HEAT PUMP APPARATUS AND METHOD

• US 20080173034A1
• Filed: 01/19/2007
• Published: 07/24/2008
• Est. Priority Date: 01/19/2007
• Status: Abandoned Application

• Current Assignee: Northeast Bank
• Original Assignee: Hallowell International
• Inventors: Shaw, David N.
• Application Number:
  US11/624,743
• Publication Number:
  US 20080173034A1
• Time in Patent Office: Days
• US Class Current: 62/160
• CPC Class Codes: F25B 1/10 with multi-stage compression with cascade operation F25B7/00
• CPC Class Codes: F25B 13/00 Compression machines, plants or systems, with reversible cycle defrosting cycles F25B47/02
• CPC Class Codes: F25B 2313/02741 using one four-way valve
• CPC Class Codes: F25B 2313/0315 Temperature sensors near the outdoor heat exchanger
• CPC Class Codes: F25B 2400/01 Heaters
• CPC Class Codes: F25B 2400/0401 for the compressor
• CPC Class Codes: F25B 2400/13 Economisers
• CPC Class Codes: F25B 2700/2106 of fresh outdoor air

Abstract

A heat pump system and method is presented having a primary compressor, a booster compressor, an economizer, a microprocessor, an air temperature sensor, and a temperature sensor for sensing a temperature commensurate with the boiling temperature of refrigerant in the outside coil. The microprocessor effects controlled operation of the primary compressor, the booster compressor and the economizer when a thermostat calls for heat and in accordance with predetermined ranges of air temperature. The microprocessor calculates a defrost trigger temperature, and defrost operation is initiated when the sensed refrigerant boiling temperature is lower than the trigger temperature for a period of time.

Claims

1. A heat pump system including:

a primary compressor;

a booster compressor;

at least said primary compressor being a variable capacity compressor,

a refrigerant conduit system, said primary compressor and said booster compressor being in series in said refrigerant conduit system, and said conduit system including a first conduit segment connected to deliver refrigerant to the inlet to said primary compressor when said booster compressor in inoperative, and said conduit system including a second conduit segment between the discharge from said booster compressor and the inlet to said primary compressor to deliver refrigerant between said booster compressor and said primary compressor when both of said compressors are operating;

a first temperature sensor for sensing the temperature of outdoor ambient air;

a controller, said controller being connected between a thermostat and said primary and booster compressors, said controller receiving signals from said first temperature sensor and from the thermostat to operate said primary compressor and said booster compressor in a predetermined sequence as follows;

(a) effect a first mode of operation of partial capacity operation of said primary compressor (M1) when the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor air temperature in a first range of temperatures;

(b) effect operation in M1 and effect a second mode of operation of full capacity operation of said primary compressor (M2) when the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor air temperature in a second range of temperatures;

(c) effect operation in M2 and effect a third mode of operation of full capacity operation of said primary compressor, and operation of said booster compressor (M3) when the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor air temperature in a third range of temperatures.

2. A heat pump system as in claim 1 including;

an electrical resistance backup heater in the heat pump system;

said controller operating to effect full capacity operation of said primary compressor and said booster compressor, and operation of said electrical resistance backup heater when the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor air temperature in a fourth range of temperatures.

3. A heat pump system as in claim 1 wherein:

M3 operation is effected on a cyclical basis.

4. A heat pump system as in claim 1 wherein:

said thermostat is a multi-stage thermostat; and

said controller effects operation in M1 when a first stage of said thermostat calls for heat and the outdoor ambient temperature sensed by said first temperature sensor is in said first range of temperatures; and

,

said controller effects operation in M2 when a second stage of said thermostat calls for heat and the outdoor ambient temperature sensed by said first temperature sensor is in said second range of temperatures; and

said controller effects operation in M2 when a first stage of said thermostat calls for heat and the outdoor ambient temperature sensed by said first temperature sensor is in said third range of temperatures; and

said controller effects operation in M3 when a second stage of said thermostat calls for heat and the outdoor ambient temperature sensed by said first temperature sensor is in said third range of temperatures.

5. A heat pump system as in claim 1 including:

an electrical resistance backup heater in the heat pump system; and

wherein

said thermostat is a multistage thermostat; and

wherein;

said controller allows operation in M3 when a first stage of said thermostat calls for heat and the outdoor ambient temperature sensed by said first temperature sensor is in a fourth range of temperatures; and

said controller allows operation in M3 and allows operation of said backup heater when a second stage of said thermostat calls for heat and the outdoor ambient temperature sensed by said first temperature sensor is in a fourth range of temperatures

6. A heat pump system as in claim 1 including:

an outdoor coil in said conduit system;

said controller calculating a defrost trigger temperature T1 based on the outdoor ambient temperature sensed at said first temperature sensor;

a second temperature sensor, said second temperature sensor being positioned to sense a temperature commensurate with the temperature of refrigerant in said conduit system in or adjacent to said outdoor coil;

said second temperature sensor delivering a second temperature signal T2 to said controller; and

said controller operating to effect a defrost operation of said heat pump system when T2 is equal to or less than T1 for a predetermined period of time.

7. A heat pump system as in claim 6 wherein:

said controller determines T1 in accordance with a first algorithm when the heat pump system is operating in mode M2.

8. A heat pump system as in claim 7 wherein said first algorithm is:

T1=0.85×

A°

F.−

10.5

where A°

F. is the temperature of outside air entering said outside coil.

9. A heat pump system as in claim 6 wherein:

said controller determines T1 in accordance with a second algorithm when the heat pump system is operating in mode M3.

10. A heat pump system as in claim 9 wherein said second algorithm is:

T1=0.7075×

A°

F.−

19.625

where A°

F. is the temperature of outside air entering said outside coil.

11. A heat pump system as in claim 1 including:

an economizer in said refrigerant conduit system; and

a third conduit segment from said economizer to said second conduit segment; and

wherein

said mode M3 includes operation of said economizer.

12. A heat pump system as in claim 11 wherein:

operation of said economizer is cyclical.

13. A heat pump system including:

a primary compressor;

a booster compressor;

at least said primary compressor being a variable capacity compressor,

a refrigerant conduit system, said primary compressor and said booster compressor being in series in said refrigerant conduit system, and said conduit system including a first conduit segment connected to deliver refrigerant to the inlet to said primary compressor when said booster compressor in inoperative, and said conduit system including a second conduit segment between the discharge from said booster compressor and the inlet to said primary compressor to deliver refrigerant between said booster compressor and said primary compressor when both of said compressors are operating;

an economizer in said refrigerant conduit system;

a third conduit segment from said economizer to said second conduit segment;

a first temperature sensor for sensing the temperature of outdoor ambient air;

a controller, said controller being connected between a two step thermostat and said primary and booster compressors, said controller receiving signals from said first temperature sensor and from the thermostat to operate said primary compressor, said booster compressor and said economizer in a predetermined sequence as follows;

(a) effect a first mode of operation of partial capacity operation of said primary compressor (M1) when either stage of the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor air temperature in a first range of temperatures;

(b) effect operation in M1 when the first stage of the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor temperature in a second range of temperatures; and

effect a second mode of operation of full capacity operation of said primary compressor (M2) when the second stage of the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor air temperature in the second range of temperatures;

(c) effect operation in M2 when either stage of the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor temperature in a third range of temperatures; and

(d) effect operation in M2 when the first stage of the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor air temperature in a fourth range of temperatures; and

effect a third mode of operation of full capacity operation of said primary compressor, said booster, and said economizer (M3) when the second stage of the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor air temperature in the fourth range of temperatures.

14. A heat pump system as in claim 13 including;

an electrical resistance backup heater in the heat pump system;

said controller operating to effect operation in M3 when the first stage of the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor air temperature in a fifth range of temperatures; and

said controller operating to effect operation of said backup heater (M4) when the second stage of the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor air temperature in the fifth range of temperatures.

15. A heat pump system as in claim 13 wherein:

said first range of temperatures is from about 60°

F. and above.

16. A heat pump system as in claim 13 wherein:

said second range of temperatures is from about 38°

F. to about 59°

F.

17. A heat pump system as in claim 13 wherein:

said third range of temperatures is from about 31°

F. to about 37°

18. A heat pump system as in claim 13 wherein:

said fourth range of temperatures is from about 19°

F. to about 30°

F.

19. A heat pump system as in claim 14 wherein:

said fifth range of temperatures is from about 18°

F. and below.

20. A heat pump system as in claim 13 including:

an outdoor coil in said conduit system;

said controller calculating a defrost trigger temperature T1 based on the outdoor ambient temperature sensed at said first temperature sensor and in accordance with an algorithm;

a second temperature sensor, said second temperature sensor being positioned to sense a temperature commensurate with the temperature of refrigerant in said conduit system in or adjacent to said outdoor coil;

said second temperature sensor delivering a second temperature signal T2 to said controller; and

said controller operating to effect a defrost operation of said heat pump system when T2 is equal to or less than T1 for a predetermined period of time.

21. A heat pump system as in claim 20 wherein:

said controller determines T1 in accordance with a first algorithm when the heat pump system is operating in mode M2.

22. A heat pump system as in claim 21 wherein said first algorithm is:

T1=0.85×

A°

F.−

10.5

where A°

F. is the temperature of outside air entering said outside coil.

23. A heat pump system as in claim 20 wherein:

said controller determines T1 in accordance with a second algorithm when the heat pump system is operating in mode M3.

24. A heat pump system as in claim 23 wherein said second algorithm is:

T1=0.7075×

A°

F.−

19.625

where A°

F. is the temperature of outside air entering said outside coil.

25. A heat pump system as in claim 13 including:

a refrigerant accumulator, said accumulator being connected to the discharge from said booster compressor to receive from the booster compressor upon operation thereof and to store excess refrigerant absorbed in the oil of said booster compressor when said booster compressor is not operating.

26. 1. A defrost system for a heat pump system including:

at least one compressor;

an outdoor coil in said heat pump system;

a refrigerant conduit system, said compressor and said outdoor coil being being in said refrigerant conduit system;

a first temperature sensor for sensing the temperature of outdoor ambient air and generating a first signal commensurate with the outdoor ambient air temperature;

a second temperature sensor, said second temperature sensor being positioned to sense a temperature commensurate with the temperature of refrigerant in said conduit system in or adjacent to said outside coil, said second temperature sensor generating a second signal commensurate with the temperature of refrigerant in or adjacent to said outdoor coil;

a controller, said controller receiving said first signal from said first temperature sensor and calculating a defrost trigger temperature T1 based on the outdoor ambient temperature sensed at said first temperature sensor, and said controller receiving said second temperature signal T2 from said second temperature sensor;

said controller operating to effect a defrost operation of said heat pump system when T2 is equal to or less than T1 for a predetermined period of time.

27. A defrost system for a heat pump system as in claim 26 wherein:

said controller determines T1 in accordance with an algorithm linear with outdoor ambient air temperature.

28. A method of operating a heat pump system having a primary compressor and a booster compressor, at least said primary compressor being a variable capacity compressor, and said compressors being operable in series, the method including the steps of:

(a) sensing the temperature of outdoor ambient air;

(b) effecting a first mode of operation of partial capacity operation of said primary compressor (M1) when heat is called for and the outdoor air temperature is in a first range of temperatures;

(c) effecting operation in M1 and effecting a second mode of operation of fall capacity operation of said primary compressor (M2) when heat is called for and the outdoor air temperature is in a second range of temperatures;

(d) effecting operation in M2 and effecting a third mode of operation of full capacity operation of said primary compressor, said booster, and said economizer (M3) when heat is called for and the outdoor air temperature is in a third range of temperatures.

29. A method of operating a heat pump system as in claim 28 wherein the system includes an electrical resistance backup heater, the method including the step of:

effecting fall capacity operation of said primary compressor and said booster, and effecting operation of electrical resistance backup heat when heat is called for and the outdoor air temperature is in a fourth range of temperatures.

30. A method of operating a heat pump system as in claim 28 wherein the system includes a multi-stage thermostat;

the method including the steps of;

effecting operation in M1 when a first stage of the thermostat calls for heat and the outdoor ambient temperature is in said first range of temperatures; and

,

effecting operation in M2 when a second stage of the thermostat calls for heat and the outdoor ambient temperature is in said second range of temperatures; and

effecting operation in M2 when a first stage of said thermostat calls for heat and the outdoor ambient temperature is in said third range of temperatures; and

effecting operation in M3 when a second stage of said thermostat calls for heat and the outdoor ambient temperature is in said third range of temperatures.

31. A method of operating a heat pump system as in claim 28 wherein the system includes an electrical resistance backup heater, and a multistage thermostat, the method including the steps of:

effecting operation in M3 when a first stage of the thermostat calls for heat and the outdoor ambient temperature is in a fourth range of temperatures; and

effecting operation in M3 and effecting operation of the backup heater when a second stage of the thermostat calls for heat and the outdoor ambient temperature is in a fourth range of temperatures

32. A method of operating a heat pump system as in claim 28 wherein the system includes a conduit system for the flow of refrigerant, and an outdoor coil in said conduit system for extracting heat energy from outside ambient air, the method including the steps of:

calculating a defrost trigger temperature T1 based on the outdoor ambient temperature;

sensing the temperature T2 of refrigerant in the conduit system in or adjacent to the outdoor coil; and

effecting a defrost operation of said heat pump system when T2 is equal to or less than T1 for a predetermined period of time.

33. A method of operating a heat pump system as in claim 32 wherein:

the temperature T1 is determined in accordance with a first algorithm when the heat pump system is operating in mode M2.

34. A method of operating a heat pump system as in claim 33 wherein said first algorithm is typically:

T1=0.85×

A°

F.−

10.5

where A°

F. is the temperature of outside air entering said outside coil.

35. A method of operating a heat pump system as in claim 34 wherein:

the temperature T1 is determined in accordance with a second algorithm when the heat pump system is operating in mode M3.

36. A method of operating a heat pump system as in claim 35 wherein said second algorithm is typically:

T1=0.7075×

A°

F.−

19.625

where A°

F. is the temperature of outside air entering said outside coil.

37. A method of operating a heat pump system having a primary compressor, a booster compressor, and an economizer, at least said primary compressor being a variable capacity compressor, and said compressors being operable in series, the method including the steps of:

(a) sensing the temperature of outdoor ambient air;

(b) effecting a first mode of operation of partial capacity operation of said primary compressor (M1) when heat is called for and the outdoor air temperature is in a first range of temperatures;

(c) effecting operation in M1 and effecting a second mode of operation of full capacity operation of said primary compressor (M2) when heat is called for and the outdoor air temperature is in a second range of temperatures;

(d) effecting operation in M2 when heat is called for and the outdoor air temperature is in a third range of temperatures;

(e) effecting operation in M2 and effecting a third mode of operation of full capacity operation of said primary compressor, said booster, and said economizer (M3) when heat is called for and the outdoor air temperature is in a fourth range of temperatures.

38. A method of operating a heat pump system as in claim 37 wherein the system includes an electrical resistance backup heater, the method including the step of:

effecting full capacity operation of said primary compressor and said booster, and effecting operation of electrical resistance backup heat when heat is called for and the outdoor air temperature is in a fifth range of temperatures.

39. A method of operating a heat pump system as in claim 37 wherein:

said first range of temperatures is from about 60°

F. and above.

40. A method of operating a heat pump system as in claim 37 wherein:

said second range of temperatures is from about 38°

F. to about 59°

F.

41. A method of operating a heat pump system as in claim 37 wherein:

said third range of temperatures is from about 31°

F. to about 37°

F.

42. A method of operating a heat pump system as in claim 37 wherein:

said fourth range of temperatures is from about 30°

F. and below.

43. A method of operating a heat pump system as in claim 38 wherein:

said fifth range of temperatures is from about 18 and below.

44. A method of operating a heat pump system having a primary compressor, a booster compressor, and an economizer, and a multi-stage thermostat, at least said primary compressor being a variable capacity compressor, and said compressors being operable in series, the method including the steps of:

(a) sensing the temperature of outdoor ambient air;

(b) effecting a first mode of operation of partial capacity operation of said primary compressor (M1) when the outdoor air temperature is in a first range of temperatures and either the first stage or the second stage of the thermostat is calling for heat;

(c) effecting operation in M1 when the outdoor air temperature is in a second range of temperatures, and the first stage of the thermostat is calling for heat; and

effecting a second mode of operation of full capacity operation of said primary compressor (M2) when the outdoor air temperature is in the second range of temperatures and the second stage of the thermostat is calling for heat;

(d) effecting operation in M2 when the outdoor air temperature is in a third range of temperatures and either the first stage or the second stage of the thermostat is calling for heat;

(e) effecting operation in M2 when the outdoor air temperature is in a fourth range of temperatures and the first stage of the thermostat is calling for heat, and effecting full capacity operation of said primary compressor, said booster, and said economizer (M3) when the outdoor air temperature is in a fourth range of temperatures and the second stage of the thermostat is calling for heat.

45. A method of operating a heat pump system as in claim 44 wherein the system includes an electrical resistance backup heater, the method including the step of:

effecting full capacity operation of said primary compressor, said booster, and said economizer when the outdoor temperature is in a fifth range of temperatures and the first stage of the thermostat is calling for heat, and effecting operation of electrical resistance backup heat when the outdoor air temperature is in a fifth range of temperatures and the second stage of the thermostat is calling for heat.

46. A method of operating a heat pump system as in claim 44 wherein:

said first range of temperatures is from about 60°

F. and above.

47. A method of operating a heat pump system as in claim 44 wherein:

said second range of temperatures is from about 38°

F. to about 59°

F.

48. A method of operating a heat pump system as in claim 44 wherein:

said third range of temperatures is from about 31°

F. to about 37°

F.

49. A method of operating a heat pump system as in claim 44 wherein:

said fourth range of temperatures is from about 30°

F. and below.

50. A method of operating a heat pump system as in claim 45 wherein:

said fifth range of temperatures is from about 18 and below.

51. A method of operating a heat pump system as in claim 44 wherein the system includes a conduit system for the flow of refrigerant, and an outdoor coil in said conduit system for extracting heat energy from outside ambient air, the method including the steps of:

calculating a defrost trigger temperature T1 based on the outdoor ambient temperature;

sensing the temperature T2 of refrigerant in the conduit system in or adjacent to the outdoor coil; and

effecting a defrost operation of said heat pump system when T2 is equal to or less than T1 for a predetermined period of time.

52. A method of operating a heat pump system as in claim 44 wherein:

the temperature T1 is determined in accordance with a first algorithm when the heat pump system is operating in mode M2.

53. A method of operating a heat pump system as in claim 44 wherein said first algorithm is typically:

T1=0.85×

A°

F.−

10.5

where A°

F. is the temperature of outside air entering said outside coil.

54. A method of operating a heat pump system as in claim 44 wherein:

the temperature T1 is determined in accordance with a second algorithm when the heat pump system is operating in mode M3.

55. A method of operating a heat pump system as in claim 44 wherein said second algorithm is typically:

T1=0.7075×

A°

F.−

19.625

where A°

F. is the temperature of outside air entering said outside coil.

56. A heat pump system including:

a primary compressor;

a booster compressor;

at least said primary compressor being a variable capacity compressor,

a refrigerant conduit system, said primary compressor and said booster compressor being in series in said refrigerant conduit system, and said conduit system including a first conduit segment connected to deliver refrigerant to the inlet to said primary compressor when said booster compressor in inoperative, and said conduit system including a second conduit segment between the discharge from said booster compressor and the inlet to said primary compressor to deliver refrigerant between said booster compressor and said primary compressor when both of said compressors are operating;

a first temperature sensor for sensing the temperature of outdoor ambient air;

a controller, said controller being connected between a two step thermostat and said primary and booster compressors, said controller receiving signals from said first temperature sensor and from the thermostat to operate said primary compressor, said booster compressor and said economizer in a predetermined sequence as follows;

(a) effect a first mode of operation of partial capacity operation of said primary compressor (M1) when either stage of the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor air temperature in a first range of temperatures;

(b) effect operation in M1 when the first stage of the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor temperature in a second range of temperatures; and

effect a second mode of operation of full capacity operation of said primary compressor (M2) when the second stage of the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor air temperature in the second range of temperatures;

(c) effect operation in M2 when the first stage of the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor temperature in a third range of temperatures; and

effect operation in M2 and cyclical on-off operation of said booster compressor (M3-C) when the second stage of the thermostat is calling for heat and the signal from the first temperature sensor indicates an outdoor temperature in a third range of temperatures;

(d) effect operation in M3-C when the first stage of the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor air temperature in a fourth range of temperatures; and

effect full capacity operation of said primary compressor and said booster (M3), when the second stage of the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor air temperature in the fourth range of temperatures.

57. A heat pump system as in claim 56 including;

an electrical resistance backup heater in the heat pump system;

said controller operating to effect operation in M3 when the first stage of the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor air temperature in a fifth range of temperatures; and

said controller operating to effect operation of said backup heater (M4) when the second stage of the thermostat is calling for heat and the signal from said first temperature sensor indicates an outdoor air temperature in the fifth range of temperatures.

58. A heat pump system as in claim 56 including:

an economizer in said refrigerant conduit system;

a third conduit segment from said economizer to said second conduit segment; and

wherein

each of modes M3-C and M3 include cyclical on-off operation of said economizer.

59. A heat pump system operating in a cooling mode, including:

a primary compressor;

a booster compressor;

at least said primary compressor being a variable capacity compressor,

a refrigerant conduit system, said primary compressor and said booster compressor being in series in said refrigerant conduit system, and said conduit system including a first conduit segment connected to deliver refrigerant to the inlet to said primary compressor when said booster compressor in inoperative, and said conduit system including a second conduit segment between the discharge from said booster compressor and the inlet to said primary compressor to deliver refrigerant between said booster compressor and said primary compressor when both of said compressors are operating;

a first temperature sensor for sensing the temperature of outdoor ambient air;

a controller, said controller being connected between a multi-stage thermostat and said primary and booster compressors, said controller receiving signals from said first temperature sensor and from the thermostat to operate said primary compressor and said booster compressor in a predetermined sequence as follows;

(a) effect a first mode of operation of partial capacity operation of said primary compressor (M1) when a first stage of the thermostat calls for cooling, and without regard to the signal from said first temperature sensor;

(b) effect a second mode of operation of full capacity operation of said primary compressor (M2) when M1 is not sufficient to meet the need for cooling and a second stage of the thermostat calls for more cooling.

60. A heat pump system operating in a cooling mode as in claim 59, including:

an economizer in said cooling system;

the predetermined operating sequence including to effect M1 and M2 when the signal from said first temperature sensor indicates a an outdoor temperature in a first range of temperatures; and

effect a third mode of operation of full capacity operation of said primary compressor and operation of said booster compressor and operation of said economizer, or cyclical on-off operation thereof, when the thermostat is calling for cooling and the signal from said first temperature sensor indicates an outdoor air temperature higher than said first range of temperatures.

61. A method of operating a heat pump system in cooling, the system having a primary compressor and a booster compressor, at least said primary compressor being a variable capacity compressor, and said compressors being operable in series, the method including the steps of:

(a) effecting a first mode of operation of partial capacity operation of said primary compressor (M1) when a first stage of a thermostat calls for cooling is called for and without regard to the signal from said first temperature sensor;

(b) effecting a second mode of operation of full capacity operation of said primary compressor (M2) when cooling is called for and the outdoor air temperature is in a second range of temperatures;

(c) effecting operation in M2 and effecting a third mode of operation of full capacity operation of said primary compressor, said booster, and said economizer (M3) when M1 is not sufficient to meet the need for cooling and a second stage of the thermostat calls for more cooling.

62. A method of operating heat pump system in a cooling mode as in claim 61, including:

an economizer in said cooling system; and

including the steps of

effecting operation in M1 and M2 when the signal from said first temperature sensor indicates a an outdoor temperature in a first range of temperatures; and

effecting a third mode of operation of full capacity operation of said primary compressor and operation of said booster compressor and operation of said economizer, or cyclical operation thereof, when the thermostat is calling for cooling and the signal from said first temperature sensor indicates an outdoor air temperature higher than said first range of temperatures.