Using a model and empirical data to analyze manufactured home conservation retrofits

Approximately 600 of the 3200 homes participating in the Hood River Conservation Project (HRCP) were manufactured (mobile) homes. The variation in their thermal characteristics before and after retrofit allowed us to estimate the energy savings associated with specific energy conservation measures (ECMs). We used the PRISM model and an adjustment procedure to provide estimates of heating energy consumption. The estimated relationship between the heating consumption and the estimated design load coefficient (UA) was used to determine the space-heating energy savings associated with individual ECMs. We then developed cost-estimating relationships for each component based on HRCP data and used the estimated costs with the energy savings estimates to determine the levelized costs of retrofit measures. Levelized costs less than 4 ¢/kWh were considered to be cost-effective. The results indicated that ceiling retrofits were the most cost-effective way to save energy. On an incremental basis and assuming 30-year remaining lifetimes, ceiling insulation up to R-5.4 (m² °C)/W was cost-effective. On an average basis, levels up to R-6.8 (where physically possible) were cost-effective. Floor insulation retrofits to R-2.5 were nearly cost-effective. The levelized costs of window retrofits, however, were substantially beyond cost-effective levels. The assumed lifetime of the home critically affected the cost-effectiveness of the retrofits: a 10-year lifetime increased levelized costs by a factor of about 2.5 over costs for a 30-year lifetime.