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Title: Durability of high-albedo roof coatings and implications for cooling energy savings. Final report

Abstract

Twenty-six spot albedo measurements of roofs were made using a calibrated pyranometer. The roofs were surfaced with either an acrylic elastomeric coating, a polymer coating with an acrylic base, or a cementitious coating. Some of the roofs` albedos were measured before and after washing to determine whether the albedo decrease was permanent. Data indicated that most of the albedo degradation occurred within the first year, and even within the first two months. On one roof, 70% of one year`s albedo degradation occurred in the first two months. After the first year, the degradation slowed, with data indicating small losses in albedo after the second year. Measurements of seasonal cooling energy savings by Akbari et al. (1993) included the effects of over two months of albedo degradation. We estimated {approximately}20% loss in cooling-energy savings after the first year because of dirt accumulation. For most of the roofs we cleaned, the albedo was restored to within 90% of its initial value. Although washing is effective at restoring albedo, the increase in energy savings is temporary and labor costs are significant in comparison to savings. By our calculations, it is not cost-effective to hire someone to clean a high-albedo roof only to achievemore » energy savings. Thus, it would be useful to develop and identify dirt-resistant high-albedo coatings.« less

Authors:
;
Publication Date:
Research Org.:
Lawrence Berkeley Lab., CA (United States)
Sponsoring Org.:
USDOE, Washington, DC (United States); California Inst. for Energy Efficiency, Berkeley, CA (United States)
OSTI Identifier:
10180653
Report Number(s):
LBL-34974
ON: DE94018539
DOE Contract Number:
AC03-76SF00098
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: Jun 1994
Country of Publication:
United States
Language:
English
Subject:
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION; ROOFS; REFLECTIVE COATINGS; ALBEDO; REFLECTION; WEATHERING; ENERGY ABSORPTION; COOLING; PYRANOMETERS; COST RECOVERY; ENERGY CONSERVATION; SERVICE LIFE; SURFACE CLEANING; PROGRESS REPORT; 320107; BUILDING SYSTEMS

Citation Formats

Bretz, S.E., and Akbari, H. Durability of high-albedo roof coatings and implications for cooling energy savings. Final report. United States: N. p., 1994. Web. doi:10.2172/10180653.
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Bretz, S.E., & Akbari, H. Durability of high-albedo roof coatings and implications for cooling energy savings. Final report. United States. doi:10.2172/10180653.
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Bretz, S.E., and Akbari, H. Wed . "Durability of high-albedo roof coatings and implications for cooling energy savings. Final report". United States. doi:10.2172/10180653. https://www.osti.gov/servlets/purl/10180653.
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@article{osti_10180653,
title = {Durability of high-albedo roof coatings and implications for cooling energy savings. Final report},
author = {Bretz, S.E. and Akbari, H.},
abstractNote = {Twenty-six spot albedo measurements of roofs were made using a calibrated pyranometer. The roofs were surfaced with either an acrylic elastomeric coating, a polymer coating with an acrylic base, or a cementitious coating. Some of the roofs` albedos were measured before and after washing to determine whether the albedo decrease was permanent. Data indicated that most of the albedo degradation occurred within the first year, and even within the first two months. On one roof, 70% of one year`s albedo degradation occurred in the first two months. After the first year, the degradation slowed, with data indicating small losses in albedo after the second year. Measurements of seasonal cooling energy savings by Akbari et al. (1993) included the effects of over two months of albedo degradation. We estimated {approximately}20% loss in cooling-energy savings after the first year because of dirt accumulation. For most of the roofs we cleaned, the albedo was restored to within 90% of its initial value. Although washing is effective at restoring albedo, the increase in energy savings is temporary and labor costs are significant in comparison to savings. By our calculations, it is not cost-effective to hire someone to clean a high-albedo roof only to achieve energy savings. Thus, it would be useful to develop and identify dirt-resistant high-albedo coatings.},
doi = {10.2172/10180653},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Jun 01 00:00:00 EDT 1994},
month = {Wed Jun 01 00:00:00 EDT 1994}
}
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Technical Report:
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DOI:  10.2172/10180653
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  • ; ;
    One simple and effective way to mitigate urban heat islands, i.e., the higher temperatures in cities compared to those of the surrounds, and their negative impacts on cooling energy consumption is to use high-albedo materials on major urban surfaces such as rooftops, streets, sidewalks, school yards, and the exposed surfaces of parking lots. High-albedo materials can save cooling energy use by directly reducing the heat gain through a building's envelope (direct effect) and also by lowering the urban air temperature in the neighborhood of the building (indirect effect). This project is an attempt to address high-albedo materials for buildings andmore » to perform measurements of roof coatings. We search for existing methods and materials to implement fighter colors on major building and urban surfaces. Their cost effectiveness are examined and the possible related technical, maintenance, and environmental problems are identified. We develop a method for measuring albedo in the field by studying the instrumentation aspects of such measurements. The surface temperature impacts of various albedo/materials in the actual outdoor environment are studied by measuring the surface temperatures of a variety of materials tested on an actual roof. We also generate an albedo database for several urban surfaces to serve as a reference for future use. The results indicate that high-albedo materials can have a large impact on the surface temperature regime. On clear sunny days, when the solar noon surface temperatures of conventional roofing materials were about 40{degrees}C (72{degrees}F) warmer than air, the surface temperature of high-albedo coatings were only about 5{degrees}C warmer than air. In the morning and in the late afternoon, the high-albedo materials were as cool as the air itself. While conventional roofing materials warm up by an average 0.055{degrees}C/(W m{sup {minus}2}), the high-albedo surfaces warm up by an average 0.015{degrees}C/(W m{sup {minus}2}).« less

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