Session: 02-01: Building Energy Efficiency Technologies

Paper Number: 124141

124141 - Assessing Energy Savings: A Comparative Study of Reflective Roof Coatings in Four USA Climate Zones 

Abstract: 

High-albedo reflective roof coatings are designed with the specific aim of reflecting a greater proportion of solar radiation compared to traditional roofing materials, thereby lowering the solar energy absorption into the roof. This deliberate design aims to enhance energy savings by reducing the surface temperature of rooftops. That is why these are also known by the name cool roof reflective coatings. They serve as a crucial solution in counteracting the urban heat island effect by reducing surface temperatures in urban areas. This contributes to a more sustainable and cooler urban environment, addressing critical challenges associated with elevated temperatures. In this paper we present the energy saving potential of silicone, acrylic and aluminum roof coatings using EnergyPlus, a building energy simulation engine by the U.S. Department of Energy (DOE). As a continuously evolving tool since its initial release in 2001 by DOE, EnergyPlus proves highly reliable to computationally model energy savings. Two of the DOE prototype commercial buildings - a standalone retail (24,692 ft²) and a strip-mall (22,500 ft²) building across four different cities namely Phoenix, AZ (climate zone 2B), Houston, TX (climate zone 2A), Los Angeles, CA (climate zone 3B coast), and Miami, FL (climate zone 1A) have been used to model the effects of different types of coatings. The performance with reflective coatings was compared with respect to a black roof having a solar reflectance of 5% and a thermal emittance of 90%. We also examined how the two important properties, namely solar reflectance, and thermal emittance, impact the performance of a roof coating. A contour plot between these properties reveals that high values of both result in reduced cooling needs and a heating penalty which is insignificant when compared with cooling savings for cooling-dominant climates like Phoenix where the cooling demand significantly outweighs the heating demand, yielding significant energy savings. Furthermore, we quantified the capacity of various coatings to reduce rooftop temperatures, a key factor contributing to energy savings. This factor plays a crucial role in all three heat transfer mechanisms: conduction, convection, and radiation. The rooftop surface temperature exhibits considerable variation depending on the solar reflectance and thermal emittance attributes of the roof. We plotted average daily and hourly temperature values corresponding to different solar reflectance and emittance levels. High-reflectivity roof coatings, coupled with exceptionally high emittance values, have the potential to decrease temperatures by 20-25°C on the warmest day of the year based on typical meteorological data.

Presenting Author: Ajay Sharma Arizona State University

Presenting Author Biography: I'm Ajay Kumar Sharma, a Master of Science student in Mechanical Engineering at Arizona State University. With a strong academic foundation and a deep commitment to advancing sustainable technologies, my educational journey has been focused on building energy modeling and energy efficiency. As part of my masters thesis, I'm working on an industry sponsored project to model the effect of reflective roof coatings in commercial buildings. This project is particularly significant as it explores the energy-saving potential of reflective coatings across a diverse range of climate zones in the United States, a topic of immense relevance in the context of environmental sustainability.

Authors:

Ajay Sharma Arizona State University
Patrick Phelan Arizona State University
Narayanan Neithalath Arizona State University
Divya Chopra Carlisle Weatherproofing Technologies
Zhiyong Zhu Carlisle Weatherproofing Technologies