Soiling of building envelope surfaces and its effect on solar reflectance – Part II: Development of an accelerated aging method for roofing materials

TitleSoiling of building envelope surfaces and its effect on solar reflectance – Part II: Development of an accelerated aging method for roofing materials
Publication TypeJournal Article
Year of Publication2014
AuthorsSleiman, Mohamad, Thomas W. Kirchstetter, Paul Berdahl, Haley E. Gilbert, Sarah Quelen, Lea Marlot, Chelsea V. Preble, Sharon Chen, Amandine Montalbano, Olivier Rosseler, Hashem Akbari, Ronnen M. Levinson, and Hugo Destaillats
JournalSolar Energy Materials and Solar Cells
Volume122
Start Page271
Pagination271-281
Date Published3/2014
ISSN09270248
KeywordsAccelerated aging, cool roofs, Natural exposure, Soiling, soot, Weathering
Abstract

Highly reflective roofs can decrease the energy required for building air conditioning, help mitigate the urban heat island effect, and slow global warming. However, these benefits are diminished by soiling and weathering processes that reduce the solar reflectance of most roofing materials. Soiling results from the deposition of atmospheric particulate matter and the growth of microorganisms, each of which absorb sunlight. Weathering of materials occurs with exposure to water, sunlight, and high temperatures. This study developed an accelerated aging method that incorporates features of soiling and weathering. The method sprays a calibrated aqueous soiling mixture of dust minerals, black carbon, humic acid, and salts onto preconditioned coupons of roofing materials, then subjects the soiled coupons to cycles of ultraviolet radiation, heat and water in a commercial weatherometer. Three soiling mixtures were optimized to reproduce the site-specific solar spectral reflectance features of roofing products exposed for 3 years in a hot and humid climate (Miami, Florida); a hot and dry climate (Phoenix, Arizona); and a polluted atmosphere in a temperate climate (Cleveland, Ohio). A fourth mixture was designed to reproduce the three-site average values of solar reflectance and thermal emittance attained after 3 years of natural exposure, which the Cool Roof Rating Council (CRRC) uses to rate roofing products sold in the US. This accelerated aging method was applied to 25 products–single ply membranes, factory and field applied coatings, tiles, modified bitumen cap sheets, and asphalt shingles–and reproduced in 3 days the CRRC's 3-year aged values of solar reflectance. This accelerated aging method can be used to speed the evaluation and rating of new cool roofing materials.

URLhttp://dx.doi.org/10.1016/j.solmat.2013.11.028
DOI10.1016/j.solmat.2013.11.028
DOI10.1016/j.solmat.2013.11.028