Performance of an air-source heat pump with multi-circuit outdoor coil for continuous heating during defrosting

Abstract

Reverse cycle defrosting (RCD) is currently the most commonly used air-source heat pump (ASHP) defrosting method. Indoor heating is interrupted in a RCD process, which seriously affect the comfort of the indoor human. It is essential to develop a method for continuous heat supply during ASHP defrosting. This study developed a novel defrosting method for an ASHP working in low temperature and high humidity environment. The outdoor heat exchanger of the ASHP is divided into three independent circuits for partial reverse cycle defrosting (PRCD) in turn. When a defrost operation is required, one of the circuits uses part of the compressor outlet high temperature gas to defrost. At this time, part of the high-temperature gas still enters the indoor heat exchanger for heating. Then two parts of liquid refrigerant enter the other two circuits of the outdoor heat exchanger for evaporation. By this way, the defrosting process can perform with the heating process simultaneously. Performance of the ASHP with multi-circuit outdoor coil for continuous heating during defrosting was explored. The novel PRCD method is compared with the traditional RCD method also. The results show that due to the PRCD, the system can provide continuous heating during defrosting and the heating capacity during defrosting could reach 20% of the normal heating capacity. The defrosting time was reduced by 40% compared to the RCD method and the cumulated COP was increased by 7% compared to the traditional RCD in a defrost operations cycle. It has been proved that continuous heating and energy savings could be achieved by this new technology.