Proportioning composites for efficient thermal storage walls

Abstract Thermal storage walls for use in passive solar collectors are analyzed with the purpose of establishing guidelines for the design of low-mass, high-efficiency walls. Numerical results for the efficiency of thermal transfer are shown to be well approximated by a simple, stationary-state formula, with which general design objectives are identified, in particular the desirability of materials having prescribed thermal heat capacity and conductivity. The required proportioning of metals, masonry and phase change materials to yield materials with such properties is determined for the case of parallel layering. Illustrations of binary and ternary composites are presented. Compared with concrete, paraffin-metal mixtures are found to offer thermal storage walls having a 90 per cent reduction in storage mass and a 20 per cent relative increase in efficiency.