Integration of thermal energy storage with chilled water-cooling systems: Experimental analysis of PCM solidification and cooling performance

The escalating demand for cooling systems to maintain thermal comfort in buildings, driven by extreme weather conditions, has significantly increased global greenhouse gas emissions. One promising strategy to address this challenge is to improve building energy efficiency through novel air conditioning systems, reduce energy consumption, and enable peak shaving. This study proposes an innovative approach to improve chilled water-based air conditioning systems by integrating a Thermal Energy Storage (TES). The TES unit utilizes Phase Change Materials (PCMs) RT-42 and RT-25 to store excess chilled water cooling by solidification during off-peak hours and releases it during peak times, thereby reducing the peak load and cooling the refrigerant before it enters the condenser. Experimental investigations focus on the charging (solidification) and discharging (melting) of PCMs in a cylindrical TES system with helical heat transfer pipes, under varying flow rates. The experimental setup involved a chilled water loop from the chiller to a test room equipped with a fan coil unit (FCU). The room temperature was maintained with chilled water flow rates, while excess chilled water during lower cooling demand regimes was diverted to TES to store excess cooling in the form of solidified PCM. The stored cold energy was then used to cool the refrigerant before entering the condenser, significantly enhancing the cooling system’s efficiency. A maximum temperature drop of 50 °C was recorded when using RT-25HC at a 2 L·min⁻1 flow rate, compared to an 11 °C drop achieved with RT-42 under similar conditions. RT-25HC and RT-42 offer high thermal performance under varied melting and solidification conditions. RT-42 achieved a maximum energy storage of 47.40 kWh, while RT-25HC stored a maximum of 52 kWh. Significant temperature drops (up to 50 °C) and controlled flow rates significantly influenced the phase change. These findings highlight the potential of PCM for improving the efficiency of district cooling systems (DCS).