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Map illustrating the buildings and roof installation at the PPPL test site. The weather stations (red markers) were placed in close proximity to the heat flux sensors and thermocouples installed inside the roof layers. Figure reproduced from Ramamurthy et al. [2]. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) 

Map illustrating the buildings and roof installation at the PPPL test site. The weather stations (red markers) were placed in close proximity to the heat flux sensors and thermocouples installed inside the roof layers. Figure reproduced from Ramamurthy et al. [2]. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) 

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The advanced Princeton Roof Model (PROM) is evaluated and then applied to quantify the heat transferred through various modular roof structures over an entire year. The goal is to identify an optimal combination of roof reflectivity and insulation thickness that will reduce energy consumption and minimize cost. Meteorological data gathered over the...

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... at the Princeton Plasma Physics Lab (PPPL) rooftops located in Princeton, New Jersey (40.3489 • N 74.6029 • W). According to the Koppen index [24], the region experiences a continental humid climate. Heat flux and tempera- ture measurements were made at five different rooftops, each with varying albedo, roof thickness and insulation materials. Fig. 2 shows the plan view of the installation site. We will denote the roofs as ADMw-R8.4, THYb-R3.6, LSBb-R4.2, LSBw-R4.2, EGRb-R6.3, where the first three upper case letters indicate the building, the 4th lower case letter indicate whether the roof is white (w) or black (b) and the two digits after the R indicate the R value (insulation) ...

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Citations

... Gentle et al. [4] studied the energy behavior of a roof, analyzing different combinations of solar albedo, thermal emittance, and thermal resistance of a roof; a cost benefit assessment of the different combinations was performed that concluded the importance of high values for the roof albedo. Ramamurthy et al. [5] used the minimization of yearly costs for heating and cooling in order to determine the optimal combination of roof solar albedo and insulation thickness; they concluded that an albedo greater than 0.7, combined with a polyiso foam insulation of 18 cm, significantly reduces thermal flux through the roof when applied to new constructions; likewise, they found that, if installations costs are included in the analysis, the optimal combination is reached for a 4-inch insulation thickness with a payback period of 13 years. Arumugam et al. [6] studied the combination of solar reflective coating, radiant barriers, and thermal insulation for a roof by using EnergyPlus; a total of five climatic zones in India and 88 different roof combinations were analyzed; through an economic analysis, they found that the use of solar reflective coating and radiant barriers on the roof reduced the need for insulation layer for all the climatic regions analyzed. ...
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Social housing built in the middle of the last century in Spain suffers from poor thermal insulation conditions that cause situations of discomfort and energy poverty. For this reason, the energetic refurbishment of the envelope of this social building stock is necessary to overcome these situations and reduce energy consumption aimed at achieving interior comfort for its occupants. The goal of this work is to optimize a constructive solution that combines cool roof techniques with the use of thermal insulation applied to the refurbishment of the roof of buildings belonging to a quarter of social housing in Seville, Spain. The optimization analysis is based on the computation of the energy performance of the roofs when the energy retrofitting measure is applied, considering a variety of combinations of solar reflective coatings and insulation layer thickness, performing a dynamic analysis that accounts for the aging effect of the cool coats on the monthly roof energy performance and on the economic balance for the whole life cycle (LC) span. Economic and energy optimization analysis show that a suitable combination of cool roof emissivity and insulation layer thickness produces significant savings in the operational energy and in the economic profitability of the proposed retrofitting measure: the optimum combination obtained provides for the entire life cycle timespan an energy savings of 5.71 GJ/m2 and a cost savings equivalent to the 63.1% of the total costs when compared to the non-refurbished roof. The application of a time-dependent pattern for the changes on time produced by the aging effect on the cool roof emissivity, and its effects on the optimization of the combination of cool roof and insulation layer, can be considered novel in literature, both from an energy and an economic point of view.
... In Tunisia, the benefits of increasing the roof reflectivity in summer were greater than winter penalties, and a higher reflectivity was desirable. Ramamurthy et al. [12] quantified the heat transmitted over a year through the roof in northeastern United States. The objective was to identify the optimal combination of the roof reflectivity and insulation thickness to minimize the energy consumption. ...
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To delay fossil energy depletion and implement the Paris Climate Change Accord, the South Korean government is attempting to reduce greenhouse gas emissions with the establishment of the 2030 Roadmap. The insulation performance of external walls is being continuously enhanced in the architectural domain. However, Korea’s policy and construction market focuses only on the heat resistance of buildings’ external walls to enhance the insulation performance, leading to an increased thickness of the insulation materials. In this study, the relationship between the surface reflectivity and insulation thickness of external walls was examined to formulate an effective insulation strategy for buildings in Korea. Office buildings of 12 regions in the Korean Peninsula were considered. The dynamic energy simulation program EnergyPlus was used to perform the heating and cooling load analyses. The present worth method was adopted to perform the economic analysis. The analysis of the cooling and heating loads indicated that a change occurred not only in terms of the latitude but also between the Eastern and Western regions. The energy consumption could be reduced by increasing the reflectivity in the Southern region and lowering the reflectivity in the Northern region, based on the total load. In addition, a higher latitude corresponded to a higher energy saving effect owing to the increased insulation thickness. In the case of Jeju Island and Busan, regions with a relatively large cooling load and small heating load, the total load is little affected by insulation thickness at high reflectivity. If the external skin was considered to have the optimal reflectivity, the regions for optimal insulation thickness could be divided into three categories: north, central and south.
... increase in roof 's albedo Akridge [102] 1998 high-albedo acrylic coating vs. conventional roof 33 • C decrease of roof peak temperature Doulos et al [103] 2004 thermal properties of 93 commonly used pavement materials "cold" materials = smooth and light colored and/or made of marble/mosaic/stone Synnefa et al [33] 2004 reflective coatings vs. white tile coatings were cooler up to 4 • C under hot summer conditions Santamouris et al [97] 2008 low cost cool coating using lime vs. they highlighted that the overall mitigation potential could be substantially enhanced with the implementation of cool materials in the pavement and road infrastructure. Ramamurthy et al [112] performed yearlong simulations with Princeton Roof Model concerning a cool roof application in the New York City Metropolitan region. They showed that a highly reflective (albedo = 0.7) roof membrane can substantially decrease the annual energy demand. ...
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Urban environment well-being has become a crucial public issue to face, given the huge concentration of population and climate change-related hazards at a city scale. In this view, Urban Heat Island (UHI) is now very well-acknowledged to be able to produce a serious threat to populations around the world and compromise human well-being due to aggressive overheating, exacerbated by anthropogenic actions. The same anthropogenic actions are also responsible for other discomfort causes such as noise pollution, which has also been demonstrated to heavily impact societal life and health conditions in urban systems. Both these phenomena typically co-exist in terms of space and time coincidence, and they both may be mitigated by means of smart adaptive and multifunctional surfaces including urban pavements and building envelopes. This review bridges the gap between only-thermophysical analysis about UHI mitigation and only-acoustics analysis of urban noise pollution, here defined as Urban Noise Island (UNI). To this aim, the key physics background of mitigation techniques is presented and the most innovative and promising solutions for counteracting UHI and UNI are described, with the final purpose to foster research and innovation towards more livable cities through a multiphysics and holistic view.
... e.g., Rafael et al. (2016) simulated using the WRF-SUEWS modelling system and roofs with an albedo of 80 % for Porto (Portugal) a maximum reduction in sensible heat flux of 62.8 W/m 2 . Ramamurthy et al. (2015) showed that the wintertime penalty of white roofs, also for cool climates with 5 times more heating degree days than cooling degree days is insignificant compared to the summertime benefits. Žuvela-Aloise et al. (2018) simulated using MUKLIMO for Vienna a reduction of up to 6 summer days when assuming a roof albedo of 70 %. ...
... Increasing the albedo of a very low insulation roof from 0.05 to 0.75 is roughly equivalent to adding 14 cm of insulation thickness (Ramamurthy et al., 2015). While it is a challenge to maintain the reflective properties of a white roof, insulations have longer lasting effects (Ramamurthy et al., 2015). ...
... Increasing the albedo of a very low insulation roof from 0.05 to 0.75 is roughly equivalent to adding 14 cm of insulation thickness (Ramamurthy et al., 2015). While it is a challenge to maintain the reflective properties of a white roof, insulations have longer lasting effects (Ramamurthy et al., 2015). Roman et al. (2016) found that increasing insulation results in an increase in sensible heat flux and surface temperatures during the day and a reduction at night. ...
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The energy balance of the Earth’s surface fundamentally defines the magnitude and amplitude of different ecosystem’ state variables. Ecosystems are sensitive to present climate extremes, such as heat waves. Moreover, such systems are at risk due to amplifications caused by climate change. Inland waters are vulnerable systems with limited migration potentials. Likewise vulnerable are urban areas, already home to the majority of the global human population trending upwards. In this thesis, the energy fluxes and state variables within a pre-alpine river and the Viennese urban canopy layer are analysed using numerical modelling to address the following key issues: How do surface properties and vegetation affect selected state variables? Will the behaviour of the systems change due to changes in climate? How are the living conditions of organisms affected? Long-term meteorological measurements and campaigns were performed to collect data used to force and evaluate the numerical models applied to the studied systems. Land cover and urban parameters were calculated, land use scenarios developed to feed the models and simulate and analyse present and future heat waves. Both environments are facing serious health threats. A shift of one fish zone in Eastern Austrian rivers will pose a mortal threat to cold-water species. All energy fluxes apart from the latent heat flux add energy to the water surface. Stream temperature minima increase stronger than the maxima for all vegetation scenarios. Stream temperature maxima are best reduced by dense shade, but the expected increase in air temperature cannot be compensated. In urban systems, an increase in maximum urban canopy air temperature by 6.7 K is noted under heat wave conditions. The radiation balance and sensible heat flux dominate the energy balance. At night, heat stress can be reduced by up to 1 K using higher albedo and low thermal conductance of urban materials. During daytime, shade is the most effective measure.
... Therefore, all negative effects of decreased thermal conductivity should be mitigated. Ramamurthy et al. (2015) analyzed the effectiveness insulation and high reflective roofs with an urban canopy model and suggests a combination. We note that the increase in albedo values does not depend on water availability and space demands, but it does compete with available surface areas for photovoltaic and green roof surfaces. ...
... Increasing the albedo of a very low insulation roof from 0.05 to 0.75 is roughly equivalent to adding 14 cm of insulation thickness (Ramamurthy et al., 2015). While it is a challenge to maintain the reflective properties of a white roof, insulations have longer lasting effects (Ramamurthy et al., 2015). ...
... Increasing the albedo of a very low insulation roof from 0.05 to 0.75 is roughly equivalent to adding 14 cm of insulation thickness (Ramamurthy et al., 2015). While it is a challenge to maintain the reflective properties of a white roof, insulations have longer lasting effects (Ramamurthy et al., 2015). Roman et al. (2016) found that increasing insulation results in an increase in sensible heat flux and surface temperatures during the day and a reduction at night. ...
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In this study we produce two urban development scenarios estimating potential urban sprawl and optimized development concerning building construction, and we simulate their influence on air temperature, surface temperatures and human thermal comfort. We select two heat waves representative for present and future conditions of the mid 21st century and simulations are run with the Town Energy Balance Model (TEB) coupled online and offline to the Weather Research and Forecasting Model (WRF). Global and regional climate change under the RCP8.5 scenario causes an increase of daily maximum air temperature in Vienna by 7 K. The daily minimum air temperature will increase by 2–4 K. Changes caused by urban growth or densification mainly affect air temperature and human thermal comfort locally where new urbanisation takes place and does not occur significantly in the central districts. A combination of near zero-energy standards and increasing albedo of building materials on the city scale accomplishes a maximum reduction of urban canyon temperature achieved by changes in urban parameters of 0.9 K for the minima and 0.2 K for the maxima. Local scale changes of different adaptation measures show that insulation of buildings alone increases the maximum wall surface temperatures by more than 10 K or the maximum mean radiant temperature (MRT) in the canyon by 5 K. Therefore, measures to reduce MRT within the urban canyons like tree shade are needed to complement the proposed measures. This study concludes that the rising air temperatures expected by climate change puts an unprecedented heat burden on Viennese inhabitants, which cannot easily be reduced by measures concerning buildings within the city itself. Additionally, measures such as planting trees to provide shade, regional water sensitive planning and global reduction of greenhouse gas emissions in order to reduce temperature extremes are required.
... The insulation thickness increase was demonstrated to provide incremental benefits in energy savings which were reduced after a limit. Similarly, Ramamurthy et al. [29,30] studied the joint influence of these two roof characteristics on building energy performance through a two-step experimental and numerical analysis. They highlighted the role of both albedo and insulation thickness for the reduction of the annual energy load attributable to the roof, and that wintertime penalties are negligible compared to summertime benefits with cool roofs. ...
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Cool roof effectiveness in improving building thermal-energy performance is affected by different variables. In particular, roof insulation level and climate conditions are key parameters influencing cool roofs benefits and whole building energy performance. This work aims at assessing the role of cool roof in the optimum roof configuration, i.e., combination of solar reflectance capability and thermal insulation level, in terms of building energy performance in different climate conditions worldwide. To this aim, coupled dynamic thermal-energy simulation and optimization analysis is carried out. In detail, multi-dimensional optimization of combined building roof thermal insulation and solar reflectance is developed to minimize building annual energy consumption for heating–cooling. Results highlight how a high reflectance roof minimizes annual energy need for a small standard office building in the majority of considered climates. Moreover, building energy performance is more sensitive to roof solar reflectance than thermal insulation level, except for the coldest conditions. Therefore, for the selected building, the optimum roof typology presents high solar reflectance capability (0.8) and no/low insulation level (0.00–0.03 m), except for extremely hot or cold climate zones. Accordingly, this research shows how the classic approach of super-insulated buildings should be reframed for the office case toward truly environmentally friendly buildings.
... The Princeton urban canopy model considers the single-layer "big-canyon" representation for urban areas featuring a detailed surface exchange scheme that couples energy transport and hydrological processes over natural and engineered surfaces, also taking into account sub-facet heterogeneity. The model was validated under different climate conditions, using extensive field measurements taken in different towns and cities including Baltimore, Beijing, Phoenix, Vancouver, Princeton, and Montréal, in an offline (standalone) mode driven by 5 to 30-min averaged meteorological data obtained from meteorological towers [45,46,50,51]. In this paper, we will use this same validated offline mode where the urban feedbacks to the atmosphere are shut off, and atmospheric state observations are imposed on the UCM. ...
... This cool roof behaviour is good in terms of UHI mitigation potential during the hottest months of the year, where this roof is positively affected by the reduced radiative absorption of incoming solar radiation. While the cool roof impact on building-scale winter-heating energy consumption is not very significant if the building is well insulated [50,55], cool roofs inevitably negate some of the winter-time benefits of the UHI at the city-scale by reducing its intensity [32]. Our results indeed confirm this as illustrated by the reduction in HR in the winter months relative to dark roofs. ...
Article
In recent years, the urgent need for reducing building energy consumption has prompted the scientific community to investigate and develop new adaptive materials for the built environment, and to use field monitoring and multiscale advanced modeling for analyzing and improving the urban microclimate conditions using these new materials. In this work, the Princeton Urban Canopy Model (PUCM) is used to investigate the potential of an advanced urban roofing material to counteract urban overheating in summer, while simultaneously taking advantage of solar passive heating in winter. The roofing applications are characterized by an adaptive dynamic temperature-dependent optical behavior. In particular, the effect of thermochromic materials on local energy transport phenomena is assessed and benchmarked against a traditional dark roof and a more common cool roof solution. These materials undergo a rapid albedo increase when the surface temperature exceeds a certain threshold. Results demonstrate that using thermochromic materials produces a smart optical response to local environmental stimuli and allows enhanced shortwave solar reflection in summer conditions, reduced reflected solar fraction in winter, and adaptive properties during transition periods.
... The surface albedo of different materials impacts the outgoing shortwave (solar) radiation and thus the surface energy balance fluxes and other atmospheric variables. Modifying roof albedo has been suggested extensively as a method to cool urban areas (e.g., Santamouris et al., 2011;Li et al., 2014;Ramamurthy et al., 2015). In the example, we conduct simulations from January 2012 to July 2012 with the first 6 months as the spin-up period. ...
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Accurate and agile modelling of cities weather, climate, hydrology and air quality is essential for integrated urban services. The Surface Urban Energy and Water balance Scheme (SUEWS) is a state-of-the-art, widely used, urban land surface model (ULSM) which simulates urban-atmospheric interactions by quantifying the energy, water and mass fluxes. Using SUEWS as the computation kernel, SuPy (SUEWS in Python), with a Python-based data stack to streamline the pre-processing, computation and post-processing that are involved in the common modelling-centred urban climate studies. This paper documents the development of SuPy, including: the SUEWS interface modification, F2PY (Fortran to Python) configuration and Python frontend implementation. In addition, the deployment of SuPy via PyPI (Python Package Index) is introduced along with the automated workflow for cross-platform compilation. This makes SuPy available for all mainstream operating systems (Windows, Linux, and macOS). Three online tutorials in Jupyter notebooks are provided to users of different levels to become familiar with SuPy urban climate modelling. The SuPy package represents a significant enhancement that supports existing and new model applications, reproducibility, and enhanced functionality.
... As such, heat islands are widely recognized as stumbling blocks in the sustainable pathways of metropolitan areas, and recent years have seen substantial resources dedicated to investigating and implementing UHI mitigation strategies (Gartland, 2012;Rizwan, Dennis, & Chunho, 2008). The proposed strategies that are most studied in the literature and adopted by cities are the use of high-albedo materials and green infrastructure (Norton et al., 2015;Ramamurthy, Sun, Rule, & Bou-Zeid, 2015;Santamouris, 2014). Because urban land is highly valuable, and because highly-reflective materials could degrade outdoor human thermal comfort when applied at ground level by reflecting radiation towards pedestrians (Yang, Wang, Kaloush, & Dylla, 2016), strategies focusing on building rooftops have been increasingly promoted to create cooling spaces. ...
... Consequently, waste heat release from air conditioning systems during the summer, which contributes more than 1°C to UHIs in some urban locations (de Munck et al., 2013;Salamanca, Georgescu, Mahalov, https & Wang, 2014), can be reduced to provide further urban cooling. Building-to-block scale numerical simulations reported benefits consistent with the in-situ measurements (Ramamurthy et al., 2015;Sailor, Elley, & Gibson, 2012;Yang, Wang, Kaloush et al., 2016;Zinzi & Agnoli, 2012). ...
... The implementation of green and cool roofs in WRF cannot be directly validated, because the model grid size (1 km in this study) is much larger than building rooftops where field experiments have been conducted. Nevertheless, the same urban canopy model implemented here in WRF has been validated in "offline mode" (interactions between urban land and overlying atmosphere are turned off) under the forcing of atmospheric observations (Ramamurthy et al., 2015;Sun, Bou-Zeid, Wang, Zerba, & Ni, 2013). The offline UCM can be applied over the canyon scale (∼10-100 m), and therefore its simulated effects of green and cool roofs can be evaluated against in-situ measurements. ...
Article
Cool and green roofs are widely adopted measures for curtailing summertime urban heat islands. Existing numerical studies to assess their effectiveness and cooling benefits usually assume an unrealistic 100% coverage across the entire metropolis. This study investigates the scale dependence of the absolute cooling benefits and efficiency (cooling per adapted roof area) of cool and green roofs in a typical summer when they are installed over 25% of building rooftops at local, city, or regional scales. Six major U.S. cities with active climate action plans in different geoclimatic zones are compared through high-resolution simulations using the Weather Research and Forecasting model. The results reveal that reductions in 2-m air temperature over the urban core increase non-linearly with the intervention area, and the benefits of both roof types scale similarly. This scale-dependence of urban core cooling is not universal, but is rather controlled by the shape of metropolitan areas and wind pattern. The siting of mitigation measures hence plays an important role especially under windy conditions, and some urban cores are not able to achieve a noticeable and consistent cooling by retrofitting their own rooftops. Regional-scale deployments of mitigation strategies, on the other hand, yield a more substantial temperature reduction but with a lower efficiency. The scale-dependence of regional cooling efficiency showed remarkable similarity across studied cities, yielding a potentially generalizable power law. The successful resiliency plans for cities should account for the scale dependence and geoclimatic determinants of the achievable cooling, and identify the target neighborhoods of most interest.
... Meanwhile, an adequate insulation level decreases the heating penalty. The joint influence of albedo and insulation on roof performance has been studied by Ramamurthy et al. [42]. They have concluded that for new constructions or for retrofits in the region of the North-eastern United States, around 46 cm thick of roof insulation and albedo of 0.6 (or greater), would significantly reduce the both heating and cooling loads. ...
Article
During the cooling season, the beneficial effects of cool colors and cool paints are multiple and undebatable. Really, it is not well-know their impact during the heating season, when a heated external surface could be useful in order to reduce the heat losses. This paper, by means of experiments and numerical simulations, investigates the effect of high-reflective and high-emissive coatings on the building energy performance in Mediterranean climate. Four coatings are used; among these, an acrylic white paint of household appliances or automotive sector has been tested since it is characterized by very fast drying, good adhesion directly to different type of materials, greater durability than traditional paints and lower costs. The experiments have been carried out by using the test-room of the University of Sannio; the results of wintertime monitoring campaign are presented. By means of simulations, using as case study a typical office building, the effect of combination of roof reflectivity, roof technology and insulation thickness is discussed. Research results can support design strategies for optimizing the yearly energy performance of the building, reducing environmental impacts but these also demonstrate the performance of unconventional cool material, as the acrylic paint, with a lower aging and maintenance needs.