Modeling and Dynamic Simulation of a Phase-Change Material Tank for Powering Chiller Generators in District Cooling Networks

Abstract

Latent heat storage in district cooling systems (DCS) offers advantages such as energy efficiency, load shifting, and flexibility. It optimizes energy utilization by storing thermal energy during off-peak hours and using it during peak periods. This results in cost savings, a reduced environmental impact, and the enhanced reliability of the cooling system. In the present study, a novel system consisting of a phase-change material (PCM) tank coupled to a 120 kW chiller generator for cooling is proposed. During peak cooling loads, the proposed PCM tank is intended to supply consistent thermal power at an appropriate temperature. The system is modeled using the lumped-capacitance approach, and the effective thermal capacity approach is used to model the PCM’s phase-transition phenomena. The system’s dynamic performance is evaluated, and the impact of various parameters during the PCM-tank discharging process is analyzed. The computational findings are compared to experimental data taken from a real district network, and there is excellent agreement. Results showed that increasing the needed heat rate for the cooling process from 120 kW to 160 kW decreases the PCM tank’s discharging duration by about 20% and increases pump energy consumption. It was also found that increasing the capacity of the PCM tank is advantageous for the cooling process as it extends the duration of 120 kW constant power production by about 62% when the tank volume is increased from 5 m3 to 10 m3. Finally, it was shown that the choice of the PCM type is crucial for improving the cooling performance. Erythritol is a suitable storage medium in the tank compared to A118 and MgCl2·6H2O, and using erythritol instead of PCM A118 increases the period of continuous thermal power generation by about 67%.