To assess cool-roof benefits, the temperatures, heat flows, and energy uses in two similar single-family, single-story homes built side by side in Fresno, California were measured for a year. The “cool” house had a reflective cool concrete tile roof (initial albedo 0.51) with above-sheathing ventilation, and nearly twice the thermal capacitance of the standard dark asphalt shingle roof (initial albedo 0.07) on the “standard” house.
Cool-roof energy savings in the cooling and heating seasons were computed two ways. Method A divides by HVAC efficiency the difference (standard − cool) in ceiling + duct heat gain. Method B measures the difference in HVAC energy use, corrected for differences in plug and window heat gains.
Based on the more conservative Method B, annual cooling (compressor + fan), heating fuel, and heating fan site energy savings per unit ceiling area were 2.82 kWh/m2 (26%), 1.13 kWh/m2 (4%), and 0.0294 kWh/m2 (3%), respectively. Annual space conditioning (heating + cooling) source energy savings were 10.7 kWh/m2 (15%); annual energy cost savings were $0.886/m2 (20%). Annual conditioning CO2, NOx, and SO2 emission reductions were 1.63 kg/m2 (15%), 0.621 g/m2 (10%), and 0.0462 g/m2 (22%). Peak-hour cooling power demand reduction was 0.88 W/m2 (37%).
