Numerical simulation of phase change material composite wallboard in a multi-layered building envelope

Residential buildings account for a large portion of total energy consumption in the United States. Residential energy usage can be dramatically reduced by improving the efficiency of building envelope systems. One such method is to incorporate thermally massive construction materials into the building envelope. This benefits building operation by reducing the energy requirement for maintaining thermal comfort, downsizing the AC/heating equipment, and shifting the time of the peak load on the electrical grid. Phase change materials (PCMs) are promising material for that purpose. When impregnated or encapsulated into wallboard or concrete systems, PCMs can greatly enhance their thermal energy storage capacity and effective thermal mass. In this work, a numerical study is conducted to investigate the characteristics of PCMs in building applications. For that purpose a one-dimensional, transient heat equation for a multi-layered building envelope is solved using the Crank-Nicolson scheme. The effect of PCM is modeled with a latent heat source term. The code also incorporates sun loading and uses real weather data. Using this code a PCM composite wallboard incorporated into the walls and roof of a residential building was examined. The PCM performance was studied under all seasonal conditions using TMY3 data for exterior boundary conditions. Comparisons were made between different PCM wallboard locations. This work shows that there is an optimized location for PCM placement within building envelope and the location depends on the thermal resistance of the layers between the PCM and the exterior boundary. The energy savings potential was identified by comparing the performance of the PCM wallboard with the performance of a building envelope without PCM. This work shows that a PCM composite wallboard enhanced building can reduce the annual cooling load from the walls by as much as 19.7% and from the roof by as much as 8.1%. Similarly, the annual heating loads can be reduced by as much as 6% and 6.4% for the walls and roof respectively. It was also shown that the peak electricity load can be shifted by as much as three hours in the summer for a south facing wall. Studies are also conducted to compare the PCM performance across three climate zones. This work shows that PCM performance varies significantly across these zones.