Quantifying the direct and indirect benefits of a ‘cool' roof renovation project in hot dry climate zones
Jin Ho Jo, National Center of Excellence on SMART Innovations for Urban Climate and Energy, Arizona State University, Tempe, AZ; and J. Carlson, K. S. Bae, H. Bryan, and J. S. Golden
Buildings account for 60% of the total electrical power use in the United States every year. In hot arid climates a majority of this power goes towards cooling loads induced by thermal gains from their surrounding environment. The elevated roof temperatures and exhaust heat from cooling systems are also shown to contribute to the formation of urban heat islands (UHI). The United States Environmental Protection Agency (US EPA) and the US Green Building Council (USGBC) recommend ‘cool roof' systems with high reflectance and emittance properties can reduce building heat-gain and lower the impact on ambient air temperatures which will in turn lowers air conditioning cost for building owners and the greenhouse-gas (GHG) emissions associated with power production.. One of Arizona's largest power utility companies has replaced a 20-year-old roof with an alternative cool roofing product with a high Solar Reflective Index (SRI). The objective of this research investigation is to determine the financial benefits from energy savings and regional climatic impacts resulting from using the existing traditional multi-colored aggregate and black flood coat, the new White Tremco Rock-it series roof, and the new highly reflective single ply membrane on the roof of the facility. Each type of roofing will be implemented on separate sections of the large commercial building. The project methodology involves both data collection in the field and computer model simulations. The field portion includes installing the roof with sensors to monitor energy balance (net radiation and convective heat transfer) on the outside roof surface and heat gain within the interior surfaces. A heat and mass transfer software FLUENT™ will be used to simulate the convective, radiation, and conduction heat transfer between the roof and the atmosphere considering the local meteorological conditions measured near the site. Information about the building's design and mechanical systems will also be used to develop a full scale modeling in EnergyPlus™ to simulate the energy performance and benefits of the roof retrofit over the entire year. The results of the energy and air temperature model simulations will be compared to the actual energy savings of the facility and the data collected in the field. This study will present practical benefits of the application of ‘cool' roofing products and the results may be used in future energy and UHI mitigation policy decisions and demand side management (DSM) incentives for Arizona commercial roofing renovation projects.
Session 5, Urban Heat Islands—Mitigation Studies
Thursday, 15 January 2009, 3:30 PM-5:00 PM, Room 124B
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