Effect of supply water temperature on frosting performance of air source heat pump and indoor thermal environment in space heating

During the space heating in winter, the air source heat pump (ASHP) often encounters frosting problem. In former studies, it was found that the frosting performance of ASHP and indoor thermal environment vary significantly when the supply water temperature changes. However, the influence mechanism of supply water temperature is still unknown. To solve this problem, the frosting performance variations of ASHP and its effect on indoor thermal environment variations at the supply water temperature of 41-50 degrees C were investigated in the psychrometric chamber and artificial environmental chamber, respectively. Results showed that increasing supply water temperature can effectively suppress the frosting speed and reduce the impact of frosting-defrosting on indoor thermal environment. When the supply water temperature raises from 30 degrees C to 50 degrees C, the frosting duration prolongs from 50 min to 101 min. Meanwhile, the indoor temperature drop caused by frosting- defrosting decreased by about 45 % when supply water temperature rises from 41 degrees C to 50 degrees C. Besides, with the increase of supply water temperature, the impact of frosting on the heating performance of the ASHP decreases. When it rises from 30 degrees C to 50 degrees C, the attenuation degree of the average coefficient of performance during frosting-defrosting cycle drops from 9.85 % to 7.25 %, compared to those at non-frosting condition. However, although the frosting performance of ASHP and its effect on indoor thermal environment both get better with the increase of supply water temperature, the overall heating performance of the ASHP still declines.