@article {57384, title = {Economic Comparison of White, Green, and Black Flat Roofs in the United States}, journal = {Energy and Buildings}, volume = {71}, year = {2014}, month = {3/2014}, pages = {20-27}, abstract = {

White and {\textquotedblleft}green{\textquotedblright} (vegetated) roofs have begun replacing conventional black (dark-colored) roofs to mitigate the adverse effects of dark impervious urban surfaces. This paper presents an economic perspective on roof color choice using a 50-year life-cycle cost analysis (LCCA). We find that relative to black roofs, white roofs provide a 50-year net savings (NS) of $25/m2 ($2.40/ft2) and green roofs have a negative NS of $71/m2 ($6.60/ft2). Despite lasting at least twice as long as white or black roofs, green roofs cannot compensate for their installation cost premium. However, while the 50-year NS of white roofs compared to green roofs is $96/m2 ($8.90/ft2), the annualized cost premium is just $3.20/m2 -year ($0.30/ft2 -year). This annual difference is sufficiently small that the choice between a white and green roof should be based on preferences of the building owner. Owners concerned with global warming should choose white roofs, which are three times more effective than green roofs at cooling the globe. Owners concerned with local environmental benefits should choose green roofs, which offer built-in stormwater management and a {\textquotedblleft}natural{\textquotedblright} urban landscape esthetic. We strongly recommend building code policies that phase out dark-colored roofs in warm climates to protect against their adverse public health externalities.

}, keywords = {Building codes, energy efficiency, Green roofs, Life-cycle cost analysis (LCCA), Stormwater management, urban heat island, White roofs}, issn = {03787788}, doi = {10.1016/j.enbuild.2013.11.058}, author = {Julian Sproul and Man-Pun Wan and Benjamin H. Mandel and Arthur H. Rosenfeld} } @article {57527, title = {Cool roofs as a strategy to tackle global warming: economical and technical opportunities}, journal = {Advances in Building Energy Research}, volume = {7}, year = {2013}, month = {10/2013}, pages = {254 - 268}, chapter = {254}, abstract = {

There is a growing consensus within the scientific community that the Earth{\textquoteright}s climate system is unequivocally warming and it is very likely (according to the formal uncertainty language used in the AR4, the term {\textquotedblleft}very likely{\textquotedblright} refers to \>90\% assessed probability of occurrence) due to the increase in anthropogenic greenhouse gas concentrations. Urgent solutions need to be adopted, which are environmentally sustainable, in order to tackle global warming in the short term. At present, the most accredited global warming mitigation methods are represented by the emissions reduction technologies. Such technologies include energy from renewable sources such as solar and wind. A potential alternative is to modify the Earth{\textquoteright}s albedo by reflective surfaces (pavements and roofs), which are already employed to reduce building energy consumption and to mitigate heat island effects.

In this paper a procedure is proposed which evaluates the influence of changes in the Earth{\textquoteright}s albedo on the Earth{\textquoteright}s temperature and, as a consequence, quantifies the high albedo surface size required to compensate or offset global warming from changes in CO2. Additionally, a technical-economical comparison is carried out here between the proposed albedo system and the main technologies for the production of electric and thermal energy from renewable sources in order to evaluate its effectiveness in terms of cost of carbon dioxide equivalent (CO2eq) emission reduction.

}, keywords = {albedo, CO2 offset, cool roofs, global warming, high albedo surface}, issn = {1751-2549}, doi = {10.1080/17512549.2013.865555}, author = {Federico Rossi and Franco Cotana and Mirko Filipponi and Andrea Nicolini and Surabi Menon and Arthur H. Rosenfeld} } @article {55883, title = {Cool roofs could save money, save planet}, journal = {KGO-TV (abc7news)}, year = {2009}, month = {03/2009}, keywords = {cool roof, Heat Island}, url = {http://abclocal.go.com/kgo/story?section=news/drive_to_discover\&id=6689052}, author = {Hashem Akbari and Arthur H. Rosenfeld} } @article {springerlink:10.1007/s10584-008-9515-9, title = {Global cooling: increasing world-wide urban albedos to offset CO2}, journal = {Climatic Change}, volume = {94}, year = {2009}, month = {06/2009}, pages = {275-286}, publisher = {Springer Netherlands}, abstract = {

Increasing urban albedo can reduce summertime temperatures, resulting in better air quality and savings from reduced air-conditioning costs. In addition, increasing urban albedo can result in less absorption of incoming solar radiation by the surface-troposphere system, countering to some extent the global scale effects of increasing greenhouse gas concentrations. Pavements and roofs typically constitute over 60\% of urban surfaces (roof 20{\textendash}25\%, pavements about 40\%). Using reflective materials, both roof and pavement albedos can be increased by about 0.25 and 0.15, respectively, resulting in a net albedo increase for urban areas of about 0.1. On a global basis, we estimate that increasing the world-wide albedos of urban roofs and paved surfaces will induce a negative radiative forcing on the earth equivalent to offsetting about 44 Gt of CO2 emissions. At ~$25/tonne of CO2, a 44 Gt CO2 emission offset from changing the albedo of roofs and paved surfaces is worth about $1,100 billion. Furthermore, many studies have demonstrated reductions of more than 20\% in cooling costs for buildings whose rooftop albedo has been increased from 10{\textendash}20\% to about 60\% (in the US, potential savings exceed $1 billion per year). Our estimated CO2 offsets from albedo modifications are dependent on assumptions used in this study, but nevertheless demonstrate remarkable global cooling potentials that may be obtained from cooler roofs and pavements.

}, keywords = {Advanced Very High Resolution Radiometer, Global Cooling, Heat Island, Pave Surface, Radiative Force, Urban Surface}, issn = {0165-0009 (Print), 1573-1480 (Online)}, doi = {10.1007/s10584-008-9515-9}, author = {Hashem Akbari and Surabi Menon and Arthur H. Rosenfeld} } @article {55867, title = {Painting the town white: California Energy Commissioner, Art Rosenfeld, explains the benefits of cool roofs}, journal = {National Public Radio}, number = {3}, year = {2009}, keywords = {cool roof, Heat Island}, url = {http://www.loe.org/shows/segments.htm?programID=09-P13-00007\&segmentID=7}, author = {Arthur H. Rosenfeld} } @techreport {55892, title = {Equivalent CO2 avoided by reflective roofs and pavements in California}, year = {2008}, note = {

A memo to Dr. Bart Croes, CARB

}, month = {10/2008}, keywords = {Global Cooling, Heat Island}, author = {Hashem Akbari and Surabi Menon and Arthur H. Rosenfeld} } @techreport {55882, title = {White roofs cool the world, directly offset CO2 and delay global warming}, year = {2008}, month = {11/2008}, keywords = {cool roof, Heat Island}, author = {Hashem Akbari and Arthur H. Rosenfeld} } @conference {55891, title = {Global cooling: effect of urban albedo on global temperature}, booktitle = {2nd PALENC and 28th AIVC Conference}, year = {2007}, note = {

Building Low Energy Cooling and Advanced Ventilation Technologies in the 21st Century

}, month = {09/2007}, pages = {1-5}, address = {Crete}, abstract = {

In many urban areas, pavements and roofs constitute over 60\% of urban surfaces (roof 20-25\%, pavements about 40\%). The roof and the pavement albedo can be increased by about 0.25 and 0.10, respectively, resulting in a net albedo increase for urban areas of about 0.1.

Many studies have demonstrated building cooling-energy savings in excess of 20\% upon raising roof reflectivity from an existing 10-20\% to about 60\%. We estimate U.S. potential savings in excess of $1 billion (B) per year in net annual energy bills. Increasing albedo of urban surfaces can reduce the summertime urban temperature and improve the urban air quality.

Increasing the urban albedo has the added benefit of reflecting more of the incoming global solar radiation and countering the effect of global warming. We estimate that increasing albedo of urban areas by 0.1 results in an increase of 3x10-4 in Earth albedo. Using a simple global model, the change in air temperature in lowest 1.8 km of the atmosphere is estimated at 0.01K. Modelers predict a warming of about 3K in the next 60 years (0.05K/year). Change of 0.1 in urban albedo will result in 0.01K global cooling, a delay of ~0.2 years in global warming. This 0.2 years delay in global warming is equivalent to 10 Gt reduction in CO2 emissions.

}, keywords = {Global Cooling, Heat Island}, url = {http://www.escholarship.org/uc/item/0pz748p6}, author = {Hashem Akbari and Surabi Menon and Arthur H. Rosenfeld} } @conference {55850, title = {Cool colored roofs to save energy and improve air quality}, booktitle = {ACEEE Summer Study on Energy Efficiency in Buildings, August 22-27, 2004}, volume = {1}, year = {2004}, month = {08/2004}, pages = {1-16}, publisher = {American Council for an Energy-Efficient Economy}, organization = {American Council for an Energy-Efficient Economy}, edition = {1}, abstract = {

Raising the solar reflectance of a roof from a typical value of 0.1 {\textendash} 0.2 to an achievable 0.6 can reduce cooling-energy use in buildings by more than 20\%. Cool roofs also reduce ambient outside air temperature, thus further decreasing the need for air conditioning and retarding smog formation.

We are collaborating with pigment manufacturers to characterize colorants, and with manufacturers of roofing materials to produce cool colored products, including asphalt shingles, tiles, metal roofing, wood shakes, membranes, and coatings. Significant efforts are being devoted to the identification and characterization of pigments suitable for cool-colored coatings, and to the development of engineering methods for applying cool coatings to roofing materials. We are also measuring and documenting the laboratory and in-situ performances of roofing products. Demonstration of energy savings can accelerate the market penetration of cool-colored roofing materials. Early results from this program have yielded colored concrete, clay, and metal roofing products with solar reflectances exceeding 0.4. Obtaining equally high reflectances for roofing shingles is more challenging, but we expect manufacturers to soon have several cost-effective colored shingles with reflectances of at least 0.25.

}, keywords = {cool roof, Heat Island}, url = {http://aceee.org/proceedings-paper/ss04/panel01/paper01}, author = {Hashem Akbari and Paul H. Berdahl and Ronnen M. Levinson and Stephen Wiel and Andre Desjarlais and William A. Miller and Nancy Jenkins and Arthur H. Rosenfeld and Chris Scruton} } @article {55909, title = {Cool communities}, journal = {Macmillan Encyclopedia of Energy}, volume = {1}, number = {LBL-44129}, year = {2000}, note = {Added to JabRef: 2010.04.28}, pages = {305-8}, abstract = {

As modern urban areas have grown, there has been a corresponding growth in darker surfaces and a decline in vegetation, affecting urban climate, energy use, and habitability. Dark roofs heat up more and thus raise the summertime cooling demands of buildings, collectively with reduced vegetation, warming the air over urban areas and creating "heat islands." On a clear summer afternoon, the air temperature in a typical city can be as much as 2.5{\textordmasculine}C (4.5{\textordmasculine}F) higher than in surrounding rural areas. (The peak heat island effect occurs during cold winter evenings and is caused primarily by the rapid cooling of the rural areas - the thermal storage of pavements and dark-roofed buildings is much greater than greenery.) Peak urban electric demand rises by 2 to 4 percent for each 1{\textordmasculine}C (1.8{\textordmasculine}F) rise in daily maximum temperature above 15 to 20{\textordmasculine}C (59 to 68{\textordmasculine}F), so the additional airconditioning

use caused by higher urban air temperature is responsible for 5 to 10 percent of urban peak electric demand, costing U.S. ratepayers several billion dollars annually. Temperatures in cities are increasing. Figure I depicts summertime monthly maximum

and minimum temperatures between 1877 and 1997 in downtown Los Angeles, clearly indicating that these maximum temperatures are now about 2.5{\textordmasculine}C (4.5{\textordmasculine}F) higher than in 1920. Minimum temperatures are about 4{\textordmasculine}C (7.2{\textordmasculine}F) higher than in 1880. In California from 1965 to 1989, the average urban-rural temperature differences, measured at thirtyone pairs of urban and rural stations, have increased by about 1{\textordmasculine}C (1.8{\textordmasculine}F). In Washington, D.C., temperatures rose 2{\textordmasculine}C (3.6{\textordmasculine}F) between 1871 and 1987. This recent warming trend is typical of most U.S. metropolitan areas and exacerbates demand for energy. In Los Angeles, we estimate a heat-island induced increase in power consumption of 1 to 1.5 GW, costing ratepayers $100 million per year. Besides increasing systemwide cooling loads, summer heat islands increase smog production. Smog production is a highly temperature-sensitive process. At maximum daily temperatures below 22{\textordmasculine}C (71.6{\textordmasculine}F), maximum ozone concentration in Los Angeles is below the California standard of 90 parts per billion. At 35{\textordmasculine}C (95{\textordmasculine}F), practically all days in Los Angeles are smoggy (see Figure 2).

}, keywords = {Heat Island, urban heat island}, author = {Hashem Akbari and Arthur H. Rosenfeld} } @article {55873, title = {Reflective surfaces for cooler buildings and cities}, journal = {Philosophical Magazine Part B}, volume = {79}, number = {9}, year = {1999}, note = {

Added to JabRef: 2010.04.21

}, pages = {1457-1476}, abstract = {

Many roofs and pavements are dark coloured. In warm and sunny climates these surfaces become hot by absorbing sunlight. This can have the undesirable consequences of increasing the heat flow into the building beneath the hot roofs, which then increases the demand for air conditioning. The hot surfaces also heat the outside air, again increasing air conditioning demand but also increasing the concentration of ozone (smog). We estimate the benefits of replacing (as part of routine maintenance) the present dark surfaces with more reflective surfaces. We conclude that it is a practical way to save energy and to reduce smog in warm climates.

}, keywords = {cool roof, Heat Island}, doi = {10.1080/13642819908216984}, author = {Melvin Pomerantz and Hashem Akbari and Paul H. Berdahl and Steven J. Konopacki and Haider Taha and Arthur H. Rosenfeld} } @article {55911, title = {Cool communities: strategies for heat island mitigation and smog reduction}, journal = {Energy and Buildings}, volume = {28}, number = {1}, year = {1998}, note = {

0378-7788Added to JabRef: 2010.04.21

}, pages = {51-62}, abstract = {

Adopting our {\textquoteright}cool communities{\textquoteright} strategies of reroofing and repaying in lighter colors and planting shade trees can effect substantial energy savings, directly and indirectly. In our target city of Los Angeles, annual residential air-conditioning (A/C) bills can be reduced directly by about US$100 M and, because these strategies serve to cool the air in the Los Angeles basin and reduce smog exceedance levels by about 10\%, an additional savings of US$70 M in indirect cooling and US$360 M in smog-reduction benefits{\textemdash}a total savings of about US$1/2 B per year{\textemdash}is possible. Trees are most effective if they shade buildings, but the savings are significant even if they merely cool the air by evapotranspiration. In Los Angeles, avoided peak power for air conditioning can reach about 1.5 GW (more than 15\% of the city{\textquoteright}s air conditioning). Generalized to the entire US, we estimate that 25 GW can be avoided with potential annual benefits of about US$5B by the year 2015. Recent steps taken by cities in the warm half of US towards adoption of cool communities include

  1. incorporation of cool roofs in the revised ASHRAE building standards S90.1 and
  2. inclusion of cool surfaces and shade trees as tradable smog-offset credits in Los Angeles.

Other step underway include

  1. plans by the US Environmental Protection Agency (EPA) to approve heat island mitigation measures in the state implementation plan to comply with ozone standards and
  2. plans for ratings and labeling of cool surfaces.
}, keywords = {Heat Island, urban heat island}, doi = {10.1016/S0378-7788(97)00063-7}, author = {Arthur H. Rosenfeld and Hashem Akbari and Joseph J. Romm and Melvin Pomerantz} } @article {55845, title = {Practical issues for using solar-reflective materials to mitigate urban heat islands}, journal = {Atmospheric Environment}, volume = {32}, number = {1}, year = {1998}, note = {

1352-2310Conference on the Benefits of the Urban ForestAdded to JabRef: 2010.04.19

}, pages = {95-101}, abstract = {

Solar-reflective or high-albedo, alternatives to traditionally absorptive urban surfaces such as rooftops and roadways can reduce cooling energy use and improve urban air quality at almost no cost. This paper presents information to support programs that mitigate urban heat islands with solar-reflective surfaces: estimates of the achievable increase in albedo for a variety of surfaces, issues related to the selection of materials and costs and benefits of using them. As an example, we present data for Sacramento, California. In Sacramento, we estimate that 20\% of the 96 square mile area is dark roofing and 10\% is dark pavement. Based on the change in albedo that is achievable for these surfaces, the overall albedo of Sacramento could be increased by 18\%, a change that would produce significant energy savings and increase comfort within the city. Roofing market data indicate which roofing materials should be targeted for incentive programs. In 1995, asphalt shingle was used for over 65\% of residential roofing area in the U.S. and 6\% of commercial. Built-up roofing was used for about 5\% of residential roofing and about 30\% of commercial roofing. Single-ply membranes covered about 9\% of the residential roofing area and over 30\% of the commercial area. White, solar-reflective alternatives are presently available for these roofing materials but a low-first-cost, solar-reflective alternative to asphalt shingles is needed to capture the sloped-roof market. Since incoming solar radiation has a large non-visible component, solar-reflective materials can also be produced in a variety of colors.

}, keywords = {Cool Pavements, Heat Island}, doi = {10.1016/S1352-2310(97)00182-9}, author = {Sarah E. Bretz and Hashem Akbari and Arthur H. Rosenfeld} } @proceedings {55888, title = {Cool buildings and cool communities}, journal = {Proceedings of the Second International Conference on Buildings and the Environment}, volume = {2}, year = {1997}, note = {Added to JabRef: 2010.04.21}, month = {1997/june 9--12}, pages = {301-308}, abstract = {

Analysis of temperature trends for the last 100 years in several large U. S. cities has indicated that since -1940 there has been a steady increase in downtown temperatures of 0.1-0.5DC per decade (-0.5{\textdegree}C for larger cities like Los Angeles and 0.1{\textdegree}C for smaller cities). Typically, electricity demand in cities increases by 2-4\%/{\textdegree}C, hence, about 5-10\% of the current urban electricity demand is spent to cool buildings just to compensate for the urban heat island effect. Downtown Los Angeles, for example, is now 3{\textdegree}C warmer than in 1940 leading to an increase in electricity demand of 1500 MW. In L.A., smoggy episodes are absent below about 21{\textdegree}C, but smog becomes unacceptable by 32{\textdegree}C, so a rise of 3{\textdegree}C, because of the heat island effects, can be significant. Urban trees and high-albedo surfaces can offset or reverse the heat island effect, and can potentially reduce the national energy use of air conditioning by 10\% and save over $4B per year. The albedo of a city may be increased gradually if high-albedo surfaces are chosen to replace darker materials during routine maintenance of roofs and roads. Incentive programs, product labeling, and standards could promote the use of high-albedo materials for buildings and roads. Similar incentive-based programs need to be developed for urban trees.

}, keywords = {energy savings, Heat Island}, author = {Hashem Akbari and Arthur H. Rosenfeld} } @article {55875, title = {Painting the Town White{\textemdash}and Green}, journal = {MIT Technology Review}, volume = {100}, number = {2}, year = {1997}, note = {


}, pages = {52-59}, chapter = {52}, abstract = {

On a summer afternoon, central Los Angeles registers temperatures typically 5{\textdegree}F higher than the surrounding suburban and rural areas. Hot roofs and pavements, baked by the sun, warm the air blowing over them. The resulting urban "heat island" causes discomfort, hikes air-conditioning bills, and accelerates the formation of smog.

Heat islands are found in many large cities, including Chicago, Washington, and (as the Olympic athletes and fans can attest) Atlanta. The effect is particularly well recognized in cities that quote two airport temperatures on the weather report. Thus Chicago-Midway airport is typically a few degrees hotter than suburban O{\textquoteright}Hare, and the same difference applies between Washington National airport and Dulles.

}, keywords = {cool roof, Heat Island}, url = {http://www.sfrc.ufl.edu/urbanforestry/Resources/PDF\%20downloads/Rosenfeld_1997.pdf}, author = {Arthur H. Rosenfeld and Joseph J. Romm and Hashem Akbari and Alan C. Lloyd} } @techreport {55842, title = {Paving materials for heat island mitigation}, year = {1997}, note = {

Added to JabRef: 2010.04.21

}, abstract = {

This report summarizes paving materials suitable for urban streets, driveways, parking lots and walkways. The authors evaluate materials for their abilities to reflect sunlight, which will reduce their temperatures. This in turn reduces the excess air temperature of cities (the heat island effect). The report presents the compositions of the materials, their suitability for particular applications, and their approximate costs (in 1996). Both new and resurfacing are described. They conclude that, although light-colored materials may be more expensive than conventional black materials, a thin layer of light-colored pavement may produce energy savings and smog reductions whose long-term worth is greater than the extra cost.

}, keywords = {Cool Pavements, Heat Island}, doi = {10.2172/291033}, author = {Melvin Pomerantz and Hashem Akbari and Allan Chen and Haider Taha and Arthur H. Rosenfeld} } @conference {55918, title = {Policies to reduce heat islands: Magnitudes of benefits and incentives to achieve them}, booktitle = {1996 ACEEE Summer Study on Energy Efficiency in Buildings}, volume = {9}, year = {1996}, month = {05/1996}, pages = {177-186}, edition = {18}, address = {Asilomar Conference Grounds, Pacific Grove, CA}, abstract = {

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

}, keywords = {Heat Island, urban heat island}, author = {Arthur H. Rosenfeld and Joseph J. Romm and Hashem Akbari and Melvin Pomerantz and Haider Taha} } @article {55844, title = {Cool construction materials offer energy savings and help reduce smog}, journal = {ASTM Standardization News}, volume = {23}, number = {11}, year = {1995}, note = {Added to JabRef: 2010.04.28}, pages = {32-37}, keywords = {Cool Pavements, Heat Island}, url = {http://www.docstoc.com/docs/17477497/Cool-Construction-Materials-Offer-Energy-Savings-and-Help-Reduce}, author = {Hashem Akbari and Arthur H. Rosenfeld and Haider Taha} } @article {55910, title = {Mitigation of urban heat islands: materials, utility programs, updates}, journal = {Energy and Buildings}, volume = {22}, number = {3}, year = {1995}, note = {

0378-7788Added to JabRef: 2010.04.21

}, month = {08/1995}, pages = {255-265}, abstract = {

Elevated temperatures in urban "heat islands" increase cooling energy use and accelerate the formation of urban smog. Urban shade trees and light-colored surfaces can offset or reverse the heat island and conserve energy. Implementation of heat island mitigation measures is now a prominent part of President Clinton{\textquoteright}s Climate Change Action Plan to control the emissions of greenhouse gases, necessitating a better understanding of the quantitative benefits of these control measures. We present recent measurements of the air-conditioning savings for houses in Sacramento and Florida, and air temperature measurements at White Sands National Monument, New Mexico. We also discuss the results of meteorological and smog simulations for the Los Angeles Basin. The albedo of a city may be increased gradually if high-albedo surfaces are chosen to replace darker materials during routine maintenance of roofs and roads. Such high-albedo surfaces may last longer than their conventional dark counterparts. Utility-sponsored incentive programs, product labeling, and standards could promote the use of high-albedo materials for buildings and roads, and several paint manufacturers have expressed interest in participating in a "cool surfaces" labeling program. We examine the spectral reflectance of various white coatings and building materials that might be labeled in such a program.

}, keywords = {Air-conditioning electricity savings, Cool roads, cool roofs, Smog mitigation, Urban heat islands, Utility programs}, doi = {10.1016/0378-7788(95)00927-P}, author = {Arthur H. Rosenfeld and Hashem Akbari and Sarah E. Bretz and Beth L. Fishman and Dan M. Kurn and David J. Sailor and Haider Taha} } @techreport {55813, title = {Implementation of solar-reflective surfaces: materials and utility programs}, year = {1992}, note = {

Added to JabRef: 2010.04.21

}, month = {06/1992}, pages = {67}, institution = {LBNL}, address = {Berkeley, CA}, abstract = {

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

}, keywords = {Codes \& Standards, Heat Island}, doi = {10.2172/10172670}, author = {Sarah E. Bretz and Hashem Akbari and Arthur H. Rosenfeld and Haider Taha} } @techreport {55839, title = {Monitoring peak power and cooling energy savings of shade trees and white surfaces in the Sacramento Municipal Utility District (SMUD) service area: project design and preliminary results}, year = {1992}, note = {

Added to JabRef: 2010.04.21

}, month = {12/1992}, abstract = {

Urban areas in warm climates create summer heat islands of daily average intensity of 3-5 \°C, adding to discomfort and increasing air-conditioning loads. Two important factors contributing to urban heat islands are reductions in albedo (lower overall city reflectance) and loss of vegetation (less evapotranspiration). Reducing summer heat islands by planting vegetation (shade trees) and increasing surface albedos, saves cooling energy, allows down-sizing of air conditioners, lowers air-conditioning peak demand, and reduces the emission of CO2 and other pollutants from electric power plants. The focus of this multi-year project, jointly sponsored by SMUD and the California Institute for Energy Efficiency (CIEE), was to measure the direct cooling effects of trees and white surfaces (mainly roofs) in a few buildings in Sacramento. The first-year project was to design the experiment and obtain base case data. We also obtained limited post retrofit data for some sites. This report provides an overview of the project activities during the first year at six sites. The measurement period for some of the sites was limited to September and October, which are transitional cooling months in Sacramento and hence the interpretation of results only apply to this period. In one house, recoating the dark roof with a high-albedo coating rendered air conditioning unnecessary for the month of September (possible savings of up to 10 kWh per day and 2 kW of non-coincidental peak power). Savings of 50\% relative to an identical base case bungalow were achieved when a school bungalow{\textquoteright}s roof and southeast wall were coated with a high-albedo coating during the same period. DOE-2 simulations of these two buildings indicated savings of significantly lower magnitude than those measured. Given these results, the large measured savings may in part be attributed to generally lower insolation during the post-monitoring period. Our measured data for the vegetation sites do not indicate conclusive results because shade trees were small and the cooling period was almost over. We need to collect more data over a longer cooling season in order to demonstrate savings conclusively. The DOE-2 simulations of these buildings appear to indicate very small or no savings from trees. The issue of comparing DOE-2 simulations with measured data will be addressed in further detail during the second year of the project.

}, keywords = {Case Studies, Heat Island}, doi = {10.2172/10129204}, author = {Hashem Akbari and Sarah E. Bretz and James W. Hanford and Arthur H. Rosenfeld and David J. Sailor and Haider Taha and Willem Bos} } @article {55923, title = {Heat island and oasis effects of vegetative canopies: micro-meteorological field-measurements}, journal = {Theoretical and Applied Climatology}, volume = {44}, number = {2}, year = {1991}, note = {

Added to JabRef: 2010.04.21

}, pages = {123-138}, abstract = {

Dry-bulb temperature, dew-point, wind speed, and wind direction were measured in and around an isolated vegetative canopy in Davis CA from 12 to 25 October 1986. These meteorological variables were measured 1.5 m above ground along a transect of 7 weather stations set up across the canopy and the upwind/downwind open fields. These variables were averaged every 15 minutes for a period of two weeks so we could analyze their diurnal cycles as well as their spatial variability. The results indicate significant nocturnal heat islands and daytime oases within the vegetation stand, especially in clear weather. Inside the canopy within 5 m of its upwind edge, daytime temperature fell by as much as 4.5{\textdegree}C, whereas the nighttime temperature rose by 1{\textdegree}C. Deeper into the canopy and downwind, the daytime drop in temperature reached 6{\textdegree}C, and the nighttime increase reached 2{\textdegree}C. Wind speed was reduced by ~ 2 ms-1 in mild conditions and by as much as 6.7 ms-1 during cyclonic weather when open-field wind speed was in the neighborhood of 8 ms-1. Data from this project were used to construct correlations between temperature and wind speed within the canopy and their corresponding ambient, open-field values.

}, keywords = {Heat Island, vegetation}, doi = {10.1007/BF00867999}, author = {Haider Taha and Hashem Akbari and Arthur H. Rosenfeld} } @proceedings {55919, title = {Summer heat islands, urban trees, and white surfaces}, journal = {Proceedings of the 1990 ASHRAE Winter Conference}, year = {1990}, note = {

Added to JabRef: 2010.04.21

}, month = {1990/february 11}, abstract = {

Temperature trends for the last 100 years in several US cities were analyzed. Since approximately 1940 there has been a steady overall increase in urban temperatures. Summer monthly averages have increased by 0.25-1\°F per decade (approximately 1\°F for larger cities like Los Angeles and 0.25\°F for smaller cities). There is no evidence that this rise is moderating, and of course global greenhouse warming will add a comparable rise. Typical electric demand of cities increases by 1\% to 2\% of the peak for each \°F and most major cities are now approximately 5\°F warmer than they were in the early 1900s. Hence, we estimate that about 5\% to 10\% of the current urban electric demand is spent to cool buildings just to compensate for the heat island effect. For example, downtown Los Angeles is now 5\°F hotter than in 1940 and so the L.A. basin demand is up by 1500 MW, worth $150,000 per hour on a hot afternoon (the equivalent national bill is approximately$1M/hour). In major cities, smog episodes are absent below about 70\°F, but they become unacceptable by 90\°F, so a rise of 10\°F because of past and future heat island effects is very significant. There are some strategies that can alleviate the heat island effect. Computer simulations and field studies have quantified the potential of trees and lighter surfaces for reducing summer heat islands. Results indicate that the cost of saved energy and avoided CO2, through greening and whitening of urban areas, is less than 1 cents kWh and 2 cents/kg of carbon, respectively.

}, url = {http://isswprod.lbl.gov/library/view-docs/public/output/LBL-28308.pdf}, author = {Hashem Akbari and Arthur H. Rosenfeld and Haider Taha} } @article {55913, title = {Residential cooling loads and the urban heat island\—the effects of albedo}, journal = {Building and Environment}, volume = {23}, number = {4}, year = {1988}, note = {

0360-1323Added to JabRef: 2010.04.21

}, pages = {271-283}, abstract = {

The urban heat island has become the target of recent research aiming at improving urban climates and energy efficiency of cities. In the warm, mid- and low-latitude cities, the typical heat island intensity averages up to 3-5{\textdegree}C on a summer day, adding to discomfort and increasing the air-conditioning loads, whereas in some temperate and cold, high-latitude cities a 2{\textdegree}C heat island is considered as a mild asset in winter. Some of these cities have been built to retain the urban heat. The objective of our ongoing research is to identify ways to mitigate summer heat islands in hot climates, for example by increasing the urban albedo, expanding evaporative surfaces and vegetation covers, and increasing urban thermal mass. From the energy consumption point of view, simple techniques such as these can be effective in reducing air-conditioning costs by modifying and improving the urban micro- and meso-climates. In this work, we have correlated the residential cooling energy and power consumption in Sacramento, California, with the urban heat island intensity. The effects of selected strategies, such as the ones mentioned above, upon changing the urban micro-climate and reducing the heat island induced cooling loads were simulated. The main focus in this paper is placed on albedo. The simulations were performed using the DOE-2.1C building energy analysis program in conjunction with micro-climate and planetary boundary layer models that predict the effects of albedo modifications on ambient conditions and micro-climates. The simulations indicate that there exists significant potential energy and peak power savings by using such simple conservation strategies. Simulations for Sacramento indicate that whitewashing the buildings can result in direct savings of up to 14\% and 19\% on cooling peak power and electrical cooling energy, respectively. Modifying the overall urban albedo, in addition to whitewashing, can result in total savings of up to 35\% and 62\% respectively.

}, keywords = {Heat Island, urban heat island}, doi = {10.1016/0360-1323(88)90033-9}, author = {Haider Taha and Hashem Akbari and Arthur H. Rosenfeld and Yu Joe Huang} } @article {55929, title = {The potential of vegetation in reducing summer cooling loads in residential buildings}, journal = {Journal of Climate and Applied Meteorology}, volume = {26}, number = {9}, year = {1987}, note = {

Added to JabRef: 2010.04.19

}, month = {09/1987}, pages = {1103-1116}, chapter = {1103}, abstract = {

The potential of trees and other vegetation to reduce building cooling loads has been recorded in a number of studies but the meso- and microclimate changes producing such savings are not well understood. This paper describes a preliminary attempt to model the effects of landscaping on temperature, humidity, windspeed and solar gain in urban climates using information from existing agricultural and meteorological studies, with particular attention placed on quantifying the effects of plant evapotranspiration. The climate model is then used in conjunction with the DOE-2.1C building simulation program to calculate the net reductions in air-conditioning requirements due to trees and other vegetation.

Preliminary results show that an additional 25\% increase in the urban tree cover can save 40\% of the annual cooling energy use of an average house in Sacramento, and 25\% in Phoenix and Lake Charles. If this additional tree cover is located to optimize summer shading, the savings are further increased to more dun 50\% in Sacramento and 33\% in the other two cities. The calculated savings are minimal for Los Angeles because the base case cooling energy use is small (65 hours) on the assumption that window venting is used whenever possible in lieu of mechanical cooling. There are additional benefits in lowering peak power consumption, where the savings are as much as 34\% in Sacramento, 18\% in Phoenix, 22\% in Lake Charles, and 44\% in Los Angeles. Parametric analysis reveals that most of the savings can be attributed to the effects of increased plant evapotranspiration, and only 10\% to 30\% to shading. The energy penalties of reduced windspeeds are found to be small in all four locations.

The preliminary results suggest that while the conservation benefits of planting trees are appreciable at the individual house level, equally dramatic savings can be realized at the urban level through modifications of the urban climate by increasing the total amount of vegetative cover. Such a conservation strategy may be elective in counteracting the summer heat island evident in cities and may improve ambient conditions as well as reduce summertime air-conditioning requirements.

}, doi = {10.1175/1520-0450(1987)026<1103:TPOVIR>2.0.CO;2}, author = {Hashem Akbari and Yu Joe Huang and Haider Taha and Arthur H. Rosenfeld} }