A new method for preventing air-source heat pump water heaters from frosting

This paper proposes a frost-free air-source heat pump water heater (ASHPWH) system with integrated solid desiccant, in which frosting can be retarded by dehumidifying air before it enters the ASHPWH evaporator. The system consists of a conventional heat pump water heater and an extra heat exchanger coated by a solid desiccant. During the desorption process of the desiccant, regeneration air is cycled between the desiccant-coated heat exchanger and the evaporator to recover the sensible heat and latent heat of the regeneration air. A numerical simulation is carried out at a dry-bulb temperature of −7 °C–5.5 °C and a relative humidity of 60%–80% depending on the frosting conditions. The results show that the coefficient of performance (COP) is within the range 3.3–3.8, which is 5–30% higher than that of the ASHPWH system using the hot-gas defrosting method.

► We propose a frost-free air-source heat pump water heater system with integrated desiccant-coated heat exchanger.
► The system can provide heat water continuously.
► The coefficient of performance of the system is within the range 3.3–3.8, at Ta = −7 °C–5 °C and RH = 60%–80%.
► The high system performance is mainly due to the efficient regeneration of the desiccant by recycling air.