Cool walls have the potential to save as much or more energy as cool roofs in warm sunny parts of the United States, according to a study from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (LBNL).
Researchers analyzed more than 100,000 building simulations and found that in climate 1A to 4B, cool walls could save 4.6 percent of annual HVAC costs for medium-sized office buildings and up to 11 percent for stand-alone retail stores. The study accounted for both energy savings in the cooling season and elevated energy costs in the heating season.
The savings from cool walls would be greatest for buildings built before the 1980s, because later codes called for better insulation in wall assemblies. A lower amount of insulation relative to what’s on the building’s roof is another reason cool walls perform favorably, even though they receive less direct sunlight than the roof.
Painting exterior walls with light colored paint would be one way to move in the direction of cool walls, though there are also cool paints available in a wide-variety of colors that can reflect infrared radiation, keeping the surface cooler. Cool walls, and cool roofs, save energy by reflecting solar energy before it can be absorbed as heat, and doing a good job at radiating absorbed heat as well. This helps to reduce demand for cooling in the building.
There is no formal definition of cool walls yet, but the Cool Roof Rating Council voted on June 12 to amend its bylaws to expand into rating of wall surface products, according to LBNL.
Naomi Millán is senior editor of Building Operating Management.
