Black Roof Research Articles

Measuring the Effect of Vegetated Roofs on the Performance of Photovoltaic Panels in a Combined System

Experiments were conducted in summer using two identical photovoltaic (PV) panels at two heights using three roofing types: white, black, and green (vegetated). For experiments at an 18 cm height, the mean power output of the PV-green roof system was 1.2% and 0.8% higher than the PV-black and PV-white roofs, respectively. At a 24 cm height, the benefit of the green roof was slightly diminished with power output for the PV above a green roof being 1.0% and 0.7% higher than the black and white roof experiments, respectively. These results were consistent with measured variations in mean panel surface temperatures; the green roof systems were generally cooler by 1.5–3 °C. A unique aspect of this research is the investigation into the effect of vegetation on the convective cooling of the PV panels. Panel heat transfer coefficients for the PV-green roof were 10–20% higher than for the white and black roof configurations, suggesting a mixing benefit associated with the roughness of the plant canopy. While the best PV performance was obtained by locating PV above a green roof, the relative benefits diminish with distance between the PV and the roof.

Cool black roof impacts into the cooling and heating load demand of a residential building in various climates

This paper describes the impacts of different cool black paints on cooling and heating load demand of a residential building in different climates. Cool paints with dark appearance and high reflectance in near infrared portion of sunlight are of great interest by the owners of homes to satisfy both desired visual and energy saving aspects. Three copper oxide (CuO) powders, different in pigment size, and a chromium–iron oxide (Cr2O3–Fe2O3) powder, as a commercial cool black pigment, are used to make the black paints. The samples are made on both conventional black and cool white base coats. The spectral reflectance of all samples in solar range (0.3–2.5µm) and infrared region (2.5–25µm) is measured. The thermal emittance of the samples is estimated using the spectral reflectance measurement and validated by the measurement of infrared camera. A typical residential single-stage single-family home in three different climates of Iran is considered and the impacts of applying the different black paints on cooling and heating load demand are discussed. The results show that the peak and annual cooling load demand decrease by 0.4–1.4kW (6–13%) and 405–2202kWh (6–14%), respectively, depends on the type of pigmented coating and climate conditions.

Green roofs energy performance in Mediterranean climate

This paper quantifies green roofs energy savings which is a challenging topic, namely in Mediterranean climate with distinct heating and cooling seasons. The thermal behavior of a green roof case study in Lisbon, Portugal, was assessed through an experimental campaign during heating and cooling periods of the year of 2013. These experimental results were then used to calibrate a building energy simulation in EnergyPlus. After validation, the numerical model was used to compare the energy performance of intensive, semi-intensive and extensive green roofs. The three green roof types lead to similar heating energy needs but extensive green roof solution shows higher cooling energy needs than semi-intensive and intensive ones, of 2.8 and 5.9 times more, respectively. Furthermore, the performance of each type of green roof and different insulation properties was compared to traditional roof solutions. With no thermal insulation, extensive green roofs require 20% less energy use than black roofs and show a similar annual behavior than white roofs. Semi-intensive and intensive green roofs energy use is 60–70% and 45–60% lower than black and white roofs, respectively. Well insulated roofs do not take full advantage of evapotranspiration cooling effects, which is particularly noticeable when comparing with high reflective white roofs.

Photovoltaic Energy Variations Due to Roofing Choice

Roofs comprise 20-25% of the total urban surface area and with different roofing technologies and photovoltaic, present an opportunity for sustainable building designs. The operation temperature of photovoltaic (PV) modules has a significant impact on the conversion efficiency and output energy of the PV system. This research investigated the thermal interactions between the building envelope and PV panels by examining the PV panel temperature differences for those installed over a green roof (PV-green) and those installed over a black roof (PV-black). A LEED platinum certified educational building with roof mounted PV panels was used as a case study for the experimental phase of the study. PV panels over the green roof consistently recorded lower temperatures than PV panels over the black roof. Therefore, the PV panels over the green roof had more energy output compared to the PV panels over the black roof.

The joint influence of albedo and insulation on roof performance: An observational study

This article focuses on understanding the temperature and heat flux fields in building roofs, and how they are modulated by the interacting influences of albedo and insulation at annual, seasonal and diurnal scales. High precision heat flux plates and thermocouples were installed over multiple rooftops of varying insulation thickness and albedo in the Northeastern United States to monitor the temperature and the heat flux into and out of the roof structures for a whole year. Our analysis shows that while membrane reflectivity (albedo) plays a dominant role in reducing the heat conducted inward through the roof structures during the warmer months, insulation thickness becomes the main roof attribute in preventing heat loss from the buildings during colder months. On a diurnal scale, the thermal state of the white roof structures fluctuated little compared to black roof structures; membrane temperature over white roofs ranged between 10°C and 45°C during summer months compared to black membranes that ranged between 10°C and 80°C. Insulation thickness, apart from reducing the heat conducted through the roof structure, also delayed the transfer of heat, owing to the thermal inertia of the insulation layer. This has important implications for determining the peak heating and cooling times.

New York City Panel on Climate Change 2015 Report. Chapter 6: Indicators and monitoring.

William Solecki,1,a Cynthia Rosenzweig,2,a Reginald Blake,3,a Alex de Sherbinin,4 Tom Matte,5 Fred Moshary,6 Bernice Rosenzweig,7 Mark Arend,6 Stuart Gaffin,8 Elie Bou-Zeid,9 Keith Rule,10 Geraldine Sweeny,11 and Wendy Dessy11 1City University of New York, CUNY Institute for Sustainable Cities, New York, NY. 2Climate Impacts Group, NASA Goddard Institute for Space Studies, Center for Climate Systems Research, Columbia University Earth Institute, New York, NY. 3Physics Department, New York City College of Technology, CUNY, Brooklyn, NY; Climate Impacts Group, NASA Goddard Institute for Space Studies. 4 Center for International Earth Science Information Network (CIESIN), Columbia University, Palisades, NY. 5New York City Department of Health and Mental Hygiene, New York, NY. 6NOAA CREST, City College of New York, CUNY, New York, NY. 7CUNY Environmental Crossroads, City College of New York, CUNY, New York, NY. 8Center for Climate Systems Research, Columbia University Earth Institute, New York, NY. 9Department of Civil & Environmental Engineering, Princeton University, Princeton, NJ. 10Princeton Plasma Physics Laboratory, Princeton, NJ. 11New York City Mayor’s Office of Operation, New York, NY

Heat mitigation strategies in winter and summer: Field measurements in temperate climates

Natural elements such as vegetation and water bodies may help reduce heat in urban spaces in summer or in hot climates. This effect, however, has rarely been studied during cold seasons. This paper briefly studies the effect of vegetation and water in summer and more comprehensively in winter. Both studies are done in courtyards on two university campuses in temperate climates. A scale model experiment with similar materials supports the previous studies. The summer study is done in Portland (OR), USA, and the winter study (along with the scale model) in Delft, the Netherlands. The summer study shows that a green courtyard at most has a 4.7 °C lower air temperature in the afternoon in comparison with a bare one. The winter study indicates that the air temperature above a green roof is higher than above a white gravel roof. It also shows that, although a ‘black’ courtyard has higher air temperatures for a few hours on sunny winter days, a courtyard with a water pond and with high amounts of thermal mass on the ground has a warmer and more constant air temperature in general. Both the summer and winter studies show that parks in cities have a lower and more constant air temperature compared to suburbs, both in summer and winter. The scale model also demonstrates that although grass has a lower albedo than the used gravel, it can provide a cooler environment in comparison with gravels and black roof.1

SYSTEM FOR MEASURING RODENTS' VISUAL FUNCTION: DESIGN AND IMPLEMENTATION

The aim of the work presented in this paper is the design, manufacturing and assembling of a system able to measure rodents' (mice and rats) visual function and to study the evolution of degenerative retina diseases. Measurement of contrast sensitivity and visual acuity is essential to design new drugs and understand mechanisms of visual development to evaluate treatments' effectiveness. Classical methods to study visual perception of animals such as electroretinogram (ERG) or histological analysis are not supplying enough information because connection between eyes and brain is not considered. The system proposed in this work consists of four screens forming a cube with black methacrylate plastic floor and roof. Screens display visual stimulus and the rodent's behaviour (placed over a platform in the middle of the cube) is analized to determine its visual acuity and contrast sensitivity. These visual stimuli are generated from a FPGA board designed in this project. This board has a USB link with a computer and it controls screens via VGA signals. Rodents' behaviour is analized using computer vision algorithms under OpenCV libraries. To test the system, more than 30 mice (C57 and RD10 type) have been used to validate the hardware, the software, the procedure and protocol.

Economic comparison of white, green, and black flat roofs in the United States

White and “green” (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 “natural” 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.

Geotechnical Properties and Chemical Composition of Black Roof Shale as an Industrial Raw Material

Cretaceous pyritic roof shale from Onyeama mine in Enugu colliery was studied for the geotechnical and compositional characteristics relevant to its use in civil engineering construction and other industries. Properties investigated included moisture absorption, particle size distribution, plasticity, linear shrinkage, compaction, California bearing ratio (CBR), permeability, consolidation, the pH the sulphate content and chemical composition. The shale had a high fines content of 85%, a liquid limit of 55 %, a good standard Proctor compaction strength of 1690 kg/m3, preconsolidation pressure of 36 kN/m2, pH of 6.1 and sulphate content of 0.37%. The shale-water extract indicated a possibility of sulphate attack on concrete in contact with weathered pyritic shale. Permeability impairment of between 1x10-7cm/s to1x10-8 cm/s was observed on the compacted shale exposed to water and atmosphere. This was attributed to the formation of jarosite and ferric oxide which are the oxidation products of shale weathering. The relatively high silica content of 56% and the low combined potash and sodium content of 1.74% pointed to the potential of the oxidized black shale as a foundation for road bed, as a raw material for brick and a wide range of structural ceramics, and as filler for paints and plastics. The objectionable pyrite in the clay shale can be removed prior to use by treatment with sulphur-and iron-oxidizing bacterium-Thiobacillus ferroxidans or by aging the shale stockpile.

Variations in photovoltaic performance due to climate and low-slope roof choice

With urban space at a premium, roofs are being targeted as an opportunity to deploy sustainable energy technologies for buildings. This research evaluates the combination of green roofs and solar photovoltaics specifically through their temperature and electricity production relationship. Measurements over a one year study period from July 1, 2011 to June 30, 2012 from a large field project in Pittsburgh, Pennsylvania were used to determine the differences in power output from green and black roofs as well as to derive two regression functions for back-surface panel temperature and photovoltaic (PV) output. These estimation functions were applied to three different cities (San Diego, CA; Huntsville, AL; and Phoenix, AZ) chosen to represent a wide range of irradiance and temperature values. Based on the specific test-bed configuration, the green or black roof choice under the PV panels had little impact on the PV performance. The difference in magnitude of power generation for green roof–PV compared with black roof–PV assemblies was small (0.5%) corresponding to an annual loss of $9/60panels in Pittsburgh and a benefit of approximately $8/60panels per year in Phoenix. Results also suggest that sites consistently above 25°C (77°F) will most likely see a small, positive impact from a green roof–PV combination. Building managers and designers should consider this temperature and power output interaction a minor economic factor in roof decisions.

Enhancement of life cycle assessment (LCA) methodology to include the effect of surface albedo on climate change: Comparing black and white roofs

Traditionally, life cycle assessment (LCA) does not estimate a key property: surface albedo. Here an enhancement of the LCA methodology has been proposed through the development and employment of a time-dependent climatological model for including the effect of surface albedo on climate. The theoretical findings derived by the time-dependent model have been applied to the case study of a black and a white roof evaluated in the time-frames of 50 and 100 years focusing on the impact on global warming potential. The comparative life cycle impact assessment of the two roofs shows that the high surface albedo plays a crucial role in offsetting radiative forcings. In the 50-year time horizon, surface albedo is responsible for a decrease in CO2eq of 110–184 kg and 131–217 kg in 100 years. Furthermore, the white roof compared to the black roof, due to the high albedo, decreases the annual energy use of about 3.6–4.5 kWh/m2.

Long-term hygrothermal performance of white and black roofs in North American climates

When solar radiation hits a roof surface, a part of solar energy is reflected and part is absorbed. The absorbed part of solar energy results in an increase of the surface temperature of the roof. Cool reflective (white) roofs use bright surfaces to reflect a significant portion of the incident short-wave solar radiation, which lowers the surface temperature compared to conventional (black) roofs with bituminous membrane. As such, white roofs help reduce the urban heat island effect during the summer. The question is “do white roofs lead to moisture-related problems in northern and southern climates?” To help answer this question, numerical simulations were conducted to compare the hygrothermal performance of a single kind of white and black roofs under different outdoor and indoor conditions. The outdoor conditions are obtained from the weather database of the National Research Council of Canada, Institute for Research in Construction (NRC–IRC). The indoor conditions are taken based on the European standard (EN 15026) and ASHRAE recommendations for conditioned space. The type of roofs considered in this study is Modified-Bitumen (MOD-BIT) roofing systems. The numerical simulations were conducted for the outdoor climate of Toronto (ON), Montreal (QC), St John’s (NL), Saskatoon (SK), Seattle (WA), Wilmington (NC) and Phoenix (AZ). Results showed that for the outdoor climates of St John’s and Saskatoon, the white roofs could lead to longer-term moisture-related problems. However, for the outdoor climates of Toronto, Montreal, Seattle, Wilmington and Phoenix, buildings with white roofs were shown to have a low risk of experiencing moisture damage. Also, buildings with white roofs in these locations were predicted to show a net yearly energy savings compared to buildings with black roofs. ► Long-term hygrothermal simulations were conducted for white and black roof systems. ► The roofs were subjected to a number of North American climates. ► White roofs in St John’s and Saskatoon could lead to longer-term moisture-related problems. ► White roofs were shown to have low risk of moisture damage in Toronto, Montreal, Seattle, Wilmington and Phoenix.

Quantifying the direct benefits of cool roofs in an urban setting: Reduced cooling energy use and lowered greenhouse gas emissions

Cool roofs, cool pavements, and urban vegetation reduce cooling energy use in buildings, lower local air pollution, and decrease greenhouse gas (GHG) emissions from urban areas. To promote widespread and large-scale implementation of cool roofs to moderate urban heat-island phenomenon, more awareness and understanding of cool roof benefits at the local level is needed. As part of an investigation of strategies to mitigate urban heat-island effects, field data gathered from a monitoring project on cool roofs in India were reviewed. An innovative field-based analytical method was developed to quantify cooling energy savings resulting from the installation of cool roofs on commercial buildings. For buildings monitored in the Metropolitan Hyderabad region, the measured annual energy savings from roof-whitening of previously black roofs ranged from 20 to 22 kWh/m 2 of roof area, corresponding to a cooling energy use reduction of 14–26%. The application of white coatings to uncoated concrete roofs resulted in annual savings of 13–14 kWh/m 2 of roof area, corresponding to cooling energy savings of 10–19%. The annual direct CO 2 reductions associated with the reduced cooling energy use were estimated to be 11–12 kg CO 2/m 2 of flat roof area. Additional field work on various building types and locations will help to understand magnitudes of regional or global potential in energy savings and GHG emission reductions from applying cool roofs. Knowledge about quantified cool roof benefits at both the local and regional level may promote the formulation of new policies and programs throughout the world.

Economic benefits for green roofs: a case study of the skaggs pharmacy building, university of utah

This paper reports a return on investment (ROI) feasibility study of applying a green roof on a future pharmacy building at the University of Utah. A 40-year life cycle costs versus benefi ts comparative analysis has been performed for green roof, black roof, and refl ective roof alternatives to quantify the economic benefi ts from green roofs. A green roof has a larger initial capital investment when compared with black or a refl ective roof; however, the life cycle accumulative values of benefi ts from a green roof have been calculated at 27 years, positive net present value, and 100% ROI. This conclusion makes the green roof alternative a better advisable investment than the other two roof alternatives.

Modeling impacts of roof reflectivity, integrated photovoltaic panels and green roof systems on sensible heat flux into the urban environment

This study presents results of a modeling effort to explore the role that sustainable roofing technologies play in impacting the rooftop energy balance, and the resultant net sensible heat flux into the urban atmosphere with a focus on the summertime urban heat island. The model has been validated using data from a field experiment conducted in Portland Oregon. Roofing technologies explored include control dark membrane roof, a highly reflective (cool) roof, a vegetated green roof, and photovoltaic (PV) panels elevated above various base roofs. Energy balance models were developed, validated with experimental measurements, and then used to estimate sensible fluxes in cities located in six climate zones across the US. On average the black roof and black roof with PV have the highest peak daily sensible flux to the environment, ranging from 331 to 405 W/m 2. The addition of PV panels to a black roof had a negligible effect on the peak flux, but decreased the total flux by an average of 11%. Replacing a black roof with a white or green roof resulted in a substantial decrease in the total sensible flux. Results indicate that if a black membrane roof is replaced by a PV-covered white or a PV-covered green roof the corresponding reduction in total sensible flux is on the order of 50%. The methodology developed for this analysis provides a foundation for evaluating the relative impacts of roof design choices on the urban climate and should prove useful in guiding urban heat island mitigation efforts.

I See a Black Roof and I Want to Paint it White: A Tax Plan for Energy Savings

One of Secretary of Energy Steven Chu’s ideas that quickly caught the media’s attention was having people change the color of roofs from predominantly black to completely white. This Article examines this idea from science to implementation.Part I of the Article discusses the scientific basis for this idea. White roofs make a house - or any building - cooler; thus, the costs of cooling the house will be reduced and there will be reduced electricity usage as a result. Part II examines two ways that the federal government can encourage individual behavior - through government spending programs and through the federal tax code. Part III then describes, in depth, what a government program would look like, first as a spending program then as a tax expenditure. Part IV then further describes what I believe would be the government’s best method for implementing a program to encourage citizens to change the color of their roofs.

HYDROLOGIC BEHAVIOR OF VEGETATED ROOFS1

ABSTRACT: Control of stormwater runoff from impervious surfaces is an important national goal because of disruptions to downstream ecosystems, water users, and property owners caused by increased flows and degraded quality. One method for reducing stormwater is the use of vegetated (green) roofs, which efficiently detain and retain stormwater when compared to conventional (black) roofs. A paired green roof‐black roof test plot was constructed at the University of Georgia and monitored between November 2003 and November 2004 for the green roof's effectiveness in reducing stormwater flows. Stormwater mitigation performance was monitored for 31 precipitation events, which ranged in depth from 0.28 to 8.43 cm. Green roof precipitation retention decreased with precipitation depth; ranging from just under 90 percent for small storms (< 2.54 cm) to slightly less than 50 percent for larger storms (> 7.62 cm). Runoff from the green roof was delayed; average runoff lag times increased from 17.0 minutes for the black roof to 34.9 minutes for the green roof, an average increase of 17.9 minutes. Precipitation and runoff data were used to estimate the green roof curve number, CN = 86. This information can be used in hydrologic models for developing stormwater mitigation programs.

Technical College Buildings

Dr Topping, whose own college is as yet less than half complete, notes some important considerations which should be borne in mind in the planning stages of new college buildings. The front cover photograph is of a model of Brunel as it is planned to appear in about 1964. The buildings with black roofs are already in use; construction of the others has not yet begun, in fact much of the site is still occupied by other buildings. Photographs 1, 2 and 3 are by The School of Photography, The Polytechnic, Regent Street, London. Brunel's architect is C. G. Stillman, FRIBA, Middlesex County Architect.