An experimental study on the starting characteristics of an improved radiant-convective air source heat pump system

The application of air source heat pump (ASHP), a kind of environmental-friendly energy-saver used for space heating, can help to slow down energy crisis and global warming problems. Recently, to improve the indoor thermal environment, several studies on investigating novel indoor heating terminals of ASHP have been carried out. In this paper, a novel radiant-convective heating terminal was designed and coupled into an ASHP, and its starting characteristics were experimentally investigated. The experimental results showed that both compressor frequency and indoor air fan opening criteria significantly impacted the starting characteristics of the improved ASHP. With an increase in compressor frequency, the values of radiant-convective panel surface temperatures, discharge temperature and pressure, and compressor input power at the end of the starting stages increased, but the suction pressure decreased. Besides, the time point for turning on indoor air fan was prolonged from 100 to 680 s when the temperature of air fan opening criteria increased from 28.0 to 43.0 °C, and the shortest starting time of the improved ASHP occurred when employing the indoor air fan opening criteria of 38.0 °C. Furthermore, an optimized control strategy for the improved ASHP was presented. Compared to a conventional control strategy, the optimized control strategy can significantly shorten the starting time of improved ASHP from 29 to 11 min.