JP2019168150A - Air conditioning device - Google Patents

Abstract

An air conditioner that can efficiently use an outdoor heat exchanger during low-load heating operation is provided. When a heating operation is performed, a CPU determines whether or not a calculated capacity ratio D is equal to or smaller than a threshold capacity ratio Dt. If the capacity ratio D is not equal to or smaller than the threshold capacity ratio Dt, the CPU 210 sets the target refrigerant superheat degree to the first target value SHp1, and if the capacity ratio D is equal to or smaller than the threshold capacity ratio Dt, the CPU 210 sets the target refrigerant superheat degree to the second target value. SHp2. The CPU 210 takes in the suction pressure Ps and the suction temperature Ts, calculates a refrigerant superheat degree on the refrigerant outlet side of the outdoor heat exchanger 23 using these, and calculates the refrigerant superheat degree as the first target value SHp1, or The target refrigerant superheat control that adjusts the opening of the outdoor unit expansion valve 24 so as to be any one of the second target values SHp2 is executed. [Selection diagram] FIG.

Description

  The present invention relates to an air conditioner, and more particularly, to opening degree adjustment of an outdoor unit expansion valve during low-load heating operation.

  When a heating operation is performed with the air conditioner, a so-called liquid back in which liquid refrigerant is sucked into the compressor without the refrigerant being completely evaporated by the outdoor heat exchanger functioning as an evaporator may occur. In order to prevent this liquid back, in the conventional air conditioner, the rotational speed of the outdoor unit fan during heating operation is set to the maximum rotational speed, and the degree of refrigerant superheating on the refrigerant outlet side of the outdoor heat exchanger is increased. For example, the opening degree of the outdoor unit expansion valve is adjusted so that the refrigerant superheat degree becomes 2 degrees to 4 degrees (see, for example, Patent Document 1).

JP 2000-205630 A

  In the case of a multi-room type air conditioner in which multiple indoor units are connected to one outdoor unit, all indoor units operate and the total value of the air conditioning capacity required by all indoor units is Even if the maximum value is reached, a compressor having a large capacity is provided in the outdoor unit in order to supply each indoor unit with an amount of refrigerant that satisfies the capacity required for each indoor unit.

  When the multi-room type air conditioner as described above performs heating operation, if the total heating capacity required for each indoor unit is smaller than the rated capacity of the outdoor unit, that is, low-load heating. In the case of operation, the rotation speed of the compressor is made lower than in the case of not being in the low load heating operation. For this reason, the refrigerant | coolant amount which circulates through the refrigerant circuit at the time of low load heating operation becomes small compared with the case where it is not at low load heating operation.

  In order to prevent the above-described liquid back during low-load heating operation, the rotational speed of the outdoor unit fan is set to the maximum rotational speed, and the degree of refrigerant superheating on the refrigerant outlet side of the outdoor heat exchanger increases. Thus, when the opening degree of the outdoor unit expansion valve is adjusted, the liquid refrigerant flowing into the outdoor heat exchanger or the refrigerant in the gas-liquid two-phase state is close to the refrigerant inlet side in the refrigerant flow path of the outdoor heat exchanger. All are evaporated to become gas refrigerant.

  During low-load heating operation, if all of the refrigerant evaporates into a gas refrigerant near the refrigerant inlet side in the refrigerant flow path of the outdoor heat exchanger, all the refrigerant in the refrigerant flow path of the outdoor heat exchanger has evaporated. Between the location and the refrigerant outlet side, the temperature of the gas refrigerant rises and the refrigerant superheat degree is high. In such a state, the temperature difference between the temperature of the outside air flowing into the outdoor heat exchanger and the temperature of the refrigerant flowing from the position where all the refrigerant has evaporated to the refrigerant outlet side becomes small, or the temperature difference is reduced. Disappear. Accordingly, there has been a problem that heat cannot be exchanged between the refrigerant and the outside air between the location where all the refrigerant in the refrigerant flow path of the outdoor heat exchanger has evaporated and the refrigerant outlet side, and the outdoor heat exchanger cannot be used efficiently. .

  The present invention solves the above-described problems, and an object thereof is to provide an air conditioner that can efficiently use an outdoor heat exchanger during low-load heating operation.

  In order to solve the above problems, an air conditioner according to the present invention includes a compressor, an outdoor heat exchanger, an outdoor unit expansion valve, an outdoor unit fan, a suction pressure detecting means for detecting a suction pressure of the compressor, and a compressor. An outdoor unit having an intake temperature detecting means for detecting an intake temperature, a plurality of indoor units having an indoor heat exchanger and an indoor unit expansion valve, and a control unit for adjusting the opening degree of the outdoor unit expansion valve . When performing the heating operation in which the outdoor heat exchanger functions as an evaporator and each indoor heat exchanger functions as a condenser, the control means sets the total required capacity, which is the total required capacity of each indoor unit, of the outdoor unit. When the capacity ratio divided by the rated capacity is compared with a predetermined threshold capacity ratio and the capacity ratio is larger than the threshold capacity ratio, the target refrigerant that is the target value of the refrigerant superheat degree on the refrigerant outlet side of the outdoor heat exchanger When the superheat degree is the first target value and the capacity ratio is smaller than the threshold capacity ratio, the target refrigerant superheat degree is set to the second target value smaller than the first target value. The control means calculates the refrigerant superheat degree by subtracting the suction temperature detected by the suction temperature detection means from the evaporation temperature obtained by using the suction temperature detected by the suction pressure detection means, and the calculated refrigerant superheat degree is the target refrigerant. The opening degree of the outdoor unit expansion valve is adjusted so that the degree of superheat is reached.

  In the air conditioning apparatus of the present invention as described above, the target refrigerant superheat degree is lowered when the capacity ratio is smaller than the threshold capacity ratio, that is, during low-load heating operation. Thereby, an outdoor heat exchanger can be used efficiently at the time of low load heating operation.

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 an indoor unit required capability table in embodiment of this invention. It is a flowchart which shows the process at the time of performing target refrigerant | coolant superheat degree control at the time of heating operation in 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 10 indoor units with a rated capacity of 2 kW are connected in parallel to one outdoor unit with a rated capacity of 20 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 ten 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 unit expansion valve 24, a closing valve 25 to which the liquid pipe 8 is connected, and a closing valve to which the gas pipe 9 is connected. 26, an accumulator 27, an outdoor unit fan 28, and an outdoor unit control means 200. And these each apparatus except the outdoor unit fan 28 and the outdoor unit control means 200 are mutually connected by each refrigerant | coolant piping explained in full detail below, and form the outdoor unit refrigerant circuit 20 which makes a part of refrigerant circuit 10. ing.

  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.

  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 an outdoor unit 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 unit expansion valve 24 is provided in the outdoor unit liquid pipe 44. The outdoor unit 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 by adjusting the opening degree according to the number of pulses applied to the pulse motor, or The amount of refrigerant flowing out of the outdoor heat exchanger 23 is adjusted. The opening degree of the outdoor unit expansion valve 24 is such that when the air-conditioning apparatus 1 is performing a heating operation, the degree of refrigerant superheating on the refrigerant outlet side of the outdoor heat exchanger becomes a target refrigerant superheating degree described later. Is adjusted. The opening degree of the outdoor unit expansion valve 24 is fully opened when the cooling operation is performed.

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

  In addition to the configuration described above, the outdoor unit 2 is provided with various sensors. As shown in FIG. 1A, the discharge pipe 41 includes a discharge pressure sensor 31 that detects a discharge pressure that is a pressure of the refrigerant discharged from the compressor 21, and a temperature of the refrigerant discharged from the compressor 21. A discharge temperature sensor 33 for detection 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 suction pressure sensor 32 is the suction pressure detection means of the present invention, and the suction temperature sensor 34 is the suction temperature detection means of the present invention.

  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 between the outdoor heat exchanger 23 and the outdoor unit expansion valve 24 in the outdoor unit liquid pipe 44. A heat exchange 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.

  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 is, for example, a flash memory, and is transmitted from the control program of the outdoor unit 2 and detection values corresponding to detection signals from various sensors, the driving state of the compressor 21 and the outdoor unit fan 28, and the indoor units 5. Operation information (including operation / stop information, operation modes such as cooling / heating), the rated capacity of the outdoor unit 2 and the required 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 unit expansion valve 24 and controls the drive of the compressor 21 and the outdoor unit fan 28 based on the various pieces of input information.

<Configuration of each indoor unit>
Next, the ten indoor units 5 will be described. The ten indoor units 5 all have the same configuration, and include an indoor heat exchanger 51, an indoor unit expansion valve 52, a liquid pipe connection unit 53, a gas pipe connection unit 54, and an indoor unit fan 55. I have. These constituent devices other than the indoor unit 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.

  As described above, in the present embodiment, ten indoor units 5 are connected to the outdoor unit 2 and the rated capacity of each indoor unit 5 is the same rated capacity: 2 kW. The rated capacity of the indoor unit 5 may be different.

  The indoor heat exchanger 51 exchanges heat between the refrigerant and indoor air taken into the indoor unit 5 from a suction port (not shown) by rotation of an indoor unit 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 unit expansion valve 52 is provided in the indoor unit liquid pipe 71. The indoor unit 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 unit expansion valve 52 is the refrigerant outlet of the indoor heat exchanger 51 ( The refrigerant superheat degree at the gas pipe connection portion 54 side) is adjusted to be the target refrigerant superheat degree. Further, when the indoor heat exchanger 51 functions as a condenser, that is, when the indoor unit 5 performs a heating operation, the opening degree of the indoor unit expansion valve 52 is the refrigerant outlet (liquid pipe connection) of the indoor heat exchanger 51. The refrigerant subcooling degree at the section 53 side) is adjusted to be 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 unit fan 55 is formed of a resin material and is disposed in the vicinity of the indoor heat exchanger 51. The indoor unit fan 55 is rotated by a fan motor (not shown), thereby taking indoor air into the interior of the indoor unit 5 from a suction port (not shown), and a blower outlet (not shown) for indoor air heat exchanged with the refrigerant in the indoor heat exchanger 51. To 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 unit expansion valve 52 in the indoor unit liquid pipe 71, 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 heating operation will be described, and detailed description will be omitted for the case where cooling operation is performed. Moreover, the arrow in FIG. 1 has shown the flow of the refrigerant | coolant at the time of heating operation.

  As shown in FIG. 1, when the air conditioner 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 d of the four-way valve 22 communicate with each other, and the port b And the port c are 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.

  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 passes through the outdoor unit gas pipe 45 from the four-way valve 22. Flows into the gas pipe 9 via the closing valve 26.

  The refrigerant flowing through the gas pipe 9 is divided into each indoor unit 5 via the gas pipe connection portion 54. The refrigerant flowing into each indoor unit 5 flows through each indoor unit gas pipe 72 and flows into each indoor heat exchanger 51. The refrigerant flowing into each indoor heat exchanger 51 is condensed by exchanging heat with the indoor air taken into each indoor unit 5 by the rotation of each indoor unit fan 55.

  In this way, each indoor heat exchanger 51 functions as a condenser, and the indoor air heated by exchanging heat with the refrigerant in each indoor heat exchanger 51 is blown into the room from a blower outlet (not shown). The room in which ten indoor units 5 are installed is heated.

  The refrigerant flowing into each indoor unit liquid pipe 71 from each indoor heat exchanger 51 is adjusted in opening degree so that the refrigerant subcooling degree on the refrigerant outlet side of each indoor heat exchanger 51 becomes the target refrigerant subcooling degree. The pressure is reduced when passing through each indoor unit expansion valve 52. Here, the target refrigerant supercooling degree is determined based on the cooling capacity required for each indoor unit 5.

  The refrigerant decompressed by each indoor unit expansion valve 52 flows out from each indoor unit liquid pipe 71 to the liquid pipe 8 via each liquid pipe connection portion 53. The refrigerant that joins in the liquid pipe 8 and flows into the outdoor unit 2 through the closing valve 25 flows through the outdoor unit liquid pipe 44, and the degree of refrigerant superheat on the refrigerant outlet side of the outdoor heat exchanger 23 is the target refrigerant superheat degree described later. The pressure is further reduced when passing through the outdoor unit expansion valve 24 whose opening degree is adjusted to be.

  The refrigerant depressurized by the outdoor unit expansion valve 24 flows through the outdoor unit liquid pipe 44 and flows into the outdoor heat exchanger 23, and is sucked into the outdoor unit 5 (not shown) by the rotation of the outdoor unit fan 28 having the maximum rotation speed. Evaporates by exchanging heat with the outside air flowing in from the mouth. The refrigerant that flows into the refrigerant pipe 43 from the outdoor heat exchanger 23 flows in the order of 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 a cooling operation, the four-way valve 22 is in a state indicated by a broken 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 communicate with each other. Can be switched. 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.

<Opening adjustment of outdoor unit expansion valve during low-load heating operation>
Next, the opening degree adjustment of the outdoor unit expansion valve 24 when the air-conditioning apparatus 1 of the present embodiment is performing the low load heating operation will be described with reference to FIGS. 1 to 3.

  As described so far, in the air conditioner 1 of the present embodiment, ten indoor units 5 are connected to one outdoor unit 2. In such an air conditioner 1, even if all the indoor units 5 are operated and the total value of the air conditioning capacity required by all the indoor units 5 is the maximum value, it is required for each indoor unit 5. The outdoor unit 5 is provided with a compressor 21 having a capacity capable of supplying a sufficient amount of refrigerant to each indoor unit 5.

  When the air conditioning apparatus 1 is performing the heating operation, the total heating capacity required for each indoor unit 5 is smaller than the rated capacity of the outdoor unit 2, that is, the low-load heating operation is performed. In this case, the rotation speed of the compressor 21 is lowered as compared with the case where the low load heating operation is not performed. For this reason, the refrigerant | coolant amount which circulates through the refrigerant circuit 10 at the time of low load heating operation becomes small compared with the case where it is not low load heating operation.

  On the other hand, when the air conditioner 1 performs the heating operation, in order to prevent the occurrence of liquid back to the compressor 21, the rotational speed of the outdoor unit fan 28 is set to the maximum rotational speed, and the outdoor heat exchanger 23 The opening degree of the outdoor unit expansion valve 24 is adjusted so that the degree of refrigerant superheating on the refrigerant outlet side is increased (for example, 4 deg). When such control is performed during the low load heating operation, the liquid refrigerant or the gas-liquid two-phase refrigerant flowing into the outdoor heat exchanger 23 is located near the refrigerant inlet side in the refrigerant flow path of the outdoor heat exchanger 23. All of this evaporates into a gas refrigerant.

  If all the refrigerant evaporates at a location near the refrigerant inlet side in the refrigerant flow path of the outdoor heat exchanger 23 to become a gas refrigerant, the refrigerant outlet side from the location where all the refrigerant evaporates in the refrigerant flow path of the outdoor heat exchanger 23 In the meantime, the temperature of the gas refrigerant rises and the refrigerant superheat degree is high. In such a state, the temperature of the outside air flowing into the outdoor heat exchanger 23 and the refrigerant on the refrigerant outlet side of the outdoor heat exchanger 23 from the location where all the refrigerant in the refrigerant flow path of the outdoor heat exchanger 23 evaporates The temperature difference from the temperature of the refrigerant flowing between the portion where all of the gas evaporates and the refrigerant outlet side of the outdoor heat exchanger 23 becomes small, or the temperature difference disappears. For this reason, the heat exchange between the refrigerant and the outside air cannot be performed between the location where all the refrigerant in the refrigerant flow path of the outdoor heat exchanger 23 evaporates and the refrigerant outlet side of the outdoor heat exchanger 23. There was a problem that it could not be used efficiently.

  Therefore, in the air conditioner 1 of the present embodiment, when the heating operation is performed, a value obtained by dividing the total required capacity that is the total value of the heating capacity required for each indoor unit 5 by the rated capacity of the outdoor unit 2. When the capacity ratio is a threshold capacity ratio, for example, 0.25 or less, it is determined that the low load heating operation is being performed. When the capacity ratio is larger than the threshold capacity ratio, the target refrigerant superheat degree, which is the target value of the refrigerant superheat degree on the refrigerant outlet side of the outdoor heat exchanger 23 during the low load heating operation, is distinguished from the low load heating operation. Therefore, the value may be smaller than the target refrigerant superheat degree.

  Here, the threshold capacity ratio is obtained by performing a test or the like in advance and is stored in the storage unit 220 of the outdoor unit control means 200, and each indoor unit 5 whose capacity ratio is equal to or less than the threshold capacity ratio. When the refrigerant superheat degree on the refrigerant outlet side of the outdoor heat exchanger 23 is increased to prevent the liquid back to the compressor 21 described above, the total heating capacity required by the It is a known value that the outdoor heat exchanger 23 cannot be used efficiently due to the fact that all the refrigerant evaporates into a gas refrigerant near the refrigerant inlet side in the refrigerant flow path.

  FIG. 2 shows an indoor unit required capacity table 300 stored in the storage unit 220 of the outdoor unit control means 200 of the outdoor unit 2. In the indoor unit required capacity table 300, the operation state (driving or stop) of each indoor unit 5 for every 10 indoor units 5 (numbers 1 to 10 are assigned in the indoor unit required capacity table 300). ) And required capacity required for each indoor unit 5 during cooling operation or heating operation (unit: KW, hereinafter referred to as required capacity Ai). Further, in the indoor unit required capacity table 300, the total required capacity (unit: KW, hereinafter referred to as total required capacity Aiadd), which is the total value of the required capacity of each indoor unit 5, and the total required capacity Aiadd are stored outdoors. A value obtained by dividing the rated capacity (unit: KW, hereinafter referred to as a rated capacity Ao) of the machine 2 is stored as a capacity ratio (hereinafter referred to as a capacity ratio D).

  Here, as for the operation state of each indoor unit 5 in the indoor unit required capacity table 300, each time the user starts / stops the operation in each indoor unit 5, a signal including that is transmitted from each indoor unit 5, and the outdoor unit 5 The CPU 210 of the unit control means 200 updates the operating state of the indoor unit 5 that has transmitted the signal every time this signal is captured via the communication unit 230, based on the contents included in the captured signal.

  In addition, the required capacity Ai of each indoor unit 5 in the indoor unit required capacity table 300 is transmitted from each indoor unit 5 as a signal indicating that if the user changes the required capacity Ai in each indoor unit 5, the CPU 210 Each time this signal is captured via the communication unit 230, the required capacity Ai of the indoor unit 5 that has transmitted the signal is updated based on the content included in the captured signal. As for the total required capacity Aiadd and the capacity ratio D in the indoor unit required capacity table 300, each time the required capacity Ai of each indoor unit 5 is updated, the CPU 210 calculates and updates it to a new value.

  In addition, in the indoor unit required capacity table 300 shown in FIG. 2, the state when the air conditioning apparatus 1 is performing the heating operation is shown as an example, and the numbers 3 and 5 among the ten indoor units 5 and , 8 does not perform the heating operation or is thermo-off, so the operation state is “stopped”. Moreover, since each indoor unit 5 other than the numbers 3, 5, and 8 is performing the heating operation, the operation state is “operation”. With respect to the required capacity Ai, since the current operation is heating operation, the required capacity Ai of “cooling” is all “-----”, that is, has no value. In addition, regarding the required capacity Ai of “heating”, the required capacity Ai corresponding to the indoor unit 5 that is in operation is the value shown in FIG. 2, and the required capacity Ai of the stopped indoor unit 5 is It is "-----".

  The total required capacity Aiadd is 4.6 kW which is a value obtained by adding all the required capacities Ai of the indoor units 5 performing the heating operation, and the capacity ratio D is the total required capacity Aiadd: 4.6 KW. Is a value obtained by dividing the rated capacity Ao of the outdoor unit 2 by 20 KW. That is, in the indoor unit required capacity table 300 of FIG. 2, since the capacity ratio D is 0.23 and smaller than 0.25, the required capacity of each indoor unit 5 is in the state shown in the indoor unit required capacity table 300. Becomes low load heating operation.

  As described above, in the air conditioner 1 of the present embodiment, the capacity ratio D is the threshold capacity ratio (hereinafter referred to as the threshold capacity ratio Dt. The threshold capacity ratio Dt is, for example, 0.25 as described above). If it is larger, it is assumed that the normal heating operation is being performed, and the target refrigerant superheat degree that is the target value of the refrigerant superheat degree on the refrigerant outlet side of the outdoor heat exchanger 23 is set to the first target value (hereinafter referred to as the first target value). SHp1), for example, 4 deg, and the opening degree of the outdoor unit expansion valve 24 is adjusted so that the refrigerant superheat degree on the refrigerant outlet side of the outdoor heat exchanger 23 becomes the target refrigerant superheat degree. Further, during the normal heating operation, the rotational speed of the outdoor unit fan 28 is set to the maximum rotational speed, for example, 900 rpm. During the normal heating operation, the refrigerant superheat degree on the refrigerant outlet side of the outdoor heat exchanger 23 is set to the first target value, and the outdoor unit fan 28 is driven at the maximum rotation speed, thereby preventing liquid back to the compressor 21. It is out.

  On the other hand, when the capacity ratio D is equal to or less than the threshold capacity ratio Dt, it is assumed that the low load heating operation is being performed, and the target refrigerant superheat degree is set to the first target value without changing the rotational speed of the outdoor unit fan 28. The second target supercooling degree smaller than SHp1 (hereinafter referred to as second target value SHp2), for example, 1 deg. If the target refrigerant superheat degree is the second target value SHp2, the opening degree of the outdoor unit expansion valve 24 is set to the normal heating operation in order to set the refrigerant superheat degree on the refrigerant outlet side of the outdoor heat exchanger 23 to the second target value SHp2. Bigger than time.

  As a result, more refrigerant flows into the outdoor heat exchanger 23 than when the target refrigerant superheat degree is set to the first target value during the low-load heating operation. For this reason, in the part close to the refrigerant inlet side in the refrigerant flow path of the outdoor heat exchanger 23, all of the refrigerant evaporates to become a gas refrigerant, and the outdoor heat starts from the part where all the refrigerant in the refrigerant flow path of the outdoor heat exchanger 23 evaporates. It does not occur that heat exchange between the refrigerant and the outside air cannot be performed between the refrigerant outlet sides of the exchanger 23. Therefore, the outdoor heat exchanger 23 can be used efficiently even during the low load heating operation.

  Note that if the target refrigerant superheat degree is reduced from the first target value SHp1 to the second target value SHp2 during the low-load heating operation, there is a concern about liquid back to the compressor 21, but the normal heating operation is performed during the low-load heating operation. Since the total required capacity Aiadd is smaller than the time and thereby the rotational speed of the compressor 21 is also lowered, the refrigerant circulation amount in the refrigerant circuit 10 is smaller than that in the normal heating operation. As a result, even if the target refrigerant superheat degree is reduced and the opening degree of the outdoor unit expansion valve 24 is increased during low-load heating operation, the amount of refrigerant flowing into the outdoor heat exchanger 23 is reduced during normal heating operation, that is, the compressor. Since the opening degree of the outdoor unit expansion valve 24 is small when the rotational speed of 21 is high, the possibility of occurrence of liquid back is low.

<Flow of processing related to opening adjustment of outdoor unit expansion valve during heating operation>
Next, the flow of processing related to the opening degree adjustment of the outdoor unit expansion valve 24 when the air-conditioning apparatus 1 performs the heating operation will be described with reference to FIG. FIG. 3 is a flowchart showing processing performed by the CPU 210 of the outdoor unit control means 200 in adjusting the opening degree of the outdoor unit expansion valve 24 during heating operation. In FIG. 3, ST represents a process step, and the number following this represents a step number. Note that FIG. 3 refers only to processing related to the present invention, and description and description of other general controls related to the air conditioner 1 are omitted.

  In FIG. 3, in addition to the above-described required capacity Ai, total required capacity Aiadd, capacity ratio D, threshold capacity ratio Dt, first target value SHp1, and second target value SHp2, detection is performed by the suction pressure sensor 32. The suction pressure is Ps, the suction temperature detected by the suction temperature sensor 34 is Ts, and the refrigerant superheat degree is SH.

  First, the CPU 210 determines whether or not the user's operation instruction is a heating operation (ST1). If the operation instruction is not the heating operation (ST1-No), the CPU 210 executes a cooling operation start process (ST17). Here, the cooling operation start processing means that the CPU 210 operates the four-way valve 22 to set the refrigerant circuit 10 to the cooling cycle, and when the cooling operation is performed from the state where the air conditioner 1 is stopped, or It is a process performed when switching from heating operation to cooling operation.

  Next, the CPU 210 starts cooling operation control (ST18), and proceeds to ST13. In the cooling operation control, the CPU 210 drives the compressor 21 at a rotational speed corresponding to the required capacity Ai at the time of the cooling operation required by each indoor unit 5 and the outdoor unit fan 28 according to the rotational speed of the compressor 21. Drive at a different rotational speed. Further, the CPU 210 fully opens the opening of the outdoor unit expansion valve 24. Furthermore, the CPU 210 instructs each indoor unit 5 to start opening adjustment of the indoor unit expansion valve 52 and drive control of the indoor unit fan 55 via the communication unit 230.

  In ST1, if the operation instruction is the heating operation (ST1-Yes), the CPU 210 executes a heating operation start process (ST2). The heating operation start process is that the CPU 210 operates the four-way valve 22 to set the refrigerant circuit 10 to the heating cycle. When the heating operation is performed from the state where the air conditioner 1 is stopped, or from the cooling operation. It is a process performed when switching to heating operation.

  Next, the CPU 210 takes in the required capacity Ai from each indoor unit 5 via the communication unit 230 (ST3). As described above, the required capacity Ai is transmitted from each indoor unit 5 every time it is changed in each indoor unit 5, and the CPU 210 stores the changed required capacity Ai in the storage unit 220 every time it receives the changed required capacity Ai. The required capacity Ai of the indoor unit required capacity table 300 is updated.

  Next, the CPU 210 calculates the total required capacity Aiadd by adding each required capacity Ai (ST4), and the rated capacity Ao of the outdoor unit 2 that stores the total required capacity Aiadd calculated in ST4 in the storage unit 220. The capacity ratio D is calculated by dividing (ST5). As described above, the CPU 210 calculates the total required capacity Aiadd and the capacity ratio D every time the required capacity Ai is updated in the indoor unit required capacity table 300, and the total required capacity Aiadd of the indoor unit required capacity table 300 The capacity ratio D is updated.

  Next, the CPU 210 drives the compressor 21 at the rotational speed corresponding to the total required capacity Aiadd calculated at ST4 (ST6) and drives the outdoor unit fan 28 at the maximum rotational speed (ST7). Then, CPU 210 determines whether or not ability ratio D calculated in ST5 is equal to or less than threshold ability ratio Dt (ST8).

  If the capacity ratio D is not less than or equal to the threshold capacity ratio Dt (ST8-No), that is, if the capacity ratio D is greater than the threshold capacity ratio Dt, the CPU 210 sets the target refrigerant superheat degree as the first target value SHp1 ( The process proceeds to ST16) and ST10. On the other hand, if the capacity ratio D is equal to or less than the threshold capacity ratio Dt (ST8-Yes), the CPU 210 sets the target refrigerant superheat degree to the second target value SHp2 smaller than the first target value SHp1 (ST9), and proceeds to ST10. .

  Next, the CPU 210 takes in the suction pressure Ps and the suction temperature Ts (ST10). The CPU 210 fetches the suction pressure Ps detected by the suction pressure sensor 32 and the suction temperature Ts detected by the suction temperature sensor 34 periodically (for example, every 30 seconds) via the sensor input unit 240, and the storage unit 220. I remember it.

  Next, the CPU 210 obtains the low-pressure saturation temperature, that is, the evaporation temperature in the outdoor heat exchanger 23, using the suction pressure taken in in ST10, subtracts the suction temperature Ts from the obtained evaporation temperature, and outputs the refrigerant outlet of the outdoor heat exchanger 23. The refrigerant superheat degree SH on the side is calculated (ST11).

  Next, CPU210 performs target refrigerant superheat degree control (ST12). Here, the target refrigerant superheat degree control is performed so that the refrigerant superheat degree SH obtained in ST11 becomes either the first target value SHp1 determined in ST16 or the second target value SHp2 determined in ST9. The CPU 210 adjusts the opening of the expansion valve 24, and the CPU 210 determines the degree of superheat of the refrigerant obtained in ST11 and the first target value SHp1 or the second target value SHp2. Increase or decrease the opening.

  Next, CPU 210 determines whether or not there is an operation mode switching instruction from the user (ST13). Here, the operation mode switching instruction is an instruction to switch from the heating operation to the cooling operation, or to switch from the cooling operation to the heating operation.

  When there is an operation mode switching instruction (ST13-Yes), the CPU 210 returns the process to ST1. When there is no operation mode switching instruction (ST13-No), the CPU 210 determines whether or not there is an operation stop instruction by the user (ST14). The operation stop instruction indicates that all the indoor units 5a to 5c stop the operation.

  If there is an operation stop instruction (ST14-Yes), the CPU 210 executes an operation stop process (ST15) and ends the process. In the operation stop process, the CPU 210 stops the compressor 21 and the outdoor unit fan 28 and fully closes the outdoor unit expansion valve 24. In addition, the CPU 210 transmits an operation stop signal for stopping the operation to each indoor unit 5 via the communication unit 230. Each indoor unit 5 that has received the operation stop signal fully closes the indoor unit expansion valve 52 and stops the indoor unit fan 55.

  If there is no operation stop instruction in ST14 (ST14-No), CPU 210 determines whether or not the current operation is a heating operation (ST19). If the current operation is the heating operation (ST19-Yes), the CPU 210 returns the process to ST3. If the current operation is not the heating operation (ST19-No), that is, if the current operation is the cooling operation, the CPU 210 returns the process to ST18.

  As described above, in the air-conditioning apparatus 1 of the present embodiment, when the heating operation is performed and the low load heating operation is performed, the target refrigerant superheat degree is set to the first target value SHp1 during the normal heating operation. It changes to 2nd target value SHp2 which is a smaller value, and the opening degree of the outdoor unit expansion valve 24 is adjusted so that the refrigerant superheat degree on the refrigerant outlet side of the outdoor heat exchanger 23 becomes the second target value SHp2. Thereby, the outdoor heat exchanger 23 can be efficiently used at the time of low load heating operation.

DESCRIPTION OF SYMBOLS 1 Air conditioning apparatus 2 Outdoor unit 5 Indoor unit 21 Compressor 23 Outdoor heat exchanger 24 Outdoor unit expansion valve 28 Outdoor unit fan 32 Suction pressure sensor 34 Suction temperature sensor 51 Indoor heat exchanger 52 Indoor unit expansion valve 55 Indoor unit fan 200 Outdoor unit control means 210 CPU
Ai Required capacity Aiadd Total required capacity D Capacity ratio Dt Threshold capacity ratio Ps Suction pressure Pd1 First discharge pressure Pd2 Second discharge pressure Ps Suction pressure Ts Suction temperature SH Refrigerant superheat SHp1 First target value SHp2 Second target value

Claims (1)

A compressor, an outdoor heat exchanger, an outdoor unit expansion valve, an outdoor unit fan, suction pressure detection means for detecting the suction pressure of the compressor, and suction temperature detection means for detecting the suction temperature of the compressor; An outdoor unit having
A plurality of indoor units having an indoor heat exchanger and an indoor unit expansion valve;
Control means for adjusting the opening of the outdoor unit expansion valve;
Have
The control means includes
When performing the heating operation of causing the outdoor heat exchanger to function as an evaporator and causing each of the indoor heat exchangers to function as a condenser,
Comparing the capacity ratio obtained by dividing the total required capacity, which is the total value of the required capacity of each indoor unit, by the rated capacity of the outdoor unit, and a predetermined threshold capacity ratio,
When the capacity ratio is larger than the threshold capacity ratio, a target refrigerant superheat degree that is a target value of the refrigerant superheat degree on the refrigerant outlet side of the outdoor heat exchanger is set as a first target value,
When the capacity ratio is smaller than the threshold capacity ratio, the target refrigerant superheat degree is set as a second target value smaller than the first target value,
The refrigerant superheat degree is calculated by subtracting the suction temperature detected by the suction temperature detection means from the evaporation temperature obtained using the suction temperature detected by the suction pressure detection means, and the calculated refrigerant superheat degree is the target refrigerant superheat degree. Adjusting the opening degree of the outdoor unit expansion valve so as to be
An air conditioner characterized by that.

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