Modeling of Phase Change Material Peak Load Shifting

Abstract

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.

Diurnal thermal analysis of microencapsulated PCM-concrete composite walls

“…The goal in implementing composite PCM walls is to significantly reduce and time-shift the maximum thermal load on the building in order to reduce and smooth out the electricity demand for heating and cooling. This could also help ratepayers take advantage of TOU electricity rate schedules while reducing the ecological footprint of buildings [3,4,[9][10][11][12]. The choice of PCM should be adapted to the climate and building orientation so as to maximize the above mentioned benefits.…”

Building power demand response methods toward smart grid

“…The modeling and optimal control of the building integrated PCM are essential for accurately estimating the thermal performance. An idealized model for peak load shifting and a simplified RC-model have been respectively developed for investigating the indoor thermal performance (Halford and Boehm 2007;Zhu et al 2010). The results showed that the developed models could represent the thermal characteristics of the PCM quite well.…”

Analytical model for solidification and melting in a finite PCM in steady periodic regime

“…From the different numerical models available in the literature, we considered that used by Halford et al [15], which is based on an explicit time-variant scheme, in which the thermal balance equation at the bi-phase interface is formulated in a manner that is more adherent to the physical phenomenon. In particular, the discontinuity of the heat flux at the interface is considered substituting the relative incremental ratio DX M =Dt at the derivative dX M =dt.…”

“…While Halford [15] examined the influence of the layer thickness and of the outdoor climatic conditions on the time lag and on the attenuation of the peak load. Instead, the influence of the position and the melting temperature of the PCM layer on the annual energy requirement has been studied by Mathieu-Potvin et al [16].…”