Estimating operating parameters of vapor compression cycle equipment

• US 20030019221A1
• Filed: 05/10/2002
• Published: 01/30/2003
• Est. Priority Date: 05/11/2001
• Status: Active Grant

• Current Assignee: Mcloud Technologies (USA) Inc.
• Original Assignee: Field Diagnostic Services, Inc. (mCloud Technologies Corp.)
• Inventors: Rossi, Todd M., Douglas, Jonathan D., Bianchi, Marcus V. A.
• Granted Patent: US 6,701,725 B2
• Time in Patent Office: Days
• US Class Current: 62/127
• CPC Class Codes: F25B 2500/19 Calculation of parameters
• CPC Class Codes: F25B 2700/02 Humidity
• CPC Class Codes: F25B 2700/1933 Suction pressures
• CPC Class Codes: F25B 2700/195 of the condenser
• CPC Class Codes: F25B 2700/21151 at the suction side of the compressor
• CPC Class Codes: F25B 2700/21161 of the fluid heated by the condenser
• CPC Class Codes: F25B 2700/21163 of the refrigerant at the outlet of the condenser
• CPC Class Codes: F25B 2700/21172 at the inlet
• CPC Class Codes: F25B 49/005 of safety devices F25B49/02 and F25B49/04 take precedence
• CPC Class Codes: F25B 49/02 for compression type machines, plants or systems

Abstract

A process for estimating the capacity and the coefficient of performance by taking common measurements and using compressor manufacturer'"'"'s performance data is presented. A process for determining a capacity index and an efficiency index for a vapor compression cycle relative to desired operating conditions.

Claims

1. In vapor compression equipment having a compressor, a condenser, an expansion device and an evaporator arranged in succession and connected via a conduit in a closed loop for circulating refrigerant through the closed loop, said equipment operating within its nominal vapor compression cycle parameters, a process for determining the operating efficiency of the system, the process comprising the steps of:

measuring liquid line pressure, suction line pressure, suction line temperature, and liquid line temperature;

obtaining the suction dew point and discharge dew point temperatures from the suction line and liquid line pressures;

obtaining the suction line superheat;

obtaining the mass flow rate that corresponds to the compressor in the vapor compression cycle for the dew point temperatures and suction line superheat;

obtaining the enthalpies at the suction line and at the inlet of the evaporator; and

calculating the capacity of the vapor compression cycle from the mass flow rate and the enthalpies across the evaporator.

2. The process of claim 1 wherein said step of obtaining the mass flow rate comprises the step of calculating compressor performance data from ARI (Air-Conditioning and Refrigeration Institute) Standard 540-1999 performance equations available for the specific compressor.

3. The process of claim 1 wherein said step of obtaining the mass flow rate comprises the step of determining the compressor map equation by reading relevant information from the compressor manufacturer'"'"'s look-up table for the specific compressor.

4. The process of claim 1 wherein said step of obtaining the mass flow rate comprises the step of determining the compressor map equation by reading relevant information from the compressor manufacturer'"'"'s look-up table for a compressor similar to the specific compressor used in the vapor compression cycle.

5. The process of claim 1, where the mass flow rate is determined from a compressor similar to but not exactly to said specific compressor in the vapor compression cycle.

6. The process of claim 1, where the refrigerant leaves the condenser as a two-phase mixture and its enthalpy is determined by means of the heat of vaporization of the refrigerant at nominal conditions, and the refrigerant mass flow rate, the average overall heat transfer coefficient and the area of the two-phase region of the condenser at actual and nominal conditions.

7. The process of claim 6, where the enthalpy of the refrigerant leaving the condenser is calculated approximating the product of the average overall heat transfer coefficient by the area, both of the two-phase region of the condenser, divided by the mass flow rate, as a constant value.

8. The process of claim 1, further comprising the step of correcting the mass flow rate when the suction line superheat is different than the one specified by the compressor manufacturer, multiplying it by the ratio of the design suction line absolute temperature over the actual suction line absolute temperature.

9. The process of claim 1 further comprising the steps of:

obtaining the power input to the compressor from the compressor performance data, by means of the suction and discharge dew point temperatures; and

determining the coefficient of performance of the vapor compression cycle, equal to the ratio of the capacity over the power input to the compressor.

10. The process of claim 9 wherein said step of obtaining the power input to the compressor comprises the step of calculating compressor performance data from polynomials that utilize ARI Standard 540-1999 performance equations available for the specific compressor.

11. The process of claim 9 wherein said step of obtaining the power input to the compressor comprises the step of determining the compressor map equation by reading relevant information from the compressor manufacturer'"'"'s look-up table for the specific compressor used in the vapor compression cycle.

12. The process of claim 9 wherein said step of obtaining the power input to the compressor comprises the step of determining the compressor map equation by reading relevant information from the compressor manufacturer'"'"'s look-up table corresponding to a compressor similar to the specific compressor used in the vapor compression cycle.

13. The process of claim 9, where the power input to the compressor is determined for a compressor similar to but not exactly like said compressor in the vapor compression cycle.

14. The process of claim 9, where the power input to the compressor is measured by a power meter.

15. The process of claim 9, further comprising the step of correcting the power input to the compressor when the suction line superheat is different than the one specified by the compressor manufacturer, multiplying it by the ratio of the design suction line absolute temperature over the actual suction line absolute temperature.

16. The process of claim 9, further comprising the steps of

determining the driving load by measuring the temperature of the air entering the condenser, the return air temperature and the return air humidity entering the evaporator;

determining the desired conditions, as defined by the suction pressure, liquid pressure, suction temperature, liquid temperature for the cycle for the current driving load from previously obtained data for the same equipment without faults;

performing calculations to determine the mass flow rate based on the compressor map under desired conditions;

performing calculations to determine the capacity of the cycle under desired conditions and

determining the capacity index of the unit as the ratio of the actual capacity of the cycle over the capacity of the cycle under desired conditions.

17. The process of claim 16, where only the outside ambient temperature is available for the current driving load and the desired conditions are determined by setting the evaporating temperature, the suction line superheat, the liquid line subcooling, and the condensing over ambient temperature to values based on experience.

18. The process of claim 16, further comprising the steps of:

performing calculations to determine the power input to the cycle under desired conditions;

determining the coefficient of performance of the cycle under desired conditions, as the ratio of the capacity over the power input;

determining the efficiency index of the unit as the ratio of the actual coefficient of performance of the cycle over the coefficient of performance of the cycle under desired conditions.

19. The process of estimating the annual operating costs of a vapor compression cycle system once EI and CI are known, the process comprising the steps of:

calculating the capacity of the system, by multiplying the nominal unit capacity, as published by the manufacturer, by the capacity index;

calculating the annual energy consumption of the unit by means of its nominal capacity, its SEER, the calculated capacity and efficiency indices, and the estimated percentage of the power used by for purposes other than compressing the gas in the compressor;

calculating the actual annual running time of the unit as the ratio of the nominal annual running time over the capacity index;

estimating the annual operating costs by multiplying the actual annual running time of the unit, the electricity price, and the calculated energy consumption.

20. In a vapor compression cycle having a compressor, a condenser, an expansion device and an evaporator arranged in succession and connected via conduit in a closed loop in order to circulate refrigerant through the closed loop, said vapor compression cycle, a predetermined process for determining if the compressor is operating near design performance, the process comprising the steps of:

measuring liquid line pressure and suction line pressure;

obtaining the suction and discharge dew point temperatures;

obtaining the theoretical current draw of compressor through the ARI Standard 540-1999 equation;

measure actual current draw in all legs leading to compressor;

comparing actual current draw to theoretical current draw to establish whether compressor is operating near design performance.

21. The process of claim 20, where instead of measuring the current draw, the power input to the compressor is measured and compared with the calculated.