JP2009243847A - Multiple air conditioner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multiple air conditioner capable of controlling an opening of an expansion valve to suppress both low-pressure and quantity of liquid refrigerant within allowable ranges, reducing probability of failure of a compressor, and miniaturizing an accumulator and an outdoor unit. <P>SOLUTION: In this multiple type air conditioner 1 wherein a plurality of indoor units 11A, 11B respectively having indoor electric expansion valves 47 are connected in parallel to at least one outdoor unit 3, and a control section 51 is disposed to control an operation, the control section 51 is provided with a stable operation mode 53 for controlling the openings of the indoor electric expansion valves 47 so that the low-pressure pressure as the pressure of the refrigerant sucked into the compressor 13 is over a prescribed control pressure, and the quantity of liquid refrigerant flowing into the compressor 13 is kept within a prescribed range when the low-pressure pressure is over a control pressure, and in the stable operation mode 53, the openings of the indoor electric expansion valves 47 are changed by a prescribed amount at every prescribed time. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a multi-type air conditioner of a multi-type air conditioner.

The multi-type air conditioner is configured by connecting a plurality of indoor units in parallel to one outdoor unit (see Patent Document 1).
Such a multi-type air conditioner is used, for example, in a place having a large number of rooms (indoor unit installation locations) such as a building, so that the distance between the outdoor unit and the indoor unit becomes long. Together with this, the length of the pipe connecting each indoor unit and the outdoor unit becomes long, so that the amount of refrigerant to be sealed increases.
For this reason, since the amount of liquid refrigerant returning to the compressor side inevitably increases, the possibility that it will return to the compressor increases.
In addition, since a large number of indoor units are provided, for example, if a number of indoor units are turned off all at once, or if there is a sudden change in the indoor load due to reaching a set temperature, that is, a drop or the like, There is a situation where the refrigerant cannot be completely evaporated in the indoor unit. Thus, when the expansion valve opening degree and the operating state of the system deviate, the liquid refrigerant flows into the compressor.

In such a case, if the liquid refrigerant flows in more than a predetermined amount allowed for the compressor, the compressor is overloaded and may cause a failure such as seizure.
Therefore, various devices have been proposed and used in order to prevent the liquid refrigerant from returning to the compressor.
For example, when a sudden drop in the indoor load occurs, the opening of the expansion valve is reduced to control the liquid refrigerant to evaporate in the indoor unit.
Alternatively, this can be avoided by installing a large-capacity accumulator that separates gas and liquid and stores liquid refrigerant on the suction side of the compressor.

JP 2007-40563 A

By the way, when the opening degree of the expansion valve is reduced when the indoor load is suddenly reduced by the control, the low pressure, which is the pressure of the refrigerant sucked into the compressor, may be suddenly reduced by restricting the expansion valve.
When the low-pressure pressure is suddenly lowered and falls below a predetermined pressure value in this way, the compressor is broken, and the compressor must be stopped for protection. When the compressor is stopped, the refrigerant is not circulated, so that the air conditioning performance in the indoor unit is lowered and the comfort in the room is impaired.

In addition, in the case of using a buffer such as an accumulator, it is necessary to circulate the refrigerant stored as the load increases. However, once it is stored in the accumulator, it cannot be smoothly performed. In other words, it takes time. For this reason, the air-conditioning performance in an indoor unit falls temporarily and indoor comfort will be impaired.
In this case, it is necessary to secure a space for installing a large accumulator in the outdoor unit, which becomes a bottleneck in reducing the size and size of the outdoor unit. In addition, it is difficult to reduce or eliminate the accumulator and reduce the cost.

  In view of such circumstances, the present invention controls the opening degree of the expansion valve so as to suppress both the low pressure and the amount of liquid refrigerant to an allowable range, thereby reducing the possibility of compressor failure, as well as the accumulator and the outdoor unit. An object of the present invention is to provide a multi-type air conditioner capable of reducing the size of the machine.

In order to solve the above problems, the present invention employs the following means.
That is, the multi-type air conditioner according to the present invention includes a plurality of indoor units each having an indoor expansion valve for adjusting the flow rate of the refrigerant and decompressing and expanding the refrigerant with respect to at least one outdoor unit having the compressor. A multi-type air conditioner that is connected in parallel and includes a control unit that controls operation, wherein a low-pressure pressure that is a pressure of a refrigerant sucked into the compressor is a predetermined control pressure. And the opening degree of the indoor expansion valve is controlled so that the amount of liquid refrigerant flowing into the compressor falls within a predetermined range when the low pressure exceeds the control pressure. The stable operation mode is characterized in that the opening degree of the indoor expansion valve is changed by a predetermined amount every predetermined time.

When the multi-type air conditioner is operated, the refrigerant pressure (low pressure) returning to the compressor and the amount of liquid refrigerant included vary depending on the operating conditions of the plurality of indoor units.
According to the present invention, when the operation of the multi-type air conditioner is started and the stable operation mode is started, the opening of the indoor expansion valve is a low pressure that is the pressure of the refrigerant sucked into the compressor by the stable operation mode. The pressure is controlled to exceed a predetermined control pressure. That is, when the low pressure measured by the low pressure sensor is lower than the control pressure, the stable operation mode adjusts the opening of the indoor expansion valve to increase the amount of refrigerant returning to the compressor. The pressure can be in the vicinity of the control pressure.
By appropriately selecting the control pressure, it is possible to suppress the low pressure that leads to the failure of the compressor, and therefore it is possible to prevent a situation where the compressor has to be stopped for protection. Thereby, the air-conditioning performance in an indoor unit does not fall, and indoor comfort can be maintained.

In the stable operation mode, when the low pressure exceeds the control pressure, the opening of the indoor expansion valve is controlled so that the amount of liquid refrigerant flowing into the compressor falls within a predetermined range. That is, when the amount of liquid refrigerant flowing into the compressor exceeds a predetermined range, the stable operation mode is adjusted so that the opening of the indoor expansion valve is closed, that is, closed, and the liquid passing through the indoor heat exchanger is Since the amount of the refrigerant is reduced and reliably evaporated, the amount of the liquid refrigerant flowing into the compressor can be reduced, and the compressor can be prevented from malfunctioning due to overload.
The amount of liquid refrigerant flowing into the compressor is, for example, the degree of superheat below the dome, which is the compressor lower temperature minus the refrigerant saturation temperature at low pressure, and the refrigerant saturation at low pressure from the compressor suction pipe temperature. Either the suction superheat degree subtracting the temperature, the discharge superheat degree subtracting the refrigerant saturation temperature at the high pressure from the compressor discharge pipe temperature, the outside air temperature, the heat exchange temperature of the indoor unit, or the like And can be estimated.

Furthermore, since the opening degree of the indoor expansion valve is changed by a predetermined amount every predetermined time in the stable operation mode, the opening degree of the indoor expansion valve gradually changes over time. Thereby, since the state of a refrigerant | coolant can be changed gradually, stabilization of control can be aimed at.
In this case, the predetermined time and the predetermined amount are appropriately selected depending on the configuration of the target multi-type air conditioner, but the predetermined amount is 5 to 10% of the opening range of the control target. Is preferred. Moreover, about predetermined time, 5 to 30 second is preferable, for example, and 10 to 20 second is more preferable.
The above numerical values are determined from the time required for the operation of the indoor expansion valve to affect the temperature and pressure under the general installation conditions of the multi-type air conditioner (measured in a test). Below the lower limit, there is no response to temperature or pressure, and the next action cannot be determined. The upper limit is the time for the reaction to appear reliably, and is preferably as early as possible.
In addition, since the change speed of the low pressure is fast, it is preferable that the predetermined time be shorter than that of the liquid refrigerant. Also, it is preferable to increase the predetermined amount.

As described above, the stable operation mode can suppress the decrease in the low-pressure pressure and the inflow of the liquid refrigerant exceeding the allowable predetermined amount, so that it is possible to suppress the possibility that the compressor breaks down. As a result, it is possible to prevent a situation where the compressor must be stopped for protection, so that the air conditioning performance in the indoor unit is not deteriorated, and the indoor comfort can be maintained.
In addition, it is not necessary to install a large accumulator, the cost can be reduced by downsizing the accumulator, and the downsizing of the outdoor unit can be achieved. It is also possible to eliminate the accumulator.

  In the multi-type air conditioner of the present invention, the stable operation mode is characterized in that the indoor expansion valve is fully opened when the low pressure is less than a predetermined limit pressure lower than the control pressure.

Since the change speed of the low pressure is fast, detecting the control pressure and gradually opening the opening of the indoor expansion valve by a predetermined amount may not be in time and may adversely affect the compressor.
According to the present invention, the predetermined limit pressure lower than the control pressure is set, and the stable operation mode is such that when the low pressure falls below the limit pressure, the indoor expansion valve is fully opened. Even in a situation where the pressure suddenly decreases, it is possible to suppress a low pressure that leads to a compressor failure.

  In the multi-type air conditioner of the present invention, the stable operation mode is performed when the outdoor unit performs a cooling operation and the compressor is activated.

In the cooling operation, the pipes after the evaporator are longer than in the heating operation, and the amount of refrigerant accumulated therein is large, so that the amount of liquid refrigerant returning to the compressor also increases accordingly. When the compressor is started, the liquid refrigerant that has accumulated may flow in.
According to the present invention, even in such a severe condition, the return of the liquid refrigerant can be reliably suppressed to a predetermined amount that is allowed.

According to the present invention, the control unit flows into the compressor so that the low pressure, which is the pressure of the refrigerant sucked into the compressor, exceeds a predetermined control pressure, and when the low pressure exceeds the control pressure. A stable operation mode for controlling the opening of the indoor expansion valve is provided so that the amount of liquid refrigerant to be performed falls within a predetermined range, and the stable operation mode changes the opening of the indoor expansion valve by a predetermined amount every predetermined time. Therefore, it is possible to suppress the possibility that the compressor breaks down. As a result, it is possible to prevent a situation where the compressor must be stopped for protection, so that the air conditioning performance in the indoor unit is not deteriorated, and the indoor comfort can be maintained.
In addition, it is not necessary to install a large accumulator, the cost can be reduced by downsizing the accumulator, and the downsizing of the outdoor unit can be achieved. Further, in some cases, it is possible to eliminate the accumulator.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 shows a refrigerant cycle diagram of a multi-type air conditioner 1 according to the present embodiment.
The multi-type air conditioner 1 includes a single outdoor unit 3, a gas side pipe 5 and a liquid side pipe 7 led out from the outdoor unit 3, and a branching device between the gas side pipe 5 and the liquid side pipe 7. 9, a plurality of indoor units 11 </ b> A and 11 </ b> B connected in parallel via 9.

  The outdoor unit 3 includes an inverter-driven compressor 13 that compresses refrigerant, an oil separator 15 that separates lubricating oil from refrigerant gas, a four-way switching valve 17 that switches a circulation direction of the refrigerant, and refrigerant and outside air. An outdoor heat exchanger 19 for heat exchange, a supercooling coil 21 integrally formed with the outdoor heat exchanger 19, an outdoor electric expansion valve (EEVH) 23 for heating, a receiver 25 for storing liquid refrigerant, A supercooling heat exchanger 27 that supercools the liquid refrigerant, a supercooling electric expansion valve (EEVSC) 29 that controls the amount of refrigerant that is diverted to the supercooling heat exchanger 27, and a refrigerant gas that is drawn into the compressor 13 A small-capacity accumulator 31 that separates the liquid component from the inside and stores the liquid refrigerant, a gas side operation valve 33, and a liquid side operation valve 35 are provided.

As known, these are connected via refrigerant pipes such as a discharge pipe 37A, a gas pipe 37B, a liquid pipe 37C, a gas pipe 37D, a suction pipe 37E, and a branch pipe 37F for supercooling to constitute an outdoor refrigerant circuit 39. is doing.
The outdoor unit 3 is provided with an outdoor fan 41 that blows outside air to the outdoor heat exchanger 19.

The gas side pipe 5 and the liquid side pipe 7 are refrigerant pipes connected to the gas side operation valve 33 and the liquid side operation valve 35 of the outdoor unit 3.
The lengths of the gas side pipe 5 and the liquid side pipe 7 are appropriately determined according to the distance between the outdoor unit 3 and the indoor units 11A and 11B connected to the outdoor unit 3 at the time of installation on site.
An appropriate number of branching devices 9 are provided in the middle of the gas side piping 5 and the liquid side piping 7, and an appropriate number of indoor units 11 </ b> A and 11 </ b> B are connected via the branching devices 9.
Thereby, one sealed refrigeration cycle 43 is configured.

The indoor units 11A and 11B include an indoor heat exchanger 45 for exchanging heat between the refrigerant and room air for indoor air conditioning, an indoor electric expansion valve for cooling (indoor expansion valve; EEVC) 47, and indoor heat exchange. And an indoor fan 49 that circulates the room air through the vessel 45.
The indoor electric expansion valve 47
The indoor units 11A and 11B are connected to the branching device 9 via indoor branch gas pipes 5A and 5B and branch liquid pipes 7A and 7B.

On the outdoor unit 3 side of the multi-type air conditioner 1, a control unit 51 that controls the operation of the multi-type air conditioner 1 is provided. The controller 51 is provided with a stable operation mode 53 that protects the compressor 13 and stably operates the multi-type air conditioner 1.
The control unit 51 is provided with an expansion valve opening command unit 54 having a function of commanding a predetermined valve opening to each indoor electric expansion valve (EEVC) 47 in response to an instruction from the stable operation mode 53, for example. It has been.

The suction pipe 37E is provided with a suction pipe temperature sensor 55 that measures the temperature of the suction pipe 37E and a low-pressure sensor 63 that measures the pressure of the low-pressure refrigerant gas sucked into the compressor 13.
Below the compressor 13, a dome lower temperature sensor 57 that measures the external temperature of the main body (dome) of the compressor 13 is provided.
The discharge pipe 37 </ b> A is provided with a discharge pipe temperature sensor 59 that measures the temperature of the discharge pipe 37 </ b> A and a high-pressure sensor 61 that measures the pressure of the high-pressure refrigerant gas discharged from the compressor 13.

On the outside air intake side of the outdoor heat exchanger 19, an outside air temperature sensor 65 that measures the temperature of the outside air to be taken in is provided.
The indoor heat exchanger 45 is provided with a heat exchange temperature sensor 67 for measuring the temperature of the heat exchange member.

In the multi-type air conditioner 1 described above, the cooling operation is performed as follows.
The high-temperature and high-pressure refrigerant gas compressed by the compressor 13 is discharged to the discharge pipe 37A. The refrigerant gas is circulated to the gas pipe 37 </ b> B side by the four-way switching valve 17 after the lubricating oil contained in the refrigerant is separated by the oil separator 15.
The refrigerant gas passing through the gas pipe 37B is heat-exchanged with the outside air blown by the outdoor fan 41 in the outdoor heat exchanger 19 to be condensed and liquefied to be a liquid refrigerant.
The liquid refrigerant is cooled by the supercooling coil 21, passes through the outdoor electric expansion valve 23, and is temporarily stored in the receiver 25 to adjust the circulation amount.

In the process of passing through the supercooling heat exchanger 27, the liquid refrigerant from the receiver 25 is partially exchanged with the subcooling branch pipe 37 </ b> F and heat-exchanged with the refrigerant adiabatically expanded by the supercooling electric expansion valve (EEVSC) 29. It is cooled to a predetermined degree of supercooling.
The liquid refrigerant to which a predetermined degree of supercooling is given is led out from the outdoor unit 3 to the liquid side pipe 7 via the liquid side operation valve 35. The liquid refrigerant led out to the liquid side pipe 7 is diverted to the branch liquid pipes 7A and 7B of the indoor units 11A and 11B by the branching unit 9.

The liquid refrigerant branched into the branch liquid pipes 7A and 7B is adiabatically expanded by the indoor electric expansion valve (EEVC) 47 and flows into the indoor heat exchanger 45 as a gas-liquid two-phase flow.
In the indoor heat exchanger 45, heat is exchanged between the indoor air circulated by the indoor fan 49 and the refrigerant, and the indoor air is cooled and provided for indoor cooling.
On the other hand, the refrigerant is gasified, reaches the branching device 9 through the branch gas pipes 5A and 5B, and merges with the refrigerant gas from the other indoor units in the gas side pipe 5.

The refrigerant gas merged in the gas side pipe 5 returns to the outdoor unit 3 again, and reaches the suction pipe 37E through the gas side operation valve 33, the gas pipe 37D, and the four-way switching valve 17. The refrigerant gas merges with the refrigerant gas from the branch pipe 37 </ b> F and is introduced into the accumulator 31.
In the accumulator 31, the liquid component contained in the refrigerant gas is separated, only the gas component is sucked into the compressor 13, and the refrigerant is compressed again in the compressor 13.
The cooling operation is performed by repeating the above cycle.

On the other hand, the heating operation is performed as follows.
The high-temperature and high-pressure refrigerant gas compressed by the compressor 13 is discharged to the discharge pipe 37A. This refrigerant gas is circulated to the gas pipe 37 </ b> D side by the four-way switching valve 17 after the lubricating oil contained in the refrigerant is separated by the oil separator 15.
The refrigerant is led out from the outdoor unit 3 through the gas side operation valve 33 and the gas side pipe 5, and is further introduced into the indoor units 11A and 11B through the branching unit 9 and the indoor side branch gas pipes 5A and 5B.
The high-temperature and high-pressure refrigerant gas introduced into the indoor units 11A and 11B is heat-exchanged with the indoor air circulated by the indoor fan 49 in the indoor heat exchanger 45, and the indoor air is heated and used for indoor heating.

On the other hand, the liquid refrigerant cooled and condensed and liquefied by the indoor air reaches the branching device 9 via the indoor electric expansion valve (EEVC) 47 and the branch liquid pipes 7A and 7B, and is merged with the refrigerant from other indoor units. Then, it returns to the outdoor unit 2 through the liquid side pipe 7.
During heating, in the indoor units 11A and 11B, the opening degree of the indoor electric expansion valve (EEVC) 47 is controlled so that the degree of subcooling of the refrigerant at the outlet of the indoor heat exchanger 45 functioning as a condenser becomes a constant value. Is done.

The liquid refrigerant that has returned to the outdoor unit 3 passes through the liquid side operation valve 35, and the liquid refrigerant flows into the receiver 25 and is temporarily stored, and the circulation amount is adjusted.
This liquid refrigerant reaches the outdoor electric expansion valve (EEVH) 23 through the liquid pipe 37C, where it is adiabatically expanded and flows into the outdoor heat exchanger 19 through the supercooling coil 21.
In the outdoor heat exchanger 19, heat is exchanged between the outside air blown by the outdoor fan 41 and the refrigerant, and the refrigerant absorbs heat from the outside air and is evaporated.

This gas refrigerant is introduced from the outdoor heat exchanger 19 into the accumulator 31 through the gas pipe 37B, the four-way switching valve 17, and the suction pipe 37E.
In the accumulator 31, the liquid component contained in the refrigerant gas is separated and only the gas component is sucked into the compressor 13, and the refrigerant is compressed again by the compressor 13.
A heating operation is performed by repeating the above cycle.

Next, the operation in the stable operation mode 53 will be described. FIG. 2 shows a flow of the stable operation mode 53. 3 and 4 show stable operation modes based on the flow of FIG. 2 corresponding to the superheat degree change locus KK assumed for the under-dome superheat degree (under the dome SH) and the low pressure change locus TK assumed for the low pressure (LP), respectively. 53 shows the change in the opening degree command.
Here, the opening degree of the indoor electric expansion valve 47 is, for example, 470 pulses when fully opened, and the normal opening degree control is between 20 pulses and 60 pulses (that is, the opening degree range to be controlled is 40 pulses). It will be described as being performed. The initial opening is set to 50 pulses, for example.

The amount of the liquid refrigerant flowing into the compressor is determined by, for example, the degree of superheat under the dome (under the dome SH), and specifically, the under-dome SH is in the range of 10 to 20 ° C.
The low pressure LS has a target control pressure of 0.2 MPa, for example, and a limit pressure of 0.1 MPa, for example.
This limit pressure is set as a value that approaches a region where there is a possibility that the compressor 13 may be adversely affected depending on the lowering speed of the low pressure LS. This 0.1 MPa or 0.2 MPa is only illustrated, and is appropriately selected according to various situations such as the configuration of the multi-type air conditioner 1 and the use conditions.

As shown in FIG. 2, when the outdoor unit 3 is operated by turning on the power (step S1), it is determined whether or not the start condition for the stable operation mode 53 is satisfied (step S2).
As a starting condition, for example, when the compressor 13 is started in a cooling operation, where liquid back is likely to occur, or under this condition, for example, a condition where there is a possibility of liquid back, for example, at a low outside temperature. May be added.

If this start condition is satisfied, the opening degree of the indoor electric expansion valve 47 is set to 50 pulses of the initial opening degree via the expansion valve opening degree command unit 54 (see FIGS. 3 and 4).
Then, in the stable operation mode 53, it is determined whether or not the low pressure LS exceeds 0.1 MPa (step S3).
When the low pressure LS becomes 0.1 MPa or less (NO) in step S3, it is determined that the low pressure decreases and approaches a region where there is a possibility of adversely affecting the compressor 13, and the expansion valve opening command The opening degree of the indoor electric expansion valve 47 is fully opened via the part 54 (step S4).

For example, as indicated by point A in FIG. 3, when the low pressure LS drops and exceeds 0.1 MPa, the indoor electric expansion valve 47 is fully opened, so that the refrigerant flowing through the indoor heat exchanger 45 increases and enters the outdoor unit 3. The return refrigerant increases. Thereby, since the low pressure LS increases rapidly, it can be suppressed that the low pressure LS becomes a low low pressure LS that leads to a failure of the compressor 13 even in a situation where the low pressure LS rapidly decreases.
When it is fully opened in step S4, for example, for 5 seconds, the process returns to step S3.

If the low pressure LS exceeds 0.1 MPa (YES) in step S3, it is determined whether or not the opening degree of the indoor electric expansion valve (EEVC) 47 is fully open (step S6).
If the opening degree of the indoor electric expansion valve 47 is fully open in step S6 (YES), that is, if it is fully open in step S4, the opening degree of the indoor electric expansion valve 47 is the opening degree before being fully opened. To 10 degrees (step S7), and the process returns to step S3.

For example, step S7 is entered in a situation where the opening degree of the indoor electric expansion valve (EEVC) 47 is fully opened and the low-pressure pressure LS is rising as indicated by point B in FIG. In this case, the opening degree of the indoor electric expansion valve 47 is 33 pulses obtained by adding 10 pulses to the 23 pulses that are the opening degree before being fully opened.
Here, 10 pulses, that is, an amount corresponding to 25% of the controlled opening range, is again decreased to exceed 0.1 MPa even under a situation where the low pressure LS drops rapidly. This is so that there is no such thing.

  In this way, in a situation where the low pressure LS drops rapidly, the opening degree of the indoor electric expansion valve 47 is increased, so even if the changing speed of the low pressure LS is fast, there is a possibility that the compressor 13 will be adversely affected. It is possible to effectively prevent the area from coming out. Therefore, it is possible to prevent the operation of the compressor 13 from being interrupted due to an abnormal drop in the low pressure, so that the air conditioning performance in the indoor unit is not lowered and the indoor comfort can be maintained.

In step S6, when the opening degree of the indoor electric expansion valve 47 is not fully opened (NO), it is determined whether or not the low pressure LS exceeds 0.2 MPa (step S8).
When the low pressure LS becomes 0.2 MPa or less in Step S8 (NO), for example, 3 pulses (predetermined amount) are added to the current opening degree of the indoor electric expansion valve 47, and the opening degree is set to, for example, Command for 10 seconds (predetermined time) (step S9).

Since 3 pulses is an amount corresponding to 7.5% of the controlled opening range, the opening of the indoor electric expansion valve 47 gradually changes over time. Thereby, since the state of a refrigerant | coolant can be changed gradually, stabilization of control can be aimed at.
In addition, about this addition amount, it is preferable to set it as 5 to 10% of the opening range of control object.
Further, the command for 10 seconds can sufficiently cope with the fluctuation of the low-pressure pressure having a high change rate. For example, the duration time is preferably 5 to 30 seconds, and more preferably 10 to 20 seconds. For example, if it is shorter than 5 seconds, it is also related to the amount of addition of the opening, but there is a possibility that fluctuations across the control pressure increase and control stabilization is impaired.

When 10 seconds have elapsed, the process returns to step S3, and steps S3, S6, S8, and S9 are repeated to keep the low pressure (LP) in the system at 0.2 MPa or more. As a result, the operation of the compressor 13 is prevented from being interrupted due to an abnormal drop in low pressure.
For example, as shown in the region C of FIG. 4, three pulses are added every 10 seconds. However, when 60 pulses, which is the maximum value of the controlled opening range, is reached, it is not further increased as in region D of FIG. 4, and 60 pulses are maintained.

  Thus, since the low pressure can be maintained at a magnitude in the vicinity of 0.2 MPa, which is the control pressure, it is possible to suppress the low pressure LS leading to the failure of the compressor 13. As a result, it is possible to prevent a situation where the compressor 13 has to be stopped for protection, so that the air conditioning performance in the indoor unit does not deteriorate, and the indoor comfort can be maintained.

When the low pressure LS exceeds 0.2 MPa in step S8 (YES), it is determined whether or not the dome SH is continuously kept at 20 ° C. or higher for 20 seconds (step S10).
In step S10, if it is determined that the under-dome SH has continued to be 20 ° C. or higher for 20 seconds, for example, the state of region E in FIG. 4 (YES), it is determined that the refrigerant amount is insufficient. Then, the opening degree of the indoor electric expansion valve 47 is set as the opening direction.
In this case, it is determined whether the opening degree of the indoor electric expansion valve 47 is less than 60 pulses (step S11).

When the opening degree is less than 60 pulses in step S11 (YES), for example, 3 pulses (predetermined amount) are added to the current opening degree of the indoor electric expansion valve 47, and the opening degree is set, for example, for 20 seconds. Command (predetermined time) (step S12). However, the addition is limited so as not to exceed 60 pulses, which is the maximum value of the controlled opening range.
When 20 seconds have elapsed, the process returns to step S3 and the above is repeated.
For example, as shown in a region E in FIG.
If the opening is 60 pulses or more in step S11 (NO), that is, 60 pulses, this opening is held (step S13), the process returns to step S3, and the above is repeated.

If it is determined in step S10 that the SH under the dome has not continued to be 20 ° C. or higher for 20 seconds (NO), it is determined whether the SH under the dome has been continuously 10 ° C. or lower for 20 seconds ( Step S14).
In step S14, when it is determined that SH under the dome is continuously 10 ° C. or lower for 20 seconds (YES), it is determined that there is a possibility that liquid refrigerant more than expected may be sucked into the compressor 13, The opening degree of the indoor electric expansion valve 47 is set to be reduced.
This is, for example, a state like the superheat degree change locus KK of FIG.
In this case, it is determined whether the opening degree of the indoor electric expansion valve 47 exceeds 20 pulses (step S15).

When the opening degree exceeds 20 pulses in step S15 (YES), for example, 3 pulses (predetermined amount) are subtracted from the current opening degree of the indoor electric expansion valve 47, and the opening degree is, for example, 20 Commands for a second (predetermined time) (step S16).
When 20 seconds have elapsed, the process returns to step S3 and the above is repeated.
If the opening is 20 pulses or more in step S15 (NO), that is, if it is 20 pulses, this opening is held (step S17), the process returns to step S3, and the above is repeated.

For example, the opening degree is subtracted by 3 pulses every 20 seconds as in regions F and H of FIG.
However, when 20 pulses, which is the minimum value of the opening degree range to be controlled, are reached, the number of pulses is not reduced as shown in region H of FIG.
At the end of the region H, since the low pressure LS has become smaller than 0.2 MPa, the opening degree is added by 3 pulses in step S9 to become 23 pulses.

  When the amount of liquid refrigerant flowing into the compressor 13 exceeds the predetermined range, the stable operation mode 53 adjusts the opening degree of the indoor electric expansion valve 47 to be narrowed, that is, closes, and the indoor heat exchanger 45 Since the amount of liquid refrigerant passing through the refrigerant is reduced and reliably evaporated, the amount of liquid refrigerant flowing into the compressor 13 can be reduced, and the compressor 13 can be prevented from malfunctioning due to overload. it can.

In steps S12 and S16, the opening degree to be added and subtracted is 3 pulses, which has the same meaning as in step S9 described above.
Further, the command for 20 seconds is longer than that in step S9. This is because the quantitative change of the liquid refrigerant is gentler than the change rate of the low-pressure pressure, so that stabilization of control is taken into consideration. . From this point of view, the opening degree to be added or subtracted may be made smaller than that in step S9.

  In the present embodiment, the amount of liquid refrigerant flowing into the compressor 13 is determined by the magnitude of the degree of superheat under the dome. This is, for example, from the suction pipe temperature of the compressor 13 to the low pressure. It is estimated by using the suction superheat degree obtained by subtracting the refrigerant saturation temperature, the discharge superheat degree obtained by subtracting the refrigerant saturation temperature at high pressure from the compressor discharge pipe temperature, the outside air temperature, the heat exchange temperature of the indoor unit, etc. Also good.

As described above, the stable operation mode 53 can suppress the decrease in the low-pressure pressure LS and the inflow of the liquid refrigerant exceeding the allowable predetermined amount, so that it is possible to suppress the possibility that the compressor 13 breaks down.
As a result, it is possible to prevent a situation where the compressor 13 has to be stopped for protection, so that the air conditioning performance in the indoor unit does not deteriorate, and the indoor comfort can be maintained.
In addition, it is not necessary to install a large accumulator, the cost can be reduced by downsizing the accumulator, and the downsizing of the outdoor unit 3 can be achieved. Further, if the control accuracy is improved, the accumulator can be eliminated.

The present invention is not limited to the invention according to the above-described embodiment, and can be appropriately modified without departing from the gist thereof.
For example, in the above embodiment, the number of indoor units 11A and 11B connected in parallel to the outdoor unit 3 may be any number as long as it is two or more, and is not particularly limited. The number of outdoor units 3 is not particularly limited as long as it is one or more.
Furthermore, it is needless to say that specific numerical values such as time and temperature exemplified in the above embodiment are merely examples, and are not limited thereto.

It is a refrigerating cycle figure of the multi type air harmony machine concerning one embodiment of the present invention. It is a flowchart of the stable operation mode in the multi-type air conditioner concerning one Embodiment of this invention. It is a sequence diagram which shows the change of the opening degree instruction | command by the stable operation mode based on the flow of FIG. 2 when the change locus | trajectory of under-dome superheat degree and low pressure is assumed. It is a sequence diagram which shows the change of the opening degree instruction | command by the stable operation mode based on the flow of FIG. 2 when the another change locus | trajectory of under-dome superheat degree and low pressure is assumed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multi type air conditioner 3 Outdoor unit 11A, 11B Indoor unit 13 Compressor 47 Indoor electric expansion valve 51 Control part 53 Stable operation mode

Claims (3)

A control unit that controls the operation of a plurality of indoor units that are connected in parallel to at least one outdoor unit having a compressor, each having an indoor expansion valve for adjusting the flow rate of refrigerant and decompressing and expanding the refrigerant; A multi-type air conditioner,
The control unit flows into the compressor so that the low pressure, which is the pressure of the refrigerant sucked into the compressor, exceeds a predetermined control pressure, and when the low pressure exceeds the control pressure. A stable operation mode for controlling the opening of the indoor expansion valve is provided so that the amount of liquid refrigerant falls within a predetermined range,
In the stable operation mode, the opening degree of the indoor expansion valve is changed by a predetermined amount every predetermined time.   2. The multi-type air conditioner according to claim 1, wherein in the stable operation mode, the indoor expansion valve is fully opened when the low-pressure pressure becomes less than a predetermined limit pressure lower than the control pressure. The multi-type air conditioner according to claim 1 or 2, wherein the stable operation mode is performed when the outdoor unit performs a cooling operation and the compressor is activated.

Images