Cold storage for low-cost air-conditioning

Building heating, ventilation and air-conditioning (HVAC) consumes 50% of the building energy consumption. Such high costs are based on the conventional HVAC cycles for air cooling based on grid connected buildings. However, there are alternative passive and active cold storage systems that can be used to reduce building HVAC costs for on grid systems and provide a solution for off-grid HVAC. Such systems depend on harnessing the night time cold and using it for day time air cooling. Such systems can be driven by a solar photovoltaic powered fan. Although there is no mechanism for humidity control to attain recommended conditions (40–60% relative humidity and 21–26°C dry bulb temperature), temperatures can be attained to improve indoor thermal comfort. This paper reports tests conducted in Johannesburg that demonstrate the potential of such technology under sub-tropical conditions. Tests were conducted for a phase change material with a melting point of 25°C for varying air flow rates and air temperature. The PCM was encapsulated in aluminium casing providing good thermal contact between the PCM and air. Although the tests were conducted on a special test rig, results demonstrated potential to reduce air temperature by 3°C before supplying into the conditioned space.