| Summary: | For finned-tube heat exchangers, owing to the extremely different refrigerant pressure drop characteristics between condensation and evaporation processes, the optimum refrigerant circuits of these two conditions are different. However, for a typical heat pump type air conditioner, refrigerant circuit of the conventional heat exchanger (CHX) is fixed no matter what operation condition is conducted. To solve this problem, a modified variable-circuit heat exchanger (VCHX) is developed for air conditioner outdoor unit applications. The VCHX, for which the refrigerant circuit can be easily switched by using a globe valve, could provide better matching characteristics between refrigerant circuit and operation condition variations. With a developed simulation model, refrigerant circuit of the VCHX is optimized by using the entropy generation minimization theory. Then, comparative experimental works were conducted to investigate the performance of VCHX and CHX systems in detail. Experimental results show that the presented VCHX is more suitable for high heating capacity and low cooling capacity applications. Based on the Chinese APF (annual performance factor) Standard, the VCHX system yields 6.5% higher APF value over CHX system. Significantly, economic analysis indicates that the investment payback period of VCHX system is 1.46 year, which is much lower than the designed lifetime of a residential air conditioner. In general, the VCHX technique has a great application potential for improving the overall performance of a heat pump type air conditioner.
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