Experimental study on a direct steam generation unit of high temperature air source heat pump

In industrial production, high temperature steam (>100 °C) used for heating typically comes from coal-fired, gas-fired or electric boilers. For scenarios where there's no waste heat available or it's difficult to recover it, air source heat pump steam systems are the optimal alternative for reducing carbon emissions. The existing air source heat pump steam generation technology generally generates high temperature hot water first, which is then depressurized to generate steam, requiring additional flash tanks. This method leads to significant system losses and larger footprint requirements. This study proposes a direct steam generation unit of high temperature air source heat pump, which can directly generate high temperature steam at the outlet of the unit. Performance tests were conducted in an enthalpy difference laboratory under different ambient temperatures and steam temperatures. The results indicate that the unit can produce saturated steam at up to 125 °C, achieving a maximum temperature lift of 145 °C, with a COP of 1.26 under this condition. During normal heating operation, the steam mass flow rate and heating capacity showed no significant degradation across various ambient temperatures and steam temperatures. Under defrosting conditions, the maximum steam mass flow rate degradation was 21.05 %, and the heating capacity dropped to a minimum of 99.79 kW. The energy consumption per unit mass of steam Wper ranged from 0.35 kWh/kg(s) to 0.58 kWh/kg(s) under different operating conditions. This study provides valuable perspectives for enhancing the performance of air source heat pump steam generation technology, presenting a high-efficiency, low-emission alternative for industrial steam heating.