Illustrating the relationship between the coefficient of performance and the coefficient of system performance by means of an R404 supermarket refrigeration system

Because the coefficient of performance (COP) is primarily concerned with the core refrigeration system, using it for optimisation purposes may lead to higher than necessary energy consumption. This hypothesis was studied with a simple equation relating this coefficient to the coefficient of system performance (COSP), and with a software model based on an R404A refrigeration system installed in a supermarket in north east England. In both approaches the condenser fan power usage was excluded from the COP but included in the COSP. The results showed that, especially for part load conditions, optimising the core refrigeration system for minimum power consumption led to an appreciably higher overall energy consumption with the implication that the condenser fan and compressor controls should be developed together. When using this holistic approach it was found that energy savings of 4.5% could have been achieved based on six months' data from the installed system