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Selecting a high albedo (solar reflectance) waterproofing layer on the top of a roof helps lower the roof’s surface temperature and reduce the air conditioning energy consumption in the top floor of a building. The annual energy savings depend on factors including weather, internal loads, and building operation schedule. To demonstrate the energy saving potential of high albedo roofs, an apparatus consisting of two nearly identical test chambers (A and B) has been built in four Indian climates: Chennai (hot & humid), Bangalore (temperate), Jhagadia (Hot & dry) and Delhi (composite). Each chamber has well-insulated walls to mimic the core of an office building. Both chambers have the same construction, equipment, and operating schedule, differing only in roof surface. The reinforced cement concrete roof of Chamber A is surfaced with a low-albedo cement layer, while that of Chamber B is surfaced with a high-albedo water proof membrane (change in solar reflectance of 0.28). The experiment will be carried out for one year to explore seasonal variations in energy savings. Initial results in the month of July (post summer) shows that savings from high albedo roof ranges from 0.04 kWh/m2/day in temperate climates, to 0.08 kWh/m2/day in hot & dry climate.

Selecting a high albedo (solar reflectance) waterproofing layer on the top of a roof helps lower the roof’s surface temperature and reduce the air conditioning energy consumption in the top floor of a building. The annual energy savings depend on factors including weather, internal loads, and building operation schedule. To demonstrate the energy saving potential of high albedo roofs, an apparatus consisting of two nearly identical test chambers (A and B) has been built in four Indian climates: Chennai (hot & humid), Bangalore (temperate), Jhagadia (Hot & dry) and Delhi (composite). Each chamber has well-insulated walls to mimic the core of an office building. Both chambers have the same construction, equipment, and operating schedule, differing only in roof surface. The reinforced cement concrete roof of Chamber A is surfaced with a low-albedo cement layer, while that of Chamber B is surfaced with a high-albedo water proof membrane (change in solar reflectance of 0.28). The experiment will be carried out for one year to explore seasonal variations in energy savings. Initial results in the month of July (post summer) shows that savings from high albedo roof ranges from 0.04 kWh/m2/day in temperate climates, to 0.08 kWh/m2/day in hot & dry climate.

We evaluate two mitigation strategies for urban heat island (UHI) in the Kansas City Metropolitan Area (KCMA). Using the Weather Research and Forecasting (WRF) model, we assess the potential benefits of reflective “cool” roofs and urban irrigation on air temperature in typical summer conditions between 2011 and 2015, and during six of the strongest historical heat waves from 2005 to 2016. Under the typical summer conditions, we simulate 2-m air temperature for 10 summer weeks, finding average daytime (07:00–19:00 local time) temperature reductions of 0.08 and 0.28 °C for cool roofs and urban irrigation, respectively. During the six heat-wave episodes, we find daytime temperature reductions of 0.02 and 0.26 °C for the two scenarios, similar to those under typical summer conditions. Our results suggest that urban irrigation can be more efficient than cool roofs in mitigating UHI in metropolitan regions where the majority of the land cover is comprised of areas with low urban (i.e., non-vegetated) fractions. Finally, we find the alteration of surface conditions due to enhanced roof albedos influences precipitation within the WRF simulation, in particular during the heat waves. Further research would be necessary to determine the robustness of this last finding.

Urban air temperature rises induced by the urban heat island (UHIE) effect or by global warming (GW) can be beneficial in winter but detrimental in summer. The SCIENCE-Outdoor model was used to simulate changes to sensible heat release and CO2 emissions from buildings yielded by four UHIE countermeasures and five GW countermeasures. This model can evaluate the thermal condition of building envelope surfaces, both inside and outside. The results showed that water-consuming UHIE countermeasures such as evaporative space cooling and roof water showering provided positive effects (decreasing sensible heat release and CO2 emissions related to space conditioning) in summer. Additionally, they had no negative (unwanted cooling) effects in winter since they can be turned off in the heating season. Roof greening can provide the greatest space-conditioning CO2 emissions reductions among four UHIE countermeasures, and it reduces the amount of heat release slightly in the heating season. Since the effect on reducing carbon dioxide (CO2) emissions by UHIE countermeasures is not very significant, it is desirable to introduce GW countermeasures in order to reduce CO2 emissions. The significance of this study is that it constructed the new simulation model SCIENCE-Outdoor and applied it to show the influence of countermeasures upon both heat release and CO2 emissions.

Albedo (solar reflectance) can be measured outdoors with a pyranometer or indoors with a hemispherical reflectometer or a spectrophotometer. The current study evaluates these methods and their applicability to roofing materials by measuring and comparing the ASTM E1918 (pyranometer), non-ASTM E1918A (alternative pyranometer), ASTM C1549 (reflectometer), and E903 (spectrophotometer) albedos of 10 roofing products, including three single-ply membranes, one asphalt shingle, three roofing aggregates, and three high-profile tiles. It uses full-size (4 m × 4 m) assemblies in the E1918 and E1918A trials; corrects the E1918 albedos to remove shadow and background errors; and evaluates C1549 and E903 albedos with two different irradiance spectra, one global horizontal and the other beam normal. E1918A albedos matched E1918 corrected (E1918_cor) albedos to within 0.036. Agreement between C1549 air mass 1 global horizontal (C1549_G1) albedo and E1918_cor albedo was within 0.015 for membrane and shingle coupons, and within 0.031 for aggregates, though the uncertainty in the latter agreement was up to 0.043. After minor corrections, C1549_G1 albedos of flat or slightly convex tile chips were 0.032–0.052 higher than the E1918_cor albedos of their corresponding high-profile tile assemblies because high-profile surfaces have concavities. Switching to the beam-normal albedo C1549_1.5E increased the C1549 albedos of the 10 tested products by 0.004–0.054, with the largest increases (C1549_1.5E – C1549_G1) accruing to spectrally selective cool colors. Using C1549_1.5E albedo to characterize a chip of a cool-colored tile compounded the error induced by representing a high-profile surface by a flat or slightly convex specimen.

Raising urban albedo increases the fraction of incident sunlight returned to outer space, cooling cities and their buildings. We evaluated the angular distribution of solar radiation incident on exterior walls in 17 U S. climates to develop performance parameters for solar-retroreflective walls, then applied first-principle physics and ray-tracing simulations to explore designs. Our analysis indicates that retroreflective walls must function at large incidence angles to reflect a substantial portion of summer sunlight, and that this will be difficult to attain with materials that rely on total internal reflection. Gonio-spectrophotometer measurements of the solar spectral bi-directional reflectivity of a bicycle reflector showed little to no retroreflection at large incidence angles. Visual comparisons of retroreflection to specular first-surface reflection for four different retroreflective safety films using violet and green lasers suggest their retroreflection to be no greater than 0.09 at incidence angles up to 45°, and no greater than 0.30 at incidence angles of up to 70°. Attempts to produce a two-surface retroreflector with orthogonal mirror grooves by cutting and polishing an aluminum block indicate that residual surface roughness impedes retroreflection. Ongoing efforts focus on forming orthogonal surfaces with aluminized Mylar film, a material with very high specular reflectance across the solar spectrum. We investigated (1) folding or stamping a free film; (2) adhering the film to a pre-shaped substrate; or (3) attaching the film to a flat ductile substrate, then shaping. The latter two methods were more successful but yielded imperfect right angles.

Increasing roof albedo (using a “cool” roof) and night ventilation are passive cooling technologies that can reduce the cooling loads in buildings, but existing studies have not comprehensively explored the potential benefits of integrating these two technologies. This study combines an experiment in the summer and transition seasons with an annual simulation so as to evaluate the thermal performance, energy savings and thermal comfort improvement that could be obtained by coupling a cool roof with night ventilation. A holistic approach integrating sensitivity analysis and multi-objective optimization is developed to explore key design parameters (roof albedo, night ventilation air change rate, roof insulation level and internal thermal mass level) and optimal design options for the combined application of the cool roof and night ventilation. The proposed approach is validated and demonstrated through studies on a six-storey office building in Xiamen, a cooling-dominated city in southeast China. Simulations show that combining a cool roof with night ventilation can significantly decrease the annual cooling energy consumption by 27% compared to using a black roof without night ventilation and by 13% compared to using a cool roof without night ventilation. Roof albedo is the most influential parameter for both building energy performance and indoor thermal comfort. Optimal use of the cool roof and night ventilation can reduce the annual cooling energy use by 28% during occupied hours when air-conditioners are on and reduce the uncomfortable time slightly during occupied hours when air-conditioners are off.

Chemical and physical stress, weathering, organic and inorganic matter deposition, and microbial growth over time, or “aging”, affect the optical-radiative performance of building envelope materials. Natural exposure helps to quantify these effects, but it usually requires several years. Further, the contribution of the different degradation agents cannot be isolated, and results from different campaigns cannot be easily compared because of the variability in the boundary conditions producing aging. Here we present an adaptation of the protocol implemented by ASTM as D7897-18 “Standard Practice for Laboratory Soiling and Weathering of Roofing Materials to Simulate Effects of Natural Exposure on Solar Reflectance and Thermal Emittance”. The aim is to reproduce in the laboratory the changes in albedo (solar reflectance) and thermal emittance experienced by building envelope materials in European urban areas rather than in the United States. We tuned the spraying duration and weathering cycles, and we compared the UV–vis–NIR reflectances of naturally-aged specimens (48 months in Rome and Milan) of roofing and wall finish materials to those exposed to laboratory weathering and soiling. Excluding those materials that show early physical-chemical degradation, the mean absolute deviation between natural and laboratory exposure of roofing products is equal to 0.027 in albedo. This is a lower value than the differences between two natural exposure campaigns at the same site. We clearly defined the limits of application of the protocol, providing an appraisal of the repeatability of natural aging. Moreover, we identified possible improvements in the methodology to conduct both natural and laboratory exposure.

Solar-reflective “cool” walls reduce absorption of sunlight by the building envelope, which may decrease cooling load in warm weather and increase heating load in cool weather. Changes to annual heating, ventilation, and air conditioning (HVAC) energy use depend on climate, wall construction, wall orientation, building geometry, HVAC efficiency, and operating schedule. Changes to annual energy cost and energy-related emissions further vary with local energy prices and emission factors. We used EnergyPlus to perform over 100,000 whole-building energy simulations, spanning 10 different building categories, three building vintages, 16 California climate zones, and 15 United States (U.S.) climate zones. Cool walls yielded annual source energy, energy cost, and emission savings in all California climate zones and in warm U.S. (ASHRAE) climate zones. In California, annual whole-building HVAC energy cost savings were 4.0–27% in single-family homes, 0.5–3.8% in medium office buildings, and 0.0–8.5% in stand-alone retail stores. In warm U.S. climates—zones 1A (Miami, FL) through 4B (Albuquerque, NM)—annual HVAC energy cost savings were 1.8–8.3% in single-family homes, 0.3–4.6% in medium office buildings, and 0.5–11% in stand-alone retail stores. California and U.S. fractional source energy and emission savings were comparable to fractional energy cost savings. Per unit surface area modified, cool-wall savings often exceeded cool-roof savings because building codes typically prescribe much less wall insulation than roof insulation.

Roofs with high-reflectance (solar reflectance) coating, commonly known as cool roofs, can stay cool in the sun, thereby reducing building energy consumption and mitigating the urban heat island. However, chemical-physical degradation and biological growth can decrease their solar reflectance and the ability to save energy. In this study, the solar spectral reflectance of 12 different roofing products with an initial albedo of 0.56–0.90 was measured before exposure and once every three months over 32 months. Specimens were exposed on the roofs of dormitory buildings in Xiamen and Chengdu, each major urban areas with hot summers. The albedos of high and medium-lightness coatings stabilized in the ranges 0.45–0.62 and 0.36–0.59 in both cities, respectively. This study yielded albedo loss exceeded those reported in the latest Chinese standard by 0.08–0.15. Finally, DesignBuilder (EnergyPlus) simulations estimate that a new cool roof with albedo 0.78 on a six-story dormitory building will yield annual site energy savings (heating and cooling) for the top floor, which are 8.01 kWh/m2 (24.2%) and 9.12 kWh/m2 (26.3%) per unit floor area in Xiamen and Chengdu, respectively; while an aged cool roof with albedo 0.45 and 0.56 will yield the annual savings by 5.12 kWh/m2 (15.4%) and 2.47 kWh/m2 (10.5%) in these two cities.

Photocatalytic building surfaces can harness sunlight to reduce urban air pollution. The NOx abatement capacity of TiO2-coated granules used in roofing products was evaluated for commercial product development. A laboratory test chamber and ancillary setup were built following conditions prescribed by ISO Standard 22197-1. It was validated by exposing reference P25-coated aluminum plates to a 3 L min−1 air flow enriched in 1 ppm NO under UVA irradiation (360 nm, 11.5 W m−2). We characterized prototype granule-surfaced asphalt shingles and loose granules prepared with different TiO2 loadings and post-treatment formulations. Tests performed at surface temperatures of 25 and 60 °C showed that NOx abatement was more effective at the higher temperature. Preliminary tests explored the use of 1 ppm NO2 and of 1 ppm and 0.3 ppm NO/NO2 mixtures. Specimens were aged in a laboratory accelerated weathering apparatus, and by exposure to the outdoor environment over periods that included dry and rainy seasons. Laboratory aging led to higher NO removal and NO2 formation rates, and the same catalyst activation was observed after field exposure with frequent precipitation. However, exposure during the dry season reduced the performance. This inactivation was mitigated by cleaning the surface of field-exposed specimens. Doubling the TiO2 loading led to a 50–150% increase in NO removal and NOx deposition rates. Application of different post-treatment coatings decreased NO removal rates (21–35%) and NOx deposition rates (26–74%) with respect to untreated granules. The mass balance of nitrogenated species was assessed by extracting granules after UV exposure in a 1 ppm NO-enriched atmosphere.

White roof (WR) and Sedum lineare tray garden roof (STGR) have been convinced to improve the energy-efficiency and provide various benefits for conventional impervious grey roofs. Some national and local standards have standardized and recommended these technologies in existing building retrofits, however, they do not include assessment and choice of a particular roof retrofit in different climates. This paper presents a 40-year life-cycle cost analysis (LCCA) of an office building roof retrofitted by adding either WR or STGR over an existing grey roof in five cities, located in four Chinese climate zones. The LCCA find that the WR retrofits exhibit positive life-cycle net savings (NS) in warm winter zones, ranging 5.7–35.1 CNY/m 2 , and STGR retrofits have negative NS of -81.3– -16.7 CNY/m 2 in all climate zones. The NS of both WR and STGR generally tend to improve as one moves from the coldest cities to the warmest cities. LCCA results suggest that adding new building codes concerning crediting or prescribing WR and STGR retrofits into office buildings with grey roofs in hot summer climate zones and warm winter zone in China, respectively. And featured by more specific requirements, the localized Technical Norms help promote the implementation of new building codes.

The extent to which a solar-reflective “cool” wall can reduce a building's cooling load in summer or increase its heating load in winter scales with the wall's incident solar radiation, or solar availability. We assess how the solar availability at the wall of a central (modeled) building is affected by a neighboring wall across an urban canyon by calculating the central wall's solar availability factor (SAF), defined as the ratio of sunlight incident on the central wall in the presence of the neighboring wall to that incident in the absence of the neighboring wall. Cool-wall heating, ventilation, and air conditioning (HVAC) energy savings simulated for an isolated central building (no neighbors) can be multiplied by SAFs to account for interactions with neighboring walls. Monthly values of SAF were evaluated in 17 climates across the United States, including three in California, for north, east, south, and west central walls, over a wide range of canyon aspect ratio (height/width). Results for four representative aspect ratios—0.2, 1, 2, and 10—are presented. In Fresno, CA, monthly SAF ranges from 0.90 to 0.96 for central walls facing north, east, south, or west when the aspect ratio is 0.2 (two-story single-family homes across a street) and both the central and neighboring walls are conventional (albedo 0.25). Monthly SAFs decrease as aspect ratio rises, falling to 0.06–0.24 at an aspect ratio of 10 (adjacent 10-story buildings on the same side of the street). An example worked for a two-story single-family home in Fresno on the west side of a residential street yields SAFs of 0.47 (north), 0.92 (east), 0.50 (south), and 0.63 (west) to apply to the cool-wall annual HVAC energy savings computed for an isolated central building. Shading and reflection reduce the home's annual HVAC energy cost savings by 31%.

The effects of neighborhood-scale land use and land cover (LULC) properties on observed air temperatures are investigated in two regions within Los Angeles County: Central Los Angeles and the San Fernando Valley (SFV). LULC properties of particular interest in this study are albedo and tree fraction. High spatial density meteorological observations are obtained from 76 personal weather-stations. Observed air temperatures were then related to the spatial mean of each LULC parameter within a 500 m radius "neighborhood" of each weather station, using robust regression for each hour of July 2015. For the neighborhoods under investigation, increases in roof albedo are associated with decreases in air temperature, with the strongest sensitivities occurring in the afternoon. Air temperatures at 14:00-15:00 local daylight time are reduced by 0.31 °C and 0.49 °C per 1 MW increase in daily average solar power reflected from roofs per neighborhood in SFV and Central Los Angeles, respectively. Per 0.10 increase in neighborhood average albedo, daily average air temperatures were reduced by 0.25 °C and 1.84 °C. While roof albedo effects on air temperature seem to exceed tree fraction effects during the day in these two regions, increases in tree fraction are associated with reduced air temperatures at night.

To identify and characterize localized urban heat- and cool-island signals embedded within the temperature field of a large urban-climate archipelago, fine-resolution simulations with a modified urbanized version of the WRF meteorological model were carried out as basis for siting fixed weather monitors and designing mobile-observation transects. The goal was to characterize variations in urban heat during summer in Los Angeles, California. Air temperatures measured with a shielded sensor mounted atop an automobile in the summers of 2016 and 2017 were compared to model output and also correlated to surface physical properties focusing on neighborhood-scale albedo and vegetation canopy cover. The study modeled and measured the temperature response to variations in surface properties that already exist in the real world, i.e., realistic variations in albedo and canopy cover that are attainable through current building and urban design practices. The simulated along-transect temperature from a modified urbanized WRF model was compared to the along-transect observed temperature from 15 mobile traverses in one area near downtown Los Angeles and another in an inland basin (San Fernando Valley). The observed transect temperature was also correlated to surface physical properties characterizations that were developed for input to the model. Both comparisons were favorable, suggesting that (1) the model can reliably be used in siting fixed weather stations and designing mobile-transect routes to characterize urban heat and (2) that except for a few cases with opposite co-varying influences, the correlations between observed temperature and albedo and between observed temperature and canopy cover were each negative, ranging from -1.0 to -9.0 °C per 0.1 increase in albedo and from -0.1 to -2.2 °C per 0.1 increase in canopy cover. Observational data from the analysis domains pointed to a wind speed threshold of 3 m/s. Below this threshold the variations in air temperature could be explained by land use and surface properties within a 500-m radius of each observation point. Above the threshold, air temperature was influenced by the properties of the surface within a 1-km upwind fetch. Of relevance to policy recommendations, the study demonstrates the significant real-world cooling effects of increasing urban albedo and vegetation canopy cover. Based on correlations between the observed temperature (from mobile transects) and surface physical properties in the study domains, the analysis shows that neighborhood-scale (500-m) cooling of up to 2.8 °C during the daytime can be achieved by increasing albedo. A neighborhood can also be cooled by up to 2.3 °C during the day and up to 3.3 °C at night by increasing canopy cover. The analysis also demonstrates the suitability of using fine-resolution meteorological models to design mobile-transect routes or site-fixed weather monitors in order to quantify urban heat and the efficacy of albedo and canopy cover countermeasures. The results also show that the model is capable of accurately predicting the geographical locations and the magnitudes of localized urban heat and cool islands. Thus the model results can also be used to devise urban-heat mitigation measures.

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.

This study presents the experimental measurement of the energy consumption of three top-floor air-conditioned rooms in a typical office building in Chongqing, which is a mountainous city in the hot-summer and cold-winter zone of China, to examine the energy performance of white and sedum-tray garden roofs. The energy consumption of the three rooms was measured from September 2014 to September 2015 by monitoring the energy performance (temperature distributions of the roofs, evaporation, heat fluxes, and energy consumption) and indoor air temperature. The rooms had the same construction and appliances, except that one roof top was black, one was white, and one had a sedum-tray garden roof. This study references the International Performance Measurement and Verification Protocol (IPMVP) to calculate and compare the energy savings of the three kinds of roofs. The results indicate that the energy savings ratios of the rooms with the sedum-tray garden roof and with the white roof were 25.0% and 20.5%, respectively, as compared with the black-roofed room, in the summer; by contrast, the energy savings ratios were −9.9% and −2.7%, respectively, in the winter. Furthermore, Annual conditioning energy savings of white roof (3.9 kWh/m2) were 1.6 times the energy savings for the sedum-tray garden roof. It is evident that white roof is a preferable choice for office buildings in Chongqing. Additionally, The white roof had a reflectance of 0.58 after natural aging owing to the serious air pollution worsened its thermal performance, and the energy savings reduced by 0.033 kWh/m2·d. Evaporation was also identified to have a significant effect on the energy savings of the sedum-tray garden roof.

Fluorescent cool dark surfaces stay cool in the sun by reflecting near-infrared (NIR) radiation and by actively re-emitting in the NIR spectrum some of the energy absorbed from visible sunlight. The fraction of incident solar energy rejected by reflection and fluorescence is the “effective solar reflectance”, or ESR, of the surface. It is challenging to measure ESR with a solar spectrometer or a solar reflectometer, the radiometric instruments most commonly used to measure the solar reflectance (SR) of specimens in the laboratory. We have tested a variety of calorimetric techniques for using temperature in the sun to interpolate the effective solar absorptance (1 − ESR) of a fluorescent test specimen from the known solar absorptances of non-fluorescent reference specimens. Our experiments show that averaging out noise in the temperature signal induced by variations in convection is key. We developed a computer-controlled rotary apparatus that compares the temperatures in the sun of up to six specimens. Trials on six different fluorescent specimens indicate that it can measure ESR with a repeatability of about 0.02. To maximize the ratio of signal to noise in temperature determination, and to facilitate calculation of the fluorescence benefit (ESR − SR), measurements should be performed with specimens facing the sun.

Solar reflective “cool pavements” have been proposed as a potential heat mitigation strategy for cities. However, previous research has not systematically investigated the extent to which cool pavements could reduce urban temperatures. In this study we investigated the climate impacts of widespread deployment of cool pavements in California cities. Using the Weather Research and Forecasting model, we simulated the current climate of California at 4 km spatial resolution. Comparing this simulation to 105 weather stations in California suggested an overall mean bias (model minus observation) of -0.30°C. Widespread pavement albedo increases of 0.1 and 0.4 in California cities were then simulated. Comparing temperature reductions for each scenario showed that the climate response to pavement albedo modification was nearly linear. Temperature reductions at 14:00 local standard time were found to be 0.32°C per 0.1 increase in grid cell average albedo. Temperature reductions were found to peak in the late morning and evening when (a) boundary layer heights were low and (b) solar irradiance (late morning) and heat accumulation in the pavement (evening) was high. Temperature reductions in summer were found to exceed those in winter, as expected. After scaling the results using realistic data-derived urban canyon morphologies and an off-line urban canyon albedo model, annual average surface air temperature reductions from increasing pavement albedo by 0.4 ranged from 0.18°C (Palm Springs) to 0.86°C (San Jose). The variation among cities was due to differences in baseline climate, size of the city, urban fraction, and urban morphology.

A web-based Roof Savings Calculator (RSC) has been deployed for the United States Department of Energy as an industry-consensus tool to help building owners, manufacturers, distributors, contractors and researchers easily run complex roof and attic simulations. RSC simulates multiple roof and attic technologies for side-by-side comparison including reflective roofs, different roof slopes, above sheathing ventilation, radiant barriers, low-emittance roof surfaces, duct location, duct leakage rates, multiple substrate types, and insulation levels. Annual simulations of hour-by-hour, whole-building performance are used to provide estimated annual energy and cost savings from reduced HVAC use. While RSC reported similar cooling savings to other simulation engines, heating penalty varied significantly. RSC results show reduced cool roofing cost-effectiveness, thus mitigating expected economic incentives for this countermeasure to the urban heat island effect. This paper consolidates comparison of RSC's projected energy savings to other simulation engines including DOE-2.1E, AtticSim, Micropas, and EnergyPlus. Also included are comparisons to previous simulation-based studies, analysis of RSC cooling savings and heating penalties, the role of radiative heat exchange in an attic assembly, and changes made for increased accuracy of the duct model. Radiant heat transfer and duct interaction not previously modeled is considered a major contributor to heating penalties.

In 2006, California introduced the Global Warming Solutions Act (Assembly Bill 32), which requires the state to reduce greenhouse gas emissions to 1990 levels by 2020. "Cool community" strategies, including cool roofs, cool pavements, cool walls and urban vegetation, have been identified as voluntary measures with potential to reduce statewide emissions. In addition, cool community strategies provide co-benefits for residents of California, such as reduced utility bills, improved air quality and enhanced urban livability. To achieve these savings, Lawrence Berkeley National Laboratory (LBNL) has worked with state and local officials, non-profit organizations, school districts, utilities, and manufacturers for 4 years to advance the science and implementation of cool community strategies. This paper summarizes the accomplishments of this program, as well as recent developments in cool community policy in California and other national and international efforts. We also outline lessons learned from these efforts to characterize successful programs and policies to be replicated in the future.

We present a simple method to estimate the maximum possible energy saving that might be achieved by increasing the albedo of surfaces in a large city. We restrict this to the "indirect effect", the cooling of outside air that lessens the demand for air conditioning (AC). Given the power demand of the electric utilities and data about the city, we can use a single linear equation to estimate the maximum saving. For example, the result for an albedo change of 0.2 of pavements in a typical warm city in California, such as Sacramento, is that the saving is less than about 2 kW·h of electrical energy per modified m2 per year. This may help decision makers choose which heat island mitigation techniques are economical from an energy-saving perspective.

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.

Part of the urban heat island effect can be attributed to dark pavements that are commonly used on streets and parking lots. In this paper we consider two light colored, hence cooler, alternative paving materials that are in actual use in cities today. These are Portland cement concrete (PCC) pavements and chip seals. We report measurements of the albedos of some PCC and chip sealed pavements in the San Francisco Bay Area. The albedos of the PCC pavements ranged from about 0.18 to 0.35. The temperatures of some PCC pavements are also measured and calculated. We then consider how the albedos of the constituent materials of the PCC (stone, sand and cement) contribute to the albedos of the resulting finished concrete. The albedos of a set of chip sealed pavements in San Jose, CA, were measured and correlated with the times of their placement. It is found that the albedos decrease with age (and use) but remain higher than that of standard asphalt concrete (AC) for about five years. After that, the albedos of the chip seals are about 0.12, similar to aged AC. The fact that many PCC pavements have albedos at least twice as high as aged AC suggests that it is possible to have pavement albedos that remain high for many years.

Background and purpose: Chemistry examinations can favour the deployment of algorithmic procedures like Le Chatelier's Principle (LCP) rather than reasoning using chemical principles. This study investigated the explanatory resources which high school students use to answer equilibrium problems and whether the marks given for examination answers require students to use approaches beyond direct application of LCP. Sample: The questionnaire was administered to 162 students studying their first year of advanced chemistry (age 16/17) in three high achieving London high schools. Design and methods: The students' explanations of reversible chemical systems were inductively coded to identify the explanatory approaches used and interviews with 13 students were used to check for consistency. AS level examination questions on reversible reactions were analysed to identify the types of explanations sought and the students' performance in these examinations was compared to questionnaire answers. Results: 19% of students used a "holistic" explanatory approach: when the rates of forward and reverse reactions are correctly described, recognising their simultaneous and mutually dependent nature. 36% used a "mirrored reactions" approach when the connected nature of the forward and reverse reactions is identified, but not their mutual dependency. 42% failed to recognize the interdependence of forward and reverse reactions ("reactions not connected" approach). Only 4% of marks for AS examination questions on reversible chemical systems asked for responses which went beyond either direct application of LCP or recall of equilibrium knowledge. 37% of students attained an A grade in their AS national examinations. Conclusions: Examinations favour the application of LCP making it possible to obtain the highest grade with little understanding of reversible chemical systems beyond a direct application of this algorithm. Therefore students' understanding may be attenuated so that they are unable to use kinetic sub-micro level ideas which will support the building of deeper energetic conceptions at university. (Contains 7 tables, 5 figures and 1 note.)