Phase Change Material-Enhanced Insulation for Residential Exterior Wall Retrofits

This project assessed two technologies designed to enhance the typical “drill-and-fill” insulation retrofit of residential exterior walls: phase change material (PCM) integration and aerosol sealing of the building envelope. Through modeling validated by laboratory testing, the study evaluated the impact of PCM thickness on heating, ventilation, and air conditioning energy for varying wall insulation levels, envelope sealing, thermal mass, window opening, and nighttime ventilation. Field demonstrations of the retrofit package (insulation, PCM, and sealing) were conducted in three homes in disadvantaged communities located in Vallejo, Sacramento, and Los Angeles, California.

Field results demonstrated the potential for substantial reductions in cooling (10 percent to 41 percent) and heating (-23 percent to 24 percent) energy and reduction of peak demand (3 percent to 81 percent). These widely varying results were attributed to user behavior. The retrofit also enhanced envelope air tightness by up to 58 percent. Occupants noted improved comfort, reduced heating, ventilation, and air conditioning reliance, and decreased noise transmission, post-retrofit.

The study identified challenges to widespread adoption of PCM due to retrofit costs and limited market availability. The PCM studied was estimated to provide a thermal storage energy benefit that was equal or better for increasing standard wall insulation by 20 percent, showing that the addition of PCM on interior wall surfaces is a feasible way to reduce heating and cooling energy consumption in existing homes. However, it was demonstrated that increasing insulation has diminishing returns in terms of energy savings (approximately 200 to 300 kilo-watt-hours annually for insulation greater than four-inch wall cavity insulation). The payback period for the entire retrofit ranged from 4.5 to 41 years, depending on climate zone. Results indicated that PCM may be a cost-effective way to achieve high-performing envelopes in new construction. Aerosol sealing of envelopes through the attic and crawlspace was effective, fast, and promises to improve indoor air quality and reduce heating energy in existing homes.