Latent heat storage

The investigations of materials presumably suitable as storage media for latent heat indicate that water, some salt hydrates and eutectic mixtures of water and salt hydrates possess extreme heats of fusion. Their melting points, ranging from about -50° to + 130°C, fit well for storing low grade heat in residential energy systems. Detailed experimental investigations on a large number of these media show, however, that only a few of them satisfy the quality requirments for practical application in storage units. Flexible flat-plate storage containers especially developed for selected salt hydrates which expand on melting also show satisfactory performance over long periods of operation. In the case of water and selected water-salt hydrate eutectics the volume increases on solidification, and the expansion of solid storage material, being very inhomgeneous, breaks even flexible containers after only a few storage cycles. This ruinous local expansion can be avoided, however, by adding a small amount of special, lower melting salt hydrate eutectics which homogenize the crystallization and solidification of the storage medium.