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Abstract
The solar reflectance and thermal performance of small samples of various radiation control coatings on smooth surfaces have been tracked for several years on a roof test facility in East Tennessee. The focus is on white coatings because of their potential to weather, which causes the solar reflectance to decrease as the coatings age. Support from the federal new Technology Demonstration Program allowed extension of the study to include more small samples on smooth surfaces and entire rough-surfaced roofs at a federal facility in the Florida Panhandle. Two rough-surfaced, moderately well insulated, low solar reflectance built-up roofs were spray coated with a latex-based product including ceramic beads to improve solar reflectance. Only a small patch was left uncoatedd on each BUR to gather data throughout the project on the performance with no coating for direct comparision to data from instrumented coated areas. Because of the roughness of the grave-topped BURs solar reflectance for the ceramic coatings were only 0.53. Relfectances of fresh ceramice and acrylic elastomeric coatings on smooth surfaces measured 0.23 to0.32 higher. Weathered samples from the ongoing tests have measured solar reflectances of about the same to 0.10 higher than the fresh ceramiic coatings on the rough BURs. In the first three months after installation, the fresh BUR coatings showed temperature and the heat flux through the roof insulation. Average sunlit values were generated to exclude nighttime data, data on cloudy days, and data when the uncoated patch on one roof wasmore strongly shaded in the mid-afternoon on sunny days. Contributions from times in the early afternoon, when the instrumented coated area was more strongly shaded, enhanced the apparent performance of the coating. The shaded area showed a 15% decrease in the average sunlit temperature; for the other roof, with no shading oof the instrumented areas but a therrmally massive roof deck, the decrease was 11%. Decreases in the average sunlit heat flux were larger: 55% and 36% respectively. By contrast, during the same time period, sunlit averages for higher solar reflectance, fresh coatings on uninsulated roofs ont he test facility in East Tennessee showed 25% - 28% decreases in outside surface temperatures and 77-78% decreaes in heat fluxes through the plywood roof deck. The average power demand during occupied periods for the first month with the coating for the building with the thermally massive roof deck was 13% less than during the previous month without the coating. for the other building, with a lightweight roof eck but high internal loads, there were no clear average power savings due to the coating. The authors are continuing to monitr electricty use in these all-electric buildings to calibrate a model for the peak power and annual energy use of the buildings. Modeling results to be given at the end of the two-year project will address the effect of roof R-value, geographic location, and solar reflectance, including the effecdt of weathering, on the performance of coated roofss. The calibrated modells should allow to segregate site-specific effects such as shading and large thermal mass.
The solar reflectance and thermal performance of small samples of various radiation control coatings on smooth surfaces have been tracked for several years on a roof test facility in East Tennessee. The focus is on white coatings because of their potential to weather, which causes the solar reflectance to decrease as the coatings age. Support from the federal new Technology Demonstration Program allowed extension of the study to include more small samples on smooth surfaces and entire rough-surfaced roofs at a federal facility in the Florida Panhandle. Two rough-surfaced, moderately well insulated, low solar reflectance built-up roofs were spray coated with a latex-based product including ceramic beads to improve solar reflectance. Only a small patch was left uncoatedd on each BUR to gather data throughout the project on the performance with no coating for direct comparision to data from instrumented coated areas. Because of the roughness of the grave-topped BURs solar reflectance for the ceramic coatings were only 0.53. Relfectances of fresh ceramice and acrylic elastomeric coatings on smooth surfaces measured 0.23 to0.32 higher. Weathered samples from the ongoing tests have measured solar reflectances of about the same to 0.10 higher than the fresh ceramiic coatings on the rough BURs. In the first three months after installation, the fresh BUR coatings showed temperature and the heat flux through the roof insulation. Average sunlit values were generated to exclude nighttime data, data on cloudy days, and data when the uncoated patch on one roof wasmore strongly shaded in the mid-afternoon on sunny days. Contributions from times in the early afternoon, when the instrumented coated area was more strongly shaded, enhanced the apparent performance of the coating. The shaded area showed a 15% decrease in the average sunlit temperature; for the other roof, with no shading oof the instrumented areas but a therrmally massive roof deck, the decrease was 11%. Decreases in the average sunlit heat flux were larger: 55% and 36% respectively. By contrast, during the same time period, sunlit averages for higher solar reflectance, fresh coatings on uninsulated roofs ont he test facility in East Tennessee showed 25% - 28% decreases in outside surface temperatures and 77-78% decreaes in heat fluxes through the plywood roof deck. The average power demand during occupied periods for the first month with the coating for the building with the thermally massive roof deck was 13% less than during the previous month without the coating. for the other building, with a lightweight roof eck but high internal loads, there were no clear average power savings due to the coating. The authors are continuing to monitr electricty use in these all-electric buildings to calibrate a model for the peak power and annual energy use of the buildings. Modeling results to be given at the end of the two-year project will address the effect of roof R-value, geographic location, and solar reflectance, including the effecdt of weathering, on the performance of coated roofss. The calibrated modells should allow to segregate site-specific effects such as shading and large thermal mass.
Date
2/1998
2/1998
Author(s)
Thomas Petrie; Philip Childs; Jeff Christian
Thomas Petrie; Philip Childs; Jeff Christian
Page(s)
Keyword(s)
radiation control; coatings; built up roofs; BUR; energy; thermal reflectance; solar reflectance; reflectivity; coating color; ASHRAE; thermal performance
radiation control; coatings; built up roofs; BUR; energy; thermal reflectance; solar reflectance; reflectivity; coating color; ASHRAE; thermal performance