Advances in Measuring Solar Reflectance—or, Why That Roof isn’t as Cool as You Thought it Was

June 30, 2009 - 12:00pm
LBNL Bldg. 66 Auditorium

Solar reflectance is often used to estimate the solar heat gain and rate the “coolness” of roofs and pavements. A solar reflectance property measured by two popular ASTM standard test methods (E903, C1549) can underestimate the peak solar heat gain of a spectrally selective “cool colored” surface by nearly 100 W m-2 because it assumes that sunlight contains an unrealistically high fraction of near-infrared (invisible) energy. Its use in building energy simulations can overestimate cool-roof annual energy savings by more than 20%. I define a new and simple solar reflectance metric that predicts the peak solar heat gain of a roof or pavement to within 1 W m-2, and overestimates cool-roof annual energy savings by no more than 3%. It can be easily and accurately measured with each of three common instruments: a pyranometer, a solar spectrophotometer, or an updated version of the Solar Spectrum Reflectometer. This seminar will explore the rationale for this new solar reflectance metric and describe recently developed techniques for its measurement. For more information about this seminar, please contact: JoAnne Lambert 510.486.4835, or send e-mail to

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