Expansion valve control system and method for air conditioning apparatus

• US 20090031740A1
• Filed: 08/01/2007
• Published: 02/05/2009
• Est. Priority Date: 08/01/2007
• Status: Active Grant

• Current Assignee: Trane International Inc. (Trane Technologies plc)
• Original Assignee: American Standard Companies Incorporated (Ideal Standard International Topco SCA)
• Inventors: Douglas, Jonathan David
• Granted Patent: US 8,151,583 B2
• Time in Patent Office: Days
• US Class Current: 62/225
• CPC Class Codes: F25B 13/00 Compression machines, plants or systems, with reversible cycle defrosting cycles F25B47/02
• CPC Class Codes: F25B 2313/005 Outdoor unit expansion valves
• CPC Class Codes: F25B 2500/26 characterised by the startup of the refrigeration cycle
• CPC Class Codes: F25B 2500/27 characterised by the stop of the refrigeration cycle
• CPC Class Codes: F25B 2500/28 Means for preventing liquid refrigerant entering into the compressor
• CPC Class Codes: F25B 2600/01 Timing
• CPC Class Codes: F25B 2600/21 Refrigerant outlet evaporator temperature
• CPC Class Codes: F25B 2700/1933 Suction pressures
• CPC Class Codes: F25B 2700/2106 of fresh outdoor air
• CPC Class Codes: F25B 2700/21151 at the suction side of the compressor
• CPC Class Codes: F25B 2700/2117 of an evaporator
• CPC Class Codes: F25B 41/34 with the valve member being actuated by electric means, e.g. by piezoelectric actuators
• CPC Class Codes: F25B 41/35 by rotary motors, e.g. by stepping motors
• CPC Class Codes: Y02B 30/70 Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

Abstract

A vapor compression air conditioning system includes a motor operated expansion valve and control unit including sensors for determining the amount of superheat of the working fluid at or adjacent to the compressor inlet. Expansion valve position is adjusted to maintain a predetermined amount of superheat. The sensors may sense working fluid evaporator temperature and temperature downstream of the evaporator. Dual motor operated expansion valves may be disposed in the working fluid conduit between the heat exchangers in a reversible system. In operation, the expansion valve position may be set as a function of ambient temperature, a previous position, and predetermined superheat requirements to minimize liquid ingestion by the compressor.

Claims

1. In a vapor compression air conditioning system including a compressor, and a fluid circulating circuit including a condenser heat exchanger and an evaporator heat exchanger interconnected by a first fluid conducting conduit, the improvement comprising:

a motor operated expansion valve interposed in said first conduit between said condenser heat exchanger and said evaporator heat exchanger;

at least one sensor for measuring a parameter related to a condition of a working fluid flowing through a second conduit between said evaporator heat exchanger and an inlet to said compressor; and

a control unit operably connected to said expansion valve and said at least one sensor for setting a position of said expansion valve in a first operating mode of said system to control the flow of working fluid through said evaporator heat exchanger to maintain a predetermined amount of superheat of said working fluid in said second conduit.

2. The system set forth in claim 1 wherein:

at least two sensors are provided for measuring parameters related to the condition of said working fluid in said second conduit, said at least two sensors comprising a temperature sensor and a pressure sensor.

3. The system set forth in claim 2 including:

an ambient outdoor temperature sensor operably connected to said control unit.

4. The system set forth in claim 2 wherein:

at least two temperature sensors are provided for measuring the working fluid temperature at an inlet to said evaporator heat exchanger and at an outlet of said evaporator heat exchanger, said temperature sensors being operably connected to said control unit.

5. The system set forth in claim 1 wherein:

said system includes a working fluid flow reversing valve for converting said condenser heat exchanger to an evaporator heat exchanger and said evaporator heat exchanger to a condenser heat exchanger and said control unit is operable to cause said motor operated valve to operate in a position to provide substantially unrestricted flow of fluid between said heat exchangers.

6. The system set forth in claim 1 including:

a reversing valve for reversing the flow of working fluid between said compressor and said condenser heat exchanger and between said compressor and said evaporator heat exchanger and a second expansion valve disposed in said first conduit between said condenser heat exchanger and said evaporator heat exchanger for controlling the flow of working fluid through said system when said system is operated in a second operating mode.

7. The system set forth in claim 6 wherein:

said second expansion valve is motor operated and is operably controlled by said control unit.

8. The system set forth in claim 6 wherein:

said second expansion valve is a thermal type expansion valve.

9. The system set forth in claim 1 wherein:

said motor operated expansion valve is disposed in a component of said system disposed outdoors.

10. The system set forth in claim 1 wherein:

said motor operated expansion valve is disposed in a component of said system disposed indoors.

11. The system set forth in claim 1 wherein:

said control unit comprises an electrical control circuit connected to signal input conductor means for receiving a signal related to at least one of operation of said system to energize said compressor, a position of a working fluid circuit reversing valve and a signal from said at least one sensor.

12. The system set forth in claim 11 wherein:

said control unit includes means for inputting values to said control circuit related to at least one of the type of working fluid, the capacity of said compressor, an operating mode of said system, and a relationship between the amount of superheat of said working fluid and a change in evaporator temperature to achieve a predetermined amount of superheat.

13. The system set forth in claim 12 wherein:

said values in said control circuit related to said relationship between the amount of superheat and said evaporator temperature comprises a constant value of change in evaporator temperature.

14. In a vapor compression air conditioning system including a compressor and a fluid circulating circuit including a condenser heat exchanger and an evaporator heat exchanger interconnected by fluid conducting conduits, said system including a motor operated expansion valve interposed in a conduit between said condenser heat exchanger and said evaporator heat exchanger, at least one sensor for measuring a parameter related to a condition of a working fluid flowing between said evaporator heat exchanger and an inlet to said compressor, and a control unit operably connected to said expansion valve and said at least one sensor, a method of controlling the position of said expansion valve comprising the steps of:

in a first operating mode of said system controlling the flow of working fluid through said evaporator heat exchanger to maintain a predetermined amount of superheat of said working fluid flowing to said compressor inlet.

15. The method set forth in claim 14 including the step of:

causing said control unit to respond to a signal for energizing said system to move said expansion valve to a position based on the outdoor ambient temperature.

16. The method set forth in claim 15 including the step of:

varying the gain of said control unit as a function of a current position of said expansion valve.

17. The method set forth in claim 15 including the step of:

varying the gain of said control unit as a function of measured superheat.

18. The method set forth in claim 15 including the step of:

moving said expansion valve to an initial position based on an estimate of the evaporating temperature and condensing temperature of said working fluid and wherein said condensing temperature is based on said outdoor ambient temperature.

19. The method set forth in claim 14 including the step of:

causing said control unit to respond to a signal for energizing said system to move said expansion valve to a position based on at least one of a previous position of said expansion valve and a position based on an estimate of the operating temperature of said evaporator heat exchanger.

20. The method set forth in claim 14 including the step of:

causing said control system to move said expansion valve to a predetermined position dependent on elapsed time from a signal to start said compressor.

21. The method set forth in claim 14 including the step of:

prior to startup of said system, moving said expansion valve to a predetermined position which position is a fraction of a desired valve position and then providing a signal to energize said compressor.

22. The method set forth in claim 14 including the step of:

measuring superheat of said working fluid at said compressor inlet during operation of said system and causing said expansion valve to control flow of working fluid to maintain an evaporator heat exchanger temperature which will provide a predetermined amount of superheat of said working fluid at said compressor inlet.

23. The method set forth in claim 14 including the step of:

causing said control unit to close said expansion valve prior to de-energizing said compressor.

24. The method set forth in claim 14 including the step of:

deenergizing said compressor when the evaporator temperature is a predetermined number of degrees below the evaporator temperature just prior to a signal to de-energize said compressor to minimize ingestion of liquid working fluid by said compressor on a succeeding startup thereof.

25. The method set forth in claim 14 including the step of:

providing a signal to said expansion valve to move to a position to minimize restriction of working fluid flow directly from said evaporator heat exchanger to said condenser heat exchanger.

26. The method set forth in claim 14 including the step of:

de-energizing said compressor in response to sensing a predetermined condition of superheat of said working fluid for a predetermined period of time.

27. The method set forth in claim 14 including the step of:

de-energizing said compressor in response to operation of said system at a predetermined low pressure of said working fluid at said compressor inlet for a predetermined period of time.

28. The method set forth in claim 14 including the step of:

adjusting the position of said expansion valve based on a history of positions of said expansion valve over a predetermined period of time.