Calculate Energy Savings with Cool Metal Roofing
Research by the Heat Island Group found that buildings with lightly colored, more reflective roofs use up to 40 percent less energy for cooling than buildings with darker roofs.iii To calculate the possible savings in energy provided by a cool roof, there are two online roof calculators that estimate savings.
The DOE Cool Roof Calculator was developed by the U.S. Department of Energy’s Oak Ridge Laboratory. This calculator provides an estimate of cooling and heating savings for small to medium size buildings. DOE Calculator Link
The EPA Cool Roof Calculator is provided by ENERGY STAR. This calculator allows the designer to input specific details about a building, including heating and cooling systems as well as location and the cost of energy. Energy Star Calculator Link
The two radiative properties that characterize cool roofs are solar reflectance and thermal emittance. A cool roof minimizes the solar heat gain of a building by first reflecting incoming radiation and then by quickly re-emitting the remaining absorbed portion. As a result, the cool roof stays cooler than a traditional roof of similar construction. The measured fraction of solar energy that is reflected by a roofing material’s surface is called solar reflectance.
Thermal emittance is the relative ability of the roofing material to re-radiate absorbed heat as invisible infrared light (relative to a black body radiator). This absorbed heat will either be gradually or quickly re-radiated away from the roof; the quicker the better because the longer the heat is trapped at the surface of the roof the more likely it is to penetrate the building below.
Though most roofing materials have a fairly high thermal emittance, in order to accurately determine a roofing product’s “coolness,” or its ability to shield the building beneath it from heat, both solar reflectance and thermal emittance must be measured. Cool Metal Roofing offers both these characteristics and allows for an Energy Star Rating on all colors with proper coatings.
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[...] as high as 20% and even more after installing metal roofing. Cool coated metal roofing can display solar reflectance of at least 65% and thermal emittance of 80%. This can have a tremendous impact on energy usage by [...]