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Reflective surfaces or ground-based albedo modification (GBAM) is a
solar radiation management Solar geoengineering, or solar radiation modification (SRM), is a type of climate engineering in which sunlight (solar radiation) would be reflected back to outer space to limit or reverse human-caused climate change. It is not a substitute for ...
method of enhancing the Earth's
albedo Albedo (; ) is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that refle ...
(the ability to reflect the visible,
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
and
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
wavelengths of the sun, reducing heat transfer to the surface). The
IPCC The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations. Its job is to advance scientific knowledge about climate change caused by human activities. The World Meteorological Organization (WMO) ...
described this method as "whitening roofs, changes in land use management (e.g., no-till farming), change of albedo at a larger scale (covering glaciers or deserts with reflective sheeting and changes in ocean albedo)."de Coninck, H., A. Revi, M. Babiker, P. Bertoldi, M. Buckeridge, A. Cartwright, W. Dong, J. Ford, S. Fuss, J.-C. Hourcade, D. Ley, R. Mechler, P. Newman, A. Revokatova, S. Schultz, L. Steg, and T. Sugiyama, 2018
Strengthening and Implementing the Global Response. In: Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty
[MassonDelmotte,V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T. Waterfield (eds.)]. In Press. Pg. 348.
The most well-known type of reflective surface is a type of roof called the "cool roof". While cool roofs are mostly associated with white roofs, they come in a variety of colors and materials and are available for both commercial and residential buildings.


Method

As a method to address
global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
, the IPCC 2018 report indicated that the potential for global temperature reduction was "small," yet was in high agreement over the recognition of temperature changes of 1-3°C on a regional scale. Limited application of reflective surfaces can mitigate
urban heat island An urban heat island (UHI) is an urban or metropolitan area that is significantly warmer than its surrounding rural areas due to human activities. The temperature difference is usually larger at night than during the day, and is most apparent ...
effect. Reflective surfaces can be used to change the albedo of agricultural and urban areas, noting that a 0.04-0.1 albedo change in urban and agricultural areas could potentially reduce global temperatures for overshooting 1.0°C. The reflective surfaces approach is similar to
passive daytime radiative cooling Passive daytime radiative cooling (PDRC) is a renewable cooling method proposed as a solution to global warming of enhancing terrestrial heat flow to outer space through the installation of thermally-emissive surfaces on Earth that require zer ...
(PDRC) being that they are both ground-based, yet PDRC focuses on "increasing the radiative heat emission from the Earth rather than merely decreasing its solar absorption."


Types of reflective surfaces


Cool Roofs


Benefits

Cool roofs, in hot climates, can offer both immediate and long-term benefits including: * Savings of up to 15% of the annual air-conditioning energy use for a single-story building * Help in mitigating the
urban heat island An urban heat island (UHI) is an urban or metropolitan area that is significantly warmer than its surrounding rural areas due to human activities. The temperature difference is usually larger at night than during the day, and is most apparent ...
effect. * Reduced air pollution and
greenhouse gas emissions Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, oil, and natural gas. The largest emitters include coal in China and ...
, as well as a significant offsetting of the warming impact of greenhouse gas emissions. Cool roofs achieve cooling energy savings in hot summers but can increase heating energy load during cold winters. Therefore, the net energy saving of cool roofs varies depending on climate. However, a 2010 energy efficiency study looking at this issue for air-conditioned commercial buildings across the United States found that the summer cooling savings typically outweigh the winter heating penalty even in cold climates near the Canada–US border giving savings in both electricity and emissions. Without a proper maintenance program to keep the material clean, the energy savings of cool roofs can diminish over time due to
albedo Albedo (; ) is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that refle ...
degradation and soiling. Research and practical experience with the degradation of roofing membranes over a number of years have shown that heat from the sun is one of the most potent factors that affects durability. High temperatures and large variations, seasonally or daily, at the roofing level are detrimental to the longevity of roof membranes. Reducing the extremes of temperature change will reduce the incidence of damage to membrane systems. Covering membranes with materials that reflect ultraviolet and infrared radiation will reduce damage caused by UV and heat degradation. White surfaces reflect more than half of the radiation that reaches them, while black surfaces absorb almost all. White or white coated roofing membranes, or white gravel cover would appear to be the best approach to control these problems where membranes must be left exposed to solar radiation. If all urban, flat roofs in warm climates were whitened, the resulting 10% increase in global reflectivity would offset the warming effect of 24 gigatonnes of greenhouse gas emissions, or equivalent to taking 300 million cars off the road for 20 years. This is because a white roof will offset 10 tons of carbon dioxide over its 20-year lifetime. In a real-world 2008 case study of large-scale cooling from increased reflectivity, it was found that the Province of Almeria, Southern Spain, has cooled over a period of 20 years compared to surrounding regions, as a result of polythene-covered greenhouses being installed over a vast area that was previously open desert. In the summer the farmers whitewash these roofs to cool their plants down. When sunlight falls on a white roof much of it is reflected and passes back through the atmosphere into space. But when sunlight falls on a dark roof most of the light is absorbed and re-radiated as much longer wavelengths, which are absorbed by the atmosphere. (The gases in the atmosphere that most strongly absorb these long wavelengths have been termed "greenhouse gases"). Findings of a study conducted b
Syed Ahmad Farhan
''et al.'' from Universiti Teknologi PETRONAS and
Universiti Teknologi MARA The MARA Technological University ( Malay: ''Universiti Teknologi MARA''; Jawi: اونيۏرسيتي تيكنولوڬي مارا; abbr. UiTM) is a public university based primarily in Shah Alam, Selangor. It was established to help rural Mala ...
in 2021, which is based on the hot and humid climate of
Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federal constitutional monarchy consists of thirteen states and three federal territories, separated by the South China Sea into two regions: Peninsular Malaysia and Borneo's East Mal ...
, suggest that the selection of white
roof tiles Roof tiles are designed mainly to keep out rain, and are traditionally made from locally available materials such as terracotta or slate. Modern materials such as concrete, metal and plastic are also used and some clay tiles have a waterpr ...
significantly reduces the peaks of heat conduction transfer and roof-top surface temperature as well as the values of heat conduction transfer and roof-top surface temperature throughout diurnal profiles. Contrarily, the results also reveal that it does not influence the nocturnal profiles, as a release of heat to the sky takes place throughout the night. The release of heat from the building occurs due to the absence of solar radiation, which reduces the sky temperature and enables the sky to act as a
heat sink A heat sink (also commonly spelled heatsink) is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is dissipated away from the device, ...
that promotes the transfer of heat from the building to the sky to achieve
thermal equilibrium Two physical systems are in thermal equilibrium if there is no net flow of thermal energy between them when they are connected by a path permeable to heat. Thermal equilibrium obeys the zeroth law of thermodynamics. A system is said to be in ...
. A 2012 study by researchers at Concordia University included variables similar to those used in the Stanford study (e.g., cloud responses) and estimated that worldwide deployment of cool roofs and pavements in cities would generate a global cooling effect equivalent to offsetting up to 150 gigatonnes of carbon dioxide emissions – enough to take every car in the world off the road for 50 years.


Types


= White cool roofs

= White thermoplastic membrane roofs (PVC and TPO), are inherently reflective, achieving some of the highest reflectance and emittance measurements of which roofing materials are capable. A roof made of white thermoplastic, for example, can reflect 80 percent or more of the sun's rays and emit at least 70% of the solar radiation that the roof absorbs. An
asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term ...
roof only reflects between 6 and 26% of solar radiation. In addition to the white Thermoplastic PVC and TPO membranes used in many commercial cool roof applications, there is also research in the field of cool asphalt shingles. Asphalt shingles make up the majority of the North American residential roofing market, and consumer preferences for darker colors make creating solar-reflective shingles a particular challenge, causing asphalt shingles to have solar reflectances of only 4%-26%. 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. Though a more reflective roof can lead to higher heating costs in the colder months, studies have shown that the increased winter heating costs are still lower than the summer cooling cost savings. To satisfy the consumer demands for darker colors which still reflect significant amounts of sunlight, different materials, coating processes, and pigments are used. Since only 43% of light occurs in the visible light spectrum, reflectance can be improved without affecting color by increasing the reflectance of UV and IR light. High surface roughness can also contribute to the low solar reflectances of asphalt shingles, as these shingles are made of many small approximately spherical granules which have a high surface roughness. To decrease this, other granule materials are being investigated, such as flat rock flakes, which could reduce the reflectance inefficiencies due to surface roughness. Another alternative is to coat the granules using a dual coat process: the outer coating would have the desired color pigment, though it may not be very reflective, while the inner coating is a highly reflective titanium dioxide coating. Natural white gravel covering can be seen as an alternative option to obtain cool roofing and cool pavements. The highest SRI rating, and the coolest roofs, are stainless steel roofs, which are just several degrees above ambient under medium wind conditions. Their SRI's range from 100 to 115. Some are also hydrophobic so they stay very clean and maintain their original SRI even in polluted environments.


= Coated roofs

= An existing (or new) roof can be made reflective by applying a solar reflective coating to its surface. The reflectivity and emissivity ratings for over 500 reflective coatings can be found in the Cool Roofs Rating Council.


= Blue and red roofs

= Researchers at the
Lawrence Berkeley National Laboratory Lawrence Berkeley National Laboratory (LBNL), commonly referred to as the Berkeley Lab, is a United States national laboratory that is owned by, and conducts scientific research on behalf of, the United States Department of Energy. Located in ...
have determined that a pigment used by the ancient Egyptians known as " Egyptian blue" absorbs visible light, and emits light in the near-infrared range. It may be useful in construction materials to keep roofs and walls cool. They have also developed fluorescent ruby red coatings which have reflective properties similar to white roofs.


= Green roofs

= Green roofs provide a thermal mass layer which helps reduce the flow of heat into a building. The solar reflectance of green roofs varies depending on the plant types (generally 0.3–0.5). Green roofs may not reflect as much as a cool roof but do have other benefits such as evapotranspiration which cools the plants and the immediate area around the plants, aiding in lowering rooftop temperatures but increasing humidity, naturally. Moreover, some Green roofs need maintenance such as regular watering.


Disadvantages

A 2011 study by researchers at
Stanford University Stanford University, officially Leland Stanford Junior University, is a private research university in Stanford, California. The campus occupies , among the largest in the United States, and enrolls over 17,000 students. Stanford is conside ...
suggested that although reflective roofs decrease temperatures in buildings and mitigate the "
urban heat island An urban heat island (UHI) is an urban or metropolitan area that is significantly warmer than its surrounding rural areas due to human activities. The temperature difference is usually larger at night than during the day, and is most apparent ...
effect", they may actually increase global temperature. The study noted that it did not account for the reduction in greenhouse gas emissions that results from building
energy conservation Energy conservation is the effort to reduce wasteful energy consumption by using fewer energy services. This can be done by using energy more effectively (using less energy for continuous service) or changing one's behavior to use less service (f ...
(annual cooling energy savings less annual heating energy penalty) associated with cool roofs (meaning that one will need to use more energy to heat the living space due to reduction in heat from sunlight in winter.) However, this applies only to those areas with low winter temperatures – not tropical climates. Also, homes in areas receiving snow in winter months are unlikely to receive significantly more heat from darker roofs, as they will be snow-covered most of the winter. A response paper titled "Cool Roofs and Global Cooling," by researchers in the Heat Island Group at Lawrence Berkeley National Laboratory, raised additional concerns about the validity of these findings, citing the uncertainty acknowledged by the authors, statistically insignificant numerical results, and insufficient granularity in analysis of local contributions to global feedbacks. Also, 2012 research at
University of California, San Diego The University of California, San Diego (UC San Diego or colloquially, UCSD) is a public land-grant research university in San Diego, California. Established in 1960 near the pre-existing Scripps Institution of Oceanography, UC San Diego is ...
's
Jacobs School of Engineering Jacobs may refer to: Businesses and organisations * Jacob's, a brand name for several lines of biscuits and crackers in Ireland and the UK *Jacobs (coffee), a brand of coffee *Jacobs Aircraft Engine Company, former American aircraft engine compan ...
into the interaction between reflective pavements and buildings found that, unless the nearby buildings are fitted with reflective glass or other mitigation factors, solar radiation reflected off light-colored pavements can increase the temperature in nearby buildings, increasing air conditioning demands and energy usage. In 2014, a team of researchers, led by Matei Georgescu, an assistant professor in
Arizona State University Arizona State University (Arizona State or ASU) is a public research university in the Phoenix metropolitan area. Founded in 1885 by the 13th Arizona Territorial Legislature, ASU is one of the largest public universities by enrollment in the ...
's School of Geographical Sciences and Urban Planning and a senior sustainability scientist in the Global Institute of Sustainability, explored the relative effectiveness of some of the most common adaptation technologies aimed at reducing warming from urban expansion. Results of the study indicate that the performance of urban adaptation technologies can counteract this increase in temperature, but also varies seasonally and is geographically dependent. Specifically, what works in California's Central Valley, such as cool roofs, does not necessarily provide the same benefits to other regions of the country, like Florida. Assessing consequences that extend beyond near surface temperatures, such as rainfall and energy demand, reveals important trade-offs that are often unaccounted for. Cool roofs have been found to be particularly effective for certain areas during summertime. However, during winter, these same urban adaptation strategies, when deployed in northerly locations, further cool the environment, and consequently require additional heating to maintain comfort levels. “The energy savings gained during the summer season, for some regions, is nearly entirely lost during the winter season,” Georgescu said. In Florida, and to a lesser extent southwestern states, there is a very different effect caused by cool roofs. “In Florida, our simulations indicate a significant reduction in precipitation," he said. "The deployment of cool roofs results in a 2 to 4 millimeter per day reduction in rainfall, a considerable amount (nearly 50 percent) that will have implications for water availability, reduced stream flow and negative consequences for ecosystems. For Florida, cool roofs may not be the optimal way to battle the urban heat island because of these unintended consequences.” Overall, the researchers suggest that judicious planning and design choices should be considered in trying to counteract rising temperatures caused by urban sprawl and greenhouse gases. They add that “urban-induced climate change depends on specific geographic factors that must be assessed when choosing optimal approaches, as opposed to one-size-fits-all solutions.” A series of Advanced Energy Design Guides were developed in cooperation with
ASHRAE The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE ) is an American professional association seeking to advance heating, ventilation, air conditioning and refrigeration (HVAC&R) systems design and constructi ...
(American Society of Heating, Refrigerating and Air-Conditioning Engineers), AIA (The
American Institute of Architects The American Institute of Architects (AIA) is a professional organization for architects in the United States. Headquartered in Washington, D.C., the AIA offers education, government advocacy, community redevelopment, and public outreach to s ...
), IESNA (Illuminating Engineering Society of North America),
USGBC The U.S. Green Building Council (USGBC), co-founded by Mike Italiano, David Gottfried and Rick Fedrizzi in 1993, is a private 501(c)3, membership-based non-profit organization that promotes sustainability in building design, construction, and op ...
(United States Green Building Council) and US DOE (United States Department of Energy) in 2011. These guides were aimed at achieving 50% Energy Savings toward a Net
zero-energy building A Zero Energy Building (ZEB), also known as a Net Zero Energy (NZE) building, is a building with net zero energy consumption, meaning the total amount of energy used by the building on an annual basis is equal to the amount of renewable energy ...
and covered the building types of Small to Medium Office Buildings, Medium to Big Box Retail Buildings, Large Hospitals and K-12 School Buildings. In Climate Zones 4 and above the recommendation is to follow the
ASHRAE 90.1 ''ANSI/ASHRAE/IES Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings'' is an American National Standards Institute (ANSI) standard published by ASHRAE and jointly sponsored by the Illuminating Engineering Society (IES ...
standard for roof reflectance, which currently does not require roofs to be reflective in these zones. In Climate Zones 4 and above, Cool Roofs are not a recommended Design Strategy. A series of Advanced Energy Retrofit Guides for “Practical Ways to Improve Energy Performance” were developed in cooperation with the US DOE (United States Department of Energy) and PNNL (Pacific Northwest National Laboratory) in 2011. These guides were aimed at improvements to existing Retail and Office buildings which could improve their energy efficiency. Cool roofs were not recommended for all locations. “This measure is likely more cost-effective in the hot and humid climate zone, which has a long cooling season, than in the very cold climate zone, for example. For buildings located in warm climates, this measure is worth consideration.” The Copper Development Association has conducted several studies, beginning in 2002, which examined the elevated temperatures of wiring inside conduits at and above various color roof materials. The findings concluded that the temperatures above cool roofs were higher than those of a darker colored roof material. This illustrates the idea in which deflected solar radiation, when impeded by rooftop equipment, piping, or other materials will be subjected to the heat gain of the radiation. According to the US DOE’s "Guidelines for Selecting Cool Roofs": “Cool roofs must be considered in the context of your surroundings. It is relatively easy to specify a cool roof and predict energy savings, but some thinking ahead can prevent other headaches. Ask this question before installing a cool roof: Where will the reflected sunlight go? A bright, reflective roof could reflect light and heat into the higher windows of taller neighboring buildings. In sunny conditions, this could cause uncomfortable glare and unwanted heat for you or your neighbors. Excess heat caused by reflections increases air conditioning energy use, negating some of the energy saving benefits of the cool roof.” According to the US DOE's "Guidelines for Selecting Cool Roofs" on the subject of cool roof maintenance: "As a cool roof becomes dirty from pollution, foot traffic, wind-deposited debris, ponded water, and mold or algae growth, its reflectance will decrease, leading to higher temperatures. Especially dirty roofs may perform substantially worse than product labels indicate. Dirt from foot traffic may be minimized by specifying designated walkways or by limiting access to the roof. Steep sloped roofs have less of a problem with dirt accumulation because rainwater can more easily wash away dirt and debris. Some cool roof surfaces are “self-cleaning” which means they shed dirt more easily and may better retain their reflectance. Cleaning a cool roof can restore solar reflectance close to its installed condition. Always check with your roof manufacturer for the proper cleaning procedure, as some methods may damage your roof. While it is generally not cost effective to clean a roof just for the energy savings, roof cleaning can be integrated as one component of your roof's routine maintenance program. It is therefore best to estimate energy savings based on weathered solar reflectance values rather than clean roof values."


Properties

When the sunlight strikes a dark rooftop, about 15% of it gets reflected back into the sky but most of its energy is absorbed into the roof system in the form of heat. Cool roofs reflect significantly more sunlight and absorb less heat than traditional dark-colored roofs. There are two properties that are used to measure the effects of cool roofs: * Solar reflectance, also known as
albedo Albedo (; ) is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that refle ...
, is the ability to reflect sunlight. It is expressed either as a decimal fraction or a percentage. A value of 0 indicates that the surface absorbs all
solar radiation Solar irradiance is the power per unit area ( surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre ...
, and a value of 1 (or 100%) represents total reflectivity. *
Thermal emittance Thermal emittance or thermal emissivity (\varepsilon) is the ratio of the radiant emittance of heat of a specific object or surface to that of a standard black body. Emissivity and emittivity are both dimensionless quantities given in the range of ...
is the ability to emit absorbed heat. It is also expressed either as a decimal fraction between 0 and 1, or a percentage. Another method of evaluating coolness is the solar reflectance index (SRI), which incorporates both solar reflectance and emittance in a single value. SRI measures the roof's ability to reject solar heat, defined such that a standard black (reflectance 0.05, emittance 0.90) is 0 and a standard white (reflectance 0.80, emittance 0.90) is 100. A perfect SRI is approximately 122, the value for a perfect mirror, which absorbs no sunlight and has very low emissivity. The only practical material which approaches this level is stainless steel with an SRI of 112. High-reflectivity, low-emissivity roofs maintain a temperature very close to ambient at all times preventing heat gains in hot climates and minimizing heat loss in cold climates. High emissivity roofs have much higher heat loss in cold climates for the same insulation values.


Roof Savings Calculator

The Roof Savings Calculator (RSC) is a tool developed by the U.S. Department of Energy's
Oak Ridge National Laboratory Oak Ridge National Laboratory (ORNL) is a U.S. multiprogram science and technology national laboratory sponsored by the U.S. Department of Energy (DOE) and administered, managed, and operated by UT–Battelle as a federally funded research an ...
which estimates cooling and heating savings for low-slope roof applications with white and black surfaces. This tool was the collaboration of both
Oak Ridge National Laboratory Oak Ridge National Laboratory (ORNL) is a U.S. multiprogram science and technology national laboratory sponsored by the U.S. Department of Energy (DOE) and administered, managed, and operated by UT–Battelle as a federally funded research an ...
and
Lawrence Berkeley National Laboratory Lawrence Berkeley National Laboratory (LBNL), commonly referred to as the Berkeley Lab, is a United States national laboratory that is owned by, and conducts scientific research on behalf of, the United States Department of Energy. Located in ...
in order to provide industry-consensus roof savings for both residential and commercial buildings. 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.


Cars

Solar reflective cars or cool cars reflect more sunlight than dark cars, reducing the amount of heat that is transmitted into the car's interior. Therefore, it helps decrease the need for air conditioning, fuel consumption, and emissions of greenhouse gases and urban air pollutants.


Cool pavements

Cool color parking lots are parking lots made with a reflective layer of paint. Cool pavements which are designed to reflect solar radiation may use modified mixes, reflective coatings, permeable pavements, and vegetated pavements.


Mirrors

Mirrors are being explored as a reflective surface to reflect solar radiation and cool temperatures. MEER is a
nonprofit A nonprofit organization (NPO) or non-profit organisation, also known as a non-business entity, not-for-profit organization, or nonprofit institution, is a legal entity organized and operated for a collective, public or social benefit, in co ...
using
recycled materials Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the ...
to manufacture mirrors and polymer reflective films for potential widespread use on rooftops and in open spaces such as farmland. Trials have been undertaken in
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
and further application opportunities are developing in
New Hampshire New Hampshire is a U.S. state, state in the New England region of the northeastern United States. It is bordered by Massachusetts to the south, Vermont to the west, Maine and the Gulf of Maine to the east, and the Canadian province of Quebec t ...
,
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
, and
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
.


Climatic variables


Cool roofs

In some climates where there are more heating days than cooling days, white reflective roofs may not be effective in terms of energy efficiency or savings because the savings on cooling energy use can be outweighed by heating penalties during winter. According to the U.S. Energy Information Administration, 2003 Commercial Buildings Energy Consumption Survey, heating accounts for 36% of commercial buildings' annual energy consumption, while air conditioning only accounts for 8% in United States. Energy calculators generally show a yearly net savings for dark-colored roof systems in cool climates. A perfect roof would absorb no heat in the summer and lose no heat in the winter. To do this it would need a very high SRI to eliminate all radiative heat gains in summer and losses in winter. High SRI roofs act as a
radiant barrier A radiant barrier is a type of building material that reflects thermal radiation and reduces heat transfer. Because thermal energy is also transferred by conduction and convection, in addition radiation, radiant barriers are often supplemented wit ...
, providing a thermos-bottle effect. High emissivity cool roofs carry a climate penalty due to winter radiative heat losses, which reflective bare metal roofs, such as stainless steel, do not.


Applications


Cool roofs

In a 2001 federal study, the
Lawrence Berkeley National Laboratory Lawrence Berkeley National Laboratory (LBNL), commonly referred to as the Berkeley Lab, is a United States national laboratory that is owned by, and conducts scientific research on behalf of, the United States Department of Energy. Located in ...
(LBNL) measured and calculated the reduction in peak energy demand associated with a cool roof's surface reflectance. LBNL found that, compared to the original black rubber roofing membrane on the Texas retail building studied, a retrofitted vinyl membrane delivered an average decrease of in surface temperature, an 11% decrease in aggregate air conditioning energy consumption, and a corresponding 14% drop in peak hour demand. The average daily summertime temperature of the black roof surface was , but once retrofitted with a white reflective surface, it measured . Without considering any tax benefits or other utility charges, annual energy expenditures were reduced by $7,200 or $0.07/square foot.(This figure is for energy charges as well as peak demand charges). Instruments measured weather conditions on the roof, temperatures inside the building and throughout the roof layers, and air conditioning and total building power consumption. 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. Though a full year of actual data was collected, due to aberrations in the data, one month of data was excluded along with several other days which didn't meet the parameters of the study. Only 36 continuous pre-retrofit days were used and only 28 non-continuous operating days were used for the post-retrofit period. Another case study, conducted in 2009 and published in 2011, was completed by Ashley-McGraw Architects and CDH Energy Corp for Onondaga County Dept. of Corrections, in Jamesville, New York, evaluated energy performance of a green or vegetative roof, a dark EPDM roof and a white reflective TPO roof. The measured results showed that the TPO and vegetative roof systems had much lower roof temperatures than the conventional EPDM surface. The reduction in solar absorption reduced solar gains in the summer but also increased heat losses during the heating season. Compared to the EPDM membrane, the TPO roof had 30% higher heating losses and the vegetative roof had 23% higher losses.


Promotional programs


= Across the U.S. federal government

= In July 2010, the
United States Department of Energy The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and manages the research and development of nuclear power and nuclear weapons in the United States ...
announced a series of initiatives to more broadly implement cool roof technologies on DOE facilities and buildings across the country. 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. In October 2013, the
United States Department of Energy The United States Department of Energy (DOE) is an executive department of the U.S. federal government that oversees U.S. national energy policy and manages the research and development of nuclear power and nuclear weapons in the United States ...
ranked Cool Roofs as a 53 out of 100 (0 to 100 weighted average) for a cost-effective energy strategy. "Climate issues can affect cool roof performance. Cool roofs are more beneficial in warmer climates and may cause energy consumption for heating applications to rise in colder climates. 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. Other Federal agencies were also encouraged to do the same."


= Energy Star

= Energy Star is a joint program of the U.S.
Environmental Protection Agency A biophysical environment is a biotic and abiotic surrounding of an organism or population, and consequently includes the factors that have an influence in their survival, development, and evolution. A biophysical environment can vary in scale ...
and the U.S. Department of Energy designed to reduce greenhouse gas emissions and help businesses and consumers save money by making energy-efficient product choices. For low-slope roof applications, a roof product qualifying for the Energy Star label under its Roof Products Program must have an initial solar reflectivity of at least 0.65, and weathered reflectance of at least 0.50, in accordance with EPA testing procedures. Warranties for reflective roof products must be equal in all material respects to warranties offered for comparable non-reflective roof products, either by a given company or relative to industry standards. Unlike other Energy Star-rated products, such as appliances, this rating system does not look at the entire roof assembly, but only the exterior surface. Consumers (i.e. building owners) may believe that the Energy Star label means their roof is energy-efficient; however, the testing is not as stringent as their appliance standard and does not include the additional components of a roof (i.e. roof structure, fire rated barriers, insulation, adhesives, fasteners, etc.). A disclaimer is posted on their website "Although there are inherent benefits in the use of reflective roofing, before selecting a roofing product based on expected energy savings consumers should explore the expected calculated results that can be found on the Department of Energy's "Roof Savings Calculator" website at www.roofcalc.com. Please remember the Energy Savings that can be achieved with reflective roofing is highly dependent on facility design, insulation used, climatic conditions, building location, and building envelope efficiency."


= Cool Roof Rating Council

= Cool Roof Rating Council (CRRC) has created a rating system for measuring and reporting the solar reflectance and thermal emittance of roofing products. 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. CRRC conducts random testing each year to ensure the credibility of its rating directory. CRRC's rating program allows manufacturers and sellers to appropriately label their roofing products according to specific CRRC measured properties. The program does not, however, specify minimum requirements for solar reflectance or thermal emittance.


= Green Globes

= The
Green Globe Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 nm. In subtractive color systems, used in painting and color printing, it is created by a combin ...
system is used in Canada and the United States. In the U.S., Green Globes is owned and operated by the Green Building Initiative (GBI). In Canada, the version for existing buildings is owned and operated by BOMA Canada under the brand name 'Go Green' (Visez vert). Green Globe uses performance benchmark criteria to evaluate a building's likely energy consumption, comparing the building design against data generated by the EPA's Target Finder, which reflects real building performance. Buildings may earn a rating of between one and four globes. This is an online system; a building's information is verified by a Green Globes-approved and trained licensed engineer or architect. To qualify for a rating, roofing materials must have a solar reflectance of at least 0.65 and thermal emittance of at least 0.90. As many as 10 points may be awarded for 1–100 percent roof coverage with either vegetation or highly reflective materials or both. The basis in physics of a high emittance is quite questionable, since it merely describes a material which easily radiates infrared wavelength heat to the environment, contributing to the greenhouse effect. Highly reflective, low-emittance materials are much better at reducing energy consumption.


= LEED

= The U.S. Green Building Council's
Leadership in Energy and Environmental Design Leadership in Energy and Environmental Design (LEED) is a green building certification program used worldwide. Developed by the non-profit U.S. Green Building Council (USGBC), it includes a set of rating systems for the design, constructio ...
(LEED) rating system is a voluntary, continuously evolving national standard for developing high performance sustainable buildings. LEED provides standards for choosing products in designing buildings, but does not certify products. Unlike a
building code A building code (also building control or building regulations) is a set of rules that specify the standards for constructed objects such as buildings and non-building structures. Buildings must conform to the code to obtain planning permissi ...
, such as the
International Building Code The International Building Code (IBC) is a model building code developed by the International Code Council (ICC). It has been adopted for use as a base code standard by most jurisdictions in the United States. The IBC addresses both health and sa ...
, only members of the
USGBC The U.S. Green Building Council (USGBC), co-founded by Mike Italiano, David Gottfried and Rick Fedrizzi in 1993, is a private 501(c)3, membership-based non-profit organization that promotes sustainability in building design, construction, and op ...
and specific "in-house" committees may add, subtract or edit the standard, based on an internal review process. Model Building Codes are voted on by members and "in-house" committees, but allow for comments and testimony from the general public during each and every code development cycle at Public Review hearings, generally held multiple times a year. Under the LEED 2009 version, to receive Sustainable Sites Credit 7.2 Heat Island Effect-Roof, at least 75% of the surface of a roof must use materials having a solar reflective index (SRI) of at least 78. This criterion can also be met by installing a vegetated roof for at least 50% of the roof area, or installing a high
albedo Albedo (; ) is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that refle ...
and vegetated roof in combination that meets this formula: (Area of Roof meeting Minimum SRI Roof/0.75) + (Area of vegetated roof/0.5) ≥ Total Roof Area. Examples of LEED-certified buildings with white reflective roofs are below.


= Cool Roofs Europe and other countries

= This project is co-financed by the European Union in the framework of the Intelligent Energy Europe Programme. The aim of the proposed action is to create and implement an Action Plan for the cool roofs in EU. The specific objectives are: to support policy development by transferring experience and improving understanding of the actual and potential contributions by cool roofs to heating and cooling consumption in the EU; to remove and simplify the procedures for cool roofs integration in construction and building's stock; to change the behaviour of decision-makers and stakeholders so to improve acceptability of the cool roofs; to disseminate and promote the development of innovative legislation, codes, permits and standards, including application procedures, construction and planning permits concerning cool roofs. The work will be developed in four axes, technical, market, policy and end-users. In tropical Australia, zinc-galvanized (silvery) sheeting (usually
corrugated The term corrugated, describing a series of parallel ridges and furrows, may refer to the following: Materials *Corrugated fiberboard, also called corrugated cardboard *Corrugated galvanised iron, a building material composed of sheets of cold-r ...
) 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. European fashion trends are now using darker-colored aluminium roofing, to pursue consumer fashions.


= NYC °CoolRoofs

= NYC °CoolRoofs is a New York City initiative to coat rooftops white with volunteers. The program began in 2009 as part of
PlaNYC PlaNYC was a strategic plan released by New York City Mayor Michael Bloomberg in 2007 to prepare the city for one million more residents, strengthen the economy, combat climate change, and enhance the quality of life for all New Yorkers. The plan b ...
, and has coated over 5 million square feet of NYC rooftops white. 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. Volunteers use paintbrushes and rollers to apply an acrylic, elastomeric coating to the roof membrane. A 2011 Columbia University study of roofs coated through the program found that white roofs showed an average temperature reduction of 43 degrees Fahrenheit when compared to black roofs.


= White Roof Project

= White Roof Project is a US nationwide initiative that educates and empowers individuals to coat rooftops white. The program's outreach has helped complete white roof projects in more than 20 US states and five countries, engaged thousands in volunteer projects, an
sponsored the coating of hundreds of nonprofit and low-income rooftops


Urban heat island effect

An urban heat island occurs where the combination of heat-absorbing infrastructure such as dark asphalt parking lots and road pavement and expanses of black rooftops, coupled with sparse vegetation, raises air temperature by higher than the temperature in the surrounding countryside.
Green building Green building (also known as green construction or sustainable building) refers to both a structure and the application of processes that are environmentally responsible and resource-efficient throughout a building's life-cycle: from planni ...
programs advocate the use of cool roofing to mitigate the urban heat island effect and the resulting poorer air quality (in the form of smog) the effect causes. By reflecting sunlight, light-colored roofs minimize the temperature rise and reduce cooling energy use and smog formation. A study by LBNL showed that, if strategies to mitigate this effect, including cool roofs, were widely adopted, the Greater Toronto metropolitan area could save more than $11 million annually on energy costs.


See also

* Cool pavement *
Green roof A green roof or living roof is a roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproofing membrane. It may also include additional layers such as a root barrier and draina ...
* Insulative paint *
Passive cooling Passive cooling is a building design approach that focuses on heat gain control and heat dissipation in a building in order to improve the indoor thermal comfort with low or no energy consumption. This approach works either by preventing heat from ...
*
Passive daytime radiative cooling Passive daytime radiative cooling (PDRC) is a renewable cooling method proposed as a solution to global warming of enhancing terrestrial heat flow to outer space through the installation of thermally-emissive surfaces on Earth that require zer ...


References


External links

* {{Cite web , date=2022 , title=Smart Surfaces Guide , url=https://kilthub.cmu.edu/articles/report/Smart_Surfaces_Guide/20186438 , access-date=2022-10-15 , website=
Carnegie Mellon University Carnegie Mellon University (CMU) is a private research university in Pittsburgh, Pennsylvania. One of its predecessors was established in 1900 by Andrew Carnegie as the Carnegie Technical Schools; it became the Carnegie Institute of Technology ...
, School of Architecture Roofs Low-energy building Solar architecture Climate engineering