Chemical phase change heat or cold stores

A chamber between a pair of water, oil or refrigerant chambers 101, 102 contains a phase change material, e.g. magnesium nitrate or chloride hexahydrate, and one or more steel or aluminium members 106 facilitates heat transfer through the bulk of the phase change material. The material 107 may be contained in a heat sealed flexible polypropyline/aluminium/ polyester laminate bag 106 clamped between the chambers 101, 102 which are formed from pressed steel radiators. The heat transfer members (8, 9, Figures 1 to 3) may be metal strips welded to the walls of the radiators (1, 2) which define a sealed chamber 7 containing the phase change material. The material may be directly or indirectly electrical heated and heat may be transferred by a fluid, having a temperature close to the melt temperature of the phase change material, to a lower temperature fluid by a heat exchanger (33, Figure 6). <IMAGE>