Superheat control for HVACandR systems

Abstract

A superheat control utilizes a sensor at a location downstream of an evaporator after some heat is delivered to the refrigerant. In one embodiment, the compressor is a sealed compressor with at least a portion of the refrigerant being heated by an electric motor. The temperature is sensed after the refrigerant temperature has increased after passing over the electric motor. In another embodiment, the refrigerant temperature is measured after some minimal compression and minimal temperature rise has occurred within the compressor pumping elements. In either case, by measuring the temperature of the refrigerant after some additional heat has been added to the refrigerant, the refrigerant super-heat leaving the evaporator can be controlled to a lower value. The improved superheat control enhances the system performance by increasing system efficiency, system capacity and improving oil return to the compressor.

Claims

1. A refrigerant system comprising: a compressor, said compressor having a compressor pump unit and a suction inlet; a compressed refrigerant passing from said compressor downstream to a condenser and then downstream to an expansion device; an evaporator positioned downstream of said expansion device; a sensor for sensing a temperature of a refrigerant after heat has been added to the refrigerant downstream of the evaporator and said sensor being utilized to maintain a refrigerant thermodynamic state at a location between the expansion device and within compression elements; and a parameter at least partially defining said refrigerant thermodynamic state is selected from the following set: refrigerant temperature, refrigerant superheat, quality of the refrigerant.

2. A refrigerant system comprising: a compressor, said compressor having a compressor pump unit and a suction inlet; a compressed refrigerant passing from said compressor downstream to a condenser and then downstream to an expansion device; an evaporator positioned downstream of said expansion device; a sensor for sensing a temperature of a refrigerant after heat has been added to the refrigerant downstream of the evaporator and said sensor being utilized to maintain a refrigerant thermodynamic state at a location between the expansion device and within compression elements; and wherein said location is selected from the following set of possible locations: a) between an evaporator exit and a compressor inlet, b) near an evaporator exit, c) between the compressor inlet and an entrance to the compressor pump unit, d) within the compressor pump unit, e) within the vicinity of the compressor pump unit.

3. The refrigerant system as set forth in claim 1, wherein said compressor pump unit is driven by an electric motor.

4. The refrigerant system as set forth in claim 3, wherein said location is between the motor and the compressor pump unit.

5. The refrigerant system as set forth in claim 1, wherein said compressor is a sealed compressor and said sealed compressor having a housing with an electric motor and the compressor pump unit, and said sensor is located such that at least a portion of the refrigerant reaching said sensor has cooled the electric motor.

6. The refrigerant system as set forth in claim 1, wherein said sensor measures temperature within the compressor.

7. The refrigerant system as set forth in claim 6, wherein said sensor measures temperature within the compressor pump unit.

8. The refrigerant system as set forth in claim 6, wherein said sensor measures temperature outside of the pump unit.

9. The refrigerant system as set forth in claim 1, wherein said sensor is positioned outside of the compressor and measures temperature of a compressor shell.

10. The refrigerant system as set forth in claim 2, wherein a parameter at least partially defining said refrigerant thermodynamic state is selected from the following set: refrigerant temperature, refrigerant superheat, quality of the refrigerant.

11. The refrigerant system as set forth in claim 1, wherein said heat is added by at least one of the following: heat generated by an electric motor, heat generated by friction, heat generated by a compression process within the compressor pump unit, and heat from an ambient environment.

12. The refrigerant system as set forth in claim 1, wherein said compressor has a housing containing said compressor pump unit and an electric motor is located outside of said housing.

13. The refrigerant system as set forth in claim 1, wherein said sensor communicates with an electronic control, said electronic control controlling the refrigerant system to achieve a desired amount of superheat.

14. The refrigerant system as set forth in claim 13, wherein said electronic control controls the expansion device.

15. The refrigerant system as set forth in claim 1, wherein said sensor is a temperature sensor.

16. The refrigerant system as set forth in claim 15, wherein said sensor is a temperature transducer.

17. The refrigerant system as set forth in claim 15, wherein a thermowell is formed within a housing of the compressor.

18. The refrigerant system as set forth in claim 17, wherein a temperature sensor is located within said thermowell.

19. The refrigerant system as set forth in claim 18, wherein said sensor measures temperature at the location that is selected from the following set of possible locations: a) within the compressor pump unit, b) within the compressor, c) within the compressor oil sump, d) within the vicinity of the compressor pump unit.

20. The refrigerant system as set forth in claim 1, wherein said sensor is a bulb of a thermal expansion device.

21. The refrigerant system as set forth in claim 1, wherein a bulb communicates with said expansion device to control the refrigerant thermodynamic state.

22. The refrigerant system as set forth in claim 1, wherein said compressor pump unit is a scroll compressor, said scroll compressor having a non-orbiting scroll member having a base and a generally spiral wrap, and an orbiting scroll member having a base and a generally spiral wrap, and a suction port leading into compression chambers defined between said wraps of said orbiting and non-orbiting scroll members, said temperature sensor being adjacent to said suction port.

23. The refrigerant system as set forth in claim 1, wherein a compressor is selected from a group of a screw compressor, a rotary compressor, a centrifugal compressor and a reciprocating compressor.

24. The refrigerant system as set forth in claim 1, wherein the expansion device is a thermal expansion device.

25. The refrigerant system as set forth in claim 1, wherein the expansion device is an electronic expansion device.

26. A method of operating a refrigerant system comprising: providing a compressor, said compressor having a compressor pump unit and a suction inlet; a compressed refrigerant passing from said compressor downstream to a condenser and then downstream to an expansion device; an evaporator positioned downstream of said expansion device; a sensor for sensing a temperature of a refrigerant after heat has been added to the refrigerant downstream of the evaporator, said sensor sending a signal to control a refrigerant thermodynamic state at a location between the expansion device and within compression elements; and wherein said refrigerant thermodynamic state is at least partially defined by a parameter selected from the following set: refrigerant temperature, refrigerant superheat, quality of the refrigerant.

27. The method as set forth in claim 26, wherein said location is selected from the following set of possible locations: a) between the evaporator exit and the compressor inlet, b) near the evaporator exit, c) between the compressor inlet and the entrance to the compressor pump unit, d) within the compressor pump unit, e) within the vicinity of the compressor pump unit.

28. The method as set forth in claim 26, wherein said compressor pump unit is driven by an electric motor.

29. The method as set forth in claim 28, wherein said location is between the motor and the compressor pump unit.

30. The method as set forth in claim 26, wherein said compressor is a sealed compressor and said sealed compressor having a housing with an electric motor and the compressor pump unit, and said sensor is located such that at least a portion of the refrigerant reaching said sensor has cooled the electric motor.

31. The method as set forth in claim 26, wherein said sensor measures temperature within the compressor.

32. The method as set forth in claim 31, wherein said sensor measures temperature within the pump unit.

33. The method as set forth in claim 31, wherein said sensor measures temperature outside of the pump unit.

34. The method as set forth in claim 26, wherein said sensor is positioned outside of the compressor and measures temperature of a compressor shell.

35. The method as set forth in claim 26, wherein said heat is added by at least one of the following: heat generated by an electric motor, heat generated by friction, heat generated by a compression process within the compressor pump unit, and heat from an ambient environment.

36. The method as set forth in claim 26, wherein said compressor has a housing containing said compressor pump unit and an electric motor is located outside of said housing.

37. The method as set forth in claim 26, wherein said sensor communicates with an electronic control, said electronic control controlling the refrigerant system to achieve a desired amount of superheat.

38. The method as set forth in claim 37, wherein said electronic control controls an expansion device.

39. The method as set forth in claim 26, wherein said sensor is a temperature sensor.

40. The method as set forth in claim 39, wherein said sensor is a temperature transducer.

41. The method as set forth in claim 39, wherein a thermowell is formed within a housing for the compressor.

42. The method as set forth in claim 41, wherein a temperature sensor is located within said thermowell.

43. The method as set forth in claim 42, wherein said sensor is formed to measure temperature at the location that is selected from the following set of possible locations: a) within the compressor pump unit, b) within the compressor, c) within the compressor oil sump, d) within the vicinity of the pump unit.

44. The method as set forth in claim 26, wherein said sensor is a bulb of a thermal expansion device.

45. The method as set forth in claim 26, wherein a bulb communicates with said expansion device to control the refrigerant thermodynamic state.

46. The method as set forth in claim 26, wherein said compressor pump unit is a scroll compressor, said scroll compressor having a non-orbiting scroll member having a base and a generally spiral wrap, and an orbiting scroll member having a base and a generally spiral wrap, and a suction port leading into compression chambers defined between said wraps of said orbiting and non-orbiting scroll members, said temperature sensor being adjacent to said suction port.

47. The method as set forth in claim 26, wherein a compressor is selected from a group of a screw compressor, a rotary compressor, a centrifugal compressor and a reciprocating compressor.

48. The method as set forth in claim 26, wherein the expansion device is a thermal expansion device.

49. The method as set forth in claim 26, wherein the expansion device is an electronic expansion device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a cross-sectional view of a refrigerant system incorporating the present invention.

(2) FIG. 2 is a schematic view of a second embodiment.

(3) FIG. 3 is a partial view of another embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) A refrigerant system 20 is illustrated in FIG. 1 incorporating, as an example, a scroll compressor 22 delivering compressed refrigerant downstream to a condenser 24. An expansion device 26 is preferably an electronic expansion device, and is generally known in the industry. Refrigerant having passed through the expansion device 26 passes through an evaporator 28 through an optional suction modulation valve 30, and through a suction line 38 back to the compressor 22. A compressor shell 34 houses an electric motor 36, and a compressor pump unit incorporating a non-orbiting scroll member 42 and an orbiting scroll member 44. As is shown in this Figure, a temperature sensor 46 is placed within the housing shell 34 and adjacent to a suction entrance for the compressor pump unit. The sensor 46 communicates with an electronic controller 32, which in turn controls the electronic expansion device 26, or/and the optional suction modulation valve 30.

(5) It is known in the art to utilize a temperature sensed at the evaporator 28 exit location or on the compressor suction line 38, before refrigerant enters the compressor 22, and communicate the value of this temperature to an electronic controller, with the electronic controller than controlling the electronic expansion device 26, or/and the suction modulation valve 30. By measuring a temperature inside the compressor shell 34, the present invention takes advantage of the fact that the refrigerant having passed over the motor 36 cools the motor, causing the refrigerant temperature to increase. As seen in the FIG. 1, after the refrigerant enters the compressor, some portion of the refrigerant is delivered directly to the scroll elements 42 and 46 and the other part of the refrigerant finds its way to the bottom of the motor through the gaps 112 between the compressor shell 34 and the motor stator 116 as well as the gap 114 between the motor rotor 118 and the stator 116. The refrigerant then finds its way back from the bottom of the shell through these and other gaps back into the compression elements 42 and 46, cooling the motor. Thus, additional motor heat has been consumed by the refrigerant. As in case of the prior art, if the temperature sensor would had been located on the suction line outwardly of the housing shell 34, the temperature of the refrigerant that is utilized to determine the refrigerant superheat would not take into account this additional heat added to the refrigerant prior to the refrigerant entering the compression elements. By utilizing this downstream location for the temperature sensor 46, the present invention allows a compressor designer to better match the provided superheat with that minimum superheat which is desired. The present invention thus allows the compressor designer to lower the superheat value of the refrigerant leaving the evaporator to the values far below the commonly used 6-12 range of the prior art and enhance system performance while assure reliable compressor operation. Additionally, the compressor discharge and oil temperatures are reduced, further improving compressor reliability.

(6) FIG. 2 shows another embodiment 50, wherein an electric motor 52 is located outside of the compressor 54 and has a drive transmission 62. A suction line 56 and a discharge line 58 communicate the compressor with other components of a refrigerant system, such as shown in FIG. 1. In this case, the temperature sensor 60 is located preferably within the compressor pump unit 54 at a location before a substantial compression has occurred. At this location, the refrigerant will be heated additionally by the compression process provided by the elements of the compressor pump unit 54. Thus, by taking the temperature at this location, the control is better equipped to minimize the amount of superheat deemed necessary at the evaporator 28. This embodiment is particularly well suited for screw or centrifugal compressors. The compressor pump unit 54 is disclosed as a screw compressor. As in the previous embodiment, a small amount of liquid in a two-phase refrigerant would be allowed at the evaporator exit.

(7) FIG. 3 shows another embodiment 70, wherein the compressor shell 34 includes a thermowell 36 preferably positioned at the same location of the FIG. 1 sensor 46. This invention is particularly useful for a thermal expansion device 126 having a bulb 74 as a sensing element that contains a substance, which expands and contracts in response to the sensed temperature. The bulb can be made to be a part of the thermowell installation. Again, this type of control is known in the art. It is the location of the bulb that is inventive here.

(8) A worker of ordinary skill in the art would recognize how to use the sensed refrigerant temperature to control the expansion devices 26 and 126 or/and the suction modulation valve 30 to achieve a desired superheat. This control forms no portion of this invention. Rather, it is the use of such control to obtain more optimal superheat values that provide enhanced system performance and reliable compressor operation that is inventive here. If the electronic expansion is replaced by the TXV (thermal expansion device) then the use of a controller may not be needed at all, as the amount of superheat can be directly (mechanically) controlled by the TXV type expansion device itself. In summary, the refrigerant temperature is measured either inside of the compressor or on the compressor shell to control the thermodynamic state of refrigerant (the amount of superheat or amount of liquid) at various possible locations between the evaporator and compressor pumping elements.

(9) Although the present invention is predominantly illustrated for a scroll compressor, other type of compressors would naturally fall within the scope of this invention such as screw compressors, reciprocating compressors, rotary compressors, centrifugal compressors, etc. An example of refrigerant systems that fall with the scope of this invention include air conditioning systems and heat pump systems for cooling or/and respectively heating houses, building, computer rooms, etc. The refrigerant systems also include refrigeration systems to cool and freeze products in refrigeration containers, truck-trailer units, and supermarket installations. As known, the refrigerant systems can be equipped with multiple circuits, have various means of compressor unloading, as well as being equipped with various performance enhancement options and features such as for instance an economizer cycle. A variety of different type of refrigerants can be used in these systems including, but not limited to, R410A, R134a, R404A, R22, and CO.sub.2.

(10) Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.