Performance investigation on an air source heat pump system with latent heat thermal energy storage

Abstract

This paper proposes an air source heat pump (ASHP) system integrated with a latent heat thermal energy storage (LTES) unit based on a specially-designed heat exchanger, condensing heat storage unit, to further improve system performance in cold region. The innovation of this device is that heat is transferred directly between refrigerant and phase change material (PCM), which significantly reduces heat loss. Experimental investigation on thermal performance of the system is carried out. Besides, a mathematical model of condensing heat storage unit is developed to investigate charging/discharging characteristics and validated by experimental data. Experimental results show that heat storage capacity reaches 31.83 kWh and average heat release power is 4.73 kW. Simulation results indicate that both smaller fin pitch and larger fin thickness accelerate the melting rate of PCM, but variations of tube diameter show little impact on it. In order to maintain heat release power, circulating water flow rate should be increased with discharging time. Three-stage PCM improves both energy and exergy performance compared to single-stage PCM. COP improvement could reach 4.01% and overall exergy efficiency is increased by 4.65%. Therefore, ASHP system combined with LTES unit is a potential approach to expand its application under extremely low temperature.