Sponsored by the US Environmental Protection Agency

Also supported by the Dow Chemical Company, Advanced Materials Division and Potter's Industries

This project's goal is to develop a low cost cool roof coating formulation which improves upon the infrared reflective properties of commercially available white coatings. This is accomplished by incorporating novel materials with unique optical properties and specially engineered pigments and additives into a water based acrylic binder. This project is part of the Smart House's Heat Island Mitigation research initiative. 

Phase 1 Objectives on the EPA's website

Courtney Reid explains the project (MP3)

Photos from the 2009 National Sustainable Design Expo

More Information:

Solar Gain is in part responsible for up to 56% of energy consumed by cooling systems in residential buildings1. Additionally, high building density in the urban environment contributes to the urban heat island effect. According to the EPA2, regions exhibiting the urban heat island effect can be as much as 10ºF warmer than their rural counterparts, and these regions may see as high as a 22ºF difference in temperature between day and night. Mitigating the urban heat island effect has the potential to reduce cooling demand, peak demand, and heat related illnesses and fatalities.

By applying cool roof coatings to a building's exterior, cooling loads can be reduced and urban heat islands can in part be mitigated.3 Many commercially available cool roof coatings are white paint formulations based on titanium dioxide.4 Although titanium dioxide and other pigments are effective at scattering visible wavelengths, they exhibit strong absorption in the infrared region.5 By incorporating controlled voids in a coating as the scattering medium, the void size distribution can be optimized for broadband radiation scattering.6 The purpose of this project is to design a coating utilizing glass hollow microspheres as a means of controlling void diameter to achieve a low solar gain roof.

  

Glass Hollow Microspheres are the primary filler in our coatings. Our current formulation has been specially designed to promote polymer binder - sphere adhesion while preventing sphere breakage, visible in two of the above images. Images © 2009 Drexel University, Department of Materials Science and Engineering.

1. Department of Energy. 2007 Buildings Energy Data Book, U.S. Department of Energy. http://buildingsdatabook.eren.doe.gov/

2. Environmental Protection Agency. "Reducing Urban Heat Islands: Compendium of Strategies" Retrieved March 12, 2009. http://www.epa.gov/heatisland/resources/ pdf/BasicsCompendium.pdf

3. Environmental Protection Agency. "Reducing Urban Heat Islands: Compendium of Strategies - Cool Roofs" http://www.epa.gov/heatisland/resources/pdf/ CoolRoofsCompendium.pdf

4. J. Beltley and G. P. A. Turner, Introduction to Paint Chemistry and Principles of Paint Technology, 4th ed. (Chapman and Hall, London, 1998), p. 105-106, 110.

5. Cole, Joseph R; Halas, N.J. Optimized Plasmonic Nanoparticle Distributions for Solar Spectrum Harvesting. Appl. Phys. Lett. 89, 153120 (2006).

6. Dombrovsky, Leonid A; Randrianalisoa, Jaona H; Baillis, Dominique. Infrared radiative properties of polymer coatings containing hollow microspheres. Intl. J. of Heat and Mass Trans. 50 (2007) 1516–1527

This research has been supported by a grant from the U.S. Environmental Protection Agency's Science to Achieve Results (STAR) program.

Although the research described in the article has been funded wholly or in part by the U.S. Environmental Protection Agency's STAR program through grant SU834300, it has not been subjected to any EPA review and therefore does not necessarily reflect the views of the Agency, and no official endorsement should be inferred.