Experimental study on concentration change of spray solution used for a novel non-frosting air source heat pump system

•The NASHP system has the capability of defrosting timely and efficiently without stopping heating.•Frost will never form on the outdoor coil surface, if the solution spray subsystem operates continuously.•The solution concentration and mass flow rate has important impacts on the system performance. Frost formation on the outdoor coil surface of an air source heat pump (ASHP) unit may occur when it is used for space heating at a low ambient temperature in winter. To reduce the impact of frosting on the operational performance and energy efficiency of ASHPs, a novel non-frosting air-source heat pump (NASHP) system was proposed. The detailed introduction of NASHP prototype was given, and its test rig was developed, as well as its operating principles and modes. Then the characteristics of some conventional dehumidification solutions were compared; the glycerol was selected as spray solution for NASHP system, due to its great influence on the operating performance of the system. The glycerol solutions with different concentration and different mass flow were investigated experimentally, and the best practice by which NASHP system has the most remarkable efficiency was found finally. Such results will provide helpful reference for the potential application of NASHP system and future research work.