Effects of Soiling and Cleaning on the Reflectance and Solar HeatGain of a Light-Colored Roofing Membrane
A roof with high solar reflectance and high thermalemittance (e.g., a white roof) stays coolin the sun, reducing coolingpower demand in a conditioned building and increasing comfort in anunconditioned building. The high initial solar reflectance of a whitemembrane roof (circa 0.8) can be degraded by deposition of soot, dust,and/or algae to about 0.6 (range 0.3 to 0.8, depending on exposure) Weinvestigate the effects of soiling and cleaning on the solar spectralreflectance and solar absorptance of 15 initially white or light-graymembrane samples taken from roofs across the United States. Soot andorganic carbon were the two identifiable strongly absorbing contaminantson the membranes. Wiping was effective at removing soot, and less so atremoving organic carbon. Rinsing and/or washing removed nearly all of theremaining soil layer, with the exceptions of (a) thin layers of organiccarbon and (b) isolated dark spots of algae. Bleach was required toremove the last two features. The ratio of solar reflectance to unsoiledsolar reflectance (a measure of cleanliness) ranged from 0.41 to 0.89 forthe soiled samples; 0.53to 0.95 for the wiped samples; 0.74 to 0.98 forthe rinsed samples; 0.79 to 1.00 for the washed samples; and 0.94 to 1.02for the bleached samples. However, the influence of membrane soiling andcleaning on roof heat gain is better gauged by variations in solarabsorptance. Relative solar absorptances (indicating solar heat gainrelative to that of the unsoiled membrane) ranged from 1.4 to 3.5 for thesoiled samples; 1.1 to 3.1 for the wiped samples; 1.0 to 2.0 for therinsed samples; 1.0 to 1.9 for the washed samples; and 0.9 to 1.3 for thebleached samples.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Assistant Secretary for EnergyEfficiency andRenewable Energy
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 928707
- Report Number(s):
- LBNL-57555; R&D Project: EK241L; BnR: 600303000; TRN: US200811%%295
- Journal Information:
- Atmpsherical Environment, Vol. 39; Related Information: Journal Publication Date: 2005
- Country of Publication:
- United States
- Language:
- English
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