Fengkun Wang

Modeling and simulation of a transcritical R744 heat pump system

To analyze the performance of a carbon dioxide heat pump system, a steady state simulation model has been developed. The effects for different operating parameters such as compressor speed and water inlet temperature of the gas cooler were studied. It was shown that there was an optimum compressor speed for a certain system, and the maximum COP decreased and the optimum discharge pressure increased with the increasement of water inlet temperature of the gas cooler. The maximum COP and optimum pressure were correlated as functions of water inlet temperature of the gas cooler, and it is expected to offer useful guidelines for CO2 heat pump design and development.

Experimental study of optimum heat rejection pressure for a CO 2 heat pump water heater

As an environmentally friendly refrigerant, CO2 is seen as one of the best fluids for a heat pump water heater application system. To investigate the relationships between optimum heat rejection pressure and other related operating parameters, an experimental research has been conducted for a transcritical CO2 heat pump water heater with two throttling valves. It proved that it is relatively reliable to control the heat rejection pressure of the CO2 system with two throttling valves; there exists an optimal heat rejection pressure, under which the system can reach the maximum heating coefficient of performance. Meanwhile, the research also reveals that the optimal heat rejection pressure chiefly depends on the outlet refrigerant temperature of the gas cooler, and in the next place, the evaporating temperature; on the other hand, the superheat degree of CO2 at the inlet of the compressor was found to have little to do with the optimum heat rejection pressure.