Energy and exergy analysis of a novel direct-expansion ice thermal storage system based on three-fluid heat exchanger module

Abstract

Direct-expansion ice thermal storage (DX-ITS) system can overcome the mismatch between cold energy supply and demand, and also exhibit the characteristics of high energy efficiency, simple pipeline and minimal installation space. However, existing DX-ITS failed to achieve simultaneous high-efficiency heat transfer in the processes of charging and discharging, thereby limiting its widespread use. This study developed a novel DX-ITS system based on three-fluid heat exchanger modules employing micro heat pipe arrays to address the proceeding issue. Temperature distribution, pressure, charging and discharging power, energy efficiency ratio, exergy efficiency and ice packing factor during the charging and discharging processes at different compressor speeds, cooling-air temperature and flow rates were experimentally studied. Results demonstrated that maximum charging power, energy efficiency ratio, exergy efficiency, ice packing factor and discharging power of proposed system using a 4 HP compressor under experimental conditions reached 5.71 kW, 2.31, 11.12 %, 82.1 % and 4.99 kW, respectively. Moreover, cooling-air temperature had a more significant effect on system performance compared with cooling-air flow rate and compressor speed. The 11.7 %, 25.9 %, 24.3 %, and 20.6 % reductions in charging power, energy efficiency ratio, exergy efficiency, and ice packing factor were observed with an increase of cooling-air temperature from 18 °C to 35.5 °C.