Air-conditioning apparatus and operation control method therefor

Patent metadata

Field	Value
Publication number	US-9644877-B2
Application number	US-201214437514-A
Country	US
Kind code	B2
Filing date	Nov 22, 2012
Priority date	Nov 22, 2012
Publication date	May 9, 2017
Grant date	May 9, 2017

Abstract

Frequency of a compressor is controlled so that an evaporating temperature reaches a target evaporating temperature during cooling operation, and, when refrigerant stagnation in a condenser of an outdoor unit is detected during cooling operation, a stagnation-resolving operation is implemented. The stagnation-resolving operation includes stagnation suppression control in which the target evaporating temperature is reduced within a range in which an evaporator does not freeze so as to increase a refrigerant circulation volume in the condenser, and stagnation-avoidance priority control which is implemented when implementation of the stagnation suppression control is not able to resolve stagnation, and in which an opening degree of an expansion valve is controlled to be opened and the target evaporating temperature is further reduced so as to further increase the refrigerant circulation volume.

First claim

The invention claimed is:

1. An air-conditioning apparatus comprising:
a refrigerant circuit in which an outdoor unit including a compressor whose frequency can be varied and an outdoor heat exchanger, and a plurality of indoor units each including an indoor heat exchanger are connected with refrigerant pipes, and which performs at least a cooling operation in which the outdoor heat exchanger functions as a condenser and also the indoor heat exchanger functions as an evaporator;
an expansion valve provided between the outdoor heat exchanger and the indoor heat exchanger in the refrigerant circuit; and
a controller configured to control frequency of the compressor so that an evaporating temperature reaches a target evaporating temperature during cooling operation, and, when refrigerant stagnation in the condenser of the outdoor unit is detected during cooling operation, implement a stagnation-resolving operation,
wherein, the controller performs, as the stagnation-resolving operation,
stagnation suppression control in which the target evaporating temperature is reduced within a range in which the evaporator does not freeze so as to increase a refrigerant circulation volume in the condenser, and, when implementation of the stagnation suppression control is not able to resolve stagnation, stagnation-avoidance priority control in which an opening degree of the expansion valve is controlled to be opened and also the target evaporating temperature is further reduced so as to further increase the refrigerant circulation volume.

2. The air-conditioning apparatus of claim 1 ,
wherein the controller detects the refrigerant stagnation in the condenser in accordance with a difference in pressure between before and after the condenser.

3. The air-conditioning apparatus of claim 1 ,
wherein the controller detects the refrigerant stagnation in the condenser in accordance with the refrigerant circulation volume in the condenser.

4. The air-conditioning apparatus of claim 1 ,
wherein, in the stagnation suppression control, the controller
does a repetition of an operation of reducing the target evaporating temperature for a predetermined stagnation suppression control implementation time period so as to increase the refrigerant circulation volume flowing through the condenser to more than or equal to a refrigerant circulation volume at which the refrigerant stagnation to the condenser does not occur, and, when the refrigerant stagnation is resolved during the repetition, ends the stagnation-resolving operation, and,
when the stagnation suppression control implementation time period elapsed without the refrigerant stagnation in the condenser being resolved, performs the stagnation-avoidance priority control.

5. The air-conditioning apparatus of claim 1 ,
wherein, in the stagnation suppression control, the controller,
when a liquid pipe temperature of the evaporator is a predetermined temperature immediately before freezing or higher, does a repetition of an operation of reducing the target evaporating temperature for a predetermined stagnation suppression control implementation time period so as to increase the refrigerant circulation volume flowing through the condenser to more than or equal to a refrigerant circulation volume at which the refrigerant stagnation to the condenser does not occur, and, when the refrigerant stagnation is resolved during the repetition, ends the stagnation-resolving operation, and,
when the liquid pipe temperature of the evaporator is lower than the temperature immediately before freezing, waits without reducing the target evaporating temperature until the stagnation suppression control implementation time period elapsed, and, when the stagnation suppression control implementation time period elapsed since the stagnation suppression control was started, performs the stagnation-avoidance priority control.

6. The air-conditioning apparatus of claim 1 ,
wherein, in the stagnation-avoidance priority control, the controller,
for a predetermined stagnation-avoidance priority control implementation time period, does a repetition of a combination of an operation of controlling the opening degree of the expansion valve to be opened so as to increase the refrigerant circulation volume flowing through the condenser to more than or equal to a refrigerant circulation volume at which refrigerant does not stagnate in the condenser, and an operation of reducing the target evaporating temperature in the stagnation-avoidance priority control.

7. The air-conditioning apparatus of claim 6 ,
wherein the stagnation-avoidance priority control implementation time period is shorter than the stagnation suppression control implementation time period.

8. The air-conditioning apparatus of claim 1 ,
wherein, at a time of the stagnation-avoidance priority control, the controller
forces an air-sending device of an indoor unit which was stopped among the plurality of indoor units to be activated so as to increase a refrigerant circulation volume in the refrigerant circuit.

9. The air-conditioning apparatus of claim 1 ,
wherein the controller,
when once the refrigerant stagnation is resolved by the stagnation-resolving operation, determines, in accordance with an outdoor air temperature, a condensing temperature, and a condenser air flow rate, an interval that elapses before the stagnation-resolving operation is then performed again.

10. The air-conditioning apparatus of claim 1 ,
wherein, when all of the plurality of indoor units are stopped during stagnation-resolving operation, the controller stops the compressor, and, when a saturation temperature of the outdoor heat exchanger falls below an outdoor air temperature while the compressor is stopped, the controller drives an air-sending device of the outdoor heat exchanger so as to resolve stagnation in the outdoor heat exchanger.

11. The air-conditioning apparatus of claim 1 ,
wherein the condenser has a structure in which a plurality of plate-shaped fins disposed vertically are spaced, and in which a plurality of heat-transfer tubes extending perpendicular to and through the plurality of plate-shaped fins are provided, and
wherein, in a determination as to whether or not the refrigerant stagnation was resolved, when a state in which a difference in pressure between before and after the condenser is larger than a difference in head between an uppermost path and a lowermost path among a plurality of paths composed of the plurality of heat-transfer tubes lasts for a predetermined duration or a duration determined in accordance with a refrigerant circulation volume per path of the condenser, the controller determines that the refrigerant stagnation was resolved.

12. The air-conditioning apparatus of claim 1 ,
wherein the expansion valve whose opening degree is controlled in the stagnation-avoidance priority control is an expansion valve provided in each of the plurality of indoor units.

13. The air-conditioning apparatus of claim 1 , further comprising:
an accumulator provided between the compressor and the indoor heat exchanger; and
a bypass branched off from between the outdoor heat exchanger and the expansion valve, and extended to a suction side of the accumulator through a subcooling expansion valve,
wherein the bypass includes a subcooling heat exchanger configured to exchange heat between refrigerant between the outdoor heat exchanger and the expansion valve, and refrigerant that passed through the subcooling expansion valve in the bypass, and
wherein the expansion valve whose opening degree is controlled in the stagnation-avoidance priority control is the subcooling expansion valve.

Assignees

• Aoyama Yutaka
• Mitsubishi Electric Corp

Inventors

• Aoyama Yutaka

Classifications

• F25B2700/1933

  Suction pressures · CPC title

• F25B49/022 Primary

  Compressor control arrangements · CPC title

• F25B2600/0253

  with variable speed · CPC title

• F25B2700/21174

  of the refrigerant at the inlet of the evaporator · CPC title

• F25B49/02

  for compression type machines, plants or systems · CPC title