| THERMAL STORAGE COOLING COLD STORAGE Research on the application of phase change material heat exchangers for space cooling during summer found that significant cold energy could be stored or released. LSBUs Professor Yunting Ge discusses the findings Air flow Summer night-time temp 10-16.3oC Summer daytime temp 28.1oC 23oC Indoor room temperature 21-25oC Figure 1: PCM charging and discharging process schematics A s an efficient technology, thermal energy storage (TES) using phase change material (PCM) can be applied to decrease peak loads, and shift loads, enhance system efficiency, and reduce the size of cooling plants, while maintaining occupant thermal comfort. In this research, the performance of a latent heat storage unit comprised of organic paraffin PCM enclosed in a finned-tube heat exchanger was evaluated and analysed to determine its viability as a free cooling facility to condition a space during summer in the UK. While widely used in refrigeration and heat pump systems, finned-tube PCM heat exchangers are seldom applied in TES with PCMs. A prototype was tested and modelled with computational fluid dynamics (CFD) for the application of night-time cold storage and daytime space cooling during summer. The internal and external design conditions of a typical building were used to determine the type of PCM and the PCMs operating temperature range required for space cooling. Extensive measurements were conducted on the PCM heat exchanger at different operating conditions and for both PCM charging and discharging processes. To validate the experimental measurements, a 3D CFD model for the PCM heat exchanger was developed and validated. The combination of the CFD model and experimental investigation determined the performance of the PCM heat exchanger at various operating and design conditions. Phase change materials PCMs can be classified as organic, inorganic, or eutectic. Organic PCMs, such as paraffins, have the advantages of being non-toxic, non-corrosive, Figure 2: Schematic highlighting locations of experiment thermocouples 1 Internal PCM thermocouple sensor 2 Internal PCM thermocouple sensor 3 Air inlet thermocouple sensor 4 Air outlet thermocouple sensor 5 External surface pipe thermocouple sensor 6 External surface fin thermocouple sensor 7 External surface pipe thermocouple sensor 8 External surface fin thermocouple sensor and chemically stabilised materials at low temperatures1. The melting points of paraffins range from -30C to 120C2. They have a high latent heat of fusion, but drawbacks include a lower thermal conductivity of about 0.2Wm-1K-1, low density, and less stability at high temperatures3. Inorganic materials mainly consist of salt hydrates, metallics, and their mixtures, and they cover a wide temperature range similar to that of organic PCMs. Experimental investigation Test rig setup and measurements The experiment was conducted with an air conditioning laboratory unit that had been modified to contain a PCM finned- 36 February 2024 www.cibsejournal.com CIBSE Feb 24 pp36-38 PCM cooling Edit.indd 36 26/01/2024 16:55