Accumulator for storing heat or cold

An accumulator for heat or cold, comprising a container filled for the greater part with a layer of buffer material melting at a constant temperature and a considerably smaller layer of heat transfer liquid having a lower melting point than the buffer material and a specific gravity lower than both that of the solid and that of the liquid buffer material, said transfer liquid being virtually immiscible with the buffer material, the container having a conduit for discharging heat transfer liquid from said layer at a location near the top of the container to devices outside the accumulator, a supply conduit for returning heat transfer liquid to a distributor near the bottom of the layer of buffer material for causing the transfer liquid to flow upwardly in direct contact with the buffer material, at least one coalescer comprising a mat of knitted threads or wires united into a spatial network between the buffer material and the outlet for the heat transfer liquid for retaining solid and liquid particles of the buffer material which otherwise may be entrained with the discharged transfer liquid, said buffer material being water or a eutectic aqueous solution of one or more salts having a melting point less than or equal to 0.degree. C.