Microclimatic effects of green and cool roofs in London and their impacts on energy use for a typical office building

Virk, Gurdane; Jansz, Antonia; Mavrogianni, Anna; Mylona, Anastasia; Stocker, Jenny; Davies, Martin

doi:10.1016/j.enbuild.2014.11.039

Cited by 86 publications

(29 citation statements)

References 44 publications

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“…Green roofs have multiple benefits, making them an attractive solution for many issues facing urban areas. Similarly to cool roofs, green roofs can significantly reduce the UHI effect (Berardi et al, 2014;Gagliano et al, 2015;Santamouris, 2015;Niachou et al, 2001;Virk et al, 2015) due to increased reflectivity. In addition to reducing ambient air temperatures in hot climates, the soil and vegetation layers of green roofs provide natural insulation that mitigates short-term fluctuations in air temperature (Niachou et al, 2001).…”

Section: Introductionmentioning

confidence: 98%

An environmental cost-benefit analysis of alternative green roofing strategies

William

Goodwell

Richardson

et al. 2016

Ecological Engineering

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a b s t r a c tGreen roofs and cool roofs are alternative roofing strategies that mitigate urban heat island effects and improve building energy performance. Green roofs consist of soil and vegetation layers that provide runoff reduction, thermal insulation, and potential natural habitat, but can require regular maintenance. Cool roofs involve a reflective layer that reflects more sunlight than traditional roofing materials, but require additional insulation during winter months. This study evaluates several roofing strategies in terms of energy performance, urban heat island mitigation, water consumption, and economic cost. We use MLCan, a multi-layer canopy model, to simulate irrigated and non-irrigated green roof cases with shallow and deep soil depths during the spring and early summer of 2012, a drought period in central Illinois. Due to the dry conditions studied, periodic irrigation is implemented in the model to evaluate its effect on evapotranspiration. Traditional and cool roof scenarios are also simulated by altering surface albedo and omitting vegetation and soil layers. We find that both green roofs and cool roofs significantly reduce surface temperature compared to the traditional roof simulation. Cool roof temperatures always remain below air temperature and, similar to traditional roofs, require low maintenance. Green roofs remain close to air temperature and also provide thermal insulation, runoff reduction, and carbon uptake, but might require irrigation during dry periods. Due to the longer lifetime of a green roof compared to cool and traditional roofs, we find that green roofs realize the highest long term cost savings under simulated conditions. However, using longer-life traditional roof materials (which have a higher upfront cost) can help decrease this price differential, making cool roofs the most affordable option due to the higher maintenance costs associated with green roofs.

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Section: Introductionmentioning

confidence: 98%

An environmental cost-benefit analysis of alternative green roofing strategies

William

Goodwell

Richardson

et al. 2016

Ecological Engineering

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“…The literature has generated extensive studies on green-roof thermal effects in various climatic contexts. These studies roughly fall into three categories in terms of study approaches and objectives, including: (1) on-site monitoring to investigate green-roof impacts on summer temperature parameters and building heat flux patterns [9][10][11][12][13][14][15][16][17][18][19][20][21][22]; (2) dynamic energy modeling to analyze the heat and moisture processes within the green-roof layers and identify key influential factors [23][24][25][26][27][28]; and (3) building energy simulation or meso-scale climatic modeling to predict the cooling and energy effects of individual or multiple green-roof installations [29][30][31][32][33][34]. The studies have reported that green roofs can reduce summer daily peak surface temperature by 15 °C-45 °C and peak air temperature by up to 5 °C.…”

Section: Introductionmentioning

confidence: 99%

Seasonal and Diurnal Thermal Performance of a Subtropical Extensive Green Roof: The Impacts of Background Weather Parameters

Peng

Jim

2015

Sustainability

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Most studies explored green-roof thermal effects on a few hot summer days based on short-term monitoring data. Few studies investigated the seasonal and diurnal patterns of thermal performance and associated weather effects. This research aims to address the following two questions: (1) how green-roof thermal performance varies with different season and time; and (2) to what extent can thermal performance be predicted by background weather parameters? A retrofitted extensive green roof was established on the top of a railway station in subtropical Hong Kong. Monitoring data covering a two-year period, one year before roof greening and one year after, were collected and analyzed. Results indicated notable seasonal and diurnal patterns of green-roof thermal performance. It exhibited cooling effects in spring, summer and fall, but warming effects in winter. The cooling effects were more pronounced in summer than spring and fall, on sunny days than rainy and cloudy days, and in nighttime than daytime. Air temperature, relative humidity, wind speed, solar radiation, and soil moisture could explain 83.6%-86% of the thermal effects' variation. The multiple-regression models based on the five weather variables established in this study provide an uncomplicated and direct approach to predict the thermal performance of similar extensive green roofs in subtropical areas. OPEN ACCESSSustainability 2015, 7 11099

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“…The majority of those researches calculates the increased heating demand through energy and microclimatic simulations [21,28,31,33,36,38]; some authors, such as Kolokotroni et al [33], Stavrakakis et al [38] and Pisello et al [37] have performed on-site monitoring of some variables mainly to validate the building simulation model. Finally, some researches analyse the energy performances of cool roofs though a comparative assessment with respect to green roofs [28], or balance cooling savings with the increasing of the heating consumptions in winter [28,35].…”

Section: Discussionmentioning

confidence: 99%

“…Many other authors have instead analysed and demonstrated the effectiveness and the benefits of adopting cool roofs to reduce the energy consumptions of buildings for summer cooling in different climates [9,20,23,[26][27][28][29][30][31][32], considering buildings with different end uses [29,31,33,34].…”

Section: Introductionmentioning

confidence: 99%

“…Most of the researches have demonstrated that cool roofs involve an annual energy penalty due to their performance in winter [35], considering both analysis of the whole urbanized areas through global climate models [21,31], and specific climatic contexts [28,33,[36][37][38]. In contrast, some other authors have demonstrated that winter heating penalties for cool roofs are negligible in cold climates-even without the effect of snow- [21,39], depending on: the ratio of cloudy to sunny days (which increases during winter), less total solar radiation available on the roofs, the effect of snow.…”

Section: Introductionmentioning

confidence: 99%

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Assessment of the Impact of Cool Roofs in Temperate Climates through a Comparative Experimental Campaign in Outdoor Test Cells

Barozzi

Pollastro

2016

Buildings

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Abstract:Over the last few decades many bibliographical studies have been conducted on cool roofs, by analyzing both the energy performance during summer and winter seasons and their contribution in mitigating the urban heat island effect. This paper describes the experimentation carried out in three outdoor test cells to comparatively assess the behavior of a cool roof solution with respect to a ventilated-roof and a warm-roof. The monitored data have confirmed that in summer cool roofs are the best solution, with respect to traditional tile roofing, sensibly reducing surface temperatures as a function of the solar direct radiation level (15-25 • C for I > 600 W/m 2 and 5-15 • C for I < 300 W/m 2 , independently of the season). Furthermore, cool roofs involve an energy saving related to summer cooling by about 20% as to a warm-roof and 15%-20% as to a vented-roof. During winter, cool roofs improve the heating energy performance of a vented-roof by about 12%, against a slightly increased consumption (<5%) if compared to a warm-roof. These data confirm that, in temperate climates, cool roofs are appropriate solutions to sensibly improve summer energy performances with a negligible negative impact during winter, and to positively contribute to the mitigation of the heat island effect.

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Microclimatic effects of green and cool roofs in London and their impacts on energy use for a typical office building

Cited by 86 publications

References 44 publications

An environmental cost-benefit analysis of alternative green roofing strategies

An environmental cost-benefit analysis of alternative green roofing strategies

Seasonal and Diurnal Thermal Performance of a Subtropical Extensive Green Roof: The Impacts of Background Weather Parameters

Assessment of the Impact of Cool Roofs in Temperate Climates through a Comparative Experimental Campaign in Outdoor Test Cells

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