Compressor power modeling: Part II experimentally validated new compressor-energy-efficiency-factor (CEEF) for improved power prediction

In Compressor Power Modeling: Part I, a methodology was presented to determine the volumetric and isentropic efficiencies that were based on manufacturer's performance curves. A linear multi-variate regression analysis was used to develop curve-fits for those efficiencies as a function of saturation evaporator and condenser temperatures. it was observed that the maximum error between actual and fitted value was 13.3% for volumetric efficiency and 10.3% for the isentropic efficiency. But, since the required compressor power is directly proportional to the volumetric efficiency and is also inversely proportional to the isentropic efficiency, a new compressor-energy-efficiency-factor (CEEF) is proposed. CEEF is a ratio of volumetric efficiency to the isentropic efficiency. Upon similar linear multi-variate regression analysis, this new factor correlated to the saturation temperatures far better than the individual volumetric and isentropic efficiencies. The maximum error between actual and fitted value was observed to be 5.8%. Based on this new compressor-energy-efficiency-factor (CEEF), a compressor power model is developed. First, from the manufacturer's performance curves, correlation for the new compressor-energy-efficiency-factor (CEEF) is determined. It is assumed that this CEEF factor remains invariant with respect to the amount of superheat and the amount of subcooling. The modeled power is then the product of piston displacement times the suction vapor mass density times the isentropic enthalpy rise times the compressor-energy-efficiency-factor (CEEF). Experiments were conducted to compare this modeled power with the measured power. It was observed that the modeled power was within 10% of the measured power for a wide range of operating conditions using the new compressor-energy-efficiency-factor (CEEF).