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Energy Efficiency MeasuresCOMMERCIAL: BUILDING ENVELOPEThe skin of a building should provide an appropriate barrier between interior and exterior environments. Reflective surfaces, especially on roofs and walls, will minimize the amount of solar heat that penetrates a building. Cool roofs reflect a large portion of the sun’s heat energy back into the atmosphere. Materials should be selected for both high reflectivity and high emissivity so that they reflect solar radiation in the visible and near-infrared regions and emit (rather than retain) heat in the mid-infrared regions. There is a Cool Roof Rating Council at work developing labels suitable for cool roof products; see www.coolroofs.org for more information and a list of products. Optimized thermal insulation and air sealing is important to buffer the interior of the building from the fluctuating temperature outside. In retrofit, this means finding and air-sealing leaks and insulation gaps that can occur around windows and doors, but also around less obvious places from the boiler room to the tops of elevator shafts. Air-sealing duct systems is particularly important, as is insulating duct systems in buffer zones or whenever they are outside of the conditioned envelope. Exterior shading, such as horizontal overhangs and vertical fins, is a good way to decrease the amount of solar gain into a building and can also enhance the exterior design of a structure. In particular, shading fenestration from direct solar radiation has great potential to lower the cooling requirements of a building. This can be accomplished in ways that are consistent with ensuring good passive heating performance in winter months by choosing the geometry of the overhangs and fins with care. Two energy-efficiency strategies can be accomplished through glazing selection. Lower solar heat gain coefficient (SHGC) glazing reduces the amount of solar radiation that is allowed into a building by reflecting much of the radiation—particularly in the near-infrared—that strikes it. Selecting glazing with low SHGC but high visible transmittance on the east and west facades will allow light to enter the building and simultaneously reflect heat away from the interior. To ensure that occupants close to windows are not troubled with glare or eyestrain, this glazing strategy should be used in conjunction with the design of top-lighting (that is, skylights and roof monitors) and side-lighting (windows and clerestories) above vision windows. Vision windows should have glazing with lower visible transmittance to help control for glare and provide more even light distribution through the interior space. Solar films with a variety of properties can be cost-effectively installed on existing windows to achieve some of the glare and heat-reducing properties of modern specularly-selective glazing. |
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