An ice-making storage was selected as the cold thermal energy storage system. Compared to other static ice-making systems, such as the ice-on-coil type, the ice-encapsulated type offers the advantages of low cost, simplicity and wider heat exchange area. The phase change material (PCM), e. g., de-ionised water, is encapsulated in spherical capsules of relatively small diameter, usually in the range 50 to 100 mm. The capsules are packed into a conventional tank and the void
volume around the capsules is filled with refrigerant fluid, such as water glycol solution. The phase change process is described in . During charging, cool refrigerant flows around the capsules and ice starts forming from the internal surface towards the centre of the capsules (see Fig. 7.). The capsules are conceived to allow for ice expansion. During discharge, refrigerant circulates around the capsules and gets chilled by the frozen capsules. The ice starts melting, again from the internal surface towards the centre of the capsules (see Fig. 8.).