APPARATUS AND METHOD FOR DETERMINING REFRIGERANT CHARGE LEVEL

Abstract

A method and apparatus for non-invasively determining a charge level of a refrigerant in a vapor-compression cycle system. The method and apparatus monitor the system while the system is operated to ascertain that the system is operating at approximately steady-state. The superheat and the subcooling of the system are then determined at the suction line and at the liquid line, respectively, and the refrigerant charge level is calculated based on the determined subcooling, the determined superheat, and rated operating conditions of the system, including rated refrigerant charge level, rated liquid line subcooling, and rated suction line superheat.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically represents a refrigeration system whose refrigerant charge level can be determined and monitored with only temperature sensors in accordance with a preferred embodiment of this invention.

FIG. 2 is a graph plotting estimated versus actual refrigerant charge levels in a split air-conditioning system, in which the estimated refrigerant charge levels were determined in accordance with the present invention.

Claims

1. A method of non-invasively determining a charge level (mtotal) of a refrigerant in a vapor-compression cycle system comprising a compressor, a condenser, an expansion device, an evaporator, a discharge line fluidically connecting the compressor to the condenser, a liquid line fluidically connecting the condenser to the expansion device, a distribution line fluidically connecting the expansion device to the evaporator, and a suction line fluidically connecting the evaporator to the compressor, the method comprising: monitoring the system while operating the system to ascertain that the system is operating at approximately steady-state;determining the superheat (Tsh) and the subcooling (Tsc) of the system at the suction line and at the liquid line, respectively; andcalculating the refrigerant charge level (mtotal) based on the determined subcooling (Tsc) the determined superheat (Tsh), and rated operating conditions of the system including rated refrigerant charge level (mtotal,rated), rated liquid line subcooling (Tsc,rated) and rated suction line superheat (Tsh,rated).

2. The method according to claim 1, wherein Tsc is determined by calculating the difference between the temperature of the refrigerant in the liquid line and the temperature of the refrigerant in the condenser, and Tsh is determined by calculating the difference between the temperature of the refrigerant in the suction line and the temperature of the refrigerant in the evaporator.

3. The method according to claim 1, wherein the refrigerant charge level (mtotal) is calculated based solely on the determined subcooling (Tsc) the determined superheat (Tsh), the rated refrigerant charge level (mtotal,rated), the rated liquid line subcooling (Tsc,rated) and the rated suction line superheat (Tsh,rated).

4. The method according to claim 1, wherein the refrigerant charge level (mtotal) is calculated with the equation (mtotal−mtotal,rated)/mtotal,rated=(1/kch){(Tsc−Tsc,rated)−ksh/sc(Tsh−Tsh,rated)}

5. The method according to claim 4, wherein Tsc is determined by calculating the difference between the temperature of the refrigerant in the liquid line and the temperature of the refrigerant in the condenser, and Tsh is determined by calculating the difference between the temperature of the refrigerant in the suction line and the temperature of the refrigerant in the evaporator.

6. The method according to claim 4, wherein kch is calculated with the equation Tsc,rated/(1−αhs,o,rated)Xhigh,rated)

7. The method according to claim 4, wherein kch is about 50° C.

8. The method according to claim 4, wherein ksh/sc is between about ¼ to about ½.

9. The method according to claim 4, wherein ksh/sc is about 1/2.5.

10. The method according to claim 1, wherein the determining and calculating steps are performed without training the system to develop a model correlating the subcooling and superheat of the system to refrigerant pressures in the system, and without empirical data regression.

11. An apparatus for non-invasively determining a charge level (mtotal) of a refrigerant in a vapor-compression cycle system comprising a compressor, a condenser, an expansion device, an evaporator, a discharge line fluidically connecting the compressor to the condenser, a liquid line fluidically connecting the condenser to the expansion device, a distribution line fluidically connecting the expansion device to the evaporator, and a suction line fluidically connecting the evaporator to the compressor, the apparatus comprising: means for monitoring the system while operating the system to ascertain that the system is operating at approximately steady-state;means for determining the superheat (Tsh) and the subcooling (Tsc) of the system at the suction line and at the liquid line, respectively; andmeans for calculating the refrigerant charge level (mtotal) based on the determined subcooling (Tsc) the determined superheat (Tsh), and rated operating conditions of the system including rated refrigerant charge level (mtotal,rated) rated liquid line subcooling (Tsc,rated) and rated suction line superheat (Tsh,rated).

12. The apparatus according to claim 11, wherein the determining means determines Tsc by calculating the difference between the temperature of the refrigerant in the liquid line and the temperature of the refrigerant in the condenser, and determines Tsh by calculating the difference between the temperature of the refrigerant in the suction line and the temperature of the refrigerant in the evaporator.

13. The apparatus according to claim 11, wherein the calculating means calculates the refrigerant charge level (mtotal) based solely on the determined subcooling (Tsc) the determined superheat (Tsh) the rated refrigerant charge level (mtotal rated), the rated liquid line subcooling (Tsc,rated) and the rated suction line superheat (Tsh,rated).

14. The apparatus according to claim 11, wherein the calculating means calculates the refrigerant charge level (mtotal) with the equation (mtotal−mtotal,rated)/mtotal,rated=(1/kch){(Tsc−Tsc,rated)−ksh/sc(Tsh−Tsh,rated)}

15. The apparatus according to claim 14, wherein the determining means determines Tsc by calculating the difference between the temperature of the refrigerant in the liquid line and the temperature of the refrigerant in the condenser, and determines Tsh by calculating the difference between the temperature of the refrigerant in the suction line and the temperature of the refrigerant in the evaporator.

16. The apparatus according to claim 14, wherein the calculating means calculates kch with the equation Tsc,rated/(1−αhs,o,rated)Xhigh,rated)

17. The apparatus according to claim 14, wherein kch is about 50° C.

18. The apparatus according to claim 14, wherein ksh/sc is between about ¼ to about ½.

19. The apparatus according to claim 14, wherein ksh/sc is about 1/2.5.

20. The apparatus according to claim 11, wherein the determining means and calculating means operate without training the system to develop a model correlating the subcooling and superheat of the system to refrigerant pressures in the system, and without empirical data regression.