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Saving Energy and Improving Air Quality in Urban Heat Islands
Abstract
Temperatures in urban areas have increased because solar energy is more strongly absorbed by additional roofs and pavements. Downtown Los Angles is now 2.5 Kelvin warmer than in the 1930s, which requires 1–1.5 GWe more electricity to cool buildings on summer days, costing an extra $100 million∕year. Cool roof and pavement materials with increased reflectivity of 0.25 can lower surface temperatures by 10 K. If Los Angles urban temperatures could be reduced by 3 K, ozone concentrations could be reduced considerably.
... Simulations for Los Angeles indicated that thanks to the combined albedo and greening changes, the urban annual saving reached up to $71Million. Analysis of the hourly energy demand showed that cool pavement would save a peak power estimated 100 MW in L.A [87].Through the large-scale application of heat island mitigation strategies, about 20% of national cooling energy demand was estimated to be saved in America. This amounted to a saving of 40 TWh/year, worth over $4 Billion/year in cooling energy saving alone [87]. ...
... Analysis of the hourly energy demand showed that cool pavement would save a peak power estimated 100 MW in L.A [87].Through the large-scale application of heat island mitigation strategies, about 20% of national cooling energy demand was estimated to be saved in America. This amounted to a saving of 40 TWh/year, worth over $4 Billion/year in cooling energy saving alone [87]. Pomerantz et al. estimated the maximum energy saving by increasing the surface albedo of city, as presented in Table 2 [88]. ...
With the rapid expansion of urbanization around the world, the urban heat island effect embraced an enormous negative impact on megacities, including energy, environment and health conditions. Unfortunately, construc-tive geometry and human activities of megacities severely intensified the urban heat island phenomenon. Giving the contributions of pavement on the deterioration of urban heat island in megacities, this literature review synthesized the state-of-the-art potential strategies of pavement cooling technologies and applications to mitigate the urban heat island effect. Firstly, the optical-thermal balance on surface and the interior thermal behavior of pavement were comprehensively analyzed. Afterwards, this paper redefined the cool pavement technologies as the passive mitigation strategies, involved the application of reflective pavement, evaporation pavement, heat- induced pavement and phase change materials. Especially, urban canyon impact and urban design were emphasized, which tended to be neglected on the implementations of cool pavement. In addition, the solar collector technologies on the pavement were proposed to sustainably reuse solar energy, acting as active stra-tegies and renewable sources. Typically, representatives of solar collectors, including heat collection and ther-moelectric pavement, were described and investigated. Existing research results presented the promising potential of pavement cooling technologies to mitigate the urban heat island impact and renewable energy sustainability. Moreover, prospects were also summarized to show the opportunities and avenues for future study.
... Mitigasi pada LCZ Tipe E, untuk kawasan Bandar Udara Ahmad Yani dapat dilakukan greening parking lots dan vegetation around building, sedangkan untuk jalan beraspal dapat dilakukan high-albedo pavement. Peningkatan nilai albedo akan menghasilkan banyak radiasi yang dipantulkan, sebaliknya jika radiasi banyak yang diserap maka akan menghasilkan pemanasan udara dan peningkatan suhu (Akbari, 2008). ...
Urbanization in Indonesia has continued to increase starting in 2011. The increasing population impacted the conversion of agricultural land to non-agricultural land. Reduction in the proportion of green open space results in changes in the spatial pattern of the area which affects the increase in urban temperatures, thus triggering the occurrence of UHI. This study aims to determine the spatial distribution of LST and LCZ in Semarang City by using quantitative descriptive analysis. Semarang City has LST variation values between 24.72ºC to 32.56ºC. Semarang City has 13 types of LCZ, consisting of 6 LCZs based on building types and 7 LCZs based on land cover. LCZ type B is the largest LCZ which reaches 58.52 km² or 15.12% of the total area. The highest LST is LCZ type E, reaching 32.10 °C which displays rock landscapes or asphalt cover. The lowest value is LCZ type G, reaching 25.09°C, which is an open water body such as reservoirs and ponds. Climate-based urban planning can be carried out in the LCZ area which has a high temperature by observing and mitigating it through the constituent components of each LCZ.
... C. Korelasi Antara Perubahan Penutupan Lahan Dengan Kenaikan Suhu Permukaan Serta Kaitannya Dengan Urban Heat Island di Kota Pontianak Akbari (2008) menyatakan bahwa radiasi surya yang sampai di permukaan akan mengalami pemantulan dan penyerapan radiasi. Semua jenis tutupan lahan memiliki nilai albedo. ...
ABSTRAK Salah satu penyebab perubahan penutupan lahan adalah semakin bertambahnya jumlah penduduk. Sementara luas Kota Pontianak tidak bertambah, perkembangan pusat perdagangan, industri, permukiman dan pertambahan jumlah kendaraan bermotor akan mengubah pola penutupan lahan dan berbagai sarana dan prasarana fisik sebagai penunjang aktivitas penduduk kota. Perubahan fisik yang dilakukan di sisi lain menimbulkan dampak negatif diantaranya adalah meningkatnya suhu permukaan. Deteksi perubahan penutupan lahan mencakup penggunaan citra penginderaan jauh di wilayah tertentu dan dari data tersebut perubahan penutupan lahan serta peningkatan suhu permukaan untuk setiap waktu dapat dipetakan dan dibandingkan.Tujuan dari penelitian ini adalah untuk mengetahui korelasi antara perubahan penutupan lahan dengan perubahan sebaran suhu permukaan, dan menganalisis kaitannya dengan urban heat island. Penelitian ini menerapkan teknologi penginderaan jauh dan Sistem Informasi Geografis. Data yang tersedia dapat berupa piktoral maupun digital kemudian diolah untuk mendapatkan informasi yang diperlukan. Informasi yang diperoleh dapat digabungkan dengan data-data yang mendukung ke dalam satu Sistem Informasi Geografis. Berdasarkan hasil interpretasi dan analisis citra landsat 5 TM pada tahun 2000 dan citra landsat 7 ETM tahun 2010 didapatkan bahwa terjadi perubahan penutupan lahan dari lahan yang bervegetasi menjadi lahan yang tidak bervegetasi, Perubahan penutupan lahan tersebut berpengaruh terhadap peningkatan suhu permukaan dan penurunan kelembaban. Distribusi suhu permukaan di Kota Pontianak pada tahun 2000 berdasarkan estimasi band 6 pada citra landsat 5 TM mempunyai nilai suhu antara <20,00 0C – 31,99 0C. Nilai suhu dengan luasan distribusi terbesar adalah suhu dengan rentang 24,00 0C – 24,99 0C yang terdistribusi di seluruh wilayah Kota Pontianak. Sedangkan distribusi suhu permukaan di Kota Pontianak pada tahun 2010 berdasarkan band 6 pada citra landsat 7 ETM mempunyai nilai suhu antara 20,00 0C - ≥ 34,00 0C. Nilai suhu dengan luasan distribusi terbesar adalah suhu ≥34,00 0C yang terdistribusi di seluruh wilayah Kota Pontianak. Nilai suhu ini cukup tinggi sehingga memunculkan fenomena Urban Heat Island. Kata Kunci : penginderaan jauh, suhu permukaan, urban heat island.
... Mohan et al. (2012) explain that UHI occurs in urban areas with infrastructures and commercial centres. According to Akbari (2008), an urban centre's high air temperature is due to the strong absorption of radiation by roofs and pavements. High air temperature occurs, also, during the summer months in large international cities such as London, Los Angeles, China, and in large Indonesian cities such as DKI Jakarta, Surabaya, Semarang, and Bandung. ...
Urban Heat Island (UHI) is a phenomenon exhibited by many worldwide cities. Cities, which exhibit UHI, possess higher air temperature as compared with air temperature in the surrounding areas. However, existing UHI profiles are those occurring in subtropical areas which are, of course, very much different from those in tropical cities. Therefore, the objectives of this study are to describe the UHI’s profile and the role of tree vegetation in controlling and reducing air temperature in a tropical region’s urban areas and, particularly, in DKI Jakarta. In this study, we carried out a spatial analysis of land cover and the distribution of air temperature. In this regard, we based our analysis of the potency of tree vegetation in reducing air temperature in UHI’s profile on the distribution of air temperature in various types of land cover which extended from north to south and from east to west. The ranges of air temperature in land cover in the form of built-up areas were 29.2-39.5 ⁰C, non-tree vegetation 28.6-35.6 ⁰C, and tree vegetation 27.0-35.7 ⁰C. Accordingly, tree vegetation has the highest potential to reduce air temperature and to overcome the phenomenon of UHI.
... Hal ini harus diantisipasi karena dapat menyebabkan peningkatan suhu udara dan penurunan kenyamanan. Akbari (2008) menyatakan bahwa radiasi surya yang sampai per mukaan akan mengalami pemantulan dan penyerapan radiasi. Semua jenis tutupan lahan memiliki nilai albedo. ...
Bandung Regency is experiencing increased of air temperature, particularly in the urban area. High air temperature in urban areas is caused by increasing built-up areas and declining green open space. Green open space should be built to lower air temperature and to create a comfortable micro climate. Green open space should be developed at locations with high air temperature to reach its efficacy. This research used spatial analysis to generate air temperature distribution map. The map was used as the basis in developing green open space. The map showed that green open spaces should be developed at several sub-districts, namely Margahayu, Margaasih, Dayeuhkolot, Baleendah, Bojongsoang, Rancaekek, Cileunyi, Pameungpeuk, and Majalaya sub-districts.
... Based on the Rushayati et al. [6] research which uses dynamic system models, it is known that the percentage of high temperatures are in the area I which is the northern part of Bandung Regency region dominated by built area. Similarly, Akbari [7] research in the United States, shows that during the day in summer, the air temperature in the city could reach 2.5 Kelvin (K) as in urban land cover is dominated by built area and the streets, compared with the surrounding area. ...
In most developing countries, capital city has been facing environmental problem such as urbanization, in which infrastructure development has been very fast that replaced open space area. The objectives of the research were to analysis land use/land cover and surface temperature changes of Jakarta for the period of 2000 - 2012. Result showed that during 12 years, 49.7% of green open space was converted into other land uses, especially build-up areas. This caused the increase of surface temperature and created Urban Heat Island (UHI) phenomenon in Jakarta. Almost all of Jakarta area has high surface temperature, however, some areas with green open space indicated has lower surface temperature. In comparison to build-up areas, surface temperature of green open space was lower of about 3.2°C. This fact revealed the effectiveness of urban forest in lowering surface temperature. Other mitigation action of UHI is an idea to reduce air stagnation of air masses by developing corridors that can throw and dilute air pollutants into the coastal and sea area.
... Different factors impact household energy consumption to varying degrees. For example, factors such as whether the household comprises only one person or a family of several people; factors determining whether a building is green, such as the building design, building exterior [48], ventilation design [49,50], green roofs [51,52], and the facilities and materials used; and factors regarding the different daily energy consumption or conservation habits of each member of a household, such as using natural light, energy-conserving lamps [53][54][55], ventilation equipment [56], air conditioning [57], heating systems [58], solar energy [59], water-or electricity-conserving equipment, the type and number of vehicles, and the planting of green plants. Because of the varying impact, we first used Delphi expert assistance to select and archive criteria for this study, and confirmed the AHP hierarchical framework for each criterion, as shown in Figure 4. ...
Industry and economy are developed to satisfy the needs and material desires of people. In addition to making high greenhouse gas emissions the responsibility of industry, individuals and families should also be held responsible for the production of greenhouse gas emissions. In this study, we applied the Delphi method, the analytical hierarchy process, utility theory, and fuzzy logic theory to establish an energy conservation assessment model for households. We also emphasize that subsidy policy makers should consider the social responsibility of households and individuals, as well as sustainability of energy conservation.
For residential buildings, improving the energy efficiency of buildings helps to reduce energy consumption, as well as to benefit households through reduced energy-related costs. However, very little research has focused on understanding how energy efficiency investments are made, particularly across different socioeconomic groups. This research thus analyzes the energy efficiency investments of households in lower and higher income regions using frequency, correlation, and principal component analysis. Data used are for residential buildings in Cedar Falls, Iowa, including energy efficiency investment data for a utility rebate program, assessors data, and U.S. Census data. Among the technologies studied, air conditioners and furnaces (HVAC) were the most expensive, yet they were among the most common types of investments. Comparing efficiency investments in lower and higher income regions, overall, the higher income tract prioritized efficient lighting and HVAC systems with less insulation investments, while the lower income tract invested most in HVAC systems andinsulation. Results also suggest that for housing units in lower income regions invested more in high efficiency HVAC systems, as compared to the higher income regions. These findings highlight the importance of incentive programs that are tailored to needs and priorities of lower-income and higher-income housing units and the variations in investment behavior.
Global population growth and rapid urbanisation have resulted in the rapid transformation of natural topographies that are now dominated by engineering materials and structures. It is widely recognised that economic development is largely attributable to infrastructure development. However, this development has come about with adverse consequences. In this paper, the effects of surface characteristics, climatic parameters and material properties on the thermal environment and near-surface heat islands in urban areas were investigated. An experiment was conducted in which simple concrete structures with varying surface characteristics were constructed and instrumented. The effect of solar absorptivity was clearly visible, with structures surfaced with low absorptivity materials exhibiting lower surface and effective temperatures. Following the experimental programme, numerical simulations of the simple concrete structures were performed using finite element modelling. The analyses showed that the thermal environment of concrete structures is sensitive to changes in solar absorptivity, climatic parameters, cross-sectional dimensions, and material properties. It was found that the use of low absorptivity or highly reflective surfacing and the selection of appropriate dimensions can be used to significantly reduce the temperatures of concrete infrastructure, including buildings and pavements, thereby providing an evidential basis for the use of low absorptivity surfacing materials to mitigate climate change in Southern Africa.
p> Increasing temperatures and changes in global weather are currently affecting all countries, including Indonesia. This problem is what we can call global warming. The city of Surabaya in particular experiences this problem where there is a shift in time related to the dry season and the rainy season. The formation of green open spaces is important in a city to reduce the impact that is imposed globally. The main target expected is to take part in reducing the temperature in the city of Surabaya so that the ecological balance in it is maintained even though it is small or limited to existing sites. This is based on regional regulations regarding the proportion of green open space that must be presented according to data from Bappeko Surabaya. The method in research using literature studies, observational studies, and study designs in a form tailored to the analysis. The result of this research is to add the availability and utilization of green open space in the form of vertical vegetation in the UKDC campus building to provide additional green open space for both the UKDC campus and the city of Surabaya. So in other words, the new UKDC campus building can provide additional green open space to achieve the availability of green open space on private land. </p
Many cities globally are seeking strategies to counter the consequences of both a hotter and drier climate. While urban heat mitigation strategies have been shown to have beneficial effects on health, energy consumption, and greenhouse gas emissions, their implications for water conservation have not been widely examined. Here we use a suite of satellite-supported regional climate simulations in California to show that broad implementation of cool roofs, a heat mitigation strategy, not only results in significant cooling, but can also meaningfully decrease outdoor water consumption by reducing evaporative and irrigation water demands. Irrigation water consumption across the major metropolitan areas is reduced by up to 9% and irrigation water savings per capita range from 1.8 to 15.4 gallons per day across 18 counties examined. Total water savings are found to be the highest in Los Angeles county, reaching about 83 million gallons per day. Cool roofs are a valuable solution for addressing the adaptation and mitigation challenges faced by multiple sectors in California.
The chapter gives some thoughts gained through the analyses conducted on some Italian urban plans and considering the overview about landscape planning in the European context. It thus makes explicit the initial assumptions through which moves the whole job: what has changed in the current way of doing urban planning and what are the new methods of intervention? Instead what has been learned and what left out in the ordinary instrumentation, in terms of procedures, tools, approaches? This chapter provides a more synthetic approach, in which the emerging ideas can contribute to outline a set of theoretical and practical elements that can be put in place today to the landscape at the local level.
The purpose of this study, supported by The Scientific and Technological Research Council of Turkey (TUBITAK), was to evaluate the views of students who participated in 'Sakarya Science and Art Centre Nature Education Programme' and their parents. The data were collected by using mixed methods. The study population consisted of 120 3rd-8th grade students of 'Sakarya Science and Art Centre'. Data obtained from two different questionnaires; named as 'Parent Views of Nature Education' and 'Student Views of Nature Education'. Results indicated that students had mainly positive views about the attitudes of instructors and assistants, and the instruction. Parents found that nature education was very valuable for their children as they understood the nature better, acquired knowledge through experience, got a chance to socialize with each other and spent a meaningful summer time.
The world is facing an increasing number of natural disasters caused by more extreme weather conditions. As each country is becoming more aware of the seriousness of global warming, the attempt is to alleviate the problem by focusing on the development of alternative energies and Research and Development of energy-saving facilities and technologies. The temperature in summer around the world has been increasing noticeably each year, especially in tropical and subtropical areas. Higher temperatures lead to more frequent use of air-conditioning (AC) systems in households, malls, offices and many other places, which consequently result in a significant increase in the power consumption. In particular, air-conditioning systems in buildings, either central AC systems or local AC systems, account for a high percentage of the total power consumption of the buildings. The document 'Encouragement Policy for the Private Sector to Participate in Green Building Demonstration Projects' published by the Ministry of the Interior in Taiwan includes the improvement of air-conditioning systems as an important part of its encouragement for green buildings. To explore how to improve the energy efficiency of office air-conditioning systems in Taiwan, the Delphi method, analytical hierarchy process (AHP) and the fuzzy logic theory were used in this study to build a multi-criteria decision making (MCDM) model. Through the Delphi process in this study, three key influence factors (air-conditioning system, interior planning, building materials) of the energy efficiency of office AC systems were found. In addition, two cases were analysed in this study to illustrate the quantitative analysis functions of the model. This model is expected to serve as the guidelines for governing authorities when making decisions about providing subsidies for better energy conservation of AC systems.
Extreme global climate change has recently become increasingly apparent, leading to extremely severe disasters. Because annual summer and winter temperatures worldwide have drastically increased and decreased, respectively. These extreme temperature differences have aggravated global energy consumption. In tropical and subtropical regions, using air conditioning inside buildings resulted in increased power consumption. Therefore, the Executive Yuan (Taiwan) has promoted a policy that advocates energy conservation for buildings and greenhouse gas reduction, wherein the building energy efficiency upgrade program for reducing power consumption in buildings is one of the crucial contents outlined in the policy. In an office, the purpose of air conditioning is to reduce indoor thermal load as well as to maintain indoor environmental quality and people comfort. Therefore, in addition to reduce electricity consumption, indoor environmental comfort should be improved to enhance the working efficiency of office workers and the perception of visitors. The costs of energy conservation facilities should be considered in energy conservation effectiveness. This study focused on environmental comfort in offices and applied an analytic hierarchy process with multi-criteria decision-making characteristics and fuzzy logic theory with a quantitative assessment function to establish a multi-criteria decision-making (MCDM) model for assessing offices. This study adopted environmental comfort in offices, electricity consumption, and equipment cost as the primary assessment factors and then applied two cases to explain the practical function of the MCDM model. The model established can serve as a reference for designers and government agencies in assessing environmental comfort in offices.
Night ventilation has been applied successfully to many passively-cooled or low-energy office buildings. This paper analyses the thermal comfort achievable in office buildings in Spain according to European standard EN 15251:2007. Furthermore, the comfort level is evaluated using the Degree Hours (DH) criteria and the maximum indoor temperature. Considering the high interest of architects and engineers in the evaluation of optimal comfort condition as a function of building typology (8 typologies), glazing ratio (30% and 60%) and climate (12 different Climate Zones), a total of 192 different study cases were simulated. For every case, an optimal air change per hour (ac/h) that can range from 1 to 50 ac/h was then determined. The research shows that passive night ventilation should be considered as an effective strategy for all Spanish Climates to reduce cooling demand in buildings with high daily internal gains (i.e. office buildings), improving comfort conditions and flattening peak temperatures.
Die Fassadentemperatur selbst hat in Gebäuden mit einer bauphysikalisch guten Gebäudehülle nur einen geringfügigen Einfluss auf den Transmissionswärmestrom durch die Außenwand. Der Kühlbedarf kann aber in Gebäuden mit Fensterlüftung oder Fassadenlüftungsgeräten deutlich höher ausfallen als in der Planung prognostiziert, weil die Lufttemperatur in der Grenzschicht vor der Fassade um mehrere Kelvin höher liegt als die ungestörte Außenlufttemperatur. Monatsbilanzverfahren oder Programme zur thermischen Gebäudesimulation können in der Regel nur eine Außentemperatur für die Berechnung des Wärmeübergangs an der Gebäudehülle und des Lüftungswärmestroms verwenden. Eine Möglichkeit, den Grenzschichteffekt zu berücksichtigen, ist die Anpassung der ungestörten Außenlufttemperatur mit Hilfe eines einfachen Modells.
A simplified model to predict the temperature of the boundary layer of façades. The cooling energy demand of low-energy buildings with a high-quality building envelope is rather affected by solar and internal heat gains and the ventilation than by the heat transmission through the building envelope. Hence, the surface temperature of the façade has a small influence on the cooling energy demand. However, the higher air temperature in the boundary layer at the façade may increase the cooling load in buildings with window opening or façade integrated air-handling units. Neither monthly energy calculation programs nor building simulation programs use different temperatures for the ambient air to calculate the heat transfer through the façade and for the boundary layer to calculate the heat flux by ventilation. This article presents a methodology how to adapt the ambient air temperature to the temperature of the boundary layer.
This paper summarizes our efforts to calculate the potential annual energy savings, peak power avoidance and annual CO2 reduction from heat island reduction (HIR) measures (i.e., shade trees, reflective roofs, reflective pavements and urban vegetation) in three cities: Baton Rouge, Sacramento and Salt Lake City. We focused on three building types that offer most savings potential: single-family residence, office and retail store; and characterized each by old or new construction and with a gas furnace or electric heat pump. We simulated the impact of HIR measures on building cooling and heating energy use and peak power demand using the DOE-2.1E model. Our simulations included the impact of (1) strategically-placed shade trees near buildings, (2) use of high-albedo roofing material on building, (3) combined measures 1 and 2, (4) cooling of ambient air resulting from implementation of HIR measures, and (5) combined measures 1, 2 and 4. The results show that in Baton Rouge potential annual energy savings of $15M could be realized by rate-payers from the implementation of HIR measures, additionally, peak power avoidance is estimated at 133 MW and the reduction in annual carbon at 41 kt. In Sacramento the potential benefits are estimated at $26M, 486 MW and 92 kt, and in Salt Lake City, $4M, 85 MW and 20 kt.
An assessment of health effects due to ozone and particulate matter (PM10) suggests that each of the 12 million residents
of the South Coast Air Basin of California experiences ozone-related symptoms on an average of up to 17 days each year and
faces an increased risk of death in any year of 1/10,000 as a result of elevated PM10 exposure. The estimated annual economic
value of avoiding these effects is nearly $10 billion. Attaining air pollution standards may save 1600 lives a year in the
region.
This 14th edition of State of the World, takes a realistic look at progress toward sustainable development since the 1992 Riio Earth Summit. Some gains have been made in sustainability planning and in implementing the international convention to protect the stratopheric ozone layer, but on balance the planet's broad trends of environmental and resource degradation persist. The authors describe the contracting base of grainland and climate change's threat to disrupt the ecological foundations of our global economy. They cite vividly, in the cases of Chiapas and Rwanda, why pervasive resource loss is at the root of the 'new world disorder.' The report argues that if these trends continue unabated the pressure on the earth's natural limits will undermine food security - now already evident in the decline of marine fisheries and the shrinking grain harvest per person. Indeed, food scarcity may be the first major economic manifestation of our environmentally unsustainable global economy. To reverse this situation the report calls for us to take urgent measures to build an environmentally sustainable economy, slow population growth, value the nonmonetary services nature provides, adopt the best of simpler and less consumptive lifestyles, and abandon tax-payer subsidies that encourage the consumption of natural resources such as water and fossil fuels.
This paper reports on the first results from tests on a reflective roofing system on a commercial building in Florida. The building is a elementary school with a sloped, modified bitumen roof. Air-conditioning power was measured in a base configuration prior to the roofing system being changed to a white color. Roof, decking, and plenum air temperatures were strongly affected by the change to a white roof system. The school, which was monitored for a full year in both the pre- and post-condition, saw the measured annual chiller electric power reduced by 10%, or 13,000 kWh/yr. Cooling-load reductions during the utility summer peak were substantially greater, more than 30% during the afternoon hours.
Slurry seal is defined as a mixture of continuously graded fine aggregate, mineral filler, emulsified asphalt, and water properly proportioned, mixed, and spread as a surface treatment. When applied, the cured slurry seal should have a homogeneous appearance, fill cracks, adhere firmly to the sureface, and provide a weather proof, high-friction seal. This paper provides a vast information about slurry seal - including its gradation, use, effectiveness, properties, etc.
A series of experiments in Florida residences have measured the impact on space cooling of increasing roof solar reflectance. In tests on 11 homes with the roof color changed mid summer, the average cooling energy use was reduced by 19%. Measurements and infrared thermography showed that a significant part of the savings were due to interactions when the duct system is located in the attic space. An improved residential attic and duct simulation model, taking these experimental results into account, has been implemented in the DOE-2.1E building energy simulation program. The model was then used to estimate the impact of reflective roofing in 14 different climate locations around the United States.
In this 12th of a series on urban forestry, homeowners and community planners are offered practical guidance in selection of landscape plantings which will significantly reduce wind velocity and heat loss from homes in winter and reduce energy costs for air conditioning in summer.
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{degrees}F per decade ({approximately}1{degrees}F for larger cities like Los Angeles and 0.25{degree}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 {degrees}F and most major cities are now {approximately}5{degrees}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{degrees}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{degrees}F, but they become unacceptable by 90{degrees}F, so a rise of 10{degrees}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 CO{sub 2}, through greening and whitening of urban areas, is less than 1{cents}kWh and 2{cents}/kg of carbon, respectively. 13 refs., 6 figs., 6 tabs.
Roofing materials which are highly reflective to sunlight are currently being developed. Reflective roofing is an effective summertime energy saver in warm and sunny climates. It has been demonstrated to save up to 40% of the energy needed to cool a building during the summer months. Buildings without air conditioning can reduce their indoor temperatures and improve occupant comfort during the summer if highly reflective roofing materials are used. But there are questions about the tradeoff between summer energy savings and extra wintertime energy use due to reduced heat collection by the roof. These questions are being answered by simulating buildings in various climates using the DOE-2 program (version 2.1E). Unfortunately, DOE-2 does not accurately model radiative, convective and conductive processes in the roof-attic. Radiative heat transfer from the underside of a reflective roof is much smaller than that of a roof which absorbs heat from sunlight, and must be accounted for in the building energy model. Convection correlations for the attic and the roof surface must be fine tuned. An equation to model the insulation`s conductivity dependence on temperature must also be added. A function was written to incorporate the attic heat transfer processes into the DOE-2 building energy simulation. This function adds radiative, convective and conductive equations to the energy balance of the roof. Results of the enhanced DOE-2 model were compared to measured data collected from a school bungalow in a Sacramento Municipal Utility District monitoring project, with particular attention paid to the year-round energy effects.
The US Department of Energy (DOE) has funded several research projects, including this study, to assess the effects of site design on building space conditioning energy use. An important strategy being investigated is the use of vegetation for shading, wind control, and temperature modification. The study described in this report has been conducted concurrently with a closely related research project at the Northeastern Forest Experiment Station of the USDA Forest Service in Pennsylvania. The objective of that project is to measure wind-speed reductions and solar obstructions caused by trees around representative houses within typical neighborhoods and to develop an empirical model for estimating these effects based on the physical characteristics of different neighborhoods (Heisler 1989). The objective of this work is to combine the results of the on-site microclimate measurements from the 1989 Heisler study with work in building energy simulation to calculate the energy impacts of the observed microclimatic changes due to trees.
Under clear skies, a mid-sized sugar maple tree (Acer saccharum Marsh.) reduced irradiance in its shade on a south-facing wall by about 80% when in leaf, and by nearly 40% when leafless. Reductions by a similar-sized London plane (Platanus acerifolia W.) were generally slightly smaller. The percentage reductions varied with the fraction (DR) of diffuse radiation, and could be approximated by regressions with DR2 as the independent variable.The significance of the irradiance reductions for building radiation climate was tested by using physical models of representative tree crowns (similar to sugar maple) and a representative house to evaluate shadow patterns, along with a mathematical model of average hourly solar radiation for an average day of each month. For a mid-sized tree with a 2-m clear bole located south of the house in a cloudy climate, the ratio of desirable insolation reductions during the cooling season to undesirable insolation reductions during the heating season was a low 0.74; whereas, with the same tree on the west, the ratio was a much more beneficial 4.6. In a sunny climate, the ratios were 0.55 and 3.3 for the tree on the south and west, respectively. A taller tree with a longer clear bole on the south produced more favorable ratios of cooling season to heating season insolation reductions than the tree with the short clear bole on the south.
The large scale implementation of high-albedo building materials and urban surfaces and the reforestation of low vegetation urban areas are being encouraged as energy-saving measures. These strategies will result in modification of the physical properties of millions of buildings (e.g., roof reflectance) and their microclimates (e.g., shading, wind, and evapotranspiration effects of trees). This paper is about the atmospheric impacts of regional scale changes in building properties, paved-surface characteristics, and their microclimates. It discusses the possible meteorological and ozone air quality impacts of increases in surface albedo and urban trees in California's South Coast Air Basin (SoCAB). The photochemical model simulations of a late August period indicate that implementing high-albedo materials in the SoCAB would have a net effect of reducing ozone concentrations. Domain-wide population-weighted exceedance exposure to ozone above the California Ambient Air Quality Standard would be decreased by up to 12% during peak afternoon hours. With respect to the National Standard, exceedance exposure would be reduced by up to 17%. The simulations also indicate that the net effect of increased urban vegetation is a decrease in ozone concentrations if the additional vegetation (trees) are low emitters of biogenic hydrocarbons. With respect to the California standard, domain-wide population-weighted exceedance exposure to ozone above this threshold would be decreased by up to 14% during peak afternoon hours. With respect to the National Standard, the reduction would be up to 22%. In terms of total daytime exposure, these strategies can decrease exceedance exposure by up to 12% with respect to the California Standard and up to 20% with respect to the National Standard. Comparing the simulated air quality impacts of increased albedo and vegetation cover with the impacts of other strategies reveals that they are of the same order of magnitude. For instance, the simulations for this episode, using updated 1987 emission inventories for the SoCAB, indicate that the air quality benefits of albedo and vegetation increase strategies are comparable to those of converting at least 50% of the mobile sources operating in 1987 in the SoCAB to zero emitting vehicles (these findings are for ozone reductions only; removing or converting motor vehicles has several other advantages as well). At this time, this comparison is preliminary as there are uncertainties in the modeling system and emission inventories. In particular, mobile source emissions may be underestimated by as much as two-fold. These findings will be updated when other episodes are modeled and more representative emission inventories become available.
Large-scale tree planting programs have been proposed, and are being implemented, as a means of reducing energy demand, mitigating urban heat islands, and improving air quality. However, many species of trees emit highly photochemically reactive hydrocarbons and the rates of such emissions can vary by four orders of magnitude, depending upon the tree species. Thus, planting of high-emitting trees species on a massive scale has the potential to adversely affect air quality rather than leading to improvement. However, the selection of low-emitting trees is difficult because emission rates have been experimentally determined for only a limited number of species. The present study describes a methodology for assigning biogenic emission rates based on taxonomic relationships. Using this methodology, direct emission measurements from 124 tree and shrub species found in the California South Coast Air Basin (SoCAB) are used to assign emission rates to 253 other species found in the SoCAB but for which there are no measured emission rates. The combined listing of 377 species is ranked according to total (isoprene and monoterpenes) biogenic emission rate on an hourly basis. Although the ranking of trees developed here is specific to Southern California, the methodology described can be applied to other geographic areas to assist in the planting of low-emitting urban forests.