Final Report: Cool Roof Coatings Incorporating Glass Hollow MicrospheresEPA Grant Number: SU833924
Title: Cool Roof Coatings Incorporating Glass Hollow Microspheres
Investigators: Barsoum, Michel , Woods, Charlie , Reid, Courtney , Pugh, Daniel , Eisele, Eric , Hagarman, James , Byrnes, Sarah
Institution: Drexel University
EPA Project Officer: Nolt-Helms, Cynthia
Project Period: August 15, 2008 through August 14, 2009
Project Amount: $9,999
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2008) RFA Text | Recipients Lists
Research Category: P3 Challenge Area - Energy , P3 Challenge Area - Materials & Chemicals , Pollution Prevention/Sustainable Development , P3 Awards , Sustainability
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 10º F warmer than their rural counterparts, and these regions may see as high as a 22º F 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 During the P3 Phase I, a coating utilizing glass hollow microspheres as a means of controlling void diameter was developed. The objective of Phase II is to subject the developed roof coating to weathering tests, ASTM reflectivity and mechanical testing, and additional field testing.
The coatings project has become a major research initiative of the Drexel Smart House student organization. In addition to this, it was executed as a design project by five senior Materials Engineering students for their degree requirements. These students also worked with an outreach group within the Smart House which mentors high school students from Philadelphia’s Science Leadership Academy. Four of these students learned about scattering theory, environmental impacts, the urban heat island effect, and conducted formulation and testing in the laboratory at Drexel. This mentorship arrangement will continue for the second phase of the project.
Proposed Phase II Objectives and Strategies:
The objectives of Phase I of this project were to apply theory and analytical technique to develop a coating exhibiting strong scattering properties in the near infrared region. The theory and analytical techniques were also verified through solar simulation in the lab setting, and the work resulted in an initial formulation for the GHMS coatings. The objectives of Phase 2 are to move the formulation into a certified product ready for manufacture. This includes industry standard testing, weathering testing, investigation of scale up dynamics, economic analysis, and extensive field testing.
Candidate sites in the Philadelphia area will be fitted with data logging equipment and have the roofs coated with the developed coating along with other titanium dioxide based controls. Results will be carefully monitored throughout the summers of 2009 and 2010. In addition to temperature monitoring, thermal imaging will be used to determine the coating’s effectiveness.
Fourier Transform Infrared Spectroscopy (FTIR) and Malvern Laser Scattering particle size analysis were used to determine optimal reflectance parameters of the spheres. Particle size data was verified by Scanning Electron Microscopy. Polystyrene acrylate water based coatings were formulated using commercially available raw materials and selected microspheres. Heat gain of the applied coatings was measured using a variety of infrared sources and substrates. Results indicate that scattering models discussed in literature agree with our FTIR data. Solar simulation heat gain testing also yielded expected results, and it was found that glass hollow microsphere coatings had a surface temperature 10ºC lower than a titanium dioxide based reflective elastomeric roof coating.
It has been shown through a computational model that introducing voids of a specific diameter distribution in a coating can efficiently scatter selected wavelengths. This model has been confirmed by FTIR spectroscopy and particle size analysis. Solar simulation tests indicate that the coatings outperform other titanium dioxide based white coatings, however the coating has yet to be field tested. The team expects comparable results for the field testing phase of the project.
Supplemental Keywords:Syntactic coating, glass hollow microspheres, cool roof coating, white roof, urban heat island, NIR reflective glazing, solar gain, heat gain;