%PDF-1.5 [45] As part of the new efforts, DOE will install a cool roof, whenever cost-effective over the lifetime of the roof, during construction of a new roof or the replacement of an old one at a DOE facility. Solar reflectivity or reflectance is the ability of a material to reflect solar energy from its surface back into the atmosphere. However, this applies only to those areas with low winter temperatures – not tropical climates. It is relatively easy to specify a cool roof and predict energy savings, but some thinking ahead can prevent other headaches. In tropical Australia, zinc-galvanized (silvery) sheeting (usually corrugated) do not reflect heat as well as the truly "cool" color of white, especially as metallic surfaces fail to emit infrared back to the sky. 1 0 obj The calculator will calculate the Aged Solar Reflectance using the Initial Solar Reflectance once you hit enter or click outside the box. h�bbd``b`�S�S�����X�@�c?��$8��I&F�� �H��3� � � Without considering any tax benefits or other utility charges, annual energy expenditures were reduced by $7,200 or $0.07/square foot. There are two properties that are used to measure the effects of cool roofs: Another method of evaluating coolness is the solar reflectance index (SRI), which incorporates both solar reflectance and emittance in a single value. Solar reflectance index or solar reflectivity is the capability of a material to reflect solar energy from the surface of material back to the atmosphere. It is clear from Figs. 2 0 obj The reduction in solar absorption reduced solar gains in the summer but also increased heat losses during the heating season. The value of the solar reflectance index varies from 0 to 1. This system has been put into an online directory of more than 850 roofing products and is available for energy service providers, building code bodies, architects and specifiers, property owners and community planners. If the percentage is a higher number, that means the surface is more effective at reflecting the radiation from the sun. Cool roofs have a lower impact the more insulation is used. The Secretary of Energy directed all U.S. Department of Energy (DOE) offices to install cool roofs, when life-cycle cost-effectiveness is demonstrated, when constructing new roofs, or when replacing old roofs at DOE facilities. The solar reflectance of green roofs varies depending on the plant types (generally 0.3–0.5). ?���8��X�̓J�$$�)$����ZILp`,�k��;�dN̦�2YAa=)�U~�H���I����ƙ��s�qJ��kZ�: =�]0)� It is calculated The average daily summertime temperature of the black roof surface was 75 °C (167 °F), but once retrofitted with a white reflective surface, it measured 52 °C (126 °F). The aim of the proposed action is to create and implement an Action Plan for the cool roofs in EU. endobj When these roofs are designed to reflect increased amount of solar radiation, the urban heat island effect can be reduced through the reduced need for cooling costs in the summer. Measurements were taken with the original black rubber roofing membrane and then after replacement with a white vinyl roof with the same insulation and HVAC systems in place. In a 2001 federal study, the Lawrence Berkeley National Laboratory (LBNL) measured and calculated the reduction in peak energy demand associated with a cool roof's surface reflectance. It reports the net annual energy savings (cooling energy savings minus heating penalties) and thus is only applicable to the buildings with a heating and/or cooling system. [26], According to the US DOE’s "Guidelines for Selecting Cool Roofs": These guides were aimed at achieving 50% Energy Savings toward a Net zero-energy building and covered the building types of Small to Medium Office Buildings, Medium to Big Box Retail Buildings, Large Hospitals and K-12 School Buildings. Cool Roof Rating Council [49] (CRRC) has created a rating system for measuring and reporting the solar reflectance and thermal emittance of roofing products. Similar to solar reflectance, thermal emittance is measured on a scale from zero to one, with a higher value implying a larger release of absorbed energy. [32] To satisfy the consumer demands for darker colors which still reflect significant amounts of sunlight, different materials, coating processes, and pigments are used. endobj [59] On Wednesday, September 25, 2013 Mayor Michael R Bloomberg declared it "NYC °CoolRoofs Day" in New York City with the coating of its 500th building and reducing the carbon footprint by over 2000 tons. [15][16], A 2011 study by researchers at Stanford University suggested that although reflective roofs decrease temperatures in buildings and mitigate the "urban heat island effect", they may actually increase global temperature. endobj C) in full sun, and the … It is defined so that a standard black surface (reflectance 0.05, emittance 0.90) is 0 and a standard white surface (reflectance 0.80, emittance 0.90) is 100. It is defined so that a standard black (reflectance 0.05, emittance 0.90) is 0 and a standard white (reflectance 0.80, emittance 0.90) is 100. In Climate Zones 4 and above the recommendation is to follow the ASHRAE 90.1 standard for roof reflectance, which currently does not require roofs to be reflective in these zones. Solar reflectance, also known as albedo, is the ability to reflect sunlight. [2], Cool color parking lots are parking lots made with a reflective layer of paint. Without a proper maintenance program to keep the material clean, the energy savings of cool roofs can diminish over time due to albedo degradation and soiling.

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