ASSESSING URBAN HEAT ISLAND MITIGATION USING

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ASSESSING URBAN HEAT ISLAND MITIGATION USING GREEN ROOFS:A HARDWARE SCALE MODELING APPROACHByWilliam C. Pompeii IIA ThesisSubmitted to the Department ofGeography and Earth Science and the Graduate Councilin partial fulfillment of the requirements for the degree ofMaster of ScienceinGeoenvironmental StudiesSHIPPENSBURG UNIVERSITYShippensburg, PennsylvaniaMay, 2010

DEPARTMENT OF GEOGRAPHY AND EARTH SCIENCESHIPPENSBURG UNIVESITYUpon the recommendation of the chairperson of the department of Geography andEarth Science this thesis is hereby accepted in partial fulfillment of the requirementsfor the degree ofMaster of Sciencein Geoenvironmental StudiesThesis CommitteeCommittee ChairpersonDr. Timothy W. HawkinsDateCommittee MemberDr. Claire JantzDateCommittee MemberDr. George PomeroyDate

Table of ContentsList of FiguresiiiList of TablesvABSTRACTviChapter 1: Introduction1.1 Statement of Problem11Chapter 2: Review of Literature2.1 Background2.1.1 Urban Heat Island2.2 Green Roofs2.2.1 Origin and Types2.2.2 Benefits of Green Roofs2.3 Chicago-A Case Study City2.3.1 Green Roof Case Study-Chicago City Hall Building2.4 Methods of Study the Urban Heat Island andBenefits of Green Roof Mitigation2.4.1. Urban Heat Island Methods-Dataloggers2.4.2 Green Roof effects on Urban Heat Island MethodsDataloggers2.4.3 Green Roof Study of Chicago’s UHI2.4.4 Temperature Variation2.4.5 Hardware Models for Collecting Data333667913Chapter 3: Study Area23Chapter 4: Methods and Data4.1 Models4.2 Monitoring Equipment4.3 Data Methods4.3.1 Hourly Data4.3.2 Daily Average Data4.3.3 Statistical Analysis25252831313233Chapter 5: Results5.1 Hourly Data5.2 Daily Average Comparison343439Chapter 6: Discussion of the Results6.1 Data Comparison4646i151516181920

6.1.1 Indoor and Outdoor Hourly Average TemperatureComparison6.1.2 Relative Humidity (RH) and Dew Point HourlyAverage Comparison6.1.3 Daily Average Comparison6.1.4 Daily Average Difference Comparison6.2 Limitation of Study4649505254Chapter 7: Conclusion56References59Appendix A: Average Differences for Highest and Lowest 5%of Total Average Daily Readings Charts63ii

Lists of FiguresFigure 1:Figure 2:Urban Heat Island Profile:Late afternoon temperature profile over a city4City CanyonsReflections of solar energy off buildings4Figure 3:Chicago, Illinois10Figure 4:Sketch of Chicago’s Heat Island Profile:Late afternoon temperature profile over the City of Chicago10Figure 5:Chicago’s City Hall Green Roof13Figure 6:Study Area Location23Figure 7:Model Placement within Fenced Area24Figure 8:Downtown Hagerstown looking West, South side of Street25Figure 9:Downtown Hagerstown looking West, North side of Street25Figure 10:Downtown Hagerstown looking North, East side of Street25Figure 11:Downtown Hagerstown looking East, South side of Street25Figure 12:Green Roof Hardware Scale Model being built26Figure 13:Black Roof Hardware Scale Model being built26Figure 14:Black Roof Hardware Scale Model26Figure 15:Green Roof Hardware Scale Model26Figure 16:Green Roof plant material-Sedum Acre ‘Aureum’27Figure 17:Soil media consisting of compost, peat moss, and topsoil27Figure 18:HOBO Pro v2 (U23-001) Data Logger29Figure 19:HOBO 12 Bit (S-TMB-M017) Temperature Smart Sensor29Figure 20:HOBO Wind Sensor (S-WSA-M003)29Figure 21:HOBO Rainfall Sensor (S-RGA M002)29Figure 22:HOBO Solar Radiation Shield (M-RSA)29Figure 23:HOBO Mirco Station29Figure 24Layout of the proposed building with instrumentation30iii

Figure 25Models with monitoring equipment30Figure 26:Indoor Temperature Comparison for Green and Black Roofs35Figure 27:Outdoor Temperature Comparison for Green and Black Roofs36Figure 28:Relative Humidity Comparison for Green and Black Roofs37Figure 29:Dew Point Temp. Comparison for Green and Black Roofs38Figure 30:Rainy vs. Non-Rainy Days40Figure 31:Windy vs. Non-Windy Days41Figure 32:Warmest vs. Coolest Days42Figure 33:Monitoring Period Average Temperature and Differences45iv

List of TablesTable 1:Mean Differences in Daily Peak Temperature atthe Membrane Horizons, 2006.18Table 2:HOBO Sensors and data loggers specifications29Table 3:Average Differences for Top 5% of total Average Daily Reading 44v

ABSTRACTThis project studies the properties of green roofs and their potentialmitigating effects on the Urban Heat Island (UHI). The UHI is associated with manynegative effects such as increases in air pollution, heat related illness and mortality,water temperatures in streams, and greenhouse gas emissions. These negativeeffects will become pronounced as it is estimated that over the next century, urbantemperatures will increase by an additional 3 to 7oC.To better mitigate the effects of the current and proposed temperature trends,green initiatives, including green roofs, are being implemented. Many studies havebeen conducted concerning the UHI effect and the benefits of green roof mitigation,but studies have been limited on the overall effects or benefits green roofs couldhave on an entire city.This project used two hardware-scale models to simulate a real city to gain abetter understanding of the effects green roofs have on an entire city. One modelincorporated green roofs while the other was made of standard building materials.The model temperatures were monitored using temperature, humidity, rain, andwind sensors to assess the impact of green roofs on the overall temperature for themodel. The data were collected from June 2009 to September 2009, on an hourlybasis. The data showed that green roofs do have a beneficial effect on the UHI bylowering the temperature within the city by a couple degrees. The indoor averagetemperature data showed a 1.77oC difference between the green and black roofs.The outdoor temperature data showed a 0.24oC difference between the green andblack roofs. The differences in the indoor and outdoor temperatures show that blackroofs were warmer in both cases. Accounting for wind and rain effects on thetemperatures showed that the benefits of the green roofs were still noticeable, butnot as much as a clear and non-windy day.This study will assist real cities conducting research to understand thebenefits of green roofs on the UHI. The understanding will help these cities moveforward in possible installation of green roofs though their cities.vi

CHAPTER 1: INTRODUCTIONWith trends of increasing urban sprawl, air pollution, heat related illness andmortality, water temperatures in streams, and greenhouse gas emissions, newmitigation methods are being developed to help address these issues. One suchmethod of mitigation is green roofs. There have been multiple studies done on thebenefits of green roofs such as: the ability to assist stormwater management, actingas additional insulation for roof tops, providing outdoor areas for human as well asanimals within urban areas, ability to help clean urban air by the reduction of CO2,and the possible reduction of the urban temperature associated with the Urban HeatIsland (UHI). Of the benefits studied, there has been little documentation producedthat shows the potential benefits of green roofs on the reduction of the UHI as awhole, in relation to a city. Smaller scale research has been done to show that greenroofs can help lower surface and surrounding air temperature at that particularlocation, but what effects do green roofs have for an entire city? The hardware scalemodels used in this study will help in understanding the impact of green roofs inmitigating urban temperatures associated with the UHI. This project will help realcities understand the role of green roofs and plan for a future of developing plansthat implement and design green roofs for a whole city.1.1 Statement of ProblemThe purpose of this study was to create two hardware scale models thatwould each be equipped with the appropriate equipment to monitor for indoor and1

outdoor temperatures, relative humidity, dew point temperature, wind, and rain, toassess green roofs‟ ability to assist in mitigating the effects of the UHI. The modelswere both built to scale, one with green roofs and the other with conventionalroofing material. The models were monitored hourly from June through September2009.Hardware scale models are models based on real life features and materialsand scaled down to a workable size. The models for this study were built due to thelack of data to compare two cities, one with green roofs and one with black roofs.There currently are no cities with green roofs that have a data base of temperatureand associated data for analyzing on the scale needed to find the effects ofmitigation on the UHI. The hardware scale models were based on the City ofHagerstown, Maryland. The models were used to study the following questions: Is there a difference in indoor and outdoor temperatures between the modelcities, as well as humidity and dew point temperatures? How much of a temperature difference exists between the model cities? Do rain and wind affect the temperature difference between the cities?These questions outline the purpose and the scope of this study, which was todetermine if a city with green roofs has an overall beneficial effect of lowering theindoor and outdoor temperatures within that city compared to a city with blackroofs. The beneficial effect of lowering the city temperature then will have amitigating effect on the UHI effect.2

CHAPTER 2: REVIEW OF LITERATURE2.1 Background2.1.1 Urban Heat IslandBefore human development began disturbing natural habitats, soils andvegetation constituted part of a balanced ecosystem that managed precipitation andsolar energy effectively (Getter and Rowe 2006). These features have been replacedwith impervious areas. In the United States, it is estimated that 10% of residentialdevelopments and 71% to 95% of industrial areas and shopping centers are coveredwith impervious areas. Today, two-thirds of all impervious area is in the form ofparking lots, driveways, roads, and highways (Getter and Rowe 2006). The otherone-third consists of homes, buildings, and other non-vegetated or open soil areas.These increasing impervious areas consist of cities, towns, and suburbs. This type ofbuilding material has the ability to hold in heat during the day more effectively thanrural areas. It is documented that urbanization can have an significant affect onlocal weather and climate. Of these effects, one of the most familiar is the UHI(Streuker 2002).The UHI is the effect on a metropolitan area that causes it to be significantlywarmer than its rural surroundings (Figure 1). The thermal characteristics ofmaterials used in the urban areas (asphalt, brick, concrete, glass, etc.) differ greatlyfrom those found in the rural areas (trees, grass, water bodies, bare soil, etc.). In3

addition, the canyon structure created by tall buildings enhances warming by thesun (Figure 2).Figure 1. Late afternoon temperature profile over a city.Source: Environmental Protection gure 2. City Canyons. Reflection of solar energy offbuildings.Source: Chapman 2005.During the day, the energy is trapped by multiple reflections and absorption by thebuildings (Chapman 2005). This stored energy in urban areas is then reradiated aslong-wave radiation less efficiently than in rural areas during the night (Solecki et.al. 2005), keeping the urban areas warmer than the surrounding rural areas. Thebuildings also play a role in reducing wind speed. The combination of reducedwind speed and reduced cloud cover aid in intensifying the UHI. Heat islandintensities are largest under calm and clear weather conditions. Increasing windsmix the air and reduce the heat island effect. Increased cloud cover reducesradiative cooling at night and also reduces the heat island effect (Voogt 2004).Air temperature also is reduced through evapotranspiration which is anaturally occurring process within vegetated areas, such as lawns, fields, andwoods. Evapotranspiration occurs when plants secrete, or transpire, water vapor4

through pores in their leaves. The water draws heat as it evaporates, thus coolingthe air surrounding the leaves in the process. Trees can transpire up to 100 gallonsof water in a day. In a hot dry climate, this cooling effect is comparable to that offive air conditioners running for 20 hours per day (Gray and Finster 2008). Incontrast to the natural landscape, cities tend to have little vegetation, and due to alarge percentage of impervious surfaces there also tends to be less surface moisturein urban areas (Sailor and Dietsch 2005).Another component that adds to the creation of an UHI is from waste heat.Waste heat is emitted from a range of human activities-automobiles, air conditioningequipment, industrial facilities, and a variety of other sources, including humanmetabolism (Sailor and Dietsch 2005). Waste heat can also be considered abyproduct of urbanization, which has greatly increased over the last century.Though it may seem the study of the UHI is fairly new, it actually wasnoticed and documented as early as 1820. The first observation of the UHI was by anamateur meteorologist by the name of Luke Howard. He presented a nine-yearcomparison between temperature readings in London and in rural England in TheClimate of London (1820). He concluded that night was 3.7o warmer in the city thanthe country and the day temperature was 0.34o cooler in the city than in the country(Chapman 2006).Like Luke Howard‟s data, recent data indicate that temperature differencesare usually most noticeable in the non-daylight or night-time hours, and may exceed10oC (Chapman 2005). This increase in urban temperatures can affect public health,5

the environment, and the amount of energy that consumers use in summer cooling.Summer heat islands increase energy demand for air conditioning, raising powerplant emission of harmful pollutants. Higher temperatures also accelerate thechemical reaction that produces ground level ozone and smog (EPA 2003).