New Phase-Change Thermal Energy Storage Materials for Buildings

A new class of phase-change thermal energy storage materials is under development at SERI. These materials are unusual in two ways. They reversibly absorb large amounts of heat during a solid-state, crystal transformation more than 70 degrees C below their melting temperatures, and their solid-state transformation temperatures may be adjusted over a range from 7 degrees C to 188 degrees C byvarying the ratios of binary mixtures of the components. Because these storage materials remain solid throughout the range of their service temperatures, unique opportunities exist for incorporating them into building materials. Composites have been made with ordinary, porous construction materials such as wood, gypsum board, and lightweight concrete as the matrix and with the solid-state phasechange materials (SS PCM) filling the void space. The thermal storage capacities of such composites are thereby increased by more than 100% (see Figure 1) without changing the basic nature and workability of the matrix, construction material. Parametric analyses have been conducted to determine what combination of properties would be optimum for certain solar and energy conserving buildingapplications including Trombe wall, direct gain, and distributed cool storage (combined with night ventilation).