller (131) of the controller (130) calculates a high pressure difference (ΔPh) that is the pressure difference between the high pressure (Ph) detected by the high pressure sensor (101) and the target high pressure (Ph0).

The indoor controller (132) of the controller (130) sets a target outlet refrigerant temperature (TE0), which is a target value for the outlet refrigerant temperature (TE). The indoor controller (132) of the controller (130) calculates an outlet refrigerant temperature difference (ΔTE), which is the temperature difference between the outlet refrigerant temperature (TE) detected by the indoor heat exchanger temperature sensor (120) and the target outlet refrigerant temperature (TE0).

The first indoor controller (132A) of the controller (130) sets a first target outlet refrigerant temperature (TE0A) that is a target value of the first outlet refrigerant temperature (TEA). The first target outlet refrigerant temperature (TE0A) corresponds to the first indoor heat exchanger (64A). The first indoor controller (132A) of the controller (130) calculates a first outlet refrigerant temperature difference (ΔTEA) that is the temperature difference between the first outlet refrigerant temperature (TEA) detected by the first indoor heat exchanger temperature sensor (120A) and the first target outlet refrigerant temperature (TE0A). The first outlet refrigerant temperature difference (ΔTEA) corresponds to the first indoor heat exchanger (64A).

The second indoor controller (132B) of the controller (130) sets a second target outlet refrigerant temperature (TE0B) which is a target value of the second outlet refrigerant temperature (TEB). The second target outlet refrigerant temperature (TE0B) corresponds to the second indoor heat exchanger (64B). The second indoor controller (132B) of the controller (130) calculates a second outlet refrigerant temperature difference (ΔTEB) which is the temperature difference between the second outlet refrigerant temperature (TEB) detected by the second indoor heat exchanger temperature sensor (120B) and the second target outlet refrigerant temperature (TE0B). The second outlet refrigerant temperature difference (ΔTEB) corresponds to the second indoor heat exchanger (64B).

The indoor controller (132) of the controller (130) sets a target indoor temperature (TR0) that is a target value for the indoor temperature (TR). The indoor controller (132) of the controller (130) calculates an indoor temperature difference (ΔTR) that is the temperature difference between the indoor temperature (TR) detected by the indoor temperature sensor (122) and the target indoor temperature (TR0).

The first indoor controller (132A) of the controller (130) sets a first target indoor temperature (TR0A) that is a target value for the first indoor temperature (TRA). The first target indoor temperature (TR0A) corresponds to the first indoor heat exchanger (64A). The first indoor controller (132A) of the controller (130) calculates a first indoor temperature difference (ΔTRA) as a first temperature difference that is the temperature difference between the first indoor temperature (TRA) detected by the first indoor temperature sensor (122A) and the first target indoor temperature (TR0A). The first indoor temperature difference (ΔTRA) corresponds to the first indoor heat exchanger (64A).

The second indoor controller (132B) of the controller (130) sets a second target indoor temperature (TR0B) that is a target value for the second indoor temperature (TRB). The second target indoor temperature (TR0B) corresponds to the second indoor heat exchanger (64B). The second indoor controller (132B) of the controller (130) calculates a second indoor temperature difference (ΔTRB) as a second temperature difference that is the temperature difference between the second indoor temperature (TRB) detected by the second indoor temperature sensor (122B) and the second target indoor temperature (TR0B). The second indoor temperature difference (ΔTRB) corresponds to the second indoor heat exchanger (64B).

(9) Supercritical Operation FIG. 4 is a graph showing the relationship between the specific enthalpy (h) and pressure (P) of a refrigerant. FIG. 4 is also called a P-h diagram. The refrigerant circulating through the refrigerant circuit (6) is carbon dioxide. The critical pressure (Pc) at the critical point (C) of carbon dioxide as a refrigerant is lower than that of other natural refrigerants, specifically, the absolute pressure is 7.38 [MPa]. The critical temperature at the critical point (C) of carbon dioxide as a refrigerant is 31.1 [°C]. The critical specific enthalpy (hc) at the critical point (C) of carbon dioxide as a refrigerant is about 330 [kJ/kg]. The critical pressure (Pc), critical temperature, and critical specific enthalpy (hc) correspond to each other.

The refrigerant circuit (6) performs a refrigeration cycle to perform heating operation to heat the room by compressing the refrigerant to or above the critical pressure (Pc). The refrigerant circuit (6) performs supercritical operation. The high pressure (Ph) of the refrigerant circuit (6) becomes equal to or higher than the critical pressure (Pc).

When the refrigerant is compressed above its critical pressure (Pc), in other words when the high pressure (Ph) of the refrigerant circuit (6) becomes equal to or higher than the critical pressure (Pc), it becomes difficult to control the temperature of the refrigerant because there is no condensation temperature of the refrigerant in the region above the critical pressure (Pc).

For this reason, in supercritical operation where the refrigerant is compressed above the critical pressure (Pc), it becomes difficult to adjust the indoor temperature (TR), and it becomes difficult to adjust the indoor temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0).

The smaller the specific enthalpy (h) of a refrigerant, the greater the liquid proportion of the refrigerant and the smaller the gas proportion of the refrigerant. The greater the specific enthalpy (h) of a refrigerant, the smaller the liquid proportion of the refrigerant and the larger the gas proportion of the refrigerant.

As shown in FIG. 4, the outlet specific enthalpy (he) of the refrigerant at the outlet (E) of the indoor heat exchanger (64) is smaller than the critical specific enthalpy (hc) at the critical point (C) of the refrigerant. The refrigerant at the outlet (E) of the indoor heat exchanger (64) has a larger liquid ratio and a smaller gas ratio than the refrigerant at the critical point (C).

5 is a control flowchart of the air conditioner (1) during heating operation. In the following explanation, the functions of the outdoor controller (131) and the indoor controller (132) are simply explained as the function of the controller (130).

Starting from the start, in the first step (S1), the heating operation is started by a heating operation start command from the user to the controller (130). In the heating operation, the controller (130) stops the first compressor (21) and operates the second compressor (22) and the third compressor (23).

In heating operation, the controller (130) opens the second outdoor expansion valve (27) and the injection valve (46) to a predetermined opening degree and closes the first outdoor expansion valve (26). In heating operation, the controller (130) closes the cooling expansion valve (73). In heating operation, the controller (130) opens the indoor expansion valve (63). In heating operation, the controller (130) operates the outdoor fan (12) and the indoor fan (62) and stops the cooling fan (72). In heating operation, the controller (130) causes the indoor heat exchanger (64) to function as a radiator and the outdoor heat exchanger (24) to function as an evaporator.

The gas vent pipe (41) connects the gas storage section (25a) of the gas-liquid separator (25) to the third suction pipe (23a) on the suction side (23i) of the third compressor (23) via the intermediate flow path (18). The gas vent valve (42) of the gas vent pipe (41) is initially closed.

In the second step (S2), the controller (130) sets the target high pressure (Ph0) of the refrigerant circuit (6) to be equal to or higher than the critical pressure (Pc). In this example, the controller (130) first sets the target high pressure (Ph0) to an initial value of 9 MPa. In this example, the control range of the target high pressure (Ph0) is 8 MPa to 11 MPa.

The controller (130) calculates the high-pressure difference (ΔPh) between the high-pressure pressure (Ph) detected by the high-pressure sensor (101) and the target high-pressure (Ph0). If there is a difference between the high-pressure pressure (Ph) and the target high-pressure (Ph0), the controller (130) adjusts the rotation speed of the second compressor (22) and the rotation speed of the third compressor (23) to bring the high-pressure pressure (Ph) closer to the target high-pressure (Ph0) (brings the high-pressure pressure difference (ΔPh) closer to zero). For example, if the high-pressure pressure (Ph) is lower than the target high-pressure (Ph0), the rotation speed of the second compressor (22) and the rotation speed of the third compressor (23) are increased. If the high-pressure pressure (Ph) is higher than the target high-pressure (Ph0), the rotation speed of the second compressor (22) and the rotation speed of the third compressor (23) are decreased.

In the following description, the high pressure (Ph) and the target high pressure (Ph0) are assumed to be equal to each other. In other words, the controller (130) sets the high pressure (Ph) of the refrigerant circuit (6) to be equal to or higher than the critical pressure (Pc).

In the third step (S3), the controller (130) controls the indoor expansion valve (63) to adjust the outlet refrigerant temperature (TE) at the outlet (E) of the indoor heat exchanger (64). Specifically, the controller (130) sets a target outlet refrigerant temperature (TE0). In this example, the controller (130) sets the target outlet refrigerant temperature (TE0) to 37°, which is close to human body temperature. The controller (130) calculates the outlet refrigerant temperature difference (ΔTE) between the outlet refrigerant temperature (TE) detected by the indoor heat exchanger temperature sensor (120) and the target outlet refrigerant temperature (TE0). The controller (130) controls the indoor expansion valve (63) to bring the outlet refrigerant temperature (TE) closer to the target outlet refrigerant temperature (TE0) (bring the outlet refrigerant temperature difference (ΔTE) closer to zero).

The opening of the indoor expansion valve (63) can be adjusted, for example, between 10% and 100%. Reducing the opening of the indoor expansion valve (63) reduces the outlet refrigerant temperature (TE). Increasing the opening of the indoor expansion valve (63) increases the outlet refrigerant temperature (TE). By controlling the opening of the indoor expansion valve (63) to adjust the outlet refrigerant temperature (TE), the indoor temperature (TR), described below, can be adjusted to a certain extent.

The above-mentioned control is performed for each of the first indoor heat exchanger (64A) and the second indoor heat exchanger (64B). The controller (130) controls the first indoor expansion valve (63A) so as to bring the first outlet refrigerant temperature (TEA) closer to the first target outlet refrigerant temperature (TE0A) (bring the first outlet refrigerant temperature difference (ΔTEA) closer to zero). The controller (130) controls the second indoor expansion valve (63B) so as to bring the second outlet refrigerant temperature (TEB) closer to the second target outlet refrigerant temperature (TE0B) (bring the second outlet refrigerant temperature difference (ΔTEB) closer to zero).

In a fourth step (S4), the controller (130) sets the target indoor temperature (TR0) in response to a command from the user. As an example, the target indoor temperature (TR0) is 28°C.

In a fifth step (S5), the controller (130) calculates an indoor temperature difference (ΔTR) between the indoor temperature (TR) detected by the indoor temperature sensor (122) and the target indoor temperature (TR0). The controller (130) calculates a first indoor temperature difference (ΔTRA) between the first indoor temperature (TRA) detected by the first indoor temperature sensor (122A) and the first target indoor temperature (TR0A). The controller (130) calculates a second indoor temperature difference (ΔTRB) between the second indoor temperature (TRB) detected by the second indoor temperature sensor (122B) and the second target indoor temperature (TR0B).

In the sixth step (S6) to the twelfth step (S12), the controller (130) controls the high pressure (Ph) (target high pressure (Ph0)) of the refrigerant circuit (6) based on the indoor temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0).

Specifically, the controller (130) controls the high pressure (Ph) (target high pressure (Ph0)) of the refrigerant circuit (6) based on either or both of a first indoor temperature difference (ΔTRA) between a first indoor temperature (TRA) and a first target indoor temperature (TR0A) and a second indoor temperature difference (ΔTRB) between a second indoor temperature (TRB) and a second target indoor temperature (TR0B).

More specifically, the controller (130) controls the high pressure (Ph) (target high pressure (Ph0)) of the refrigerant circuit (6) based on the larger of the first indoor temperature difference (ΔTRA) and the second indoor temperature difference (ΔTRB).

In the sixth step (S6), it is determined whether the indoor temperature difference (ΔTR) is smaller than the lower threshold (ΔTX) as a third value (ΔTR < ΔTX?). The lower threshold (ΔTX) is an example of the third value. In this example, the lower threshold (ΔTX) is 1°C. If it is determined that the indoor temperature difference (ΔTR) is smaller than the lower threshold (ΔTX) (ΔTR < ΔTX), proceed to the seventh step (S7). If it is determined that the indoor temperature difference (ΔTR) is larger than the lower threshold (ΔTX) (ΔTR > ΔTX), proceed to the eighth step (S8). If the indoor temperature difference (ΔTR) is equal to the lower threshold (ΔTX) (ΔTR = ΔTX), proceed to the eighth step (S8).

In the seventh step (S7), the controller (130) controls the second compressor (22) and the third compressor (23) so that the high pressure (Ph) (target high pressure (Ph0)) of the refrigerant circuit (6) is set to the lower limit (Ph1) of the control range. Specifically, the controller (130) lowers the high pressure (Ph) (target high pressure (Ph0)) of the refrigerant circuit (6) to maintain it at 8 MPa, which is the lower limit (Ph1) of the control range. In particular, the controller (130) maintains the rotation speed of the second compressor (22) and the rotation speed of the third compressor (23) at their lower limits.

In summary, in the sixth step (S6) and the seventh step (S7), when the indoor temperature difference (ΔTR) becomes smaller than the lower threshold value (ΔTX) (ΔTR<ΔTx), the controller (130) controls the second compressor (22) and the third compressor (23) so that the high pressure (Ph) (target high pressure (Ph0)) of the refrigerant circuit (6) is set to the lower limit (Ph1) (8 [MPa]) of the control range. After the seventh step (S7) is completed, the process proceeds to the thirteenth step (S13).

In the eighth step (S8), it is determined whether the indoor temperature difference (ΔTR) is smaller than the intermediate threshold (ΔTY) as the first and second values (ΔTR < ΔTY?). The intermediate threshold (ΔTY) is an example of the first and second values. In this example, the intermediate threshold (ΔTY) is 5°C. If it is determined that the indoor temperature difference (ΔTR) is smaller than the intermediate threshold (ΔTY) (ΔTR < ΔTY), proceed to the ninth step (S9). If it is determined that the indoor temperature difference (ΔTR) is larger than the intermediate threshold (ΔTY) (ΔTR > ΔTY), proceed to the tenth step (S10). If the indoor temperature difference (ΔTR) is equal to the intermediate threshold (ΔTY) (ΔTR = ΔTY), proceed to the tenth step (S10).

In the ninth step (S9), the controller (130) controls the second compressor (22) and the third compressor (23) to lower the high pressure (Ph) (target high pressure (Ph0)) of the refrigerant circuit (6). In detail, the controller (130) reduces the rotation speed of the second compressor (22) and the rotation speed of the third compressor (23). As an example, the controller (130) reduces the high pressure (Ph) (target high pressure (Ph0)) of the refrigerant circuit (6) by 0.1 [MPa].

In the tenth step (S10), the controller (130) controls the second compressor (22) and the third compressor (23) to increase the high pressure (Ph) (target high pressure (Ph0)) of the refrigerant circuit (6). In detail, the controller (130) increases the rotation speed of the second compressor (22) and the rotation speed of the third compressor (23). As an example, the controller (130) increases the high pressure (Ph) (target high pressure (Ph0)) of the refrigerant circuit (6) by 0.3 MPa.

In summary, in the eighth step (S8) and the ninth step (S9), when the indoor temperature difference (ΔTR) becomes smaller than the intermediate threshold value (ΔTY) (ΔTR<ΔTY), the controller (130) controls the second compressor (22) and the third compressor (23) to lower the high pressure (Ph) (target high pressure (Ph0)) of the refrigerant circuit (6). After the ninth step (S9) is completed, the process proceeds to the thirteenth step (S13).

In summary, in the eighth step (S8) and the tenth step (S10), when the indoor temperature difference (ΔTR) becomes greater than the intermediate threshold value (ΔTY) (ΔTR>ΔTY), the controller (130) controls the second compressor (22) and the third compressor (23) to increase the high pressure (Ph) (target high pressure (Ph0)) of the refrigerant circuit (6). After the tenth step (S10) is completed, the process proceeds to the eleventh step (S11).

In the eleventh step (S11), it is determined whether the indoor temperature difference (ΔTR) is smaller than the upper threshold (ΔTZ) as the fourth value (ΔTR < ΔTZ?). The upper threshold (ΔTZ) is an example of the fourth value. In this example, the upper threshold (ΔTZ) is 8°C. If it is determined that the indoor temperature difference (ΔTR) is smaller than the upper threshold (ΔTZ) (ΔTR < ΔTZ), proceed to the thirteenth step (S13). If it is determined that the indoor temperature difference (ΔTR) is larger than the upper threshold (ΔTZ) (ΔTR > ΔTZ), proceed to the twelfth step (S12). If the indoor temperature difference (ΔTR) is equal to the upper threshold (ΔTZ) (ΔTR = ΔTZ), proceed to the twelfth step (S12).

In a twelfth step (S12), the controller (130) opens the gas vent valve (42) of the gas vent pipe (41) (see the thick dashed line in FIG. 1). As an example, the controller (130) increases the opening of the gas vent valve (42) of the gas vent pipe (41) by 10%. Note that "opening the gas vent valve (42)" includes not only newly opening the gas vent valve (42) that is currently open, but also further increasing the opening of the gas vent valve (42) that is already open.

In summary, in the eleventh step (S11) and the twelfth step (S12), when the indoor temperature difference (ΔTR) becomes greater than the upper threshold value (ΔTZ) (ΔTR>ΔTZ), the controller (130) opens the gas vent valve (42) of the gas vent pipe (41). After the twelfth step (S12) is completed, the process proceeds to the thirteenth step (S13).

In a thirteenth step (S13), it is determined whether or not there is a command from the user to the controller (130) to stop the heating operation. If there is a command from the user to the controller (130) to stop the heating operation, the controller (130) stops the heating operation and the process reaches the end. If there is no command from the user to the controller (130) to stop the heating operation, the process returns to the fifth step (S5).

(11) Effects In the air conditioner (1) according to this embodiment, the refrigerant is compressed to or above the critical pressure (Pc) (the high pressure (Ph) of the refrigerant circuit (6) becomes equal to or above the critical pressure (Pc)). Since the condensation temperature of the refrigerant does not exist in the region equal to or above the critical pressure (Pc), it becomes difficult to control the refrigerant temperature and therefore difficult to adjust the indoor temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0).

By controlling the indoor expansion valve (63) to adjust the outlet refrigerant temperature (TE) at the outlet (E) of the indoor heat exchanger (64), the indoor temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0) can be adjusted to a certain extent.

However, there are cases where the indoor temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0) cannot be sufficiently adjusted by only controlling the indoor expansion valve (63). In such cases, the indoor temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0) can be further adjusted by controlling the high-pressure pressure (Ph) of the refrigerant circuit (6) based on the indoor temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0).

As described above, in the air conditioning device (1), during heating operation in which the refrigerant is compressed to above the critical pressure (Pc) to heat the room, the indoor temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0) can be adjusted.

When the indoor temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0) is greater than the intermediate threshold value (ΔTY) as a first value, the indoor temperature (TR) can be increased by increasing the high pressure (Ph) of the refrigerant circuit (6). The indoor temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0) can be reduced.

When the indoor temperature difference (ΔTR) is smaller than the intermediate threshold value (ΔTY) as the second value, the high pressure (Ph) of the refrigerant circuit (6) is lowered, thereby reducing the load on the second compressor (22) and the third compressor (23).

When the indoor temperature difference (ΔTR) is smaller than the lower threshold value (ΔTX) serving as the third value, setting the high pressure (Ph) of the refrigerant circuit (6) to the lower limit value (Ph1) is advantageous in reducing the load on the second compressor (22) and the third compressor (23).

When the indoor temperature difference (ΔTR) is greater than the upper threshold value (ΔTZ) as the fourth value, the gas vent valve (42) of the gas vent pipe (41) is opened to promote the flow of refrigerant from the gas storage section (25a) of the gas-liquid separator (25) to the suction side (23i) of the third compressor (23). This can further increase the indoor temperature (TR), which is advantageous in reducing the indoor temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0). This is advantageous in quickly increasing the indoor temperature (TR) immediately after starting the heating operation.

The ratio of liquid in the refrigerant can be increased because the outlet specific enthalpy (he) of the refrigerant at the outlet (E) of the indoor heat exchanger (64) is smaller than the critical specific enthalpy (hc) of the refrigerant at its critical point (C). By increasing the amount of liquid refrigerant flowing into the gas-liquid separator (25), the gas-liquid separation effect of the gas-liquid separator (25) can be increased.

Even in the case of a multi-type system with two or more indoor heat exchangers (64), the indoor temperature difference (ΔTR) between the indoor temperature (TR) and the target indoor temperature (TR0) can be adjusted during heating operation, which heats the room by compressing the refrigerant to above the critical pressure (Pc).

For each air conditioning unit (60) (first air conditioning unit (60A), second air conditioning unit (60B)), the indoor expansion valve (63) (first indoor expansion valve (63A), second indoor expansion valve (63B)) adjusts the outlet refrigerant temperature (TE) (first outlet refrigerant temperature (TEA), second outlet refrigerant temperature (TEB)). For each air conditioning unit (60) (first air conditioning unit (60A), second air conditioning unit (60B)), the indoor temperature difference (ΔTR) (first indoor temperature difference (ΔTRA), second indoor temperature difference (ΔTRB)) can be controlled individually.

By adopting the worse condition (larger temperature difference) between the first indoor temperature difference (ΔTRA) and the second indoor temperature difference (ΔTRB), it is advantageous to reduce the indoor temperature difference (ΔTR).

Using carbon dioxide as a refrigerant is advantageous from an environmental protection perspective.

(12) Other embodiments In the above embodiment, the larger of the first indoor temperature difference (ΔTRA) and the second indoor temperature difference (ΔTRB) is adopted, but this is not limited to this. For example, the average value of the two or the smaller of the two may be adopted.

In the above embodiment, the first value and the second value are the same value, but this is not limited and they may be different from each other. The first value and the third value may be the same value, and the second value and the third value may be the same value. The same applies to the fourth value.

There may be only one compressor (single stage).

The indoor heat exchanger (64) serving as a radiator may be one or may be three or more.

The refrigerant circuit (6) does not need to have a gas-liquid separator (25).

The air conditioning system (1) may be configured without the cooling unit (70).

The refrigerant does not have to be carbon dioxide.

Although the embodiments and modifications have been described above, it will be understood that various modifications of form and details are possible without departing from the spirit and scope of the claims. Furthermore, elements of the above embodiments, modifications, and other embodiments may be combined or substituted as appropriate.

The descriptions "first," "second," "third," etc. mentioned above are used to distinguish the words to which they are attached, and do not limit the number or order of those words.

1 Air conditioner 6 Refrigerant circuit 23 Third compressor (compressor)
23i Intake side 24 Outdoor heat exchanger (evaporator)
25 Gas-liquid separator 25a Gas storage section 41 Gas vent pipe (gas vent passage)
42 Gas vent valve (on-off valve)
63 Indoor expansion valve (expansion valve)
63A First indoor expansion valve (first expansion valve)
63B Second indoor expansion valve (second expansion valve)
64 Indoor heat exchanger (radiator)
64A First indoor heat exchanger (first radiator)
64B Second indoor heat exchanger (second radiator)
130 Controller (control device)
E Outlet TE Outlet refrigerant temperature (refrigerant temperature)
TR Indoor temperature TRA 1st indoor temperature (indoor temperature)
TRB 2nd room temperature (room temperature)
TR0 Target indoor temperature TR0A 1st target indoor temperature (target indoor temperature)
TR0B Second target indoor temperature (target indoor temperature)
ΔTR Indoor temperature difference (temperature difference)
ΔTRA 1st indoor temperature difference (1st temperature difference)
ΔTRB Second indoor temperature difference (second temperature difference)
Ph High pressure (high pressure)
Ph1 Lower limit C Critical point Pc Critical pressure he Exit specific enthalpy (specific enthalpy)
hc Critical specific enthalpy (specific enthalpy)
ΔTX lower threshold (third value)
ΔTY Intermediate threshold (first value, second value)
ΔTZ Upper threshold (fourth value)

Claims (8)

a refrigerant circuit (6) having a compressor (23), a radiator (64), an expansion valve (63), and an evaporator (24), and performing a refrigeration cycle for performing a heating operation for heating a room by compressing a refrigerant to a critical pressure (Pc) or higher;
a control device (130) that controls the refrigerant circuit (6),
The control device (130)
controlling the expansion valve (63) to adjust a refrigerant temperature (TE) at an outlet (E) of the radiator (64);
controlling a high pressure (Ph) of the refrigerant circuit (6) based on a temperature difference (ΔTR) between a room temperature (TR) and a target room temperature (TR0) ;
The refrigerant circuit (6)
a gas-liquid separator (25) connected downstream of the radiator (64) for separating a refrigerant into a gas refrigerant and a liquid refrigerant;
a gas vent passage (41) connecting a gas storage section (25a) of the gas-liquid separator (25) and a suction side (23i) of the compressor (23);
an on-off valve (42) provided in the gas vent passage (41),
The control device (130) opens the on-off valve (42) when the temperature difference (ΔTR) becomes greater than a fourth value.
Air conditioning equipment. 2. The air-conditioning apparatus according to claim 1, wherein the control device (130) controls the compressor (23) to increase the high pressure (Ph) of the refrigerant circuit (6) when the temperature difference (ΔTR) becomes greater than a first value that is equal to or smaller than the fourth value. The air-conditioning apparatus according to claim 2, wherein the control device (130) controls the compressor (23) to lower the high pressure (Ph) of the refrigerant circuit (6) when the temperature difference (ΔTR) becomes smaller than a second value that is equal to or smaller than the first value . The air-conditioning apparatus according to claim 3, wherein the control device (130) controls the compressor (23 ) so that the high pressure (Ph) of the refrigerant circuit (6) is set to a lower limit value (Ph1) of a control range when the temperature difference (ΔTR) becomes smaller than a third value that is equal to or smaller than the second value. The refrigerant circuit (6) includes a gas-liquid separator (25) connected downstream of the radiator (64) and separating a refrigerant into a gas refrigerant and a liquid refrigerant,
5. The air-conditioning apparatus according to claim 1, wherein a specific enthalpy (he) of the refrigerant at an outlet (E) of the radiator (64) is smaller than a specific enthalpy (hc) of the refrigerant at a critical point (C). The radiator (64) includes a first radiator (64A) and a second radiator (64B) connected in parallel to each other,
The expansion valve (63) includes a first expansion valve (63A) corresponding to the first radiator (64A) and a second expansion valve (63B) corresponding to the second radiator (64B),
5. The air-conditioning apparatus according to claim 1, wherein the control device (130) controls the high pressure (Ph) of the refrigerant circuit (6) based on either or both of a first temperature difference (ΔTRA) which is the temperature difference between an indoor temperature (TRA) corresponding to the first radiator (64A) and a target indoor temperature (TR0A) and a second temperature difference (ΔTRB) which is the temperature difference between an indoor temperature (TRB) corresponding to the second radiator (64B) and a target indoor temperature (TR0B). The air conditioner according to claim 6, wherein the control device (130) controls the high pressure (Ph ) of the refrigerant circuit (6) based on the larger of the first temperature difference (ΔTRA) and the second temperature difference (ΔTRB). The air conditioner according to claim 1 , wherein the refrigerant is carbon dioxide.