Refrigerant charge adequacy gauge

• US 20060137364A1
• Filed: 12/27/2004
• Published: 06/29/2006
• Est. Priority Date: 12/27/2004
• Status: Active Grant

• Current Assignee: Carrier Corporation (Carrier Global Corporation)
• Original Assignee: Carrier Corporation (Carrier Global Corporation)
• Inventors: Kang, Pengju, Braun, Robert J. II, Galante, Timothy P., Gopalnarayanan, Sivakumar, Concha, Julio I., Kersten, Craig, Luo, Dong
• Granted Patent: US 7,712,319 B2
• Time in Patent Office: Days
• US Class Current: 62/126
• CPC Class Codes: F25B 2500/19 Calculation of parameters
• CPC Class Codes: F25B 2500/222 Detecting refrigerant leaks
• CPC Class Codes: F25B 2700/2116 of a condenser
• CPC Class Codes: F25B 2700/21163 of the refrigerant at the outlet of the condenser
• CPC Class Codes: F25B 49/005 of safety devices F25B49/02 and F25B49/04 take precedence

Abstract

A method and apparatus for determining the sufficiency of refrigerant charge in an air conditioning system by the use of only two temperature measurements. The temperature of the liquid refrigerant leaving the condenser coil is sensed and the temperature of the condenser coil itself is sensed and the difference between these two measurements is calculated to provide an indication of the adequacy of refrigerant charge in the system. This process is refined by steps taken to eliminate measurements during transient operations and by filtering signals to eliminate undesirable noise. A permitted threshold of deviation is calculated by using probability theory.

Claims

1. A method of determining the sufficiency of refrigerant charge in an air conditioning system having a compressor, a condenser coil, an expansion device and an evaporator coil fluidly interconnected in serial refrigerant flow relationship, comprising the steps of:

measuring the temperature of the liquid refrigerant leaving the condenser coil;

measuring the temperature of the condenser coil; and

computing the CTD by subtracting the liquid refrigerant temperature from the condenser coil temperature.

2. A method as set forth in claim 1 wherein said expansion device is a TXV/EXV.

3. A method as set forth in claim 1 wherein said expansion device is a fixed orifice device.

4. A method as set forth in claim 1 and including an additional step of comparing the computed CTD with a desired CTD as empirically obtained for a particular system to determine if the refrigerant charge therein is sufficient.

5. A method as set forth in claim 1, and including the steps of detecting whether the air conditioning system is undergoing transient operation and if so discounting the computed CTD.

6. A method as in claim 5, wherein transient operation is detected by comparing the standard deviation of the CTD to a predetermined threshold.

7. A method as set forth in claim 5 and including the step of waiting for a predetermined period of time after the air conditioning system is turned on before taking the temperature measurements.

8. A method as in claim 5, wherein each of said measurements and the resultant CTD are indicated by representative electrical signals, and including an additional step of eliminating high frequency noise from the CTD signal by using a filter.

9. A method as set forth in claim 8 wherein said filter is a notch or low pass filter.

10. A method as set forth in claim 9 wherein said filter is an analog or a digital filter.

11. A method as set forth in claim 4 and including the steps of:

establishing a threshold of permitted deviation from said desired CTD; and

adding or deleting charge if said comparison between said computed amount of CTD and said desired CTD exceeds said threshold.

12. A method as set forth in claim 11 wherein:

said threshold is established by the equation;

δ

1=δ

+b_max+F<sup>−

1</sup>((1−

P_F)^1/N)

where;

F is the cumulative distribution function of a zero-mean Gaussian random variable with variance σ

².

b_max is the maximum value of the sensor bias, usually obtained from manufacturers'"'"' specifications.

N is the number of samples that are taken before making a decision. For example, if the system makes one measurement per second and waits for one minute, then N=60.

P_F is a predetermined “

false alarm”

probability factor.

13. Apparatus for determining the sufficiency of refrigerant charge in an air conditioning system having a compressor, a condenser coil, an expansion device and a evaporator coil fluidly interconnected in serial refrigerant flow relationship comprising:

a temperature sensor for sensing the temperature of the liquid refrigerant leaving the condenser;

a temperature sensor for sensing the temperature of the condenser coil; and

a comparator for computing the CTD by subtracting the liquid refrigerant temperature from the condenser coil temperature.

14. Apparatus as set forth in claim 13 wherein said expansion device is a TXV/EXV.

15. Apparatus as set forth in claim 13 wherein said expansion device is a fixed orifice device.

16. Apparatus as set forth in claim 13 and including means for comparing the computed amount of CTD with empirical data for a particular system to determine if the refrigerant charge is adequate.

17. Apparatus as set forth in claim 13 and including means for detecting whether the air conditioning system is undergoing transient operation and if so discounting the computed CTD.

18. Apparatus as set forth in claim 17 wherein said means includes means for comparing the standard deviation of the computed CTD to a predetermined threshold.

19. Apparatus as set forth in claim 13 wherein said sensed temperatures and computed CTD are indicated by representative electrical signals and further including a filter for eliminating high frequency noise from the CTD signal.

20. Apparatus as set forth in claim 19 wherein said filter is a notch or low pass filter.

21. Apparatus as set forth in claim 19 wherein said filter is an analog or digital filter.

22. Apparatus as set forth in claim 13 and including means for comparing the computed CTD with a desired CTD as empirically obtained for a particular system to determine if the refrigerant charge therein is sufficient.

23. Apparatus as set forth in claim 22 and including means for establishing a threshold of permitted deviation from said desired CTD to determine if refrigerant charge should be added or subtracted from the system.

24. Apparatus as set forth in claim 23 wherein said threshold is established by the equation:

δ

1=δ

+b_max+F<sup>−

1</sup>((1−

P_F)^1/N)

where;

F is the cumulative distribution function of a zero-mean Gaussian random variable with variance σ

².

b_max is the maximum value of the sensor bias, usually obtained from manufacturers'"'"' specifications.

N is the number of samples that are taken before making a decision. For example, if the system makes one measurement per second and waits for one minute, then N=60.

P_F is a predetermined “

false alarm”

probability factor.