Characterization of Phase Change Materials for Enhancing Thermal Energy Storage in District Cooling Systems

Abstract

Thermal energy storage is a vital measure for mitigating peak electricity demand in district cooling systems with the increasing demand for cooling worldwide. The present study has experimentally investigated the potential of water–ethylene glycol mixtures as cold storage media for district cooling thermal energy storage, focussing on the charging and discharging characteristics of the cold storage tank. A thermal energy storage tank with a vapor-compression chiller was used to test six mixtures containing 0%, 10%, 20%, 30%, 40% and 50% ethylene glycol by mass. The system performance was assessed by measuring the reservoir temperature, load-side temperature, charging time, electrical energy consumption, and discharging time. The experiments revealed that ethylene glycol had positive effects on sub-zero charging. Pure water was cooled from 19.1 °C to 2.0 °C in 14.51 min with 0.64 kWh energy consumption, while the 80:20 and 70:30 water–ethylene glycol mixtures reached −6.0 °C and −9.0 °C with 1.13 and 1.54 kWh, respectively. The mixture with 90% of LiCl solution and 10% of LiCl solid gave the longest discharge time, of 191.23 min while the 80:20 mixture gave a balancing charging and discharging behaviour. The results show that water–ethylene glycol mixtures are potentially optimal as practical cold storage media for district cooling (DC) thermal storage applications.