All ETDs from UAB

Advisory Committee Chair

Jason Kirby

Advisory Committee Members

Ashraf Al-Hamdan

Ronald Domitrovic

Wilbur Hitchcock

Christopher Waldron

Document Type

Dissertation

Date of Award

2015

Degree Name by School

Doctor of Philosophy (PhD) School of Engineering

Abstract

In hot climates, such as the Southeastern United States, the roof heat gain of low-rise commercial buildings has led to widespread adoption of high reflectivity, "cool" roofing materials to reduce the building's cooling load. Cooling reduction techniques are of particular interest to electric utilities in the Southeast who are obligated to provide energy infrastructure to supply these loads. Regrettably, a consequence of cool roofs is increased heating load in cool months, thereby reducing their overall value. A potential solution is a roof surface which reversibly and automatically adapts its albedo to the building's thermal profile. Thermochromic polymers, which reversibly change color in response to temperature, offer the ability to provide this adaptive envelope reflectivity. This effort investigated the feasibility of applying thermochromic surface coatings to conventional cool roof materials thus enabling the adaptation of the roofing material's albedo to match the thermal needs of low-rise commercial buildings. Commercially available leuco dye-developer-solvent systems exhibiting a visible change from black to clear, not originally intended for this use, were investigated and applied to conventional, commercial cool roof covering materials. A spectrophotometer measured coated coupons' solar reflectance across the sun's atmospheric spectral range. Baseline conventional and cool material characterizations were obtained along with the as-coated dark and white forms of the coated materials. Minimum coating thickness was identified to ensure an insignificant change in surface reflectance due to coating thickness. The coatings produced an additional 23% absolute solar absorptivity increase from the high-temperature to low-temperature state; though, an average 15% increase in absolute minimum absorptivity was also noted. TRNSYS simulations were used to identify optimal shift temperatures which minimized the unfavorable annual heat flux of commercial roofs: these ranged from -33°C to 15.9°C based on construction types, radiative gain at the roof, and locale. Collected data were used within EnergyPlus to model energy savings using pre-constructed reference buildings and three Southern United States cities resulting in 0%-1.6% annual energy savings potential with thermochromic coatings over cool materials. While results indicated potential economic viability pending extreme cost reduction and/or technological advancements, usage is not recommended.

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