Experimental analysis on a novel frost-free air-source heat pump water heater system

• A novel frost-free ASHPWH system coupled an EHECSD with an ESD is proposed.
• Experiments are carried out to investigate the characteristics of the system.
• The COP increased 7.25% and 46.3% in comparison with HGBD and ERH.
• Test results confirm the expected potential to control the frost-free process.

Air-source heat pumps (ASHPs) are being widely used in residential and commercial buildings and have a huge potential market and development foreground for its energy-savings, high efficiency and environmental friendliness. However, at low temperatures, frost can accumulate on the surface of the finned outdoor coil which will decrease the heating capacity and coefficient of performance (COP). This paper proposes a novel frost-free air-source heat pump water heater (ASHPWH) system, which is coupled to an extra heat exchanger coated by a solid desiccant (EHECSD) with an energy storage device (ESD). To test the system performance, experiments are carried out and the results show that the relative humidity (RH) of the air can be reduced to 52% after dehumidification and the outdoor heat exchanger can be kept frost-free for 34 min at a temperature of 0 °C and relative humidity (RH) of 80%. In addition, the average COP of the system is 2.81 in a single period, which is an increase of 7.25% and 46.3% in comparison with hot-gas bypass defrosting (HGBD) and electric resistance heating (ERH) respectively. With this new technology, it has been proven that frost-free ASHPWH be achieved.