Constrained optimal high pressure equation of CO2 transcritical cycle

Abstract

CO2 transcritical cycle has been widely applied in commercial refrigeration and heat pump water heating systems. Its cycle COP (coefficient of performance) heavily depends on the high pressure optimization and control. In theory, the optimal high pressure increases quickly with the increasing gas cooler outlet temperature or ambient temperature. However, due to reliability and cost concerns, there is an upper limit of the high pressure in compressor design and system operation. In this work, we proposed a constrained optimization method for getting constrained optimal high pressure equation of CO2 transcritical cycle. With the new method, the high pressure and its upper bound were simultaneously optimized at a given level of COP loss. Two specific approaches were developed to get the constrained optimal high pressure equation. Up to 1MPa high pressure reduction was achieved with about maximum 5% and average 1% COP losses.