A version of this article appears in the May/June 2009 issue of Home Energy Magazine.
May 06, 2009
In research spanning two decades, the record shows that reflective roofs on houses reduce cooling loads. Generally, at the Florida Solar Energy Center (FSEC), where I do research, we have found cooling energy savings from white reflective roofing in residential buildings on the order of 20% over darker, less-reflective roofing. Ever wonder what improved wall reflectivity might do? We have. Energy simulations like DOE 2.1E within EnergyGauge USA (see “EnergyGauge HERS Rating Software,” p. 18) often show a 5%–15% reduction in space cooling from making walls more reflective in hot climates—particularly if the walls are less insulated, larger in area, and/or not well shaded. However, this fairly obvious influence has seldom been measured. Since we like to evaluate such things at FSEC, we used the availability of the NightCool experimental control building as a ready means to obtain data on the relationship between wall reflectivity and cooling energy use. After the roof of the control building had been changed to white metal in early June 2008, we decided to split the summer season (by painting the walls white in mid-July) and examine how air conditioning energy use changed from the pre- to post-period. The measured temperature inside the 200 ...
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