Performance study of phase change charging/discharging processes of condensing heat storage in cold regions based on a mathematical model

Highlights: • A heat pump system combined with a condensing heat storage was proposed. • The feasibility of the proposed system in cold regions was numerically investigated. • The operating characteristics and heating performance were analyzed and evaluated. • The influences of structure parameters of condensing heat storage were discussed. This paper firstly proposed and investigated a single-stage air source heat pump (ASHP) system combined with a novel phase change material (PCM) based storage device, also named as condensing heat storage, to solve the problems of poor heating performance of ASHP system under extreme conditions in cold regions. A mathematical model of the novel system was established and validated to comprehensively investigate the operating characteristics under initial conditions. The simulation results suggested that the PCM temperature in two-phase zone of condensing heat storage should not exceed its phase change end temperature during the charging process under initial conditions by controlling the charging time, in order to avoid damage to the system. The proposed system could achieve its steady state under initial conditions after operating time for 6 days. In addition, the results showed that the heat storage capacity of condensing heat storage was able to reach 100.59 kW·h and the average heat storage rate was 7.19 kW during the charging process under steady state. The heat storage capacity was sufficient to be provided for a 164 m² room for 10 h theoretically with an average heat release rate of 10.06 kW, which achieved all-day continuous heat supply by the proposed system. Besides, the model was adopted to analyze the effects of some structural parameters of condensing heat storage on system heat storage performance. The system performed well in smaller fin pitch and smaller tube pitch, since both heat storage capacity and supply water temperature were increased under these circumstances.