Performance analysis of a double cooling source system featured by composition-tuning of zeotropic mixture R32/R236fa

Abstract

Frequent temperature variation of heat source puts stress on the energy-efficient operation of air-conditioning systems under off-design conditions. A composition-adjustable double cooling source (CADCS) system is proposed that addresses active composition requirement resulting from heat source variation. The CADCS system is characterized by comprehensively utilizing the congenital superiority of glide temperature and adjustable thermophysical properties of the zeotropic mixture. Two streams of zeotropic mixture with diverse mass rates and concentration through vapor–liquid separation respectively handle the waste heat and moisture load. The composition adjustment mechanism is revealed through the theoretical models for two-phase separation condensation with zeotrope based on flow and heat transfer characteristics. The heat transfer coefficient of the liquid separation condensers are all above 5000 W/(m2.K), which guarantee excellent heat transfer and flexible composition tuning. Energy performance of the CADCS system demonstrates that the coefficient of performance and dehumidification rate can reach 5.1 and 2.2 kg/h. Exergy analysis of the CADCS system is systematically conducted, of which exergy destruction and efficiency are 2.1 kW and 22 %. Processible heat and humidity ratio based on double cooling sources ranges from 8000 to 11000 kJ/kg, which reveals that the CADCS system provides a promising application prospect for temperature and humidity respective control under multi-condition due to its excellent performance and flexibility.