Modeling of Phase Change Material Peak Load Shifting

Peak demand for electricity in many parts of the country, and particularly the desert southwest, is of critical concern to utilities. Any reasonable solutions that can be used for shifting some of the peak demand to off-peak should be seriously considered. For locations with high air conditioning demand, one possibility is to use a phase-change material in the ceiling insulation that may melt during peak demand periods and then be refrozen off peak. The purpose of our work is the development of a numerical model to evaluate the load shifting abilities of this type of approach. The simulation is based upon the solution to the one-dimensional diffusion equation driven by a sinusoidally varying ambient temperature imposed on the outer surface. In developing the model, the phase change material is taken as a horizontal layer within the insulation. Its location and mass are treated as parameters. Other variables such as the characteristic ambient temperature variations and the thermostat set point are varied relative to the phase change temperature. The output of the model is the time varying heat flux at the inner surface over the period of a day. Comparisons are made to the temporal variations of the heat flows without the application of the phase change material to those with the phase change material.