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, NO_x, 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%).