Set point optimization in vapor compression cycles

• US 5,735,134 A
• Filed: 05/30/1996
• Issued: 04/07/1998
• Est. Priority Date: 05/30/1996
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Liu, Sheng, He, Xiang-Dong
• Primary Examiner(s): Tanner, Harry B.
• Application Number:
  US08/655,533
• Time in Patent Office: 677 Days
• Field of Search: 62/230, 62/229, 62/228.4, 62/228.5, 62/180, 62/203, 62/204, 62/208, 62/209, 62/181, 62/183, 62/184, 62/205, 62/206, 62/210, 62/211, 236/91 C, 236/91 R
• US Class Current: 62/230
• CPC Class Codes: F25B 2500/19 Calculation of parameters
• CPC Class Codes: F25B 2600/21 Refrigerant outlet evaporator temperature
• CPC Class Codes: F25B 49/02 for compression type machines, plants or systems
• CPC Class Codes: G05B 13/024 in which a parameter or coefficient is automatically adjusted to optimise the performance

Abstract

A vapor compression system with set point optimization generates a set of thermodynamic operating parameters such that the system operates with optimum energy efficiency. Based on environmental conditions such as indoor and outdoor temperature as well as thermal load, the set of parameters for steady-state set point is generated. The system also monitors actual system properties in real-time and provides them as feedback to the set point computation module. Based on these actual real-time measurements, a new steady-state set point can be generated to enable the system to continue operating at maximum coefficient of performance upon change in environmental or thermal load requirements.

Claims

1. A method of controlling a vapor compression cycle in a vapor compression system comprising:

(a) generating a set of parameters which define an operating condition for the vapor compression system;

(b) operating the vapor compression system in accordance with the set of parameters;

(c) while the system operates, receiving a real-time measurement of at least one of the parameters;

(d) using the real-time measurement, calculating the real-time coefficient of performance of the vapor compression system;

(e) adjusting the at least one parameter; and

(f) repetitively performing steps (c) through (e) as required to maximize the real-time coefficient of performance.

2. The method of claim 1 wherein the at least one parameter is temperature of a refrigerant of the vapor compression system.

3. The method of claim 1 further comprising providing a multivariable controller for adjusting the at least one parameter.

4. The method of claim 3 further comprising adjusting a gain of the multivariable controller to adjust the at least one parameter.

5. The method of claim 1 further comprising receiving an environmental input used in generating the set of parameters.

6. The method of claim 1 wherein the step of repetitively performing steps (c) through (e) comprises an iterative search for a maximum real-time coefficient of performance.

7. The method of claim 1 wherein the step of adjusting the at least one parameter comprises adjusting at least one control input to control a component of the system.

8. The method of claim 5 wherein the environmental input comprises a measurement of indoor temperature.

9. The method of claim 5 wherein the environmental input comprises a measurement of outdoor temperature.

10. The method of claim 5 wherein the environmental input comprises a measurement of system thermal load.

11. The method of claim 7 wherein the at least one control input controls a valve opening.

12. The method of claim 7 wherein the at least one control input controls a condenser fan speed.

13. The method of claim 7 wherein the at least one control input controls a compressor fan speed.

14. The method of claim 7 wherein the at least one control input controls a speed of a compressor.

15. The method of claim 14 wherein the iterative search comprises a constrained gradient descent search.

16. A vapor compression system comprising:

means for generating a set of parameters which define an operating condition for the vapor compression system;

means for generating a real-time measurement of at least one of the parameters as the vapor compression system operates; and

means for repetitively calculating the real-time coefficient of performance of the vapor compression system using the real-time measurement of the at least one parameter and adjusting the at least one parameter to maximize the real-time coefficient of performance.

17. The vapor compression system of claim 16 wherein the at least one parameter is temperature of a refrigerant in the vapor compression system.

18. The vapor compression system of claim 16 further comprising a multivariable controller for adjusting at least one parameter.

19. The vapor compression system of claim 18 further comprising a gain scheduler for altering a gain in the multivariable controller to adjust the at least one parameter.

20. The vapor compression system of claim 16 further comprising means for adjusting at least one control input to control a component of the vapor compression system to adjust the at least one parameter.

21. The vapor compression system of claim 20 wherein the at least one control input controls a speed of a compressor.

22. The vapor compression system of claim 20 wherein the at least one control input controls a valve opening.

23. The vapor compression system of claim 20 wherein the at least one control input controls a condenser fan speed.

24. The vapor compression system of claim 20 wherein the at least one control input controls a compressor fan speed.

25. The vapor compression system of claim 16 further comprising means for providing an environmental input defining a condition of the environment in which the vapor compression system operates, the environmental input being used to generate the set of parameters.

26. The vapor compression system of claim 25 wherein the environmental input comprises a measurement of indoor temperature.

27. The vapor compression system of claim 25 wherein the environmental input comprises a measurement of outdoor temperature.

28. The vapor compression system of claim 25 wherein the environmental input comprises a measurement of system thermal load.

29. The vapor compression system of claim 16 wherein the means for repetitively calculating the real-time coefficient of performance of the vapor compression system performs an iterative search to maximize the real-time coefficient of performance.

30. The vapor compression system of claim 29 wherein the iterative search comprises a constrained gradient descent search.