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High-albedo materials for reducing building cooling energy use

Description: One simple and effective way to mitigate urban heat islands, i.e., the higher temperatures in cities compared to those of the surrounds, and their negative impacts on cooling energy consumption is to use high-albedo materials on major urban surfaces such as rooftops, streets, sidewalks, school yards, and the exposed surfaces of parking lots. High-albedo materials can save cooling energy use by directly reducing the heat gain through a building's envelope (direct effect) and also by lowering the urban air temperature in the neighborhood of the building (indirect effect). This project is an attempt to address high-albedo materials for buildings and to perform measurements of roof coatings. We search for existing methods and materials to implement fighter colors on major building and urban surfaces. Their cost effectiveness are examined and the possible related technical, maintenance, and environmental problems are identified. We develop a method for measuring albedo in the field by studying the instrumentation aspects of such measurements. The surface temperature impacts of various albedo/materials in the actual outdoor environment are studied by measuring the surface temperatures of a variety of materials tested on an actual roof. We also generate an albedo database for several urban surfaces to serve as a reference for future use. The results indicate that high-albedo materials can have a large impact on the surface temperature regime. On clear sunny days, when the solar noon surface temperatures of conventional roofing materials were about 40{degrees}C (72{degrees}F) warmer than air, the surface temperature of high-albedo coatings were only about 5{degrees}C warmer than air. In the morning and in the late afternoon, the high-albedo materials were as cool as the air itself. While conventional roofing materials warm up by an average 0.055{degrees}C/(W m{sup {minus}2}), the high-albedo surfaces warm up by an average 0.015{degrees}C/(W m{sup {minus}2}).
Date: January 1, 1992
Creator: Taha, H.; Sailor, D. & Akbari, H.
Partner: UNT Libraries Government Documents Department

Implementation of solar-reflective surfaces: Materials and utility programs

Description: This report focuses on implementation issues for using solar-reflective surfaces to cool urban heat islands, with specific examples for Sacramento, California. Advantages of solar-reflective surfaces for reducing energy use are: (1) they are cost-effective if albedo is increased during routine maintenance; (2) the energy savings coincide with peak demand for power; (3) there are positive effects on environmental quality; and (4) the white materials have a long service life. Important considerations when choosing materials for mitigating heat islands are identified as albedo, emissivity, durability, cost, pollution and appearance. There is a potential for increasing urban albedo in Sacramento by an additional 18%. Of residential roofs, we estimate that asphalt shingle and modified bitumen cover the largest area, and that built-up roofing and modified bitumen cover the largest area of commercial buildings. For all of these roof types, albedo may be increased at the time of re-roofing without any additional cost. When a roof is repaired, a solar-reflective roof coating may be applied to significantly increase albedo and extend the life of the root Although a coating may be cost-effective if applied to a new roof following installation or to an older roof following repair, it is not cost-effective if the coating is applied only to save energy. Solar-reflective pavement may be cost-effective if the albedo change is included in the routine resurfacing schedule. Cost-effective options for producing light-colored pavement may include: (1) asphalt concrete, if white aggregate is locally available; (2) concrete overlays; and (3) newly developed white binders and aggregate. Another option may be hot-rolled asphalt, with white chippings. Utilities could promote solar-reflective surfaces through advertisement, educational programs and cost-sharing of road resurfacing.
Date: June 1, 1992
Creator: Bretz, S.; Akbari, H.; Rosenfeld, A. & Taha, H.
Partner: UNT Libraries Government Documents Department

High-albedo materials for reducing building cooling energy use

Description: One simple and effective way to mitigate urban heat islands, i.e., the higher temperatures in cities compared to those of the surrounds, and their negative impacts on cooling energy consumption is to use high-albedo materials on major urban surfaces such as rooftops, streets, sidewalks, school yards, and the exposed surfaces of parking lots. High-albedo materials can save cooling energy use by directly reducing the heat gain through a building`s envelope (direct effect) and also by lowering the urban air temperature in the neighborhood of the building (indirect effect). This project is an attempt to address high-albedo materials for buildings and to perform measurements of roof coatings. We search for existing methods and materials to implement fighter colors on major building and urban surfaces. Their cost effectiveness are examined and the possible related technical, maintenance, and environmental problems are identified. We develop a method for measuring albedo in the field by studying the instrumentation aspects of such measurements. The surface temperature impacts of various albedo/materials in the actual outdoor environment are studied by measuring the surface temperatures of a variety of materials tested on an actual roof. We also generate an albedo database for several urban surfaces to serve as a reference for future use. The results indicate that high-albedo materials can have a large impact on the surface temperature regime. On clear sunny days, when the solar noon surface temperatures of conventional roofing materials were about 40{degrees}C (72{degrees}F) warmer than air, the surface temperature of high-albedo coatings were only about 5{degrees}C warmer than air. In the morning and in the late afternoon, the high-albedo materials were as cool as the air itself. While conventional roofing materials warm up by an average 0.055{degrees}C/(W m{sup {minus}2}), the high-albedo surfaces warm up by an average 0.015{degrees}C/(W m{sup {minus}2}).
Date: January 1, 1992
Creator: Taha, H.; Sailor, D. & Akbari, H.
Partner: UNT Libraries Government Documents Department

Paving materials for heat island mitigation

Description: This report summarizes paving materials suitable for urban streets, driveways, parking lots and walkways. The authors evaluate materials for their abilities to reflect sunlight, which will reduce their temperatures. This in turn reduces the excess air temperature of cities (the heat island effect). The report presents the compositions of the materials, their suitability for particular applications, and their approximate costs (in 1996). Both new and resurfacing are described. They conclude that, although light-colored materials may be more expensive than conventional black materials, a thin layer of light-colored pavement may produce energy savings and smog reductions whose long-term worth is greater than the extra cost.
Date: November 1997
Creator: Pomerantz, M.; Akbari, H.; Chen, A.; Taha, H. & Rosenfeld, A. H.
Partner: UNT Libraries Government Documents Department

Policies to reduce heat islands: Magnitudes of benefits and incentives to achieve them

Description: A ``Cool Communities`` strategy of lighter-colored reroofs and resurfaced pavements, and shade trees, can directly lower annual air conditioning bills in Los Angeles (LA) by about $100 million (M), cool the air in the LA Basin (thereby saving indirectly $70M more in air conditioning), and reduce smog exceedance by about 10%, worth another $360M, for a total savings of about $0.5 billion per year. Trees are most effective if they shade buildings; but they are still very cost effective if they merely cool the air by evapotranspiration. Avoided peak power for air conditioning can be about 1.5GW (more than 15% of LA air conditioning). Extrapolated to the entire US, the authors estimate 20GW avoided and potential annual electricity savings of about $5--10B in 2015. To achieve these savings, they call for ratings and labels for cool materials, buildings` performance standards, utility incentive programs, and an extension of the existing smog-offset trading market (RECLAIM) to include credit for cool surfaces and trees. EPA can include cool materials and trees in its proposed regional ``open market smog-offset trading credits``.
Date: May 1, 1996
Creator: Rosenfeld, A.H.; Romm, J.J.; Akbari, H.; Pomerantz, M. & Taha, H.G.
Partner: UNT Libraries Government Documents Department

The impact of summer heat islands on cooling energy consumption and CO{sub 2} emissions

Description: It has been well documented that summer heat islands increase the demand for air conditioning. Several studies have suggested developing guidelines to mitigate this negative effect, on both micro- and meso-scales. Reducing summer heat islands saves cooling energy, reduces peak demand, and reduces the emission of CO{sub 2} from electric power plants. This paper summarizes some of the efforts to quantify the effects of techniques to reduce heat islands. In particular, the authors summarize simulations they have made on the effects of plating trees and switching to light colored surfaces in cities. The results indicate that these techniques effectively reduce building cooling loads and peak power in selected US cities, and are the cheapest way to save energy and reduce CO{sub 2} emissions. This paper compares the economics of technologies to mitigate summer heat islands with other types of conservation measures. The authors estimate the cost of energy conserved by planting trees and recoating surfaces on a national level and compare it with the cost of energy conserved by increasing efficiencies in electrical appliances and cars. Early results indicate that the cost of energy saved by controlling heat islands is less than 1{cents}/kWh, more attractive than efficient electric appliances ({approximately} 2{cents}/kWh), and far more attractive than new electric supplies ({approximately}10{cents}/kWh). In transportation, the cost of conserving a gallon of gasoline, though far more attractive than buying gasoline at current prices, is again more expensive than controlling heat islands. By accounting for the carbon content of the fuels used for power generation and transportation, the authors restate these comparisons in terms of cents per avoided pound of carbon emitted as CO{sub 2}. The results show that the cost of avoided CO{sub 2} from planting trees/increasing albedo is about 0.3--1.3{cents}/lb. of carbon; for buying efficient electric appliances, 2.5{cents}/lb. of carbon; and for ...
Date: August 1, 1988
Creator: Akbari, H.; Huang, J.; Martien, P.; Rainer, L.; Rosenfeld, A. & Taha, H.
Partner: UNT Libraries Government Documents Department

Monitoring peak power and cooling energy savings of shade trees and white surfaces in the Sacramento Municipal Utility District (SMUD) service area: Project design and preliminary results

Description: Urban areas in warm climates create summer heat islands of daily average intensity of 3--5{degrees}C, adding to discomfort and increasing air-conditioning loads. Two important factors contributing to urban heat islands are reductions in albedo (lower overall city reflectance) and loss of vegetation (less evapotranspiration). Reducing summer heat islands by planting vegetation (shade trees) and increasing surface albedos, saves cooling energy, allows down-sizing of air conditioners, lowers air-conditioning peak demand, and reduces the emission of CO{sub 2} and other pollutants from electric power plants. The focus of this multi-year project, jointly sponsored by SMUD and the California Institute for Energy Efficiency (CIEE), was to measure the direct cooling effects of trees and white surfaces (mainly roofs) in a few buildings in Sacramento. The first-year project was to design the experiment and obtain base case data. We also obtained limited post retrofit data for some sites. This report provides an overview of the project activities during the first year at six sites. The measurement period for some of the sites was limited to September and October, which are transitional cooling months in Sacramento and hence the interpretation of results only apply to this period. In one house, recoating the dark roof with a high-albedo coating rendered air conditioning unnecessary for the month of September (possible savings of up to 10 kWh per day and 2 kW of non-coincidental peak power). Savings of 50% relative to an identical base case bungalow were achieved when a school bungalow`s roof and southeast wall were coated with a high-albedo coating during the same period. Our measured data for the vegetation sites do not indicate conclusive results because shade trees were small and the cooling period was almost over. We need to collect more data over a longer cooling season in order to demonstrate savings conclusively.
Date: December 1, 1992
Creator: Akbari, H.; Bretz, S.; Hanford, J.; Rosenfeld, A.; Sailor, D.; Taha, H. et al.
Partner: UNT Libraries Government Documents Department