Field experimental investigation on partial-load dynamic performance with variable hysteresis control of air-to-water heat pump (AWHP) system

The air-to-water heat pump (AWHP) is one of the recommended approaches for clean energy heating in the 'coalto-electricity' project among rural areas of northern China. To improve the dynamic performance under its frequent partial load conditions, a variable hysteresis control algorithm of the AWHP supply water temperature was proposed, where the lower dead band (Delta T-s,set(-)) increases piecewise with increasing outdoor air temperature. A field experiment was conducted based on a variable frequency AWHP system of a rural household in Beijing for effect investigation. The system coefficient of performance (COPsya) can be improved on the premise of ensuring the heating effect, and the optimization effect becomes better with higher outdoor air temperature. The increase of Delta T(s,set)(- )set can decrease the on-off cycling times, reduce the total running time and increase the proportion of the high-load-rate running period. Two control algorithms were proposed for application suggestions. Compared with the default constant hysteresis setting, COPsys could be increased by 12-36% under low load conditions. For the 2019-2020 heating season, the seasonal power consumption could be reduced by 7-15% and the seasonal COPsys could be increased by 8-17%. This paper provides a convenient and low-cost optimization scheme for energy saving.