JP2019138499A - Air conditioning apparatus - Google Patents

Abstract

To provide an air conditioning apparatus in which a compression mechanism section of a compressor is not poorly lubricated even when outside air temperature is low in a small capacity ratio.SOLUTION: When a capacity ratio D is a threshold capacity ratio Dt or less and an outside air temperature To is a threshold outside air temperature Tot or less, a CPU 210 takes in delivery pressure Pd and suction pressure Ps and calculates a pressure difference ΔP by subtracting the taken in suction pressure Ps from the taken in delivery pressure Pd. When the pressure difference ΔP is a first pressure difference P1 and more and less than a second pressure difference P2, the CPU 210 maintains a present compressor rotation speed Rc. When the pressure difference ΔP is less than the first pressure difference P1, the CPU 210 obtains rotation speed by adding additional rotation speed ΔRc to capacity-proportionate rotation speed Rcp. When the capacity ratio D is less than the threshold capacity ratio Dt, or taken in outside air temperature To is more than threshold outside air temperature Tot, or the pressure difference ΔP is the second pressure difference P2, the CPU 210 sets the compressor rotation speed Rc as the capacity-proportionate rotation speed Rcp.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an air conditioner, and more particularly to control of a compressor when performing a cooling operation at a low outside air temperature.

  Conventionally, in an air conditioner in which a plurality of indoor units are connected to one outdoor unit by refrigerant piping and all the indoor units perform cooling operation or heating operation simultaneously, the cooling capacity or heating capacity required for each indoor unit In response to this, the rotational speed of the compressor is determined. For example, in Patent Document 1, during the heating operation, the rotation speed of the compressor is set so that the target high pressure is determined in advance according to the outside air temperature, the length of the refrigerant pipe, and the heating capacity required for each indoor unit. An air conditioner that controls the air is described.

Japanese Patent Laid-Open No. 4-187930

  By the way, all the indoor units of the air conditioner as described above may be arranged in a room such as a server room where it is necessary to perform a cooling operation throughout the year. When such an air conditioner performs a cooling operation in winter, the following problems occur when the outside air temperature is low (for example, −5 ° C. or lower) and the number of indoor units performing the cooling operation is small. There is a fear.

  When the outside air temperature is low, the condensing capacity exhibited by the outdoor heat exchanger that functions as a condenser during the cooling operation is greater than when the outside air temperature is high. As the condensing capacity increases, the refrigerant pressure on the high pressure side in the refrigerant circuit decreases and the pressure difference from the refrigerant pressure on the low pressure side in the refrigerant circuit decreases. As the pressure difference becomes smaller, the amount of refrigerant circulating in the refrigerant circuit decreases, so the amount of refrigerant drawn into the compressor also decreases. And if the refrigerant | coolant amount suck | inhaled by the compressor reduces, the refrigerant | coolant pressure of the high voltage | pressure side in a refrigerant circuit will become still lower.

  In addition, when the number of indoor units that perform cooling operation is small in a situation where the refrigerant pressure on the high pressure side is low due to low outside air temperature, compared to the case where there are many indoor units that perform cooling operation, A small amount of refrigerant is required in an indoor unit that performs cooling operation. For this reason, since the rotation speed of a compressor is made low and the refrigerant | coolant circulation amount in a refrigerant circuit decreases, the refrigerant | coolant pressure of the high voltage | pressure side in a refrigerant circuit becomes still lower.

  As described above, when the number of indoor units that perform cooling operation in an environment where the outside air temperature is low is smaller in the refrigerant circuit than when the outside air temperature is high or the number of indoor units that perform cooling operation is large. By reducing the refrigerant pressure on the high pressure side, the pressure difference between the refrigerant pressure on the high pressure side and the refrigerant pressure on the low pressure side becomes small.

  When the compressor is a high-pressure vessel type compressor, the lower part of the closed container of the compressor storing refrigeration oil communicates with the high-pressure side of the refrigerant circuit, and the compressor's compression mechanism is the refrigerant circuit. It communicates with the low pressure side. Therefore, if the pressure difference between the high-pressure side refrigerant pressure and the low-pressure side refrigerant pressure becomes small, the pressure difference between the pressure in the lower part of the hermetic container of the compressor and the pressure in the compression mechanism part also becomes small. The compressor uses a pressure difference between the pressure in the lower part of the sealed container and the pressure in the compression mechanism part to supply the refrigeration oil from the lower part of the sealed container to the compression mechanism part. In some cases, if the above-described pressure difference is small, a sufficient amount of refrigeration oil for lubricating the compression mechanism portion of the compressor cannot be sucked from the lower part of the sealed container to the compression mechanism portion, and the compression mechanism portion of the compressor There was a risk of poor lubrication and wear and seizure of the compression mechanism.

  The present invention solves the above-described problems, and provides an air conditioner in which a compression mechanism portion of a compressor does not cause poor lubrication even when a small number of indoor units are cooled at a low outside air temperature. The purpose is to do.

  In order to solve the above problems, an air conditioner according to the present invention includes a compressor, an outdoor heat exchanger, an outside air temperature detecting means for detecting the outside air temperature, a discharge pressure detecting means for detecting the discharge pressure of the compressor, and the compressor. An outdoor unit having a suction pressure detecting means for detecting the suction pressure of the plurality of indoor units, a plurality of indoor units having an indoor heat exchanger, and a control means for controlling drive of the compressor. The control means causes the outdoor heat exchanger to function as a condenser, and when performing a cooling operation in which each indoor heat exchanger functions as an evaporator, the outside air temperature detected by the outside air temperature detecting means is a predetermined threshold outside air temperature. In the following cases, based on either the discharge pressure detected by the discharge pressure detection means or the pressure difference obtained by subtracting the suction pressure detected by the suction pressure detection means from the discharge pressure, Determine the number of revolutions.

  When the outside air temperature is equal to or lower than the threshold outside air temperature, the air conditioning apparatus of the present invention configured as described above is based on either the discharge pressure or the pressure difference obtained by subtracting the suction pressure from the discharge pressure. Determine the compressor speed during operation. Thereby, even if it is a case where a small number of indoor units are air-cooled at low outdoor temperature, it can prevent that the compression mechanism part of a compressor becomes poor lubrication.

It is explanatory drawing of the air conditioning apparatus in embodiment of this invention, (A) is a refrigerant circuit figure, (B) is a block diagram of an outdoor unit control means. It is a rotation speed control table in the embodiment of the present invention. It is an addition rotation speed table in the embodiment of the present invention. It is a flowchart which shows the process at the time of performing control of the compressor at the time of air_conditionaing | cooling operation in embodiment of this invention. It is a rotation speed control table in other embodiment of this invention.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. As an embodiment, an air conditioner in which 40 indoor units with a rated capacity of 2 kW are connected in parallel to one outdoor unit with a rated capacity of 80 kW, and a cooling operation or a heating operation can be performed simultaneously in all the indoor units. Will be described as an example. The present invention is not limited to the following embodiments, and can be variously modified without departing from the gist of the present invention.

  As shown in FIG. 1 (A), an air conditioner 1 according to this embodiment includes one outdoor unit 2 and 40 indoor units connected to the outdoor unit 2 in parallel by a liquid pipe 8 and a gas pipe 9. 5 (only two of them are drawn in FIG. 1A). More specifically, the shutoff valve 25 of the outdoor unit 2 and the liquid pipe connection portion 53 of each indoor unit 5 are connected by the liquid pipe 8. Further, the shut-off valve 26 of the outdoor unit 2 and the gas pipe connection portion 54 of each indoor unit 5 are connected by the gas pipe 9. Thus, the outdoor unit 2 and the 40 indoor units 5 are connected by the liquid pipe 8 and the gas pipe 9, and the refrigerant circuit 10 of the air conditioning apparatus 1 is formed.

<Configuration of outdoor unit>
First, the outdoor unit 2 will be described. The outdoor unit 2 includes a compressor 21, a four-way valve 22, an outdoor heat exchanger 23, an outdoor expansion valve 24, a closing valve 25 to which the liquid pipe 8 is connected, and a closing valve 26 to which the gas pipe 9 is connected. And an accumulator 27, an outdoor fan 28, and an outdoor unit control means 200. Then, these devices other than the outdoor fan 28 and the outdoor unit control means 200 are connected to each other through refrigerant pipes described in detail below to form an outdoor unit refrigerant circuit 20 that forms a part of the refrigerant circuit 10. Yes.

  The compressor 21 is a high-pressure vessel type variable-capacity compressor that can vary the operation capacity by being driven by a motor (not shown) whose rotation speed is controlled by an inverter. The refrigerant discharge side of the compressor 21 is connected to a port a of a four-way valve 22 to be described later and a discharge pipe 41, and the refrigerant suction side of the compressor 21 is connected to the refrigerant outflow side of the accumulator 27 and a suction pipe 42. Has been.

  Refrigerating machine oil that is supplied to a compression mechanism unit (not shown) disposed above the closed container of the compressor 21 and maintains the lubricity of the compression mechanism unit is retained in the lower part of the sealed container (not shown) of the compressor 21. Yes. The refrigerating machine oil is supplied from the lower part of the sealed container to the compression mechanism part due to the pressure difference between the pressure in the lower part of the sealed container of the compressor 21 and the pressure of the compression mechanism part. The lower part of the hermetic container of the compressor 21 is the refrigerant discharge side described above, and communicates with the high pressure side of the refrigerant circuit 10 via the discharge pipe 41. Further, the compression mechanism portion of the compressor 21 is the refrigerant suction side described above, and communicates with the low pressure side of the refrigerant circuit 10 via the suction pipe 42.

  The four-way valve 22 is a valve for switching the flow direction of the refrigerant in the refrigerant circuit 10 and includes four ports a, b, c, and d. The port a is connected to the refrigerant discharge side of the compressor 21 by the discharge pipe 41 as described above. The port b is connected to one refrigerant inlet / outlet of the outdoor heat exchanger 23 by a refrigerant pipe 43. The port c is connected to the refrigerant inflow side of the accumulator 27 by a refrigerant pipe 46. The port d is connected to the closing valve 26 by an outdoor unit gas pipe 45.

  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 28 described later. As described above, one refrigerant inlet / outlet of the outdoor heat exchanger 23 and the port b of the four-way valve 22 are connected by the refrigerant pipe 43. The other refrigerant inlet / outlet of the outdoor heat exchanger 23 and the closing valve 25 are connected by an outdoor unit liquid pipe 44. The outdoor heat exchanger 23 functions as a condenser when the air conditioner 1 performs a cooling operation, and functions as an evaporator when the air conditioner 1 performs a heating operation.

  The outdoor expansion valve 24 is provided in the outdoor unit liquid pipe 44. The outdoor expansion valve 24 is an electronic expansion valve driven by a pulse motor (not shown), and the amount of refrigerant flowing into the outdoor heat exchanger 23 or the outdoor volume is adjusted by adjusting the opening degree according to the number of pulses applied to the pulse motor. The amount of refrigerant flowing out of the heat exchanger 23 is adjusted. The opening degree of the outdoor expansion valve 24 is adjusted according to the discharge temperature of the compressor 21 detected by a discharge temperature sensor 33 (described later) when the air-conditioning apparatus 1 is performing a heating operation. When the operation is performed, the opening is fully opened.

  As described above, the accumulator 27 has the refrigerant inflow side connected to the port c of the four-way valve 22 and the refrigerant pipe 46, and the refrigerant outflow side connected to the refrigerant intake side of the compressor 21 and the intake pipe 42. The accumulator 27 separates the refrigerant flowing into the accumulator 28 from the refrigerant pipe 46 into a gas refrigerant and a liquid refrigerant, and causes the compressor 21 to suck only the gas refrigerant.

  The outdoor fan 28 is formed of a resin material and is disposed in the vicinity of the outdoor heat exchanger 23. The outdoor fan 28 is rotated by a fan motor (not shown) to take outside air into the interior of the outdoor unit 2 from a suction port (not shown), and the outdoor air heat exchanged with the refrigerant in the outdoor heat exchanger 23 is sent from an outlet (not shown) to the outdoor unit. 2 to the outside.

  In addition to the configuration described above, the outdoor unit 2 is provided with various sensors. As shown in FIG. 1, a discharge pressure sensor 31 that detects a discharge pressure that is a pressure of refrigerant discharged from the compressor 21 and a discharge that detects the temperature of refrigerant discharged from the compressor 21 are disposed in the discharge pipe 41. A temperature sensor 33 is provided. Near the refrigerant inlet of the accumulator 28 in the refrigerant pipe 46, a suction pressure sensor 32 that detects a suction pressure that is a pressure of the refrigerant sucked into the compressor 21, and a temperature of the refrigerant sucked into the compressor 21 are detected. A suction temperature sensor 34 is provided. The discharge pressure sensor 31 is the discharge pressure detection means of the present invention, and the suction pressure sensor 32 is the suction pressure detection means of the present invention.

  Between the outdoor heat exchanger 23 and the outdoor expansion valve 24 in the outdoor unit liquid pipe 44, the temperature of the refrigerant flowing into the outdoor heat exchanger 23 or the temperature of the refrigerant flowing out of the outdoor heat exchanger 23 is detected. A heat exchanger temperature sensor 35 is provided. An outdoor air temperature sensor 36 that detects the temperature of the outside air that flows into the outdoor unit 2, that is, the outside air temperature, is provided near the suction port (not shown) of the outdoor unit 2. The outside temperature sensor 36 is the outside temperature detecting means of the present invention.

  Further, the outdoor unit 2 is provided with an outdoor unit control means 200 which is a control means of the present invention. The outdoor unit control means 200 is mounted on a control board stored in an electrical component box (not shown) of the outdoor unit 2, and as shown in FIG. 1B, a CPU 210, a storage unit 220, a communication unit 230, The sensor input unit 240 is provided.

  The storage unit 220 includes, for example, a flash memory. The storage unit 220 transmits a detection value corresponding to a control program of the outdoor unit 2 and detection signals from various sensors, driving states of the compressor 21 and the outdoor fan 28, and transmission from each indoor unit 5. Operation information (including operation / stop information, operation modes such as cooling / heating), the rated capacity of the outdoor unit 2 and the rated capacity of each indoor unit 5 are stored. The communication unit 230 is an interface that performs communication with each indoor unit 5. The sensor input unit 240 captures detection results from various sensors of the outdoor unit 2 and outputs them to the CPU 210.

  The CPU 210 fetches the detection values of various sensors periodically (for example, every 30 seconds) via the sensor input unit 240, and a signal including operation information transmitted from each indoor unit 5 is transmitted via the communication unit 230. Entered. The CPU 210 adjusts the opening degree of the outdoor expansion valve 24 and controls the drive of the compressor 21 and the outdoor fan 28 based on the various pieces of input information.

<Configuration of each indoor unit>
Next, 40 indoor units 5 will be described. All 40 indoor units 5 have the same configuration, and include an indoor heat exchanger 51, an indoor expansion valve 52, a liquid pipe connection part 53, a gas pipe connection part 54, and an indoor fan 55. Yes. These constituent devices other than the indoor fan 55 are connected to each other through refrigerant pipes described in detail below to constitute an indoor unit refrigerant circuit 50 that forms part of the refrigerant circuit 10.

  In addition, as mentioned above, in this embodiment, 40 indoor units 5 are connected to the outdoor unit 2 and the rated capacity of each indoor unit 5 is set to the same rated capacity: 2 kW. The rated capacity of the indoor unit 5 may be different, and the total value of the rated capacity of the indoor unit 5 does not have to exceed the rated capacity of the outdoor unit 2.

  The indoor heat exchanger 51 exchanges heat between the refrigerant and the indoor air taken into the indoor unit 5 from a suction port (not shown) by rotation of an indoor fan 55 described later. One refrigerant inlet / outlet of the indoor heat exchanger 51 and the liquid pipe connecting portion 53 are connected by an indoor unit liquid pipe 71, and the other refrigerant inlet / outlet and the gas pipe connecting portion 54 a are connected by an indoor unit gas pipe 72. The indoor heat exchanger 51 functions as an evaporator when the air conditioner 1 performs a cooling operation, and functions as a condenser when the air conditioner 1 performs a heating operation. Note that the refrigerant pipes of the liquid pipe connection part 53 and the gas pipe connection part 54 are connected by welding, flare nuts, or the like.

  The indoor expansion valve 52 is provided in the indoor unit liquid pipe 71. The indoor expansion valve 52 is an electronic expansion valve, and when the indoor heat exchanger 51 functions as an evaporator, that is, when the indoor unit 5 performs a cooling operation, the opening degree of the indoor expansion valve 52 depends on the refrigerant outlet (gas The refrigerant superheat degree at the pipe connecting portion 54 side) is adjusted so as to become the target refrigerant superheat degree. Further, when the indoor heat exchanger 51 functions as a condenser, that is, when the indoor unit 5 performs the heating operation, the opening of the indoor expansion valve 52 is the refrigerant outlet (liquid pipe connection portion) of the indoor heat exchanger 51. (53 side) is adjusted so that the refrigerant subcooling degree becomes the target refrigerant subcooling degree. Here, the target refrigerant superheat degree and the target refrigerant subcool degree are the refrigerant superheat degree and the refrigerant subcool degree necessary for the indoor unit 5 to exhibit sufficient cooling capacity or heating capacity.

  The indoor fan 55 is formed of a resin material and is disposed in the vicinity of the indoor heat exchanger 51. The indoor fan 55 is rotated by a fan motor (not shown) to take indoor air from the suction port (not shown) into the indoor unit 5, and the indoor air exchanged with the refrigerant in the indoor heat exchanger 51 from the blower outlet (not shown). Release into the room.

  In addition to the configuration described above, the indoor unit 5 is provided with various sensors. Between the indoor heat exchanger 51 and the indoor expansion valve 52 in the indoor unit liquid pipe 71, there is a liquid side temperature sensor 61 that detects the temperature of the refrigerant flowing into or out of the indoor heat exchanger 51. Is provided. The indoor unit gas pipe 72 is provided with a gas side temperature sensor 62 that detects the temperature of the refrigerant flowing out of the indoor heat exchanger 51 or flowing into the indoor heat exchanger 51. A suction temperature sensor 63 that detects the temperature of indoor air flowing into the indoor unit 5, that is, the suction temperature, is provided near the suction port (not shown) of the indoor unit 5.

<Operation of refrigerant circuit>
Next, the flow of the refrigerant and the operation of each part in the refrigerant circuit 10 during the air conditioning operation of the air-conditioning apparatus 1 in the present embodiment will be described with reference to FIG. In addition, in the following description, the case where the air conditioning apparatus 1 performs a cooling operation will be described, and the detailed description of the case where a heating operation is performed will be omitted. Moreover, the arrow in FIG. 1 has shown the flow of the refrigerant | coolant at the time of air_conditionaing | cooling operation.

  As shown in FIG. 1, when the air-conditioning apparatus 1 performs a cooling operation, the four-way valve 22 is in a state indicated by a solid line, that is, the port a and the port b of the four-way valve 22 communicate with each other, and the port c And the port d are switched to communicate with each other. Thereby, the refrigerant circuit 10 becomes a cooling cycle in which each indoor heat exchanger 51 functions as an evaporator and the outdoor heat exchanger 23 functions as a condenser.

  When the compressor 21 is driven in the state of the refrigerant circuit 10 as described above, the refrigerant discharged from the compressor 21 flows through the discharge pipe 41 and flows into the four-way valve 22, and from the four-way valve 22 through the refrigerant pipe 43. It flows into the outdoor heat exchanger 23.

  The refrigerant flowing into the outdoor heat exchanger 23 is condensed by exchanging heat with the outside air taken into the outdoor unit 2 by the rotation of the outdoor fan 28. The refrigerant that has flowed out of the outdoor heat exchanger 23 into the outdoor unit liquid pipe 44 passes through the outdoor expansion valve 24 whose opening is fully opened, and flows out into the liquid pipe 8 through the closing valve 25.

  The refrigerant flowing through the liquid pipe 8 is divided into each indoor unit 5 through the liquid pipe connection portion 53. The refrigerant that has flowed into each indoor unit 5 flows through each indoor unit liquid pipe 71, and each indoor unit whose opening degree is adjusted so that the refrigerant superheat degree at each refrigerant outlet of the indoor heat exchanger 51 becomes the target refrigerant superheat degree. When passing through the expansion valve 52, the pressure is reduced.

  The refrigerant flowing into each indoor heat exchanger 51 from each indoor unit liquid pipe 71 evaporates by exchanging heat with the indoor air taken into each indoor unit 5 by the rotation of each indoor fan 55. Thus, each indoor heat exchanger 51 functions as an evaporator, and the indoor air cooled by performing heat exchange with the refrigerant in each indoor heat exchanger 51 is blown into the room from a blower outlet (not shown). Cooling of the room in which 40 indoor units 5 are installed is performed.

  The refrigerant that has flowed out from each indoor heat exchanger 51 to each indoor unit gas pipe 72 flows out to the gas pipe 9 via each gas pipe connecting portion 54. The refrigerant that merges in the gas pipe 9 and flows into the outdoor unit 2 through the closing valve 25 flows in the order of the outdoor unit gas pipe 45, the four-way valve 22, the refrigerant pipe 46, the accumulator 27, and the suction pipe 42, and is sucked into the compressor 21. And compressed again.

  When the air conditioner 1 performs the heating operation, the four-way valve 22 is in a state indicated by a broken line, that is, the port a and the port d of the four-way valve 22 communicate with each other, and the port b and the port c communicate with each other. Can be switched. Thereby, the refrigerant circuit 10 becomes a heating cycle in which each indoor heat exchanger 51 functions as a condenser and the outdoor heat exchanger 23 functions as an evaporator.

<About compressor speed control>
Next, referring to FIGS. 1 to 4, when the air conditioner 1 according to the present embodiment is installed in a room where all 40 indoor units 5 need to perform cooling operation throughout the year, such as a server room. The rotation speed control of the compressor 21 will be described.

  When the air-conditioning apparatus 1 of the present embodiment is installed as described above and performs a cooling operation throughout the year, the outside air temperature is equal to or lower than a predetermined outside air temperature (hereinafter referred to as a threshold outside air temperature), and 10 units. When the number of indoor units performing the cooling operation is small, there is a possibility that the problems described below may occur.

  When the outside air temperature is low, the condensing capacity exhibited by the outdoor heat exchanger 23 that functions as a condenser during cooling operation is greater than when the outside air temperature is high. As the condensing capacity increases, the refrigerant pressure on the high pressure side in the refrigerant circuit 10 decreases, and the pressure difference from the refrigerant pressure on the low pressure side in the refrigerant circuit 10 decreases. When the pressure difference becomes small, the refrigerant circulation amount in the refrigerant circuit 10 decreases, so the refrigerant amount sucked into the compressor 21 also decreases. And if the refrigerant | coolant amount suck | inhaled by the compressor 21 reduces, the refrigerant | coolant pressure of the high voltage | pressure side in the refrigerant circuit 10 will become still lower.

  Further, in a situation where the refrigerant pressure on the high pressure side is low due to the low outside air temperature, the number of indoor units 5 performing the cooling operation is smaller than the number of indoor units 5 performing the cooling operation. Thus, the amount of refrigerant required in the indoor unit 5 that performs the cooling operation is small. For this reason, since the rotation speed of the compressor 21 is lowered and the refrigerant circulation amount in the refrigerant circuit 10 is reduced, the refrigerant pressure on the high pressure side in the refrigerant circuit is further reduced.

  As described above, when the number of indoor units 5 that perform the cooling operation in an environment where the outside air temperature is low is smaller than the case where the outside air temperature is high or the number of the indoor units 5 that perform the cooling operation is large, the refrigerant By reducing the refrigerant pressure on the high pressure side in the circuit 10, the pressure difference between the refrigerant pressure on the high pressure side and the refrigerant pressure on the low pressure side becomes small.

  As described above, the compressor 21 is of a high-pressure container type, and the refrigerating machine oil is transferred from the lower part of the sealed container to the compression mechanism part using the pressure difference between the pressure at the lower part of the sealed container and the pressure of the compression mechanism part. The so-called differential pressure oil supply type. And the lower part of the airtight container of the compressor 21 that stores the refrigerating machine oil communicates with the high pressure side of the refrigerant circuit 10, and the compression mechanism portion of the compressor 21 communicates with the low pressure side of the refrigerant circuit 10. . Therefore, if the pressure difference between the refrigerant pressure on the high pressure side and the refrigerant pressure on the low pressure side becomes small, the pressure difference between the pressure in the lower part of the hermetic container of the compressor 21 and the pressure in the compression mechanism part also becomes small. A sufficient amount of refrigerating machine oil for lubricating the compression mechanism portion cannot be sucked from the lower part of the closed container to the compression mechanism portion, and the compression mechanism portion of the compressor 21 becomes poorly lubricated, and the compression mechanism portion is worn or seized. May occur.

  Therefore, in the air conditioner 1 of the present embodiment, when the outside air temperature is equal to or lower than the threshold outside air temperature during the cooling operation and the number of indoor units 5 performing the cooling operation is small, the rotation shown in FIG. 2 described below is performed. The rotational speed control of the compressor 21 is performed based on the number control table 200 and the additional rotational speed table 300 shown in FIG.

  In the following description, first, the rotation speed control table 200 and the addition rotation speed table 300 will be described with reference to FIGS. 2 and 3, and then the compressor during cooling operation will be described with reference to the respective tables with reference to FIG. 4. Processing performed by the CPU 210 of the outdoor unit control means 200 when controlling the number of rotations 21 will be described.

  In the following description, the outside air temperature is To and the threshold outside temperature is Tot. Here, the threshold outside air temperature Tot is determined in advance by performing a test or the like and stored in the storage unit 220. The air conditioner 1 is cooled in an environment where the outside air temperature To is equal to or lower than the threshold outside air temperature Tot. When the operation is performed, the pressure difference between the refrigerant pressure on the high pressure side in the refrigerant circuit 10 and the pressure difference between the refrigerant pressure on the low pressure side in the refrigerant circuit 10 and the pressure in the lower part of the hermetic container of the compressor 21 and the compression mechanism are reduced. There is a possibility that the pressure difference from the pressure of the part becomes small, resulting in poor lubrication of the compression mechanism part. As an example, the threshold outside air temperature is Tot of −5 ° C.

  Also, the outdoor unit rated capacity of the outdoor unit 2 is Ao, the rated capacity of each indoor unit 5 is Ai, and the indoor unit 5 is performing an air-cooling operation. Ar is the cooling capacity required by the above, D is the capacity ratio obtained by dividing the total value of the indoor unit rated capacity Ai of the indoor units performing the cooling operation by the outdoor unit rated capacity Ao, and the threshold capacity ratio is Dt.

  Here, the capacity ratio D simply represents the number of indoor units 5 performing the cooling operation. That is, if the capacity ratio D is a large value, the total value of the indoor unit rated capacity Ai of the indoor units that are performing the cooling operation is large, that is, the number of indoor units 5 that are performing the cooling operation is large. When the capacity ratio D is a small value, it indicates that the total value of the indoor unit rated capacities Ai of the indoor units that are performing the cooling operation is small, that is, the number of indoor units 5 that are performing the cooling operation is small.

  The threshold capacity ratio Dt is obtained in advance through a test or the like and stored in the storage unit 220, and the indoor unit performing the cooling operation in which the above-described capacity ratio D is equal to or less than the threshold capacity ratio Dt. If the number is 5, the pressure difference between the pressure of the lower part of the sealed container of the compressor 21 and the pressure of the compression mechanism portion becomes small, and it is found that the possibility of poor lubrication of the compression mechanism portion increases. It is what. As an example, the threshold capacity ratio Dt is when the number of indoor units 5 performing the cooling operation is two, that is, when the total value of the indoor unit rated capacities Ai of the indoor units 5 performing the cooling operation is 4 kW. The capacity ratio Dt = 4 kW / 80 kW = 0.05.

  Further, the discharge pressure of the compressor 21 detected by the discharge pressure sensor 31 (corresponding to the refrigerant pressure on the high pressure side of the refrigerant circuit 10) is Pd, and the suction pressure of the compressor 21 detected by the suction pressure sensor 32 (the low pressure of the refrigerant circuit 10). Is equivalent to the refrigerant pressure on the side) Ps, the suction pressure lower limit, which is the lower limit on the performance of the suction pressure Ps, Psmin, the threshold suction pressure of the suction pressure Ps is Pst, and the pressure difference between the discharge pressure Pd and the suction pressure Ps ( Pd−Ps) is ΔP, the first pressure difference among the pressure differences ΔP is P1, and the second pressure difference of the pressure difference ΔP is P2 (where P1 <P2). Each of the first pressure difference P1 and the second pressure difference P2 will be described in detail later.

  Further, the rotation speed of the compressor 21 is Rc, the rotation speed corresponding to the capacity, which is the rotation speed of the compressor 21 required to exhibit the cooling required capacity Ar, is Rcp, the outside air temperature To is less than the threshold outside air temperature Tot, and the capacity ratio D Is the threshold speed ratio Dt or less, the starting rotational speed of the compressor 21 is Rct, the additional rotational speed added to the rotational speed Rc of the compressor 21 is ΔRc, the first additional rotational speed is Rc1, and the second additional rotational speed is Let Rc2 (where Rc1 <Rc2). Here, the starting rotation speed Rct is obtained in advance through a test or the like and stored in the storage unit 220 of the outdoor unit control means 200. If the compressor 21 is started at the starting rotation speed Rct, The rotation speed has been found to cause no lubrication failure in the compressor 21. As an example, the starting rotational speed Rct is 30 rps. Each of the first addition rotation speed Rc1 and the second addition rotation speed Rc2 will be described in detail later.

<Rotation speed control table>
The rotation speed control table 200 shown in FIG. 2 is determined in advance by testing and stored in the storage unit 220 of the outdoor unit control means 200. In the rotation speed control table 200, the threshold outside air temperature Tot of the one outside air temperature To is −5 ° C., the first pressure difference P1 is 0.7 MPa, and the second pressure difference P2 is 0.9 MPa.

  In the rotational speed control table 200, when the outside air temperature To is higher than −5 ° C., the compressor rotational speed Rc is set as the capacity-dependent rotational speed Rcp regardless of the pressure difference ΔP. When the outdoor air temperature To is higher than the threshold outdoor air temperature Tot when the capacity ratio D is equal to or lower than the threshold outdoor power ratio Dt, the outdoor heat that functions as a condenser is compared with the case where the outdoor air temperature To is lower than the threshold outdoor air temperature Tot. Since the condensation capacity is reduced by the exchanger 23 and the condensation pressure is increased, the pressure difference ΔP is not reduced even if the rotation speed of the compressor 21 is reduced. Therefore, in the rotation speed control table 200, when the outside air temperature To is higher than the threshold outside air temperature Tot, the pressure difference ΔP can be secured regardless of the rotation speed of the compressor Rc, that is, the compression mechanism. Assuming that a sufficient pressure difference between the pressure of the lower part of the closed container of the compressor 21 and the pressure of the compression mechanism can be secured, a sufficient amount of refrigeration oil can be supplied to the compressor. It is said.

  On the other hand, when the outside air temperature To is −5 ° C. or lower, the compressor rotational speed Rc when the pressure difference ΔP is less than 0.7 MPa is determined in an additional rotational speed table 300 described later as the capacity-dependent rotational speed Rcp. The added number of rotations ΔRc is the added number of rotations. Further, the compressor rotation speed Rc when the pressure difference ΔP is 0.7 MPa or more and less than 0.9 MPa is maintained at the current compressor rotation speed Rc. Further, the compressor rotation speed Rc when the pressure difference ΔP is 0.9 MPa or more is set as the capacity-related rotation speed Rcp.

  When the capacity ratio D is equal to or less than the threshold capacity ratio Dt and the outside air temperature To is equal to or less than the threshold outside air temperature Tot, the condensing capacity is increased and the condensing pressure is decreased in the outdoor heat exchanger 23 functioning as a condenser. The pressure difference ΔP becomes smaller. At this time, if the rotation speed of the compressor 21 is lowered to reduce the refrigerant circulation amount in the refrigerant circuit 10, the condensing pressure is further reduced and the pressure difference ΔP is reduced, so that the compression mechanism portion of the compressor 21 is lubricated. There is a high possibility that a sufficient amount of refrigerating machine oil cannot be supplied to the compression mechanism. Therefore, in the rotation speed control table 200, the compressor rotation speed Rc is determined according to the pressure difference ΔP. When the pressure difference ΔP is less than the first pressure difference P1 (= 0.7 MPa), the pressure difference ΔP is set. In order to increase the compressor speed, the compressor speed Rc is set to a speed obtained by adding the additional speed ΔRc to the speed Rcp corresponding to the capacity. When the pressure difference ΔP is not less than the first pressure difference P1 and less than the second pressure difference P2 (= 0.9 MPa), the compressor rotation is performed so that the pressure difference ΔP does not decrease and become less than the first pressure difference P1. The number Rc is maintained at the current compressor speed Rc. If the pressure difference ΔP is equal to or greater than the second pressure difference P2, it is unlikely that the pressure difference ΔP will decrease and become less than the first pressure difference even if the compressor rotational speed Rc is increased. The number Rc is the rotation speed Rcp corresponding to the capacity.

<Rotation speed addition table>
The addition rotation speed table 300 shown in FIG. 3 is determined in advance by testing and stored in the storage unit 220 of the outdoor unit control means 200. In this additional rotational speed table 300, for example, the suction pressure lower limit Psmin is 0.2 MPa, the threshold suction pressure Pst is 0.5 MPa, the first additional rotational speed Rc1 is 5 rps, and the second additional rotational speed Rc2 is 8 rps.

  As described above, when the outside air temperature To is equal to or lower than the threshold outside air temperature Tot and the capacity ratio D is equal to or less than the threshold capacity ratio Dt when the air-conditioning apparatus 1 performs the cooling operation, the rotation speed control table 200 is set. Use to control the compressor speed Rc. In the rotational speed control table 200, the compressor rotational speed Rc when the outdoor air temperature To is the threshold outdoor air temperature Tot and the pressure difference ΔP is less than 0.7 MPa is added to the current compressor rotational speed Rc. The rotation speed is obtained by adding ΔRc.

  As described above, when the compressor rotational speed Rc is increased by adding the additional rotational speed ΔRc, if the suction pressure Ps is low and close to the suction pressure lower limit value Psmin, the additional rotational speed ΔRc is a large value. If so, the suction pressure Ps may fall below the suction pressure lower limit value Psmin. Therefore, in the air conditioning apparatus 1 of the present embodiment, when the compressor rotation speed Rc is controlled using the rotation speed control table 200, the suction pressure Ps detected by the suction pressure sensor 51 is used to add the rotation speed table. The addition rotational speed ΔRc corresponding to the suction pressure Ps detected with reference to 300 is determined.

  Specifically, in the addition rotation speed table 300, when the suction pressure Ps is equal to or higher than the threshold suction pressure Pst (= 0.5 MPa), that is, when the suction pressure Ps is decreased due to an increase in the compressor speed Rc, the suction is performed. When the possibility of falling below the pressure lower limit value Psmin is low, the additional rotational speed ΔRc is set to the second additional rotational speed (= 8 rps). On the other hand, when the suction pressure Ps is 0.2 MPa or more and less than 0.5 MPa, that is, when the suction pressure Ps is likely to fall below the suction pressure lower limit value Psmin when the suction pressure Ps decreases due to an increase in the compressor rotational speed Rc, The addition rotation speed ΔRc is set to a first addition rotation speed (= 5 rps) lower than the second addition rotation speed.

<Processing flow related to compressor speed control during cooling operation>
Next, the flow of processing related to the rotational speed control of the compressor 21 when the air-conditioning apparatus 1 performs the cooling operation will be described with reference to FIG. FIG. 4 is a flowchart showing processing performed by the CPU 210 of the outdoor unit control means 200 in the rotational speed control of the compressor 21 during the cooling operation. In FIG. 4, ST represents a process step, and the number following this represents a step number. Note that FIG. 4 refers only to processing related to the present invention, and description and description of processing related to other controls such as control of the air conditioner 1 during heating operation are omitted.

  When the air conditioning apparatus 1 performs the cooling operation, the CPU 210 takes in the indoor unit rated capacity Ai and the cooling required capacity Ar requested by the user from the indoor unit 5 performing the cooling operation via the communication unit 230 ( ST1). As for the indoor unit rated capacity Ai, the CPU 210 previously takes in the indoor unit rated capacity Ai of all the indoor units 5 through the communication unit, stores it in the storage unit 220, and performs the cooling operation. The indoor unit rated capacity Ai corresponding to 5 may be read from the storage unit 220.

  Next, the CPU 210 reads out the outdoor unit rated capacity Ao of the outdoor unit 2 stored in advance in the storage unit 220 (ST2).

  Next, the CPU 210 determines the rotation speed Rcp corresponding to the capacity using the cooling required capacity Ar taken in ST1 (ST3). Although illustration is omitted, the storage unit 220 stores a table in which the rotation speed Rcp corresponding to the capacity is determined in correspondence with the cooling required capacity Ar, and the CPU 210 refers to this table and takes in the cooling required capacity Ar Rotational speed Rcp corresponding to the capability is determined.

  Next, the CPU 210 starts up the compressor 21 at the starting rotation speed Rct stored in the storage unit 220 (ST4). As described above, the starting rotational speed Rct is obtained in advance through a test or the like and stored in the storage unit 220 of the outdoor unit control means 200, and the compressor 21 is started at the starting rotational speed Rct. In this case, the rotational speed is known to cause no lubrication failure in the compressor 21.

  Next, the CPU 210 determines whether or not the capability ratio D is equal to or less than the threshold capability ratio Dt (ST5). Specifically, the CPU 210 obtains the capacity ratio D by dividing the total value of the indoor unit rated capacity Ai captured in ST1 by the outdoor unit rated capacity Ao read in ST2, and stores the calculated capacity ratio D in the storage unit 220. The stored threshold ability ratio Dt is compared.

  If the capability ratio D is not less than or equal to the threshold capability ratio Dt (ST5-No), the CPU 210 advances the process to ST12. If the capacity ratio D is equal to or less than the threshold capacity ratio Dt (ST5-Yes), the CPU 210 takes in the outside air temperature To detected by the outside air temperature sensor 36 via the sensor input unit 240 (ST6), and the taken in outside air temperature To is It is determined whether or not the temperature is equal to or lower than the threshold outside air temperature Tot stored in the storage unit 220 (ST7).

  If the taken-in outside temperature To is not below the threshold outside temperature Tot (ST7-No), the CPU 210 advances the process to ST12. If the taken-in outside air temperature To is equal to or lower than the threshold outside air temperature Tot (ST7-Yes), the CPU 210 inputs the discharge pressure Pd detected by the discharge pressure sensor 31 and the suction pressure Ps detected by the suction pressure sensor 32 from the sensor input. The pressure difference ΔP is calculated by subtracting the intake pressure Ps acquired from the discharge pressure Pd acquired (ST9).

  Next, CPU 210 determines whether or not pressure difference ΔP calculated in ST9 is less than first pressure difference P1 (ST10). If the pressure difference ΔP is not less than the first pressure difference P1 (ST10-No), the CPU 210 determines whether or not the pressure difference ΔP is greater than or equal to the first pressure difference P1 and less than the second pressure difference (ST11). The first pressure difference P1 and the second pressure difference P2 are determined in the rotation speed control table 200, respectively.

  If the pressure difference ΔP is not equal to or greater than the first pressure difference P1 and less than the second pressure difference P2 (ST11-No), that is, if the pressure difference ΔP is equal to or greater than the second pressure difference P2, the CPU 210 sets the compressor rotational speed Rc. As the speed Rcp corresponding to the capacity determined in ST3 (ST12), the process returns to ST8.

  If the pressure difference ΔP is greater than or equal to the first pressure difference P1 and less than the second pressure difference P2 in ST11 (ST11-Yes), the CPU 210 maintains the current compressor speed Rc (ST15) and returns the process to ST5. .

  In ST10, if the pressure difference ΔP is less than the first pressure difference P1 (ST10-Yes), the CPU 210 refers to the addition rotational speed table 300 stored in the storage unit 220 and sets the suction pressure Ps acquired in ST8. In response, an additional rotational speed ΔRc is determined (ST13), and the compressor rotational speed Rc is determined as the rotational speed obtained by adding ΔRc determined in the additional rotational speed ST13 to the capacity-corresponding rotational speed Rcp determined in ST3 (ST14). Return processing.

  As described above, in the air conditioner 1 of the present embodiment, when the cooling operation is performed in an environment where the outside air temperature To is equal to or lower than the threshold outside air temperature Tot and the capacity ratio D is equal to or less than the threshold capacity ratio Dt. Then, the rotation speed of the compressor 21 is controlled using the compressor rotation speed table 200 and the rotation speed addition table 300. As a result, the pressure difference ΔP is reduced and the pressure difference between the pressure at the lower part of the hermetic container of the compressor 21 and the pressure of the compression mechanism portion is reduced, whereby refrigeration oil is supplied to the compression mechanism portion inside the compressor 21. Even in a difficult state, the rotation speed of the compressor 21 is controlled so that an appropriate amount of refrigeration oil is supplied to the compression mechanism section of the compressor 21, so that the compression mechanism section of the compressor 21 is lubricated. It can be prevented from becoming defective.

  Next, a second embodiment of the present invention will be described with reference to FIG. In the present embodiment, instead of the rotation speed control table 200 in the first embodiment, the rotation speed control table 200a shown in FIG. 5 is stored in the storage unit 220 of the outdoor unit control means 200. Different from the embodiment. Except for the difference in the rotational speed control table, the configuration of the refrigerant circuit 10 and the rotational speed control of the compressor 21 during the cooling operation described with reference to FIG. 4 are the same as those in the first embodiment. Therefore, detailed description is omitted.

<Rotation speed control table>
The rotation speed control table 200a shown in FIG. 5 is determined in advance by a test and stored in the storage unit 220 of the outdoor unit control means 200. In the rotation speed control table 200a, the pressure difference ΔP in the rotation speed control table 200 of FIG. 2 described in the first embodiment is changed to the discharge pressure Pd, and the outside air temperature To is equal to or lower than the threshold outside air temperature Tot. Further, the discharge pressure Pd is divided into a first discharge pressure Pd1 and a second discharge pressure Pd2 (where Pd1 <Pd2), and the compressor speed Rc is determined according to this division.

  In the rotation speed control table 200a, as an example, the first discharge pressure Pd1 is 0.9 MPa, and the second discharge pressure Pd2 is 1.1 MPa. The first discharge pressure Pd1 and the second discharge pressure Pd2 are set to the suction pressure lower limit value Psmin that is the lower limit value of the suction pressure Ps described in the first embodiment, and the first pressure difference P1 in the rotation speed control table 200 and The first pressure difference P2 is added. Specifically, the first discharge pressure Pd1: 0.9 MPa = the suction pressure lower limit value Psmin: 0.2 MPa + the first pressure difference P1: 0.7 MPa, and the second discharge pressure Pd2: 1.1 MPa = the suction pressure lower limit value. Psmin: 0.2 MPa + second pressure difference P2: 0.9 MPa. Further, the threshold outside air temperature Tot of the outside air temperature To is −5 ° C. as in the compressor rotation speed table 200.

  In the compressor rotation speed table 200a, when the outside air temperature To is higher than −5 ° C., the compressor rotation speed Rc is set as the rotation speed Rcp corresponding to the capacity regardless of the discharge pressure Pd. When the outside air temperature To is higher than the threshold outside air temperature Tot when the capacity ratio D is equal to or less than the threshold capacity ratio Dt, the outside air temperature To is condensed compared to the case where the outside air temperature To is below the threshold outside air temperature Tot (= −5 ° C.). The outdoor heat exchanger 23 functioning as a compressor has a low condensing capacity and a high condensing pressure. Therefore, even if the rotation speed of the compressor 21 is lowered, the discharge pressure Pd does not become low, that is, the pressure difference ΔP does not become small. It is considered that a sufficient amount of refrigerating machine oil for lubricating the compression mechanism portion of the compressor 21 is supplied to the compression mechanism portion. Therefore, in the rotation speed control table 200a, when the outside air temperature To exceeds the threshold outside air temperature Tot, a sufficient amount of refrigerating machine oil can be supplied to the compression mechanism section regardless of the rotation speed of the compressor Rc. The pressure difference ΔP can be secured, that is, a sufficient amount of refrigerating machine oil can be supplied to the compression mechanism section, and the pressure difference between the pressure in the lower part of the sealed container of the compressor 21 and the pressure of the compression mechanism section can be secured. The compressor rotational speed Rc is set to a speed Rc corresponding to the capacity.

  On the other hand, when the outside air temperature To is −5 ° C. or lower, the compressor rotational speed Rc when the discharge pressure Pd is less than 0.9 MPa is added to the rotational speed Rcp corresponding to the capacity. The rotation speed is obtained by adding ΔRc. Further, the compressor rotation speed Rc when the discharge pressure Pd is 0.9 MPa or more and less than 1.1 MPa is maintained at the current compressor rotation speed Rc. Further, the compressor rotation speed Rc when the discharge pressure Pd is 1.1 MPa or more is set as the capacity-related rotation speed Rcp.

  If the outdoor air temperature To is lower than the threshold outdoor air temperature Tot when the capacity ratio is equal to or lower than the threshold capacity ratio, the outdoor heat exchanger 23 functioning as a condenser increases the condensing capacity and lowers the condensing pressure. The difference ΔP is reduced. At this time, if the rotation speed of the compressor 21 is lowered to reduce the refrigerant circulation amount in the refrigerant circuit 10, the condensing pressure is further reduced and the pressure difference ΔP is reduced, so that the compression mechanism portion of the compressor 21 is lubricated. There is a high possibility that a sufficient amount of refrigerating machine oil cannot be supplied to the compression mechanism. Therefore, in the rotation speed control table 200a, the compressor rotation speed Rc is determined according to the discharge pressure Pd. When the discharge pressure Pd is less than the first discharge pressure Pd1 (= 0.9 MPa), the pressure difference ΔP is set. In order to increase the rotational speed, the rotational speed is determined by adding the additional rotational speed ΔRc to the rotational speed Rcp corresponding to the capacity. In addition, when the discharge pressure Pd is equal to or higher than the first discharge pressure Pd1 and lower than the second discharge pressure Pd2 (= 1.1 MPa), the compressor rotational speed is set so that the pressure difference ΔP does not decrease and become less than the first pressure difference. Rc is maintained at the current compressor speed Rc. When the discharge pressure Pd is equal to or higher than the second discharge pressure Pd2, the compressor rotational speed is low because it is unlikely that the pressure difference ΔP will decrease and become less than the first pressure difference even if the compressor rotational speed Rc is increased. Rc is the rotation speed Rcp corresponding to the capacity.

  The rotational speed control of the compressor 21 when the air-conditioning apparatus 1 performs the cooling operation is performed using the rotational speed control table 200a described above and the additional rotational speed table 300 illustrated in FIG. In the present embodiment, the CPU 210 controls the rotation speed of the compressor 21 during the cooling operation. In the flowchart shown in FIG. 4 described in the first embodiment, the process of ST9 is unnecessary. At the same time, the determination of ST10 and ST11 is made with the discharge pressure Pd instead of the pressure difference ΔP. The processes other than the processes of ST9 to ST11 are the same as those described in the first embodiment as described above.

  As described above, in the air conditioner 1 of the present embodiment, when the cooling operation is performed in an environment where the outside air temperature To is equal to or lower than the threshold outside air temperature Tot and the capacity ratio D is equal to or less than the threshold capacity ratio Dt. Using the compressor rotation speed table 200a and the rotation speed addition table 300, the rotation speed of the compressor 21 is controlled. As a result, as in the first embodiment, the pressure difference ΔP is reduced, and the pressure difference between the pressure at the lower portion of the hermetic container of the compressor 21 and the pressure of the compression mechanism portion is reduced. Even when it becomes difficult to supply the refrigerating machine oil to the compression mechanism unit, the rotation speed of the compressor 21 is controlled so that an appropriate amount of the refrigerating machine oil is supplied to the compression mechanism unit of the compressor 21. It is possible to prevent the compression mechanism portion of the compressor 21 from being poorly lubricated.

DESCRIPTION OF SYMBOLS 1 Air conditioning apparatus 2 Outdoor unit 6a-6e Switching unit 8a-8e Indoor unit 21 Compressor 50 Discharge pressure sensor 51 Suction pressure sensor 58 Outside temperature sensor 100 Control means 110 CPU
Ai indoor unit rated capacity Ao outdoor unit rated capacity Ar cooling requirement capacity D capacity ratio Dt threshold capacity ratio Pd discharge pressure Pd1 first discharge pressure Pd2 second discharge pressure Ps suction pressure Psmin suction pressure lower limit Pst threshold suction pressure P1 first pressure Difference P2 Second pressure difference ΔP Pressure difference Rc Compressor rotation speed Rcp Capacity appropriate rotation speed Rct Start-up rotation speed ΔRc Addition rotation speed To Outside air temperature Tot Threshold outside air temperature

Claims (4)

A compressor, an outdoor heat exchanger, an outside air temperature detecting means for detecting the outside air temperature, a discharge pressure detecting means for detecting the discharge pressure of the compressor, and a suction pressure detecting means for detecting the suction pressure of the compressor. An outdoor unit having
A plurality of indoor units having indoor heat exchangers;
Control means for performing drive control of the compressor;
Have
The control means includes
When operating the outdoor heat exchanger as a condenser and performing a cooling operation in which each indoor heat exchanger functions as an evaporator,
When the outside air temperature detected by the outside air temperature detecting means is equal to or lower than a predetermined threshold outside air temperature,
The compressor during the cooling operation according to either the discharge pressure detected by the discharge pressure detection means or the pressure difference obtained by subtracting the suction pressure detected by the suction pressure detection means from the discharge pressure Determine the number of revolutions,
An air conditioner characterized by that. When the discharge pressure is less than a predetermined first discharge pressure, the rotation speed corresponding to the capacity is the rotation speed corresponding to the cooling capacity required for the indoor unit performing the cooling operation. The number of rotations plus a predetermined number of rotations,
If the discharge pressure is greater than or equal to a predetermined second discharge pressure greater than the first discharge pressure, the rotation speed of the compressor is the rotation speed corresponding to the capacity,
When the discharge pressure is not less than the first discharge pressure and less than the second discharge pressure, the rotation speed of the compressor is maintained at the current rotation speed.
The air conditioner according to claim 1. When the pressure difference is less than a predetermined first pressure difference, the rotation corresponding to the capacity is the rotation speed corresponding to the cooling capacity required by the indoor unit performing the cooling operation. The number of rotations plus a predetermined number of rotations,
If the pressure difference is greater than or equal to a predetermined second pressure difference greater than the first pressure difference, the rotation speed of the compressor is set as the rotation speed corresponding to the capacity,
If the pressure difference is greater than or equal to the first pressure difference and less than the second pressure difference, the rotational speed of the compressor is maintained at the current rotational speed.
The air conditioner according to claim 1. The predetermined addition rotational speed is determined according to the suction pressure,
The additional rotational speed when the suction pressure is small is a value smaller than the additional rotational speed when the suction pressure is large.
The air conditioner according to any one of claims 1 to 3, wherein

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