Air conditioner

Abstract

To provide an air conditioner capable of preventing low pressure from excessively lowering and capable of suppressing deterioration in indoor comfort, in a low load operation where required capacity of an indoor unit is small.SOLUTION: An air conditioner includes: a refrigerant circuit having an outdoor unit which has a compressor and an outdoor heat exchanger, at least one first indoor unit which has an air refrigerant heat exchanger and a first expansion valve, and at least one relay unit which has a water refrigerant heat exchanger which exchanges heat between a refrigerant and water and a second expansion valve and is connected to the outdoor unit in parallel with the first indoor unit; a low pressure sensor for detecting the pressure of the refrigerant on a low pressure side of the refrigerant circuit; and a control device for controlling the first expansion valve and the second expansion valve. The control device executes first low pressure protection control which is processing for opening the second expansion valve, in the case where a detection value of the low pressure sensor is equal to or less than a first threshold value in a state where the second expansion valve is closed while the first indoor unit is in a cooling operation.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an air conditioner equipped with a relay unit that connects a refrigerant circuit and a water circuit. [Background technology]

[0002] In a multi-air conditioner connected to multiple indoor units, if the capacity required by the indoor units is low, liquid refrigerant may accumulate in the condenser. As a result, the amount of refrigerant circulating in the refrigerant circuit decreases, and the low pressure, which is the pressure of the refrigerant on the suction side of the compressor, falls below a specified value, which not only prevents the compressor from operating properly but also may cause damage to the compressor.

[0003] Therefore, a technology is known in which, when the low-pressure is below a predetermined value, the expansion valve of a stopped indoor unit is opened to return the refrigerant trapped in the indoor heat exchanger (upstream of the expansion valve in the case of cooling operation) to the compressor, thereby increasing the amount of refrigerant circulating and raising the low-pressure (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 4-208370 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the above technology is implemented during cooling operation, low-temperature refrigerant will flow through the indoor heat exchanger of an indoor unit that is not operating, which may cause the air in the room in which the indoor unit is installed to become cooled, resulting in reduced comfort.

[0006] In view of the above circumstances, an object of the present invention is to provide an air conditioner that can prevent excessive drop in low-pressure pressure and suppress a decrease in indoor comfort during low-load operation when the indoor unit's required capacity is low. [Means for solving the problem]

[0007] An air conditioner according to one embodiment of the present invention comprises an outdoor unit having a compressor and an outdoor heat exchanger, at least one first indoor unit having an air-refrigerant heat exchanger and a first expansion valve, and at least one relay unit having a water-refrigerant heat exchanger for exchanging heat between refrigerant and water and a second expansion valve and connected to the outdoor unit in parallel with the first indoor unit, a refrigerant circuit having a low pressure sensor that detects the pressure of refrigerant on the low pressure side of the refrigerant circuit, and a control device that controls the first expansion valve and the second expansion valve, and the control device executes first low pressure protection control, which is a process of opening the second expansion valve when the detection value of the low pressure sensor is below a first threshold value while the second expansion valve is closed when the first indoor unit is in cooling operation.

[0008] When the air conditioner has a plurality of the relay units and the plurality of the relay units are connected in parallel to the outdoor unit, the control device may open all of the second expansion valves sequentially or simultaneously in the first low pressure protection control.

[0009] The air conditioner may further include a water circuit having at least one second indoor unit having a water heat exchanger and a flow control valve, a pump that circulates water for heat exchange with the refrigerant between the water-refrigerant heat exchanger and the second indoor unit, and a bypass flow path connected to the water-refrigerant heat exchanger and bypassing the second indoor unit, and the control device may execute second low pressure protection control, which is a process of closing the flow control valve of the second indoor unit when the second indoor unit is stopped, and operating the pump connected to the relay unit for which the first low pressure protection control was executed when the detection value of the low pressure sensor is below the first threshold value with the second expansion valve closed while the first indoor unit is in cooling operation.

[0010] Alternatively, the air conditioner may further include a water circuit having at least one second indoor unit having a water heat exchanger and a flow control valve, and a pump that circulates water for heat exchange with the refrigerant between the water-refrigerant heat exchanger and the second indoor unit, and the control device may execute second low pressure protection control, which is a process of closing the flow control valve of the second indoor unit when it is stopped, starting the first low pressure protection control when the detection value of the low pressure sensor is below the first threshold value with the second expansion valve closed while the first indoor unit is in cooling operation, and opening the flow control valve connected to the relay unit for which the first low pressure protection control was executed when the detection value of the low pressure sensor is below the first threshold value after a predetermined time has elapsed.

[0011] Alternatively, the air conditioner may further include at least one second indoor unit having a water heat exchanger and a flow control valve, a water circuit having a pump that circulates water to be heat exchanged with the refrigerant between the water-refrigerant heat exchanger and the second indoor unit, and a water temperature sensor that detects the temperature of water flowing through the water circuit, and the control device may close the flow control valve of the second indoor unit when it is stopped, and when the detection value of the low pressure sensor is below the first threshold value with the second expansion valve closed while the first indoor unit is in cooling operation, start the first low pressure protection control, and execute second low pressure protection control which is a process of opening the flow control valve connected to the relay unit for which the first low pressure protection control was executed when the detection value of the water temperature sensor is below the second threshold value after a predetermined time has elapsed.

[0012] The air conditioner may have a plurality of the second indoor units, each of which has a room temperature sensor and is connected in parallel to the relay unit, and the control device may, in the second low pressure protection control, open the flow control valve in order from the second indoor unit having the highest detection value of the room temperature sensor among the second indoor units connected to the relay unit on which the first low pressure protection control is executed.

[0013] The second indoor unit may further include a human presence sensor that detects the presence of a person in the room, and the control device, in the second low pressure protection control, may open the flow control valve of the second indoor unit, of the second indoor units connected to the relay unit on which the first low pressure protection control is executed, in which the presence of a person is not detected by the human presence sensor, in priority to the detection value of the room temperature sensor.

[0014] The control device may execute a third low pressure protection control, which is a process of opening the first expansion valve of the first indoor unit that is stopped when the detection value of the low pressure sensor is below the first threshold value a predetermined time after starting the second low pressure protection control for all the flow control valves.

[0015] The air conditioner may have a plurality of the first indoor units, each of which has a room temperature sensor and is connected in parallel to the outdoor unit, and in the third low pressure protection control, the control device may open the first expansion valve of the first indoor unit that has the highest detection value from the room temperature sensor among the first indoor units that are stopped operating.

[0016] The first indoor unit may further include a human presence sensor that detects the presence of a person in the room, and in the third low pressure protection control, the control device may open the first expansion valve of a first indoor unit that is stopped in operation and in which the presence of a person is not detected by the human presence sensor, in priority to the detection value of the room temperature sensor. Effect of the Invention

[0017] According to the present invention, during low-load operation when the capacity required of the indoor unit is small, an excessive decrease in low-pressure pressure can be prevented and a decrease in indoor comfort can be suppressed. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a refrigerant-water circuit diagram of an air conditioner according to a first embodiment of the present invention. [Diagram 2]4 is a block diagram showing a configuration of a control device in the air conditioner. FIG. [Diagram 3] 5 is a flowchart showing an example of a processing procedure executed by the control device during cooling operation. [Figure 4] 5 is a flowchart showing an example of a processing procedure executed by the control device during cooling operation. [Diagram 5] FIG. 2 is a schematic diagram of a refrigerant-water circuit during cooling operation, for explaining the function of the air conditioner. [Figure 6] FIG. 2 is a schematic diagram of a refrigerant-water circuit during cooling operation, for explaining the function of the air conditioner. [Figure 7] FIG. 2 is a schematic diagram of a refrigerant-water circuit during cooling operation, for explaining the function of the air conditioner. [Figure 8] FIG. 2 is a schematic diagram of a refrigerant-water circuit during cooling operation, for explaining the function of the air conditioner. [Figure 9] FIG. 2 is a schematic diagram of a refrigerant-water circuit during cooling operation, for explaining the function of the air conditioner. [Figure 10] FIG. 2 is a schematic diagram of a refrigerant-water circuit during cooling operation, for explaining the function of the air conditioner. [Figure 11] FIG. 5 is a refrigerant-water circuit diagram of an air conditioner according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0020] <First embodiment> [Air conditioner configuration] 1 is a refrigerant-water circuit diagram of an air conditioner 100 according to a first embodiment of the present invention. The air conditioner 100 of this embodiment comprises an outdoor unit 2, multiple (two in this embodiment) first indoor units 3a, 3b (hereinafter also referred to collectively as the first indoor units 3 unless individually described), a relay unit 50, and a control device 90.

[0021] (Outdoor unit) The outdoor unit 2 has a compressor 21, a four-way valve 22, an outdoor heat exchanger 23, and an accumulator 25. These devices are connected by piping to the first indoor unit 3 and the relay unit 50, which are connected in parallel, to form a refrigerant circuit 20 in which a refrigerant (primary refrigerant) circulates in the refrigerant-water circuit of the air conditioner 100.

[0022] The compressor 21 is a variable displacement compressor whose operating capacity can be changed by controlling the rotation speed by an inverter (not shown). The refrigerant discharge side of the compressor 21 is connected to the port a of the four-way valve 22 by a discharge pipe 61. The refrigerant suction side of the compressor 21 is connected to the refrigerant outflow side of the accumulator 25 by a suction pipe 65.

[0023] The four-way valve 22 is a valve for switching the flow direction of the refrigerant, and has four ports a, b, c, and d. As described above, the port a is connected to the refrigerant discharge side of the compressor 21 by the discharge pipe 61. The port b is connected to one refrigerant inlet / outlet of the outdoor heat exchanger 23 by the refrigerant piping 62. The port c is connected to the refrigerant suction side of the accumulator 25 by the refrigerant piping 66. And the port d is connected to the gas refrigerant inlet / outlet 51b of the water-refrigerant heat exchanger 51 in the relay unit 50 by the outdoor unit gas pipe 64.

[0024] The outdoor heat exchanger 23 exchanges heat between the refrigerant and the outside air taken into the outdoor unit 2 by the rotation of the outdoor fan 29. One refrigerant inlet / outlet of the outdoor heat exchanger 23 is connected to the port b of the four-way valve 22 by the refrigerant piping 62 as described above, and the other refrigerant inlet / outlet is connected to the liquid refrigerant inlet / outlet 51a of the water-refrigerant heat exchanger 51 in the relay unit 50 by the outdoor unit liquid pipe 63.

[0025] The outdoor fan 29 is made of a resin material, and is disposed near the outdoor heat exchanger 23. The outdoor fan 29 is rotated by a fan motor (not shown) to take in outside air from an intake port (not shown) of the outdoor unit 2 into the interior of the outdoor unit 2, and discharges the outside air that has exchanged heat with the refrigerant in the outdoor heat exchanger 23 to the outside of the outdoor unit 2 from an outlet port (not shown) of the outdoor unit 2.

[0026] (1st indoor unit) The first indoor unit 3 has an indoor heat exchanger 31, an indoor fan 32, and a first expansion valve (indoor expansion valve) 33. The first indoor units 3a, 3b have the same configuration and are connected in parallel. By connecting the first indoor unit 3 and the outdoor unit 2, a refrigerant circuit 20 in the refrigerant-water circuit of the air conditioner 100 is formed. Note that the number of first indoor units 3 is not limited to two, and at least one is sufficient.

[0027] The indoor heat exchanger 31 is an air-refrigerant heat exchanger that exchanges heat between the refrigerant and the outside air taken into the first indoor unit 3 by the rotation of the indoor fan 32. The outdoor unit liquid pipe 63 and the first indoor unit 3 are connected by a liquid pipe 36, and the liquid pipe 36 and one of the refrigerant inlet and outlets of the indoor heat exchanger 31 are connected by an indoor unit liquid pipe 38. The outdoor unit gas pipe 64 and the first indoor unit 3 are connected by a gas pipe 37, and the gas pipe 37 and the other refrigerant inlet and outlet of the indoor heat exchanger 31 are connected by an indoor unit gas pipe 39.

[0028] The first expansion valve 33 is, for example, an electronic expansion valve. The first expansion valve 43 is disposed in the indoor unit refrigerant pipe 38, and the opening degree of the first expansion valve 43 is adjusted to reduce the pressure of the refrigerant flowing through the indoor heat exchanger 31.

[0029] The indoor fan 32 is made of a resin material and is disposed near the indoor heat exchanger 31. The indoor fan 32 is rotated by a fan motor (not shown) to take in indoor air from an intake port (not shown) of the first indoor unit 3 into the inside of the first indoor unit 3, and blows the air that has exchanged heat with the refrigerant in the indoor heat exchanger 31 out of an outlet port (not shown) of the first indoor unit 3 into the room.

[0030] (Relay unit) The relay unit 50 has a water-refrigerant heat exchanger 51 and a second expansion valve 52. The relay unit 50 is connected to the outdoor unit 2 in parallel with the first indoor unit 3. The relay unit 50 is installed outdoors as a separate unit from the outdoor unit 2, but may also be installed inside the outdoor unit 2. Note that there may be more than one relay unit 50, and at least one relay unit is sufficient.

[0031] The water-refrigerant heat exchanger 51 is, for example, a double-pipe heat exchanger and has a refrigerant side flow path 511, a water side flow path 512, a liquid refrigerant inlet / outlet 51a connected to the liquid pipe 36, a gas refrigerant inlet / outlet 51b connected to the gas pipe 37, a water inlet 51c, and a water outlet 51d.

[0032] The refrigerant-side flow passage 511 has one end connected to the liquid refrigerant inlet / outlet 51a and the other end connected to the gas refrigerant inlet / outlet 51b. The water-side flow passage 512 has one end connected to the water inlet 51c and the other end connected to the water outlet 51d. In the water-refrigerant heat exchanger 51, the refrigerant flowing through the refrigerant-side flow passage 511 and the water flowing through the water-side flow passage 512 exchange heat with each other.

[0033] The liquid refrigerant inlet / outlet 51a is connected to the other refrigerant inlet / outlet of the outdoor heat exchanger 23 by the liquid branch pipe 16 and the outdoor unit liquid pipe 63. The liquid branch pipe 16 is a refrigerant piping branching off from the liquid pipe 36. The gas refrigerant inlet / outlet 51b is connected to the port d of the four-way valve 22 by the gas branch pipe 17 and the outdoor unit gas pipe 64. The gas branch pipe 17 is a refrigerant piping branching off from the gas pipe 37. The water inlet 51c is connected to the indoor heat exchanger 41 of the second indoor unit 4 by the second water pipe 12. The water outlet 51d is connected to the indoor heat exchanger 41 of the second indoor unit 4 by the first water pipe 11.

[0034] The second expansion valve 52 is, for example, an electronic expansion valve. The second expansion valve 52 is disposed between the outdoor heat exchanger 23 and the liquid refrigerant inlet / outlet 51a, and the opening degree of the second expansion valve 52 is adjusted to reduce the pressure of the refrigerant flowing through the relay unit 50.

[0035] (water circuit) The water-refrigerant heat exchanger 51 is connected to a water circuit 40 in which water, which is a secondary refrigerant, circulates. The water circuit 40 has second indoor units 4a, 4b (hereinafter collectively referred to as the second indoor units 4 unless otherwise described individually) connected to the water-refrigerant heat exchanger 51 of the relay unit 50.

[0036] The water circuit 40 includes a second indoor unit 4 and a circulation pump 34. The second indoor unit 4 has an indoor heat exchanger 41, an indoor fan 42, and a flow rate adjustment valve 43.

[0037] The indoor heat exchanger 41 is a water-air heat exchanger that exchanges heat between water and the outside air taken into the second indoor unit 4 by the rotation of the indoor fan 42. The inlet side of the indoor heat exchanger 41 is connected to the water outlet 51d of the water-refrigerant heat exchanger 51 by the first water piping 11 and the first water branch piping 111. The outlet side of the indoor heat exchanger 41 is connected to the water inlet 51c of the water-refrigerant heat exchanger 51 by the second water piping 12 and the second water branch piping 121.

[0038] The indoor fan 42 is made of a resin material and is disposed near the indoor heat exchanger 41. The indoor fan 42 is rotated by a fan motor (not shown) to take in indoor air from an inlet (not shown) of the second indoor unit 4 into the second indoor unit 4, and blows the air that has exchanged heat with water in the indoor heat exchanger 41 out of an outlet (not shown) of the second indoor unit 4 into the room.

[0039] The flow rate adjustment valve 43 is disposed in the first water pipe 11, and is a valve with a variable opening that adjusts the flow of water from the water outlet 51d of the water-refrigerant heat exchanger 51 to the indoor heat exchanger 41. The flow rate adjustment valve 43 is individually controlled for each of the second indoor units 4a, 4b, and the flow rate adjustment valve 43 of the second indoor unit 4 that is not operating (or is to be stopped) is switched to a closed state. The flow rate adjustment valve 43 may be an opening / closing valve (on / off valve).

[0040] The circulation pump 34 is a variable capacity pump driven by a motor (not shown). When the circulation pump 34 is driven, water flows out from the water outlet 51d of the water-refrigerant heat exchanger 51 to the first water pipe 11, and circulates so that water flows into the water inlet 51c of the water-refrigerant heat exchanger 51 via the indoor heat exchanger 41, the second water branch pipe 121, and the second water pipe 12.

[0041] The flow rate of water circulated by driving the circulation pump 34 is controlled by the rotation speed of the motor. This allows water to be supplied at the same flow rate to each second indoor unit 4. In the example shown in Fig. 1, the circulation pump 34 is disposed in the second water piping 12, but it may be disposed in the first water piping 11 instead.

[0042] The water circuit 40 further includes a bypass passage 44 and a bypass valve 45 provided in the bypass passage 44 .

[0043] The bypass flow passage 44 is a water pipe connected between the first water pipe 11 and the second water pipe 12. More specifically, one end of the bypass flow passage 44 is connected to the first water pipe 11 between the water outlet 51d of the water-refrigerant heat exchanger 51 and the branch point where the first water branch pipe 111 branches off from the first water pipe 11. The other end of the bypass flow passage 44 is connected to the second water pipe 12 between the suction port of the circulation pump 34 and the branch point where the second water branch pipe 121 branches off from the second water pipe 12.

[0044] The bypass valve 45 is an on-off valve that opens or closes the bypass flow path 44. When the bypass valve 45 is opened while the circulation pump 34 is operating, the water flowing out from the water outlet 51d of the water-refrigerant heat exchanger 51 bypasses the second indoor unit 4 and is guided to the suction port of the circulation pump 34. Therefore, even when all of the flow rate control valves 43 of the second indoor units 4 are in a closed state, the water in the water circuit 40 can be circulated via the bypass flow path 44. The bypass valve 45 is normally maintained in a closed state, and is opened under predetermined conditions when low pressure protection control, which will be described later, is executed.

[0045] Note that the installation of the bypass valve 45 is not essential and may be omitted. In this case, when each flow rate control valve 43 is in a closed state, water can be circulated through the bypass flow path 44 by starting the pump 34. Also, by making the pipe diameter of the bypass flow path 44 narrower than the pipe diameters of the other pipes constituting the water circuit 40, the amount of water flowing through the bypass flow path 44 during normal operation (when the flow rate control valve 43 is open) can be reduced.

[0046] (Sensors) The air conditioner 100 is provided with various sensors. In the outdoor unit 2, the discharge pipe 61 is provided with a high-pressure sensor 71 that detects the pressure of the refrigerant discharged from the compressor 21, and a discharge temperature sensor 72 that detects the temperature of the refrigerant discharged from the compressor 21. The suction pipe 65 is provided with a low-pressure sensor 73 that detects the pressure of the refrigerant sucked into the compressor 21, and a suction temperature sensor 74 that detects the temperature of the refrigerant sucked into the compressor 21. The low-pressure sensor 73 corresponds to the "low-pressure sensor" of the present invention that detects the pressure of the refrigerant on the low-pressure side of the refrigerant circuit 20.

[0047] The outdoor heat exchanger 23 is provided with a heat exchanger temperature sensor 75 for detecting the temperature of the refrigerant flowing through the outdoor heat exchanger 23. An outdoor air temperature sensor 76 for detecting the temperature of the outdoor air flowing into the outdoor unit 2, i.e., the outdoor air temperature, is provided near an air inlet (not shown) of the outdoor unit 2.

[0048] The first indoor unit 3 and the second indoor unit 4 are each provided with a room temperature sensor 77 that detects the temperature (room temperature) of the air flowing into the first indoor unit 3 and the second indoor unit 4, and a human presence sensor 80 that detects the presence of a person in the room.

[0049] The water circuit 40 is provided with a first water temperature sensor 78 and a second water temperature sensor 79 as water temperature sensors that detect the temperature of the water flowing through the water circuit 40. The first water temperature sensor 78 is provided in the first water piping 11 connected to the water outlet 51d of the water-refrigerant heat exchanger 51 and detects the forward temperature of the water flowing through the water circuit 40, while the second water temperature sensor 79 is provided in the second water piping 12 connected to the water inlet 51c of the water-refrigerant heat exchanger 51 and detects the return temperature of the water flowing through the water circuit 40.

[0050] (Control device) The control device 90 is, for example, an outdoor unit control device provided in the outdoor unit 2, and is mounted on a control board housed in an electrical component box (not shown) of the outdoor unit 2.

[0051] 2 is a block diagram showing the configuration of the control device 90. As shown in the figure, the control device 90 has a CPU 91, a storage unit 92, a communication unit 93, a sensor input unit 94, and a rotation speed detection unit 95.

[0052] The memory unit 92 is a non-volatile memory such as a flash memory, and stores the control program and control parameters of the outdoor unit 2, detection values ​​corresponding to detection signals from various sensors, the control states of the compressor 21 and the outdoor fan 29 etc., the rotation speeds of the indoor fans 32, 42 acquired via the communication unit 93, the control states of the first indoor unit 3 and the second indoor unit 4 including the operation mode set and input by the user, etc.

[0053] The communication unit 93 is an interface for communicating with the first indoor unit 3 and the second indoor unit 4. The sensor input unit 94 takes in detection results from various sensors in the outdoor unit 2 and outputs them to the CPU 91. The rotation speed detection unit 95 detects the rotation speed of the motor of the compressor 21 and outputs it to the CPU 91. The rotation speed detection unit 95 may be configured to directly detect the rotation speed of the motor using an encoder or the like attached to the drive shaft of the motor, or may be configured to detect the rotation speed of the motor from the drive current supplied to the motor. In the following description, the rotation speed of the compressor 21 refers to the rotation speed of the motor.

[0054] The CPU 91 is a control unit that controls the operation of each part of the outdoor unit 2, including the compressor 21, by executing a program stored in the storage unit 92. The program is installed in the control device 90, for example, via various recording media. Alternatively, the program may be installed via the Internet or the like.

[0055] The CPU 91 takes in the detection results of the sensors of the outdoor unit 2 described above via the sensor input unit 94. Furthermore, the CPU 91 takes in the control signals transmitted from the indoor units 3, 4 via the communication unit 93. The control signals transmitted from the indoor units 3, 4 include the necessary operating capacity required by the indoor units 3, 4 (the total heat load of the indoor units 3, 4). Based on the taken-in detection results and control signals, the CPU 91 controls the drive of the compressor 21, the outdoor fan 29, the indoor fan 32, and the circulation pump 34, for example, setting the indicated rotation speed which is the rotation speed at which these are driven. Furthermore, the CPU 91 controls the switching of the four-way valve 22 based on the taken-in detection results and control signals. Furthermore, the CPU 91 controls the opening degree of the first expansion valve 33, the second expansion valve 52, and the flow rate adjustment valve 43, and controls the opening and closing of the bypass valve 45, based on the taken-in detection results and control signals.

[0056] [Basic operation of air conditioners] Next, a description will be given of the basic operation of the air conditioner 100. Below, a description will be given of the operation of the air conditioner 100 during cooling operation and heating operation.

[0057] (Cooling operation) When the air conditioner 100 performs cooling operation, the four-way valve 22 is switched to the state shown by the solid lines in Fig. 1, i.e., the state where port a and port b are in communication and port c and port d are in communication, and drives the compressor 21 and the circulation pump 34. Driving the compressor 21 circulates refrigerant through the refrigerant circuit 20, and driving the circulation pump 34 circulates water through the water circuit 40. As a result, the outdoor heat exchanger 23 functions as a condenser, and the indoor heat exchanger 31 of the first indoor unit 3 and the water-refrigerant heat exchanger 51 of the relay unit 50 function as evaporators.

[0058] The rotation speed of the compressor 21 and the rotation speed of the circulation pump 34 are determined according to the required operating capacity required by the first indoor unit 3 and the second indoor unit 4. Here, an example will be described in which all of the indoor units 3, 4 perform indoor cooling.

[0059] The refrigerant compressed by the compressor 21 to a high temperature and high pressure is discharged from the compressor 21, flows through the discharge pipe 61, and flows into the four-way valve 22, and then flows from the four-way valve 22 into the refrigerant piping 62 and into the outdoor heat exchanger 23. The refrigerant that has flowed into the outdoor heat exchanger 23 exchanges heat with outside air that has been drawn into the outdoor unit 2 by the rotation of the outdoor fan 29, and is condensed.

[0060] A portion of the refrigerant flowing out from the outdoor heat exchanger 23 is depressurized when it flows through the outdoor unit liquid pipe 63 and the liquid pipe 36 and passes through the first expansion valve 33. The remainder of the refrigerant flowing out from the outdoor heat exchanger 23 is depressurized when it flows through the outdoor unit liquid pipe 63 and the liquid branch pipe 16 and passes through the second expansion valve 52.

[0061] Here, the opening degree of the first expansion valve 33 is set so as to provide an evaporation pressure corresponding to the evaporation temperature in the indoor heat exchanger 31, more specifically, lower than the minimum value of the air conditioning temperature (set temperature) set in the first indoor unit 3. Furthermore, the opening degree of the second expansion valve 52 is set so as to provide an evaporation pressure corresponding to the evaporation temperature in the water-refrigerant heat exchanger 51 to achieve the set temperature during cooling operation in the room in which the second indoor unit 4 is installed, more specifically, the opening degree is set so that the evaporation temperature in the water-refrigerant heat exchanger 51 and the temperature of the water flowing out from the water-refrigerant heat exchanger 51 are lower than the minimum value of the air conditioning temperature (set temperature) set in the second indoor unit 4.

[0062] The refrigerant that has passed through the first expansion valve 33 flows into the indoor heat exchanger 31 via the indoor unit liquid pipe 38. The refrigerant that has flowed into the indoor heat exchanger 31 exchanges heat with indoor air that has been drawn into the inside of the first indoor unit 3 by the rotation of the indoor fan 32 and evaporates, thereby cooling the room in which the first indoor unit 3 is installed. The refrigerant that has flowed out of the indoor heat exchanger 31 flows into the outdoor unit gas pipe 64 via the indoor unit gas pipe 39 and the gas pipe 37, and returns to the compressor 21.

[0063] The refrigerant that has passed through the second expansion valve 52 flows into the liquid refrigerant inlet / outlet 51a of the water-refrigerant heat exchanger 51 via the liquid branch pipe 16. The refrigerant that has flowed into the liquid refrigerant inlet / outlet 51a passes through the refrigerant side flow path 511, exchanges heat with water flowing through the water side flow path 512, and evaporates, and flows from the gas refrigerant inlet / outlet 51b of the water-refrigerant heat exchanger 51 through the gas branch pipe 17 into the outdoor unit gas pipe 64. The refrigerant that has flowed into the outdoor unit gas pipe 64 flows through the four-way valve 22, refrigerant piping 66, accumulator 25, and suction pipe 65, and is sucked into the compressor 21 and compressed again.

[0064] On the other hand, the water cooled while flowing through the water-side flow path 512 flows into the first water piping 11 from the water outlet 51d of the water-refrigerant heat exchanger 51. The water that flows into the first water piping 11 passes through the first water branch piping 111 and flows into the indoor heat exchanger 41 of the second indoor unit 4 via the flow rate control valve 43 in an open state, and cools the indoor air passing through the indoor heat exchanger 41 by the rotation of the indoor fan 42. This cools the room in which the second indoor unit 4 is installed.

[0065] The water flowing out from the indoor heat exchanger 41 of each second indoor unit 4 is sucked into the circulation pump 34 via the second water branch pipe 121 and the second water pipe 12. The water sucked into the circulation pump 34 is sent to the water inlet 51c of the water-refrigerant heat exchanger 51, passes through the water-side flow path 512, and is cooled again by the refrigerant flowing in the refrigerant-side flow path 511, and then flows out from the water outlet 51d toward the second indoor unit 4.

[0066] (Heating operation) 1, i.e., in a state where port a communicates with port d and port b communicates with port c, the compressor 21 and the circulation pump 34 are driven. Driving the compressor 21 circulates refrigerant through the refrigerant circuit 20, and driving the circulation pump 34 circulates water through the water circuit 40. As a result, the outdoor heat exchanger 23 functions as an evaporator, and the indoor heat exchanger 31 of the first indoor unit 3 and the water-refrigerant heat exchanger 51 of the relay unit 50 function as condensers.

[0067] The rotation speed of the compressor 21 and the rotation speed of the circulation pump 34 are determined according to the required operating capacity required by the first indoor unit 3 and the second indoor unit 4. Here, an example will be described in which all of the indoor units 3, 4 perform indoor heating.

[0068] The refrigerant compressed by the compressor 21 to become high temperature and high pressure is discharged from the compressor 21, flows through the discharge pipe 61 and flows into the four-way valve 22, and flows from the four-way valve 22 through the outdoor unit gas pipe 64 into the gas pipe 37 and the gas branch pipe 17.

[0069] The refrigerant that has flowed into the gas pipe 37 flows into the indoor heat exchanger 31 via the indoor unit gas pipe 39. The refrigerant that has flowed into the indoor heat exchanger 31 exchanges heat with indoor air that has been drawn into the inside of the first indoor unit 3 by the rotation of the indoor fan 32 and condenses, thereby heating the room in which the first indoor unit 3 is installed. The refrigerant that has flowed out of the indoor heat exchanger 31 is decompressed by the first expansion valve 33, and flows into the outdoor unit liquid pipe 63 via the indoor unit liquid pipe 38 and liquid pipe 36.

[0070] At this time, the opening degree of the first expansion valve 33 is set so that the subcooling (degree of supercooling) of the refrigerant flowing out of the indoor heat exchanger 31 becomes the target subcooling, more specifically, the opening degree is set so that the air conditioning temperature (set temperature) is higher than the maximum value set in the first indoor unit 3.

[0071] On the other hand, the refrigerant that has flowed into the gas refrigerant inlet / outlet 51b of the water-refrigerant heat exchanger 51. The refrigerant that has flowed into the gas refrigerant inlet / outlet 51b passes through the refrigerant-side flow path 511 and heats the water flowing through the water-side flow path 512. The refrigerant condensed by heat exchange with the water flowing through the water-side flow path 512 flows out from the liquid-side inlet / outlet 51a of the water-refrigerant heat exchanger 51 to the liquid branch pipe 16, is depressurized by the second expansion valve 52, and flows into the outdoor unit liquid pipe 63.

[0072] At this time, the opening degree of the second expansion valve 52 is set so that the subcooling (degree of supercooling) of the refrigerant flowing out of the water-refrigerant heat exchanger 51 becomes a target subcooling in order to achieve the set temperature during heating operation in the room in which the second indoor unit 4 is installed, and more specifically, the opening degree is set so that the condensing temperature in the water-refrigerant heat exchanger 51 and the temperature of the water flowing out from the water-refrigerant heat exchanger 51 become higher than the maximum air conditioning temperature (set temperature) set in the second indoor unit 4.

[0073] The water heated while flowing through the water-side flow path 512 flows into the first water piping 11 from the water outlet 51d of the water-refrigerant heat exchanger 51. The water that has flowed into the first water piping 11 flows into the indoor heat exchanger 41 via the first water branch piping 111 and the flow rate control valve 43 in an open state, and heats the indoor air passing through the indoor heat exchanger 41 by the rotation of the indoor fan 42. This heats the room in which the second indoor unit 4 is installed.

[0074] The water flowing out from the indoor heat exchanger 41 flows into the second water pipe 12 via the second water branch pipe 121 and is drawn into the circulation pump 34. The water drawn into the circulation pump 34 is sent to the water inlet 51c of the water-refrigerant heat exchanger 51, passes through the water-side flow path 512, is heated again by the refrigerant flowing in the refrigerant-side flow path 511, and then flows out from the water outlet 51d toward the second indoor unit 4.

[0075] Meanwhile, the refrigerant that has flowed into the outdoor unit liquid pipe 63 flows into the outdoor heat exchanger 23. The refrigerant that has flowed into the outdoor heat exchanger 23 evaporates by exchanging heat with outside air that has been drawn into the outdoor unit 2 by the rotation of the outdoor fan 29. The refrigerant that has flowed out of the outdoor heat exchanger 23 flows through the refrigerant piping 62, and is sucked into the compressor 21 via the four-way valve 22, the refrigerant piping 66, the accumulator 25, and the suction pipe 65, and is compressed again.

[0076] [Control device details] The control device 90 controls the rotation speed of the compressor 21, the rotation speed of the circulation pump 34, and the opening degree of the first expansion valve 33 and the second expansion valve 52, respectively, according to the capacity required by the first indoor unit 3 and the second indoor unit 4. For example, during cooling or heating operation, the control device 90 determines whether the indoor temperature has reached a set temperature, and stops the operation of the indoor unit installed in the room where the set temperature has been reached (hereinafter also referred to as thermo-off). At this time, the control device 90 fully closes or slightly opens the expansion valve corresponding to the indoor unit whose operation is to be stopped, thereby stopping the flow of refrigerant through the indoor heat exchanger of that indoor unit.

[0077] Here, a compressor usually has a lower limit of the suction side pressure and an upper limit of the discharge side pressure according to the rotation speed as a specification, so if the compressor is operated under conditions outside this range, the reliability may deteriorate. In addition, in general, when the capacity required from the indoor unit is small, the condensing capacity becomes excessive, and liquid refrigerant may accumulate in the condenser. As a result, the amount of refrigerant circulating in the refrigerant circuit decreases, and the low pressure, which is the pressure of the refrigerant on the suction side of the compressor, falls below a predetermined value, which not only makes the compressor unable to operate properly, but also may cause the compressor to be damaged. Such problems are particularly likely to occur when the ambient temperature of the condenser (exterior heat exchanger during cooling operation) is low.

[0078] On the other hand, when the low pressure is below a predetermined value, a method is known in which the expansion valve of the stopped indoor unit is opened to return the refrigerant stagnating in the indoor heat exchanger (upstream of the expansion valve in cooling operation) to the compressor, thereby increasing the amount of refrigerant circulating and raising the low pressure. However, when the above method is carried out during cooling operation, low-temperature refrigerant flows through the indoor heat exchanger of the stopped indoor unit, which may cool the air in the room where the indoor unit is installed, reducing comfort.

[0079] In this embodiment, therefore, in order to prevent the low pressure from dropping excessively during low load operation when the indoor unit's required capacity is small and to suppress a drop in indoor comfort, the control device 90 executes low pressure protection control as described below. The control device 90 will be described in detail below.

[0080] Figures 3 and 4 are flowcharts showing an example of a processing procedure executed by the control device 90 during cooling operation. Figures 5 to 10 are schematic diagrams of the refrigerant-water circuit during cooling operation, illustrating the action of the air conditioner 100.

[0081] 5 to 10 omit the return paths of the refrigerant from the first indoor unit 3 and the relay unit 50 (water-refrigerant heat exchanger 51) to the compressor 21. Also, in Figures 5 to 10, the first expansion valve 33, the second expansion valve 52, the flow rate control valve 43 and the bypass valve 45 are each indicated by the same valve symbol, with white valves indicating an open state and black valves indicating a closed state.

[0082] When the cooling operation starts, the control device 90 controls the rotation speed of the compressor 21 according to the air conditioning load of the first indoor unit 3 and the second indoor unit 4 (ST101). By controlling the rotation speed of the compressor 21 according to the air conditioning load of the indoor units 3, 4 in this way, it is possible to achieve an air conditioning temperature that is comfortable for indoor users. Figure 5 shows the state when all of the indoor units 3, 4 are performing cooling operation.

[0083] The air conditioning load of the first indoor unit 3 and the second indoor unit 4 is calculated, for example, based on the temperature (room temperature) of the room in which the first indoor unit 3 and the second indoor unit 4 are installed and the air conditioning temperature (set temperature) set in the indoor units. When multiple indoor units are in operation, the air conditioning load is the total value of the air conditioning loads of the individual indoor units.

[0084] (First low voltage protection control) The controller 90 determines at predetermined time intervals during cooling operation whether or not at least one first indoor unit 3 is in operation (ST102).

[0085] For example, when an operation is performed to stop the operation of the first indoor unit 3a, or when the temperature in the room where the first indoor unit 3a is installed reaches a set temperature, the first indoor unit 3a stops cooling operation. At this time, the first expansion valve 33 corresponding to the first indoor unit 3a is closed, thereby stopping the flow of refrigerant into the indoor heat exchanger 31 of this first indoor unit 3a.

[0086] When both of the first indoor units 3a, 3b are stopped (No in ST102), the process returns to ST101. On the other hand, when at least one of the first indoor units 3a, 3b is in operation (Yes in ST102), the controller 90 determines whether the second expansion valve 52 is closed (ST103).

[0087] For example, when an operation is performed to stop the operation of the second indoor unit 4a, or when the temperature in the room where the second indoor unit 4a is installed reaches a set temperature, the second indoor unit 4a stops cooling operation. At this time, the flow rate control valve 43 corresponding to the second indoor unit 4a is closed, thereby stopping the inflow of water into the indoor heat exchanger 41 of the second indoor unit 4a. On the other hand, when all the second indoor units 4a to 4c stop operating, all the flow rate control valves 43 are closed, the circulation pump 34 is stopped, and further the second expansion valve 52 is closed.

[0088] When the second expansion valve 52 is closed (Yes in ST103), this corresponds to a state in which all second indoor units 4 have stopped operating and only the first indoor unit 3 is operating. Fig. 6 shows a state in which only the first indoor unit 3b is operating. In the state shown in Fig. 6, the required capacity of the indoor units 3, 4 is a capacity equivalent to the indoor load of one of the first indoor units 3b, so the rotation speed of the compressor 21 is low and the amount of refrigerant circulating through the refrigerant circuit 20 is small, so that the low pressure, which is the pressure of the refrigerant on the suction side of the compressor 21, falls below the lower limit value set in the specifications, which may cause damage to the compressor 21.

[0089] When the second expansion valve 52 is closed (Yes in ST103), the controller 90 determines whether the low pressure detected by the low pressure sensor 73 is equal to or lower than a first threshold value set in advance (ST104). The first threshold value is, for example, a lower limit value set in the specifications for the compressor 21.

[0090] When the low pressure exceeds the first threshold (No in ST104), the process returns to ST101 and executes the above-described process again. On the other hand, when the low pressure is equal to or less than the first threshold (Yes in ST104), the controller 90 executes first low pressure protection control, which is a process for opening the second expansion valve 52 that is in the closed state (ST105, FIG. 7).

[0091] In this way, when the second expansion valve 52 is closed while the first indoor unit 3b is in cooling operation and the detection value of the low pressure sensor 73 is equal to or lower than the first threshold value, the control device 90 executes the first low pressure protection control, which is a process of opening the second expansion valve 52. As a result, the second expansion valve 52 is in an open state, so that the resistance of the refrigerant flowing through the refrigerant circuit 20 is reduced, and further, the refrigerant flowing through the refrigerant side flow path 511 exchanges heat with the water in the water side flow path 512, so that the low pressure becomes higher, thereby ensuring the reliability of the compressor 21.

[0092] The opening degree of the second expansion valve 52 when the first low pressure protection control is executed is not particularly limited, and may be fully open or may be a predetermined opening degree that is set in advance. This increases the amount of refrigerant flowing into the water-refrigerant heat exchanger 51, and the amount of refrigerant circulating in the refrigerant circuit 20 can be easily increased.

[0093] Furthermore, by executing the first low pressure protection control, the low pressure can be increased without flowing low-temperature refrigerant to the indoor heat exchanger 31 of the first indoor unit 3a whose operation is stopped, so the air in the room in which the first indoor unit 3a is installed is not cooled, and therefore a decrease in comfort in the room can be prevented. Similarly, in the water circuit 40, the circulation pump 34 remains stopped and the flow rate control valve 43 is maintained in a closed state, so water does not flow into the indoor heat exchanger 41 of the second indoor units 4a to 4c whose operation is stopped, and therefore a decrease in comfort in the room in which the second indoor units 4a to 4c are installed is also suppressed.

[0094] Furthermore, since the housing of the indoor unit is not cooled by low-temperature refrigerant or water flowing through the indoor heat exchangers 31, 41, there is no risk of dew adhering to the housing of the indoor unit and causing dew splashing or dripping as a result.

[0095] (Second low voltage protection control: control example 1) After the first low pressure protection control is executed, the control device 90 determines whether a first predetermined time has elapsed since the start of the first low pressure protection control (ST106), and when the first predetermined time has elapsed, determines again whether the low pressure, which is the detection value of the low pressure sensor 73, is equal to or lower than the first threshold value (ST107). The first predetermined time is not particularly limited as long as it is a time during which the effect of the first low pressure protection control can be confirmed, and is, for example, 60 seconds.

[0096] When the low pressure exceeds the first threshold (No in ST107), the controller 90 closes the second expansion valve 52 (ST108) and then returns to ST101. On the other hand, when the low pressure is still equal to or lower than the first threshold (Yes in ST107), the controller 90 executes second low pressure protection control, which is a process of operating the circulation pump 34 (ST109).

[0097] In this embodiment in which the bypass valve 45 is provided in the bypass flow passage 44, the second low pressure protection control is performed by operating the circulation pump 34 and opening the bypass valve 45 (ST109, FIG. 8). In this manner, when the detection value of the low pressure sensor 73 is equal to or less than the first threshold value with the second expansion valve 52 closed during the cooling operation of the first indoor unit 3b, the control device 90 performs the second low pressure protection control, which is a process of operating the circulation pump 34 connected to the relay unit 50 for which the first low pressure protection control has been executed and opening the bypass valve 45. This causes the water in the water circuit 40 to circulate through the bypass flow passage 44. As a result, the amount of heat exchange between the refrigerant and the water in the water-refrigerant heat exchanger 51 increases, and the rise in the low pressure of the refrigerant circuit 20 is promoted, so that the reliability of the compressor 21 can be ensured.

[0098] When the bypass passage 44 is not provided with the bypass valve 45, the second low pressure protection control is executed as the second low pressure protection control, which is a process of operating the circulation pump 34 (ST109). Since all of the flow rate regulating valves 43 are in a closed state, the water is circulated in the water circuit 40 via the bypass passage 44 by driving the circulation pump 34. Therefore, even in this case, the amount of heat exchange between the refrigerant and the water in the water-refrigerant heat exchanger 51 increases, and the increase in the low pressure of the refrigerant circuit 20 is promoted, so that the reliability of the compressor 21 can be ensured.

[0099] Furthermore, because the flow rate control valve 43 is maintained in a closed state and water is circulated in the water circuit 40, it is possible to prevent water from flowing into the indoor heat exchanger 41 of the second indoor units 4a to 4c that are not operating. This makes it possible to prevent a decrease in comfort in the rooms in which the second indoor units 4a to 4c are installed.

[0100] (Second low voltage protection control: control example 2) Next, the control device 90 again determines whether the low pressure, which is the detection value of the low pressure sensor 73, is equal to or lower than the first threshold value (ST110). If the low pressure exceeds the first threshold value (No in ST110), the second expansion valve 52 and the bypass valve 45 are closed (ST111), and the process returns to ST101. On the other hand, if the low pressure is still equal to or lower than the first threshold value (Yes in ST110), the control device 90 determines whether the water temperature of the water circuit 40, which is the detection value of the first water temperature sensor 78, is equal to or lower than the second threshold value (ST112).

[0101] The second threshold is set, for example, to a water temperature at which the amount of heat exchange between the refrigerant and the water in the water-refrigerant heat exchanger 51 becomes so small that it inhibits an increase in the low pressure of the refrigerant. During cooling operation, the temperature of the refrigerant flowing through the water-refrigerant heat exchanger 51 is lower than the water temperature, so the water temperature in the water circuit 40 decreases. However, when the water temperature in the water circuit 40 decreases, the amount of heat exchange between the refrigerant and the water decreases, inhibiting an increase in the low pressure of the refrigerant. Therefore, when the control device 90 determines that the water temperature is equal to or lower than the second threshold (Yes in ST112), it executes second low pressure protection control to open the flow rate adjustment valve 43 (ST113, FIG. 9).

[0102] In this way, the control device 90 starts the first low pressure protection control when the detection value of the low pressure sensor 73 is equal to or lower than the first threshold value while the second expansion valve 52 is closed during the cooling operation of the first indoor unit 3b, and executes the second low pressure protection control, which is a process of opening the flow control valve 43 connected to the relay unit 50 for which the first low pressure protection control has been executed, when the detection value of the low pressure sensor 73 is equal to or lower than the first threshold value after the first predetermined time has elapsed. As a result, the water circulating through the water circuit 40 flows into the indoor heat exchanger 41 of the second indoor unit 4, thereby performing heat exchange between the indoor air and the water. Since the temperature of the indoor air is higher than that of the water, the water temperature of the water circuit 40 rises, which increases the low pressure of the refrigerant, thereby ensuring the reliability of the compressor 21.

[0103] The flow rate adjustment valves 43 to be subject to the opening control may be any flow rate adjustment valve corresponding to at least one of the second indoor units 4 that is not in operation. For example, all of the flow rate adjustment valves 43 may be opened simultaneously, or each flow rate adjustment valve 43 may be opened in sequence.

[0104] When opening each flow rate adjustment valve 43 in sequence, the flow rate adjustment valve 43 may be opened in sequence starting from the flow rate adjustment valve 43 of the second indoor unit 4 installed in the room determined to have the highest indoor temperature based on the detection value of the indoor temperature 77. This makes it possible to minimize the decrease in comfort due to a decrease in the indoor temperature. Furthermore, if the second indoor unit 4 is equipped with a human presence sensor 80, the flow rate adjustment valve 43 of the second indoor unit 4 in which the presence of a person is not detected by the human presence sensor 80 may be opened in preference to the detection value of the room temperature sensor 77. This makes it possible to prevent a decrease in temperature in a room where a person is present, thereby suppressing a decrease in comfort in that room.

[0105] The second low pressure protection control (opening control of the flow rate adjustment valve 43) according to Control Example 2 is not limited to being performed after the second low pressure protection control (opening control of the bypass valve 45) according to the above-mentioned Control Example 1, and may be performed instead of the above-mentioned Control Example 1. In this case, the processes of ST109 and ST110 are omitted.

[0106] Furthermore, the second low pressure protection control (open control of the flow control valve 43) according to this control example 2 may be executed when the low pressure is equal to or lower than the first threshold (Yes in ST110), regardless of the result of the determination as to whether the water temperature of the water circuit 40 is equal to or lower than the second threshold (ST112), or may be executed when the water temperature of the water circuit 40 is equal to or lower than the second threshold (Yes in ST112), regardless of the result of the determination as to whether the low pressure is equal to or lower than the first threshold (ST110).

[0107] (Third low voltage protection control) Next, the control device 90 determines whether a second predetermined time has elapsed since the start of the second low pressure protection control (control example 2) in which all flow rate adjustment valves 43 are opened (ST114), and when the second predetermined time has elapsed, determines again whether the low pressure detected by the low pressure sensor 73 is equal to or lower than the first threshold (ST115). The second predetermined time is not particularly limited as long as it is a time that allows the effect of the second low pressure protection control to be confirmed, and is, for example, 60 seconds.

[0108] When the low pressure exceeds the first threshold (No in ST115), the controller 90 closes the second expansion valve 52, the bypass valve 45, and the flow rate adjustment valve 43 (ST111), and then returns to ST101. On the other hand, when the low pressure is still equal to or lower than the first threshold (Yes in ST115), the controller 90 executes third low pressure protection control, which is a process of opening the first expansion valve 33 of the first indoor unit 3a that is not operating (ST116, FIG. 10).

[0109] In this way, the control device 90 executes the third low pressure protection control, which is a process for opening the first expansion valve 33 of the first indoor unit 3a that is stopped, when the detection value of the low pressure sensor 73 is equal to or lower than the first threshold value after the second predetermined time has elapsed since starting the second low pressure protection control for all flow rate adjustment valves 43. This allows the refrigerant that is stagnating in the stopped first indoor unit 3 to be returned to the compressor 21, increasing the amount of refrigerant circulating through the refrigerant circuit 20 and raising the low pressure.

[0110] When there are three or more first indoor units 3 and two or more first indoor units 3 have stopped operating, the first expansion valves 33 may be opened in order from the indoor unit with the highest room temperature as described above, or in order from the indoor unit in which the human presence sensor 80 detects that no human is present. This makes it possible to prevent a decrease in comfort in the room in which the first indoor units 3 are installed.

[0111] By repeatedly executing the above process, during cooling operation at low load when the required capacity of the first indoor unit 3 and the second indoor unit 4 is small, it is possible to prevent the low pressure from dropping excessively and suppress a decrease in indoor comfort.

[0112] <Second embodiment> 11 is a refrigerant-water circuit diagram of an air conditioner 200 according to a second embodiment of the present invention. The air conditioner 200 of this embodiment differs from the above-described first embodiment in that two relay units 50a, 50b connected in parallel as a relay unit 50 are connected to an outdoor unit 2. In the following explanation, the same reference numerals are used for parts common to the first embodiment, and detailed explanations thereof will be omitted.

[0113] In the air conditioner 200 of this embodiment, one second indoor unit 4 is connected to each of the relay units 50a, 50b. That is, one second indoor unit 4a is connected to one relay unit 50a via a water circuit 40a, and the other second indoor unit 4b is connected to the other relay unit 50b via a water circuit 40b. Note that a plurality of second indoor units 4 may be connected in parallel to each of the relay units 50a, 50b.

[0114] Each relay unit 50a, 50b has the same configuration and includes a water-refrigerant heat exchanger 51 and a second expansion valve 52. The control device 90 individually controls the opening degree of each second expansion valve 52 according to the required capacity of the second indoor units 4a, 4b. Furthermore, since the control during cooling operation and heating operation of the air conditioner 200 is similar to that of the first embodiment, a description thereof will be omitted.

[0115] In this embodiment as well, the control device 90 executes the above-mentioned low pressure protection control on the compressor 21 so that the low pressure of the refrigerant in the refrigerant circuit 20 does not drop excessively during cooling operation. In particular, during the first low pressure protection control (ST103-105 in FIG. 3), the second expansion valves 52 of the relay units 50a, 50b are opened sequentially or simultaneously in this embodiment. This provides the same operational effects as the first embodiment.

[0116] In this embodiment as well, it is possible to execute the second low pressure protection control (control example 2) targeting the flow rate adjustment valve 43 and the third low pressure protection control targeting the first expansion valve 33. In this case, for the second low pressure protection control, the flow rate adjustment valve of the indoor unit connected to the relay unit including the second expansion valve 52 that is the target of the first low pressure protection control is set as the control target.

[0117] Although the embodiment of the present invention has been described above, the present invention is not limited to the above-mentioned embodiment, and various modifications can be made thereto.

[0118] For example, in the above embodiment, an air conditioner in which the second indoor unit 4 is connected to the relay unit 50 has been described as an example, but this is not limited to this, and the present invention can also be applied to an air conditioner in which a hot water unit or a floor heating panel is connected to the relay unit 50. [Explanation of symbols]

[0119] 2…Outdoor unit 3(3a,3b)…1st indoor unit 4(4a,4b)…Second indoor unit 20...Refrigerant circuit 21...Compressor 22...Four-way valve 23…Outdoor heat exchanger 40 (40a, 40b)... Water circuit 31…Indoor heat exchanger (air-refrigerant heat exchanger) 32,42…Indoor fan 33…First expansion valve 41…Indoor heat exchanger (water heat exchanger) 43...Flow control valve 34…Circulation pump 50 (50a, 50b)... Relay unit 51…Water refrigerant heat exchanger 52…Second expansion valve 77…Room temperature sensor 78...First water temperature sensor (water temperature sensor) 80...Human sensor 90...Control device 100,200…Air conditioner

Claims

1. a refrigerant circuit including an outdoor unit having a compressor and an outdoor heat exchanger, at least one first indoor unit having an air-refrigerant heat exchanger and a first expansion valve, and at least one relay unit having a water-refrigerant heat exchanger for exchanging heat between a refrigerant and water and a second expansion valve, the relay unit being connected to the outdoor unit in parallel with the first indoor unit; a low pressure sensor for detecting a pressure of a refrigerant on a low pressure side of the refrigerant circuit; a control device for controlling the first expansion valve and the second expansion valve; Equipped with The control device executes a first low pressure protection control, which is a process of opening the second expansion valve when the detection value of the low pressure sensor is equal to or lower than a first threshold value in a state in which the second expansion valve is closed during a cooling operation of the first indoor unit. Air conditioner.

2. The air conditioner according to claim 1, The air conditioner has a plurality of the relay units, The relay units are connected in parallel to the outdoor unit, The control device opens all of the second expansion valves sequentially or simultaneously in the first low pressure protection control. Air conditioner.

3. The air conditioner according to claim 1, The water circuit further includes at least one second indoor unit having a water heat exchanger and a flow rate regulating valve, a pump that circulates water to be subjected to heat exchange with the refrigerant between the water-refrigerant heat exchanger and the second indoor unit, and a bypass flow path that is connected to the water-refrigerant heat exchanger and bypasses the second indoor unit, The controller further controls the pump. The control device closes a flow rate adjustment valve of the second indoor unit that is stopped, and executes second low pressure protection control, which is a process of operating the pump connected to the relay unit for which the first low pressure protection control is executed, when the detection value of the low pressure sensor is equal to or lower than the first threshold value in a state in which the second expansion valve is closed during cooling operation of the first indoor unit. Air conditioner.

4. The air conditioner according to claim 1, The water circuit further includes at least one second indoor unit having a water heat exchanger and a flow rate regulating valve, and a pump that circulates water to be subjected to heat exchange with the refrigerant between the water-refrigerant heat exchanger and the second indoor unit, The control device further controls the flow rate adjustment valve. The control device closes the flow rate adjustment valve of the second indoor unit that is stopped, and when the detection value of the low pressure sensor is equal to or lower than the first threshold value in a state in which the second expansion valve is closed during cooling operation of the first indoor unit, starts the first low pressure protection control, and when the detection value of the low pressure sensor is equal to or lower than the first threshold value after a predetermined time has elapsed, executes second low pressure protection control which is a process of opening the flow rate adjustment valve connected to the relay unit for which the first low pressure protection control was executed. Air conditioner.

5. The air conditioner according to claim 1, a water circuit including at least one second indoor unit having a water heat exchanger and a flow rate regulating valve, and a pump that circulates water to be subjected to heat exchange with the refrigerant between the water-refrigerant heat exchanger and the second indoor unit; a water temperature sensor for detecting the temperature of water flowing through the water circuit; Further equipped with The control device further controls the flow rate adjustment valve. The control device closes the flow rate adjustment valve of the second indoor unit that is stopped, and when the detection value of the low pressure sensor is equal to or less than the first threshold value in a state in which the second expansion valve is closed during cooling operation of the first indoor unit, starts the first low pressure protection control, and when the detection value of the water temperature sensor is equal to or less than the second threshold value after a predetermined time has elapsed, executes second low pressure protection control which is a process of opening the flow rate adjustment valve connected to the relay unit for which the first low pressure protection control has been executed. Air conditioner.

6. The air conditioner according to claim 4 or 5, The air conditioner has a plurality of the second indoor units, The second indoor units each have a room temperature sensor and are connected in parallel to the relay unit. In the second low pressure protection control, the control device opens the flow rate adjustment valves in order from the second indoor unit having the highest detection value of the room temperature sensor among the second indoor units connected to the relay unit in which the first low pressure protection control is executed. Air conditioner.

7. The air conditioner according to claim 6, The second indoor unit further includes a human presence sensor that detects the presence of a person in the room, In the second low pressure protection control, the control device opens the flow rate adjustment valve of the second indoor unit in which the presence of a person is not detected by the human presence sensor, in priority to the detection value of the room temperature sensor, among the second indoor units connected to the relay unit in which the first low pressure protection control is executed. Air conditioner.

8. The air conditioner according to claim 6, The control device executes a third low pressure protection control, which is a process of opening the first expansion valve of the first indoor unit that is not operating, when the detection value of the low pressure sensor after a predetermined time has elapsed since starting the second low pressure protection control for all the flow rate adjustment valves connected to the relay unit is equal to or lower than the first threshold value. Air conditioner.

9. The air conditioner according to claim 8, The air conditioner has a plurality of the first indoor units, The first indoor units each have a room temperature sensor and are connected in parallel to the outdoor unit; The control device, in the third low pressure protection control, opens the first expansion valve of the first indoor unit having the highest detection value of the room temperature sensor among the first indoor units that are stopped. Air conditioner.

10. The air conditioner according to claim 9, The first indoor unit further includes a human presence sensor that detects the presence of a person in the room, In the third low pressure protection control, the control device opens the first expansion valve of the first indoor unit in which the presence of a person is not detected by the human presence sensor, in priority to the detection value of the room temperature sensor among the first indoor units that are stopped. Air conditioner.

Images