Search

Sustainable roofing configurations, including green and white roofs, can reduce rooftop surface temperatures compared to conventional surfaces and can therefore enhance photovoltaic (PV) system performance due to the temperature dependence of PV cells. Previous research, primarily experimental, recognized the synergy of combining PV with green or cool roofs. However, the influence of geographic and climatic factors on the performance of these combined systems, particularly in future climates affected by climate change, remains unclear. This work integrates three roof configurations (gravel, green, and white) into rooftop solar energy modeling across thirteen cities with different climate types, under current and future climate scenarios. Results indicate limited efficiency gains (< 2%) across all cities and climates, challenging previous findings. Yield is expected to increase in some cities receiving more solar irradiation in the future but decrease in others due to rising temperatures. Green and cool roofs can partially offset the effects of climate change on yield. PV‐white roofs consistently outperform PV‐green roofs, with the performance gap expected to widen in future climates. PV‐green roofs excel in tropical climates with high irradiation and precipitation levels. Overall, the outcomes of this study inform the design and planning of sustainable buildings in response to climate change challenges. [ABSTRACT FROM AUTHOR]

Cool roofs are roofing systems designed to reflect significant solar radiation, reducing heat absorption and subsequent cooling energy demands in buildings. This paper provides a comprehensive review of cool roof technologies, covering performance standards, material options, energy-saving potential, and hygrothermal considerations. The review examines provisions in current codes and standards, which specify minimum requirements for solar reflectance, thermal emittance, and solar reflectance index (SRI) values. These criteria often vary based on factors like roof slope, climate zone, and building type. Different cool roof materials are explored, including reflective paints and coatings that can be applied to existing roofs as cost-effective solutions. Several studies have demonstrated the energy performance benefits of cool roofs, showing significant reductions in cooling loads, indoor air temperatures, peak cooling demand, and overall cooling energy consumption compared to traditional roofs. However, hygrothermal performance must be evaluated, especially in cold climates, to optimize insulation levels and avoid moisture accumulation risks, as reduced heat absorption can alter moisture migration patterns within the building envelope. While cool roofs provide substantial energy savings in hot climates, further research is needed to validate modeling approaches against real-world studies, investigate the impact of seasonality and green spaces on cool roof efficacy and urban heat island mitigation, and explore energy-saving potential, moisture control, and condensation risks in cold and humid environments. [ABSTRACT FROM AUTHOR]

Radiative Coolers (RCs) represent an emerging technology that has the potential to significantly reduce urban heat and improve indoor/outdoor thermal comfort in the built environment. Broadband and Selective Radiative Coolers (BRCs and SRCs, respectively) are the two main types of RCs that have been proposed for application in the built environment. Being both typically characterized by high solar reflectance, the former emits thermal radiation within the overall infrared spectrum, whilst the latter emits thermal radiation mainly within the Atmospheric Window (AW) waverange. A variety of both types of RCs have been developed and tested in both in‐lab and in‐field experimental campaigns. Yet, all experiments comprise small scale specimens that do not represent real‐life scale components of the built environment. In addition, no meso scale assessments have been performed with respect to the RCs' performance at a city scale. Here, for the first time, the thermo‐optical performance of both BRCs and SRCs is introduced and investigated in a multilayer Urban Canopy Model (UCM) coupled with extended Weather Research and Forecasting model (WRF) and we simulated 20 different scenarios representing the vast majority of urban layouts. The outcomes show that both types of RCs maintain lower surface temperature and air temperature at 2 m height inside the canyon, compared to conventional roofs. In addition, a city scale application of RCs has been found capable of decreasing ambient temperature up to 1.6°C as potentially experienced by pedestrians. [ABSTRACT FROM AUTHOR]

Cool (solar reflective) roofs and walls can reduce solar heat gain and decrease unwanted heat flowing into indoor spaces. To explore the potential of these strategies tomitigate energy and thermal comfort challenges in Los Angeles, we conducted a study that used EnergyPlus building energy simulations. Our analysis focused on single-family homes in Los Angeles under various historical and future weather conditions, including both typical meteorological year (TMY) and heatwave weather year (HWY) scenarios, based on the COordinated Regional Downscaling EXperiment (CORDEX) framework under the Representative Concentration Pathway (RCP) 8.5. Our study evaluated the impact of cool envelope strategies on heating, ventilation, and air conditioning (HVAC) primary energy intensity savings and thermal comfort improvements. We employed three thermal comfort models: predicted mean vote (PMV), adaptive, and heat stress. Our findings indicate that in Los Angeles, a package of cool roof + walls (reflective roof and reflective walls) can reduce annual HVAC energy consumption by at least 11% for buildings equipped with mechanical cooling systems. They can reduce occupants’ warm thermal discomfort (thermal-sensation-scale-unit-weighted warm exceedance hours) by at least 28% in air-conditioned buildings and by at least 16% in buildings without mechanical cooling systems. Cool envelopes can also lower daily heatwave heat stress by at least 9%.

The building envelope is the interface between the external atmospheric conditions and the indoor environment. It contributes to approximately 60%–70% of the heating and cooling load. The building envelope constitutes walls, fenestrations, and roofs from which thermal transfer from the roof is significantly very high compared to walls in low-rise buildings.This research paper aims to provide recommendations for energy-efficient roof design considering roof form, material, and external coating suitable for various climate conditions of India. The paper’s methodology consists of a literature review of related research papers, learnings from the roofing system of energy-efficient building case studies, and all possible energy-efficient roofing systems that would be simulated for energy efficiency and thermal comfort in five climate types of India. The expected outcome of this paper would be in the form of recommendations for roofing systems in different climate type and their potential for energy saving from the highest to the lowest. This research would be done in three stages viz, Step-1: Literature Review and case study of best practices: A review of the related literature and best practices examples would be done to formulate the maximum possible cases for the simulation. Step-2: The roofing systems, including building form, material (Thermal and insulation), and finishes (reflectance), would be simulated one by one for various climate types of India (composite, hot & dry, warm and humid, moderate and cold) to optimize energy efficiency and payback period. Step-3: Special roof types like Green roofs, cool roofs, Photovoltaic roofs, roof ponds, and the like are simulated and compared for their effectiveness in selected climate types. Based on the literature review, simulation results, and analysis, the recommendations are framed for energy-efficient roofing systems in the selected climate type with respect to heat transfer through the roof and thermal comfort.

Abstract Cool materials and rooftop vegetation help achieve urban heating mitigation as they can reduce building cooling demands. This study assesses the cooling potential of different mitigation technologies using Weather Research and Forecasting (WRF)- taking case of a tropical coastal climate in the Kolkata Metropolitan Area. The model was validated using data from six meteorological sites. The cooling potential of eight mitigation scenarios was evaluated for: three cool roofs, four green roofs, and their combination (cool-city). The sensible heat, latent heat, heat storage, 2-m ambient temperature, surface temperature, air temperature, roof temperature, and urban canopy temperature was calculated. The effects on the urban boundary layer were also investigated. The different scenarios reduced the daytime temperature of various urban components, and the effect varied nearly linearly with increasing albedo and green roof fractions. For example, the maximum ambient temperature decreased by 3.6 °C, 0.9 °C, and 1.4 °C for a cool roof with 85% albedo, 100% rooftop vegetation, and their combination. The cost of different mitigation scenarios was assumed to depend on the construction options, location, and market prices. The potential for price per square meter and corresponding temperature decreased was related to one another. Recognizing the complex relationship between scenarios and construction options, the reduction in the maximum and minimum temperature across different cool and green roof cases were used for developing the cost estimates. This estimate thus attempted a summary of the price per degree of cooling for the different potential technologies. Higher green fraction, cool materials, and their combination generally reduced winds and enhanced buoyancy. The surface changes alter the lower atmospheric dynamics such as low-level vertical mixing and a shallower boundary layer and weakened horizontal convective rolls during afternoon hours. Although cool materials offer the highest temperature reductions, the cooling resulting from its combination and a green roof strategy could mitigate or reverse the summertime heat island effect. The results highlight the possibilities for heat mitigation and offer insight into the different strategies and costs for mitigating the urban heating and cooling demands.

Cool roofs are roofing systems designed to reflect significant solar radiation, reducing heat absorption and subsequent cooling energy demands in buildings. This paper provides a comprehensive review of cool roof technologies, covering performance standards, material options, energy-saving potential, and hygrothermal considerations. The review examines provisions in current codes and standards, which specify minimum requirements for solar reflectance, thermal emittance, and solar reflectance index (SRI) values. These criteria often vary based on factors like roof slope, climate zone, and building type. Different cool roof materials are explored, including reflective paints and coatings that can be applied to existing roofs as cost-effective solutions. Several studies have demonstrated the energy performance benefits of cool roofs, showing significant reductions in cooling loads, indoor air temperatures, peak cooling demand, and overall cooling energy consumption compared to traditional roofs. However, hygrothermal performance must be evaluated, especially in cold climates, to optimize insulation levels and avoid moisture accumulation risks, as reduced heat absorption can alter moisture migration patterns within the building envelope. While cool roofs provide substantial energy savings in hot climates, further research is needed to validate modeling approaches against real-world studies, investigate the impact of seasonality and green spaces on cool roof efficacy and urban heat island mitigation, and explore energy-saving potential, moisture control, and condensation risks in cold and humid environments.

Cool materials and rooftop vegetation help achieve urban heating mitigation as they can reduce building cooling demands. This study assesses the cooling potential of different mitigation technologies using Weather Research and Forecasting (WRF)- taking case of a tropical coastal climate in the Kolkata Metropolitan Area. The model was validated using data from six meteorological sites. The cooling potential of eight mitigation scenarios was evaluated for: three cool roofs, four green roofs, and their combination (cool-city). The sensible heat, latent heat, heat storage, 2-m ambient temperature, surface temperature, air temperature, roof temperature, and urban canopy temperature was calculated. The effects on the urban boundary layer were also investigated. The different scenarios reduced the daytime temperature of various urban components, and the effect varied nearly linearly with increasing albedo and green roof fractions. For example, the maximum ambient temperature decreased by 3.6 °C, 0.9 °C, and 1.4 °C for a cool roof with 85% albedo, 100% rooftop vegetation, and their combination. The cost of different mitigation scenarios was assumed to depend on the construction options, location, and market prices. The potential for price per square meter and corresponding temperature decreased was related to one another. Recognizing the complex relationship between scenarios and construction options, the reduction in the maximum and minimum temperature across different cool and green roof cases were used for developing the cost estimates. This estimate thus attempted a summary of the price per degree of cooling for the different potential technologies. Higher green fraction, cool materials, and their combination generally reduced winds and enhanced buoyancy. The surface changes alter the lower atmospheric dynamics such as low-level vertical mixing and a shallower boundary layer and weakened horizontal convective rolls during afternoon hours. Although cool materials offer the highest temperature reductions, the cooling resulting from its combination and a green roof strategy could mitigate or reverse the summertime heat island effect. The results highlight the possibilities for heat mitigation and offer insight into the different strategies and costs for mitigating the urban heating and cooling demands. [ABSTRACT FROM AUTHOR]

Raising the albedo (solar reflectance) of a building’s walls reduces unwanted solar heat gain in the cooling season. This saves electricity and lowers peak power demand by decreasing the need for air conditioning. It can also cool the outside air, which can mitigate the urban heat island effect and also improve air quality by slowing the reactions that produce smog. This project quantified the energy savings, peak demand reduction, urban cooling, and air quality improvements attainable from solar-reflective “cool” walls in California; collaborated with industry to assess the performance of existing cool-wall technologies, and to develop innovative cool-wall solutions; and worked with state and federal government agencies, utilities, and industry to create a cool-wall infrastructure, including application guidelines, a product rating program, incentives, and building code credits.Simulations indicate that cool walls provide annual energy savings, peak demand reduction, annual emission reduction, and summer heat island mitigation benefits comparable to those yielded by cool roofs, and are helpful across California and in most of the southern half of the United States (that is, in U.S. climate zones 1—4). Natural exposure trials conducted at three sites in California and another three sites across the United States indicate that cool-wall materials tend to stay clean and reflective. Significant advances were made in novel cool-wall technologies, such as fluorescent cool pigments that expand the color palette for cool-wall products. We prepared guidelines for the climate- and building-appropriate use of cool walls, convened a stakeholder workshop, and created a working group. Ongoing efforts seek to introduce or expand cool-wall provisions in building energy standards, green building programs, and energy efficiency incentive programs, and to develop a cool-wall product rating system.

Different heat mitigation technologies have been developed to improve the thermal environment in cities. However, the regional impacts of such technologies, especially in the context of a tropical city, remain unclear. The deployment of heat mitigation technologies at city‐scale can change the radiation balance, advective flow, and energy balance between urban areas and the overlying atmosphere. We used the mesoscale Weather Research and Forecasting model coupled with a physically based single‐layer urban canopy model to assess the impacts of five different heat mitigation technologies on surface energy balance, standard surface meteorological fields, and planetary boundary layer (PBL) dynamics for premonsoon typical hot summer days over a tropical coastal city in the month of April in 2018, 2019, and 2020. Results indicate that the regional impacts of cool materials (CMs), super‐cool broadband radiative coolers, green roofs (GRs), vegetation fraction change, and a combination of CMs and GRs (i.e., "Cool city (CC)") on the lower atmosphere are different at diurnal scale. Results showed that super‐cool materials have the maximum potential of ambient temperature reduction of 1.6°C during peak hour (14:00 LT) compared to other technologies in the study. During the daytime hours, the PBL height was considerably lower than the reference scenario with no implementation of strategies by 700 m for super‐cool materials and 500 m for both CMs and CC cases; however, the green roofing system underwent nominal changes over the urban area. During the nighttime hours, the PBL height increased by CMs and the CC strategies compared to the reference scenario, but minimal changes were evident for super‐cool materials. The changes of temperature on the vertical profile of the heat mitigation implemented city reveal a stable PBL over the urban domain and a reduction of the vertical mixing associated with a pollution dome. This would lead to crossover phenomena above the PBL due to the decrease in vertical wind speed. Therefore, assessing the coupled regional impact of urban heat mitigation over the lower atmosphere at city‐scale is urgent for sustainable urban planning. Plain Language Summary: In this research we evaluated the impact on the city meteorology and on the lower atmosphere due to the use of several heat mitigation technologies. The numerical simulations were carried out during typical summer hot days over an Indian tropical city. The heat mitigation strategies considered include very reflective materials (cool materials (CMs), super‐cool broadband radiative coolers) green roofs (GRs), changes in the vegetation fraction, and a combination of CMs and GRs (i.e., cool city (CC)). In particular, these mitigation strategies and technologies were incorporated in a weather model (the mesoscale weather research and forecasting coupled with a single‐layer urban canopy model) at the city‐scale. Our results showed that surface and rooftop heat mitigation strategies modify the meteorological fields and the dynamics of the lower atmosphere within the city during the hot summer days. The super‐cool broadband radiative coolers are most proficient in decreasing ambient temperature and planetary boundary layer, followed by CMs, CC, GRs, and augmenting vegetation fraction. The super‐cool broadband radiative coolers produced the most efficient strategy. Nevertheless, it has unintended consequences as they modify the temperature vertical profile, enhancing the stability over the urban domain and reducing the air's vertical mixing. The results presented show that the used model can be a valuable instrument to evaluate the implementation effects of heat mitigation technologies in the urban environment for extreme urban heat management, such as the newly developed super‐cool materials. However, careful attention should be paid to unintended consequences. Key Points: weather research and forecasting model is a valuable tool to evaluate the effects of heat mitigation measures in the urban environment for urban heat managementSurface standard meteorological fields and lower atmospheric dynamics within the city are modified by heat mitigation measuresThe super‐cool broadband radiative coolers yielded the most efficient strategy for urban cooling in tropical context [ABSTRACT FROM AUTHOR]

Replacing dark conventional roofs with more reflective “cool” roofs has been proposed as a method to lower urban air temperatures. Many meteorological studies have simulated potential cool roof air temperature reductions. However, economic and logistical challenges make it difficult to perform the large-scale demonstrations needed to verify these model results. This work assesses whether a neighborhood-scale cool roof demonstration could yield an observable air temperature change. We use both an idealized theoretical framework and a meteorological model to estimate the air temperature reduction that could be induced by increasing roof albedo over ~ 1 km2 area of a city. Both the idealized analysis and model indicate that an air temperature reduction could be detected, with the model indicating a reduction of 0.5 °C and the idealized analysis indicating a larger reduction of 1.3 °C. Follow-on modeling is recommended prior to design of a neighborhood-scale demonstration.

Most of India’s current electricity demand is met by combustion of fossil fuels, particularly coal. But the country has embarked on a major expansion of renewable energy and aims for half of its electricity needs to be met by renewable sources by 2030. As climate change-driven temperature increases continue to threaten India’s population and drive increased demand for air conditioning, there is a need to estimate the local benefits of policies that increase renewable energy capacity and reduce cooling demand in buildings. We investigate the impacts of climate change-driven temperature increases, along with population and economic growth, on demand for electricity to cool buildings in the Indian city of Ahmedabad between 2018 and 2030. We estimate the share of energy demand met by coal-fired power plants versus renewable energy in 2030, and the cooling energy demand effects of expanded cool roof adaptation in the city. We find renewable energy capacity could increase from meeting 9% of cooling energy demand in 2018 to 45% in 2030. Our modeling indicates a near doubling in total electricity supply and a nearly threefold growth in cooling demand by 2030. Expansion of cool roofs to 20% of total roof area (associated with a 0.21 TWh reduction in cooling demand between 2018 and 2030) could more than offset the city’s climate change-driven 2030 increase in cooling demand (0.17 TWh/year). This study establishes a framework for linking climate, land cover, and energy models to help policymakers better prepare for growing cooling energy demand under a changing climate. [ABSTRACT FROM AUTHOR]

Urban growth, characterized by expansion of impervious at the cost of the natural landscape, causes warming and heat-related distress. Specifically, an increase in the number of buildings within an urban landscape causes intensification of heat islands, necessitating promotion of cool roofs to mitigate Urban Heat Islands (UHI) and associated impacts. In this study, we used the freely available Sentinel 2 and Landsat 8 data to determine the study area's Land Use Land Covers (LULCs), roof colours and Land Surface Temperature (LST) at a 10-m spatial resolution. Support Vector Machines (SVM) classification algorithm was adopted to derive the study area's roof colours and proximal LULCs, and the Transformed Divergence Separability Index (TDSI) based on Jeffries Mathussitta distance analysis was used to determine the variability in LULCs and roof colours. To effectively relate the Landsat 8 thermal characteristics to the LULCs and roof colours, the Gram–Schmidt technique was used to pan-sharpen the 30-m Landsat 8 image data to 10 m. Results show that Sentinel 2 mapped LULCs with over 75% accuracy. Pan-sharpening the 30-m-resolution thermal data to 10 m improved the spatial resolution and quality of the Land Surface map and the correlation between LST and Normalized Difference Vegetation Index (NDVI) used as proxy for LULC. Green-colour roofs were the warmest, followed by red roofs, while blue roofs were the coolest. Generally, black roofs in the study area were cool. The study recommends the need to incorporate other roofing properties, such as shape, and further split the colours into different shades. Furthermore, the study recommends the use of very high spatial resolution data to determine roof colour and their respective properties; these include data derived from sensors mounted on aerial platforms such as drones and aircraft. The study concludes that with appropriate analytical techniques, freely available image data can be integrated to determine the implication of roof colouring on urban thermal characteristics, useful for mitigating the effects of Urban Heat Islands and climate change. [ABSTRACT FROM AUTHOR]

The climate warming effects of accelerated urbanization along with projected global climate change raise an urgent need for sustainable mitigation and adaptation strategies to cool urban climates. Our modeling results show that historical urbanization in the Los Angeles and San Diego metropolitan areas has increased daytime urban air temperature by 1.3 °C, in part due to a weakening of the onshore sea breeze circulation. We find that metropolis-wide adoption of cool roofs can meaningfully offset this daytime warming, reducing temperatures by 0.9 °C relative to a case without cool roofs. Residential cool roofs were responsible for 67% of the cooling. Nocturnal temperature increases of 3.1 °C from urbanization were larger than daytime warming, while nocturnal temperature reductions from cool roofs of 0.5 °C were weaker than corresponding daytime reductions. We further show that cool roof deployment could partially counter the local impacts of global climate change in the Los Angeles metropolitan area. Assuming a scenario in which there are dramatic decreases in greenhouse gas emissions in the 21st century (RCP2.6), mid- and end-of-century temperature increases from global change relative to current climate are similarly reduced by cool roofs from 1.4 °C to 0.6 °C. Assuming a scenario with continued emissions increases throughout the century (RCP8.5), mid-century warming is significantly reduced by cool roofs from 2.0 °C to 1.0 °C. The end-century warming, however, is significantly offset only in small localized areas containing mostly industrial/commercial buildings where cool roofs with the highest albedo are adopted. We conclude that metropolis-wide adoption of cool roofs can play an important role in mitigating the urban heat island effect, and offsetting near-term local warming from global climate change. Global-scale reductions in greenhouse gas emissions are the only way of avoiding long-term warming, however. We further suggest that both climate mitigation and adaptation can be pursued simultaneously using 'cool photovoltaics'.

Copyright of Builder (1896-0642) is the property of PWB MEDIA Zdzieblowski sp.j. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The measurements for the short-wave solar reflectivity of a Reflective Coating Material (RCM) with various cleaning operations that were obtained in a previous study were used in this study to conduct numerical simulations in order to assess the moisture and energy performance of cool and black roofs when they were subjected to the weather conditions of Saudi Eastern Province and Kuwait City. The results of the numerical simulations showed that black roofs always work with less moisture than cool roofs. Because the highest relative humidity in the different components of the black and cool roofs was well below 80%, there was no risk of condensation and mold growth in these roofs. For both weather conditions of Saudi Eastern Province and Kuwait City, the results showed that installing cool roofs have resulted in increasing the heating energy loads in relation to black roofs. Conversely, the results showed that the decrease in the cooling energy loads due to installing cool roofs were typically much greater than the increase in the heating energy loads. As such, cool roofs have resulted in net energy savings in relation to black roofs. Replacing black roof by cool roof in Saudi climate, the results showed that the annual energy savings in the total energy load was 25% and 34% as a result of installing cool roof with RCM at no cleaning and weekly homemade cleaning, respectively. Additionally, replacing black roof by cool roof in Kuwaiti climate, the results showed that the annual energy savings in the total energy load was 23% and 31% a result of installing cool roof with RCM at no cleaning and weekly homemade cleaning, respectively. [ABSTRACT FROM AUTHOR]

A laboratory method to simulate natural exposure of roofing materials has been reported in a companion article. In the current article, we describe the results of an international, nine-participant interlaboratory study (ILS) conducted in accordance with ASTM Standard E691-09 to establish the precision and reproducibility of this protocol. The accelerated soiling and weathering method was applied four times by each laboratory to replicate coupons of 12 products representing a wide variety of roofing categories (single-ply membrane, factory-applied coating (on metal), bare metal, field-applied coating, asphalt shingle, modified-bitumen cap sheet, clay tile, and concrete tile). Participants reported initial and laboratory-aged values of solar reflectance and thermal emittance. Measured solar reflectances were consistent within and across eight of the nine participating laboratories. Measured thermal emittances reported by six participants exhibited comparable consistency. For solar reflectance, the accelerated aging method is both repeatable and reproducible within an acceptable range of standard deviations: the repeatability standard deviation sr ranged from 0.008 to 0.015 (relative standard deviation of 1.2-2.1%) and the reproducibility standard deviation sR ranged from 0.022 to 0.036 (relative standard deviation of 3.2-5.8%). The ILS confirmed that the accelerated aging method can be reproduced by multiple independent laboratories with acceptable precision. This study supports the adoption of the accelerated aging practice to speed the evaluation and performance rating of new cool roofing materials.

A laboratory method to simulate natural exposure of roofing materials has been reported in a companion article. In the current article, we describe the results of an international, nine-participant interlaboratory study (ILS) conducted in accordance with ASTM Standard E691-09 to establish the precision and reproducibility of this protocol. The accelerated soiling and weathering method was applied four times by each laboratory to replicate coupons of 12 products representing a wide variety of roofing categories (single-ply membrane, factory-applied coating (on metal), bare metal, field-applied coating, asphalt shingle, modified-bitumen cap sheet, clay tile, and concrete tile). Participants reported initial and laboratory-aged values of solar reflectance and thermal emittance. Measured solar reflectances were consistent within and across eight of the nine participating laboratories. Measured thermal emittances reported by six participants exhibited comparable consistency. For solar reflectance, the accelerated aging method is both repeatable and reproducible within an acceptable range of standard deviations: the repeatability standard deviation sr ranged from 0.008 to 0.015 (relative standard deviation of 1.2-2.1%) and the reproducibility standard deviation sR ranged from 0.022 to 0.036 (relative standard deviation of 3.2-5.8%). The ILS confirmed that the accelerated aging method can be reproduced by multiple independent laboratories with acceptable precision. This study supports the adoption of the accelerated aging practice to speed the evaluation and performance rating of new cool roofing materials.

Human health can be negatively impacted by hot or cold weather, which often exacerbates respiratory or cardiovascular conditions and increases the risk of mortality. Urban populations are at particular increased risk of effects from heat due to the Urban Heat Island (UHI) effect (higher urban temperatures compared with rural ones). This has led to extensive investigation of the summertime UHI, its impacts on health, and also the consideration of interventions such as reflective ‘cool’ roofs to help reduce summertime overheating effects. However, interventions aimed at limiting summer heat are rarely evaluated for their effects in wintertime, and thus their overall annual net impact on temperature-related health effects are poorly understood.In this study we use a regional weather model to simulate the winter 2009/10 period for an urbanized region of the UK (Birmingham and the West Midlands), and use a health impact assessment to estimate the impact of reflective ‘cool’ roofs (an intervention usually aimed at reducing the UHI in summer) on cold-related mortality in winter. Cool roofs have been shown to be effective at reducing maximum temperatures during summertime. In contrast to the summer, we find that cool roofs have a minimal effect on ambient air temperatures in winter. Although the UHI in summertime can increase heat-related mortality, the wintertime UHI can have benefits to health, through avoided cold-related mortality. Our results highlight the potential annual net health benefits of implementing cool roofs to reduce temperature-related mortality in summer, without reducing the protective UHI effect in winter.Further, we suggest that benefits of cool roofs may increase in future, with a doubling of the number of heat-related deaths avoided by the 2080s (RCP8.5) compared to summer 2006, and with insignificant changes in the impact of cool-roofs on cold-related mortality. These results further support reflective ‘cool’ roof implementation strategies as effective interventions to protect health, both today and in future.

Highly reflective roofs can decrease the energy required for building air conditioning, help mitigate the urban heat island effect, and slow global warming. However, these benefits are diminished by soiling and weathering processes that reduce the solar reflectance of most roofing materials. Soiling results from the deposition of atmospheric particulate matter and the growth of microorganisms, each of which absorb sunlight. Weathering of materials occurs with exposure to water, sunlight, and high temperatures. This study developed an accelerated aging method that incorporates features of soiling and weathering. The method sprays a calibrated aqueous soiling mixture of dust minerals, black carbon, humic acid, and salts onto preconditioned coupons of roofing materials, then subjects the soiled coupons to cycles of ultraviolet radiation, heat and water in a commercial weatherometer. Three soiling mixtures were optimized to reproduce the site-specific solar spectralreflectance features of roofing products exposed for 3 years in a hot and humid climate (Miami, Florida); a hot and dry climate (Phoenix, Arizona); and a polluted atmosphere in a temperate climate (Cleveland, Ohio). A fourth mixture was designed to reproduce the three-site average values of solar reflectance and thermal emittance attained after 3 years of natural exposure, which the Cool Roof Rating Council (CRRC) uses to rate roofing products sold in the US. This accelerated aging method was applied to 25 products?single ply membranes, factory and field applied coatings, tiles, modified bitumen cap sheets, and asphalt shingles?and reproduced in 3 days the CRRC's 3-year aged values of solar reflectance. This accelerated aging method can be used to speed the evaluation and rating of new cool roofing materials.

Building roofs are sources of unwanted heat for buildings situated in zones with a warm climate. Thus, reflective coatings have emerged as an alternative to reject a fraction of the solar energy received by roofs. In this research, the thermal behavior of concrete slab roofs with traditional and solar reflective coatings was simulated using a computational tool. The studied slab configurations belong to two groups, non-insulated and insulated roofs. In the second group, the thermal insulation thickness complies with the value recommended by a national building energy standard. Weather data from four cities in Mexico with a warm climate were used as boundary conditions for the exterior surface of the roofs. The computational tool consisted of a numerical model based on the finite volume method, which was validated with experimental data. A series of comparative simulations was developed, taking a gray roof as the control case. The results demonstrated that white roofs without insulation had an exterior surface temperature between 11 and 16 °C lower than the gray roof without insulation. Thus, the daily heat gain of these white roofs was reduced by a factor ranging between 41 and 54%. On the other hand, white roofs with insulation reduced the exterior surface temperature between 17 and 21 °C compared to the gray roof with insulation. This temperature reduction caused insulated white roofs to have a daily heat gain between 37 and 56% smaller than the control case. Another contribution of this research is the assessment of two retrofitting techniques when they are applied at once. In other words, a comparison between a non-insulated gray roof and an insulated white roof revealed that the latter roof had a daily heat gain up to 6.4-times smaller than the first. [ABSTRACT FROM AUTHOR]

Copyright of Association of Arab Universities Journal of Engineering Sciences (JAARU) is the property of Association of Arab Universities and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Heat waves are posing rising threats to the environment and society due to climate change, urban sprawl, and aging population. To help identify and reduce the vulnerability of cities to extreme heat, this study projects the spatial and temporal variation of heat waves in the twenty-first century and evaluates the performance and cost-effectiveness of heat wave mitigation strategies under future climate conditions. The heat-related condition of Washington D.C. is investigated for such purpose using the high-resolution weather research and forecasting model and the representative concentration pathway 8.5 climate scenario. Results indicate that by the end of the century, the amplitude of heat waves may grow by 5.7 °C, and frequency and duration may increase by more than twofold. The urban heat island effect plays an important role in heat wave growth even though global climate change dominates the variation. Deploying cool roofs and green roofs in Washington D.C. can effectively reduce the amplitude and duration of heat waves, whereas using reflective pavements has relatively little impact. From an economic perspective, cool roofs are more cost-efficient than green roofs and reflective pavements. [ABSTRACT FROM AUTHOR]

A growing body of research values the broad benefits of cooling down cities, such as improved energy efficiency, worker productivity, air quality, health, and equity, at hundreds of millions or even billions of dollars to a single city. However, widespread adoption of urban heat mitigation programs, such as urban greening and reflective surfaces, has been slower than their economic potential suggests it should be. One possible cause for this lag is a lack of robust engagement from important stakeholders like utilities that could fund and implement heat mitigation strategies. This paper highlights the benefits of urban heat mitigation and demonstrates how these benefits fit into private utility programs' standard cost–benefit tests. This paper serves as an introduction on how to include the wide suite of benefits that urban heat mitigation programs provide in cost–benefit tests and concludes with program design guidance. [ABSTRACT FROM AUTHOR]

While it is well-known that cool roofs can efficiently reduce cooling demand in buildings, their overall energy performance in mixed and cold climates has been a topic of debate. This paper presents a comprehensive simulation study to evaluate the combined impact of roof reflectivity, insulation level, and construction type (adhered vs attached) on annual energy demand and energy costs in the United States, for different buildings and climate zones. EnergyPlus was used to model three building types (retail, office, and school buildings) for the 16 most climate-representative locations in the US using typical reflectivity and insulation values. The results show that (i) roof reflectivity is equally important to roof insulation in warm climates; (ii) for low-rise offices and schools, the benefits of reflective roofs vs dark-colored roofs are clear for all US climatic zones, with higher savings in warm climates; (iii) for big-box-retail buildings, reflective roofs perform better except for cold climate zones 7–8; (iv) dark-colored, mechanically attached roofs achieve slightly better performance than reflective roofs in mixed and cold climates. Decision makers should consider building type, climatic conditions, roof insulation levels, and durability performance, along with roof reflectivity, when assessing the overall potential benefits of cool roofs.

In regions with hot climatic conditions such as that in Saudi Arabia, a substantial share of energy is used for cooling the buildings. Many studies have shown that cool (white) roofs can help reduce the cooling energy load and thus the demand for energy over time. Also, cool roofs help reduce the urban heat island during the summer time. This research study focused on determining: (a) whether cool roofs lead to risk of condensation and mold growth in Saudi climates, (b) the amount of energy savings as result of using cool roofs instead of black roofs of same insulation amount, and (c) the reduction in the amount of insulation in cool roof having the same energy performance level as the black roof. As such, numerical simulations were conducted for a roofing system that is commonly used in low-rise buildings in Saudi Arabia in order to asses and compare the energy and hygrothermal performance of cool and black roofs. The roof was subjected to weather conditions of the Eastern Province of Saudi Arabia. The indoor conditions were taken based simple method of ASHRAE Standard 160. The results showed no moisture accumulation occurred from year-to-year after 6 years and 7 years for the black roof and cool roof, respectively, and the highest relative humidities in the black and cool roofs were well below 80% resulting in no risk of condensation and mold growth occurred in these roofs. The main outcome of this study has shown the capabilities of using reflective materials with different short-wave solar absorption coefficients for enhancing the energy performance of roofs and/or reducing the amount of insulation that resulted in same energy performance as black roofs. This study can be used in future for upgrading the Saudi Building Code so as to allow less roof insulation if cool roof is installed.

Background: The rising global temperature and frequent heatwaves are the adverse effects of climate change. The causalities and ill impacts of the heat stress were higher among the slum dwellers because of the vulnerable household structures, which were made by heat-trapping materials like tin sheets, cement sheet (asbestos), plastic, and tarpaulin. The houses are not only dwellings but also a source of livelihood for many slum dwellers as they are involved in home-based work. The increase in the temperature of more than 40°C severely affects health and increases energy expenditures. Objective: The present study conducted to identify the efficient cool roof technologies that reduce indoor temperature of the households and improve the heat resilience of dwellings located in the urban slums of Ahmedabad. Methodology: The performances of cool roof interventions were compared with the nonintervention - roof types, namely, tin, asbestos/cement sheet, and concrete. Relative humidity/temperature data loggers (Lascar EL-USB-2-LCD, Sweden) were used to measure the indoor ambient temperature and humidity. The questionnaire-based survey also has been conducted to understand the socioeconomic status and the perceptions related to roofing and health. Results: The results revealed that selected cool roof technologies including Thermocol insulation, solar reflective white paint on the outer surface of the roof, and Modroof are effectively reducing the indoor temperature as compared to the nonintervention roofing. Conclusion: Cool roof technologies have a wider scope as number of informal settlements are increasing across the cities in India and other developing countries. The governments may not able to provide proper housing to all these inhabitants due to various reasons including the land tenure of the habitats. Validated cool roof technologies can be promoted as these structures are not requires legal sanctions and easily dismantled and installed in multiple places and safeguards the investment of urban poor. [ABSTRACT FROM AUTHOR]

Hot weather can exacerbate health conditions such as cardiovascular and respiratory diseases, and lead to heat stroke and death. In built up areas, temperatures are commonly observed to be higher than those in surrounding rural areas, due to the Urban Heat Island (UHI) effect. Climate change and increasing urbanisation mean that future populations are likely to be at increased risk of overheating in cities, although building and city scale interventions have the potential to reduce this risk. We use a regional weather model to assess the potential effect of one type of urban intervention – reflective 'cool' roofs – to reduce local ambient temperatures, and the subsequent impact on heat-related mortality in the West Midlands, UK, with analysis undertaken for the summer of 2006, as well as two shorter heatwave periods in 2006 and 2003. We show that over a summer season, the population-weighted UHI intensity (the difference between simulated urban and rural temperature) was 1.1 °C on average, but 1.8 °C when including only night times, and reached a maximum of 9 °C in the West Midlands. Our results suggest that the UHI contributes up to 40% of heat related mortality over the summer period and that cool roofs implemented across the whole city could potentially offset 18% of seasonal heat-related mortality associated with the UHI (corresponding to 7% of total heat-related mortality). For heatwave periods, our modelling suggests that cool roofs could reduce city centre daytime 2 m air temperature by 0.5 °C on average, and up to a maximum of ~3 °C. Cool roofs reduced average UHI intensity by ~23%, and reduced heat related mortality associated with the UHI by ~25% during a heatwave. Cool roofs were most effective at reducing peak temperatures during the daytime, and therefore have the potential to limit dangerous extreme temperatures during heatwaves. Temperature reductions were dependent on the category of buildings where cool roofs were applied; targeting only commercial and industrial type buildings contributed more than half of the reduction for heatwave periods. Our modelling suggested that modifying half of all industrial/commercial urban buildings could have the same impact as modifying all high-intensity residential buildings in the West Midlands. • City centre summer UHI intensity was 2.0 °C (2.6 °C at night) reaching maximum of 9 °C. • Cool roofs reduced population-weighted temperature by 0.3 °C, about 23% of the UHI. • Main impact in the daytime: mean temperature 0.5 °C lower, greatest reduction 3 °C • Cooling effect greatest when implemented in commercial/industrial areas • Cool roofs may offset 25% of heat-related mortality due to the UHI, during heatwaves. [ABSTRACT FROM AUTHOR]

Building roofs are sources of unwanted heat for buildings situated in zones with a warm climate. Thus, reflective coatings have emerged as an alternative to reject a fraction of the solar energy received by roofs. In this research, the thermal behavior of concrete slab roofs with traditional and solar reflective coatings was simulated using a computational tool. The studied slab configurations belong to two groups, non-insulated and insulated roofs. In the second group, the thermal insulation thickness complies with the value recommended by a national building energy standard. Weather data from four cities in Mexico with a warm climate were used as boundary conditions for the exterior surface of the roofs. The computational tool consisted of a numerical model based on the finite volume method, which was validated with experimental data. A series of comparative simulations was developed, taking a gray roof as the control case. The results demonstrated that white roofs without insulation had an exterior surface temperature between 11 and 16 °C lower than the gray roof without insulation. Thus, the daily heat gain of these white roofs was reduced by a factor ranging between 41 and 54%. On the other hand, white roofs with insulation reduced the exterior surface temperature between 17 and 21 °C compared to the gray roof with insulation. This temperature reduction caused insulated white roofs to have a daily heat gain between 37 and 56% smaller than the control case. Another contribution of this research is the assessment of two retrofitting techniques when they are applied at once. In other words, a comparison between a non-insulated gray roof and an insulated white roof revealed that the latter roof had a daily heat gain up to 6.4-times smaller than the first.

Cool roofs use reflective materials or coatings to reflect a portion of the incident solar radiation. This results in a lowering the surface temperature of the cool roof compared to black roofs, and thus helps reduce the cooling energy loads during the summer season. The research reported in this paper was conducted to assess experimentally and numerically the performance of cool and black roofs that were subjected to the hot, humid and dusty climate of Jubail Industrial City (JIC). This paper focused on characterizing one of the important properties of reflective coating material (RCM), which is its solar reflectivity. In this study, the effect of dust/dirt accumulation on the solar reflectivity of the RCM was investigated at different exposure times to the natural weathering conditions of JIC. The test results showed that dust and dirt can significantly contribute in reducing the solar reflectivity of the RCM. As such, a number of cleaning processes were conducted on the surface of the RCM so as to increase its solar reflectivity. The effect of each cleaning process on the solar reflectivity of the RCM was investigated. Finally, this paper provides a test protocol and procedure for characterizing the dust concentration/intensity on the surfaces of the RCM and cleaning this material after different exposure times to a natural and polluted climate.