Estimating operating parameters of vapor compression cycle equipment
First Claim
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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 ioop, 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.
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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.
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Citations
20 Claims
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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 ioop, 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:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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.
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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.
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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.
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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.
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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.
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14. The process of claim 9, where the power input to the compressor is measured by a power meter.
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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 conditions 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 for the cycle for the current driving conditions 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 vapor compression cycle under desired conditions.
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- 16. The process of claim 16, where the data to determine the desired conditions for the cycle for the current driving conditions is not available and the desired conditions are determine by setting the evaporating temperature, the suction line superheat, the liquid line subcooling, and the condensing over ambient temperature to values based on experience.
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18. The process of claim 18, further comprising the steps of:
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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 the 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;
obtaining the price of electricity in a form of currency per unit of energy;
estimating the annual operating costs by multiplying the actual annual running time of the unit, the electricity price, and the calculated energy consumption.
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19. 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:
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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.
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20. 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.
Specification