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Assessment of green roof performance for sustainable buildings under winter weather conditions
Abstract
A green roof is a specialized roof system that supports vegetation growth on rooftops. This technology is rapidly gaining popularity as a sustainable design option for buildings. In order to contribute to an understanding of green roof in regions with cold winters and snow, an on-site experimental investigation was present with a focus on the assessment of green roof performance during the winter. This field experiment took place on a six small buildings during the winter of 2010–2011. The work monitored three buildings with green roofs, two buildings with reference roofs and one building with a bare soil coverage for the roof. These six buildings were identically constructed and instrumented with sensor networks to provide heat flux data through the roofs. The 15 min averaged data were statistically analyzed for a week under the two separate periods, first without a snow cover and second with a snow cover. The results show that the roof type is a significant factor in affecting the thermal performance of these buildings. Most importantly, green roofs reduce heat flow through the roof and thus reduce the heating energy demand during the winter. However, the energy savings for buildings with the green roofs are reduced under snow conditions because the snow diminishes thermal resistance of the roof and increases the heat transfer process through the roofs.
... Studies [12,[17][18][19][20][21][22][23][24][25][26][27][28] based on in situ experiments monitor the impact of green roofs on the thermal properties of roof constructions with a comparison being made against a reference roof, either a bare roof, with an unprotected membrane, or a gravel roof where a layer of gravel applied on geotextile bears the protecting and stabilization function of the roof. ...
... With a continuous layer of snow on both roofs, the value decreased to 5%. A complementary study [27] that compared the bare roof, the bare soil roof, and the green roof with vegetation up to 19 mm high states that, regardless of whether the snow was on the roof or not, the third-mentioned roof still performed best as far as energy consumption is concerned. ...
... Following the snow layer's stabilisation at 50 mm high on February 12, a cumulative heat flux through segment S1 very similar to the one through segment S2 was measured. Studies [27,28] point to a similar phenomenon. Changing the albedo and emissivity of the surface due to the presence of the snow layer affected the heat flux of segments S1 and S2. ...
... Therefore, consistent with these methods, we consider the same value for the electricity sold to and purchased from the grid as we assume the excess electricity that is sent to the grid can be credited and hence, used by any of the candidate Percentage energy saving in cooling degree-hours due to GR installation, α, and percentage energy saving in heating degree-hours due to GR installation, β. The percentage of energy saving in cooling degree-hours achieved due to the installation of GRs differs across various 330 studies, ranging from 10% to 16.7% (Coma et al., 2016;Dunec, 2012;Ascione et al., 2013;Zhao and Srebric, 2012;Feng and Hewage, 2014;Spala et al., 2008;Raji et al., 2015). While almost all studies agree on the fact that using GRs results in savings in cooling degree-hours, there is a lack of consensus on the impact of GRs in heating degree-hours. ...
... to 10% in energy savings as a result of GRs in heating degree-hours (Dunec, 2012;Ascione et al., 2013;Raji et al., 2015;Zhao and Srebric, 2012). Therefore, in this study, we let α 345 and β assume a wide range of values to capture the different, and sometimes contradicting, estimates reported in the literature. ...
... ;Raji et al. (2015);Spala et al. (2008);Zhao and Srebric (2012) Percentage energy saving in heating degree-hours due to GR installation, β[−6.1%, 10%] −10%, 10% Ascione et al. (2013); Coma et al. (2016); Dunec (2012); Feng and Hewage (2014); Raji et al. (2015); Spala et al. al. (2005); Belzer (2009); EIA (2018b,a); Huang (2006); Loveland and Brown (1996); Mansur et al. (2005); Rosenthal et al. (1995); Ruth and Lin (2006); Sailor (2001); Sailor and Pavlova(2003);Scott et al. (2005) ...
Photovoltaic (PV) panels directly convert sunlight into electricity; but, sunlight also heats the panels, negatively impacting their efficiency. Green roofs are vegetative layers grown on rooftops, mainly to provide added insulation on the roof to save energy. Green roofs also cool near-surface air temperature. Hence, the joint installation of PV panels and green roofs may potentially lead to higher efficiency of PV panels in certain climates. We develop a two-stage stochastic programming model to optimally place PV panels and green roofs under climate change uncertainty to maximize the overall profit from energy generated and saved. We calibrate the model using the literature, industry reports, and the data from different, at times conflicting, climate projections. We then conduct a case study for a mid-size city in the U.S., perform extensive sensitivity and robustness analyses and provide insights.
... A green, or vegetated roof, is a structural design approach that brings nature and engineering together to provide a sustainable alternative to conventional roofing [1]. Among the multifunctional benefits that a green roof provides, improved building envelope thermodynamics has been an important aspect for reducing energy consumption within the building sector [2,3]. As a living system, a green roof's thermal behavior is highly influenced by the surrounding climate. ...
... In the French temperate climate, a green roof was shown to have very little impact on overall heating demands due to reduced heat losses during cold winter days along with a reduction in positive solar gains during sunny winter days [22]. Furthermore it was shown that snow effectively insulates buildings but scales down the relative benefits that a green roof can have compared to a conventional roof [2,23,24]. In the case of extreme weather conditions with sub-zero temperatures and severe wind and rain, the benefits of green roofs tend to increase [25], however, ice transfers heat energy more efficiently through its medium compared to liquid water [26], suggesting greater heat loss for frozen green roofs. ...
... During winter, there is a temperature gradient through the roofing components of both the bare and green roofs due to the temperature difference between the warm inside air and the cold outside air. The majority of heat transferred from the interior outward in a green roof is through conduction [2,10]. Integrating Fourier's equation for steady state heat conduction over the thickness of a medium, the mathematical model for heat flow by conduction is expressed as: ...
To understand how green roofs affect building energy performance under cold climatic conditions, a proper thermal analysis of the roof and its components is required. To address this, we measured the thermal conductivity of each layer of experimental green roofs, as well as equivalent thermal resistance of the complete green roof system during winter conditions in southern Finland. Three experimental green roof platforms (1 m × 2 m) with heated boxes and three identical bare roof platforms (without substrate, vegetation and other green roof layers) were equipped with thermocouples that continuously measured a vertical temperature profile through the roofs. A steady-state heat transfer analysis was performed to assess the functioning and relative thermal performance of the green roof systems. Layer analysis at various intensities of frost penetration showed that the thermal conductivity of each layer decreased when penetrated by frost. In particular, thermal conductivity of the substrate and vegetation layers decreased from 0.41 Wm⁻¹K⁻¹ and 0.34 Wm⁻¹K⁻¹ prior to freezing, to 0.12 Wm⁻¹K⁻¹ and 0.10 Wm⁻¹K⁻¹ after freezing, respectively. This phenomenon is explained by a reduction in bridge-water connectivity during freezing and a volumetric water content that was below the critical threshold value. Overall, a frost depth that extended through the complete green roof yielded the greatest equivalent thermal resistance. During times of snow cover, snow acted as an insulator and reduced the relative energy saving benefits achieved by green roofs. These results provide information for designing the substrate and vegetation layers of green roofs for optimal insulation.
... For cold seasons, modeling studies predict modest reductions in heat flow out of buildings under green roofs compared with conventional roofs [8,10,11], but the overall impact on energy budgets should be less than that of cooling during hot periods. The few empirical studies of green roof thermal properties during cold seasons tend to confirm the reduction in heat flow out of buildings compared to conventional roof systems [12][13][14][15], resulting in energy savings. ...
... In general, snow acts as an insulator, reducing temperature fluctuations and increasing average soil temperatures during winter [16]. Empirical studies of green roofs in winter suggest that snow cover reduces the magnitude of temperature fluctuations [17] and the relative advantage of green roofs compared with conventional roofs [15]. Green roofs may support greater snow accumulation [14], but there has never been a quantitative study of the effects of snow depth or coverage on green roof thermal performance nor of the effects of green roofs on the magnitude and duration of snow accumulation. ...
... When snow covered the roof, both green and conventional roof panels showed relatively constant heat flux (Figs. A.4-A.6), confirming the findings of two previous studies [14,15]. Climatic conditions during the study period (winter 2010-2011) indicate lower minimum temperatures and greater precipitation, both rain and snow, compared to 30-year climate normals (Table A.2). Warmer temperatures in a more typical year would result in greater differential savings from green roofs (as substrates would be less frequently frozen), but it is not clear what to expect in a year with less snow, as heat gain by conventional roofs depended on whether the sun was shining (Fig. 1). ...
... The benefits of green roofs in cold climates are often acknowledged [21][22][23][24]. In a detailed study in Canada, Liu and Baskaran showed that the daily surface temperature variation with a green roof was approximately 6 • C, compared to a variation up to 45 • C occurring with a traditional roof [20]. ...
... From a long-term perspective, a study compared the green roof and a cool roof for houses in St. Louis, MO, using a life cycle approach over a 10-year period, and showed significant advantages for the house with the green roof [21]. Zhao evaluated the reduction of the heat flow thanks to green roofs in extreme climates with highly snowy winters [22]. ...
... Recently, several studies have looked at the same green roof in different climates to explore advantages and disadvantages of the [7,14,17,[27][28][29] Great potential for reducing the maximum temperature Warm and dry climates Reduction of the outdoor air temperature and cooling the indoor ambient temperature [30,55] Cold climates Reduction of daily temperature swing [16,22,27,30,55] Reduction of the heat flow Doubtful energy performance in winter, spring and falls Evaporative cooling in the shoulder seasons may lead to increased building heating loads same structure. Sun et al. considered two case studies located at Princeton University in US and Tsinghua University in China, confirming different effectiveness of green roofs in these two locations [24]. ...
... Therefore, both roofs had similar heat loss under the snow coverage. Another experimental study by NRCC [38] analyzed two different green roofs with a reference roof in Toronto. The differences between green roofs were in the thickness and color of the growing media. ...
... Likewise, different plants have different plant albedo. For example, in [38] plant albedo of different types of sedum were studied where sedum tomentosum and mixed sedum species had a plant albedo of 0.23 and 11, respectively. Additionally, Ascione et al. [17] considered a plant albedo of 0.22 for both short and tall cut sedum for modeling green roofs. ...
A comprehensive parametric analysis was conducted to evaluate the influence of the green roof design parameters on the thermal or energy performance of a secondary school building in four distinctively different climate zones in North America (i.e., Toronto, ON, Canada; Vancouver, BC, Canada; Las Vegas, NV, USA and Miami, FL, USA). Soil moisture content, soil thermal properties, leaf area index, plant height, leaf albedo, thermal insulation thickness and soil thickness were used as design variables. Optimal parameters of green roofs were found to be functionally related to meteorological conditions in each city. In terms of energy savings, the results showed that the light-weight substrate had better thermal performance for the uninsulated green roof. Additionally, the recommended soil thickness and leaf area index for all four cities were 15 cm and 5 respectively. The optimal plant height for the cooling dominated climates is 30 cm and for the heating dominated cities is 10 cm. The plant albedo had the least impact on the energy consumption while it was effective in mitigating the heat island effect. Finally, unlike the cooling load, which was largely influenced by the substrate and vegetation, the heating load was considerably affected by the thermal insulation instead of green roof design parameters.
... to 10% in energy savings as a result of GRs in heating degree-hours (Dunec, 2012;Ascione et al., 2013;Raji et al., 2015;Zhao and Srebric, 2012). Therefore, in this study, we let α and β assume a wide range of values to capture the different, and sometimes contradicting, 355 estimates reported in the literature. ...
... ;Raji et al. (2015);Spala et al. (2008);Zhao and Srebric (2012) Percentage energy saving in heating degree-hours due to GR installation, β[−6.1%, 10%] −10%, 10% Ascione et al. (2013); Coma et al. (2016); Dunec (2012); Feng and Hewage (2014); Raji et al. (2015); Spala et al. al. (2005); Belzer (2009); EIA (2018c,b); Huang (2006); Loveland and Brown (1996); Mansur et al. (2005); Rosenthal et al. (1995); Ruth and Lin (2006); Sailor (2001); Sailor and Pavlova(2003);Scott et al. (2005) ...
Photovoltaic (PV) panels directly convert sunlight into electricity; but, sunlight also heats the panels, negatively impacting their efficiency. Green roofs are vegetative layers grown on rooftops, mainly to provide added insulation on the roof to save energy. Green roofs also cool near-surface air temperature. Hence, the joint installation of PV panels and green roofs may potentially lead to higher efficiency of PV panels in certain climates. We develop a two-stage stochastic programming model to optimally place PV panels and green roofs under climate change uncertainty to maximize the overall profit from energy generated and saved. We calibrate the model using the literature, industry reports, and the data from different, at times conflicting, climate projections. We then conduct a case study for a mid-size city in the U.S., perform extensive sensitivity and robustness analyses and provide insights.
... This study found that the temperatures of the insulation top layer and the roof membrane top layer were nearly identical for the two types of roof assemblies [7]. Another study confirmed that snow eliminates the potential heating energy savings by installing green roof assemblies, but the total energy savings were proved to be statistically significant regardless of the accumulated snow [8]. Additionally, an experimental study indicated that the snow layer has a strong influence on the heat transfer through the roof assembly, and reported that, with an accumulated snow layer, the green roof and the reference roof had relatively the same seasonal heat losses [9]. ...
... To compare the thermal performance of different roof types in more details, a previous study performed ANOVA analysis. The results showed that the effect of roof type on heat loss is statistically significant (pvalue < 0.05), and concluded that the green roof buildings performed better than the reference buildings due to reduced heat losses of 5%e23% as shown in Table 2 [8]. ...
... Second, the behaviour of these roofs (known as cool roofs) is not always beneficial in winter. This could be due to the shading effect of vegetation on the roof but also due to the higher thermal conductivity of water in wet green roofs and the evapotranspiration of vegetation [27]. Liu and Minor [28] showed that with a proper drainage and insulation layer this problem could be solved for a cold climate like Toronto (Canada). ...
... The winter week is simulated to check the effect of the roof during the winter. Several studies have shown that cool roofs (such as white and green roofs) can lead to additional heat loss and increased heating demand [27,37,38]. The simulations are done in a free running mode in winter (same as in summer) to not being influenced by the heating system. ...
... Studies of green roof performance during the winter season have predominately focused on building thermal aspects (Nagase et al. 2022;Tang and Qu 2016;Zhao and Srebric 2012) and the influence of snow accumulation on building heat transfer processes (Gunn et al. 2021;Lundholm et al. 2014). Lundholm et al. 2014 found that taller and denser plants contributed to greater snow depths, resulting in lower substrate temperatures and reduced heat transfer. ...
In North America, the adoption of green roofs (GRs) has been primarily driven by benefits such as stormwater management that they provide in the growing season. However, a large part of the continent, especially Canada, experiences long winters during which vegetation is dormant and the substrate is frozen. As climate change progressively impacts winter precipitation characteristics, these ground conditions contribute to an increased probability of winter floods. It is important to identify how these green stormwater systems operate year round to maximize their execution as climate adaptation solutions. This study evaluated snowpack accumulation and stormwater quality for extensive GRs that vary in vegetation type and biochar amendment. Snow depth and density measurements were collected over two winter seasons to observe the change in snow cover based on vegetation type. Vegetation analysis concluded that native plant mix contributed to significantly greater snow depths than sedum, but overall snow accumulation of both the native and the sedum GR testbeds was similar to a conventional roof. Green roof leachate samples were collected and analyzed for pH, electrical conductivity, total solids, total suspended solids , and total dissolved solids. These results were compared across GR treatments, as well as to a conventional roof membrane and undisturbed snow samples. Green roof testbeds that were partially covered with native plants had similar total solids to the testbeds with full sedum coverage, both of which were greater than the control samples. The addition of biochar did not significantly alter discharge water quality. This work demonstrated that the type of vegetation used for GR systems and its cover density potentially impacts snow accumulation. Additionally , despite the long periods of frozen growing media, these systems continue to leach pollutants through the winter seasons.
... While most studies focus on the green roof performance during summer months [12,[24][25][26][27][28][29] and aim to evaluate the potential energy saving in space cooling, only a few present year-around measurements [14,30]. This concentration of green roof studies during summer is probably because: (1) green roofs are considered more effective in reducing cooling loads in summer rather than heating loads in winter [31], (2) plants' role in decreasing heat flux due thick coverage and related higher albedo than substrate, is more relevant in summer, and (3) is easier to measure as green roofs in colder climates usually have abundant vegetation in summer but it might be dormant or completely covered by snow [3,32] or affected by frost in winter [33]. ...
Green roofs, integrated into conventional buildings, offer valuable thermal benefits, with extensive research and validated models focused on specific climates and summer conditions. However, their applicability requires further refinement, as conflicting year-round performance results have been observed. This study investigates the thermal performance of unvegetated green roofs with various depths in Melbourne, Australia, over almost a year. Utilizing Sailor’s green roof model, the research reveals reasonable accuracy for winter and deeper roofs, but notable discrepancies for 100 mm thick green roofs during the day. Additionally, the study provides experimental data on non-vegetated green roof top temperatures of a typical building in South-East Australia. Night and day comparisons are emphasized to identify model limitations due to different energy balance mechanisms of green roofs. Despite recognizing the green roof substrate’s role in regulating heat flux, few studies independently examine its thermal benefits. Implemented in EnergyPlus, the green roof model is modified for input ranges, including thermal conductivity and leaf area index (LAI), enabling simulations of the three experimental unvegetated green roofs. A refined green roof model is suggested, considering substrate moisture content variations, associated thermal conductivity, and distinct thermal mechanisms during day and night.
... However, green roofs do not always provide energy savings related to weather conditions [64]. Green roofs may greatly cut power usage for air conditioning in the rainy tropics [65], and in cold weather, even in the presence of snow, green roofs can be energy efficient [66]. However, green roofs have no significant effect on rainy weather [67]; in desert climates, they are even harmful [68]. ...
Green roofs are generally acknowledged as environmentally sustainable roof systems with several environmental, economic, and social benefits, as well as an effective and practical strategy for mitigating the negative consequences of urbanization. In this paper, we used CiteSpace and VOSviewer bibliometric software for visual analysis, citation analysis, co-authorship network, co-citation analysis, and keyword analysis for descriptive statistics on 3986 articles on “green roofs” published in the Web of Science core database since 2000. Descriptive statistics were used for citation analysis, co-authorship network, co-citation analysis, and keyword analysis. According to a review of green roofing-related research literature, (1) Through analysis from three dimensions of country, institution, and author, it was found that China, the United States, and Italy ranked among the top three countries in terms of green roof publication volume; All but three of the top 10 institutions in terms of publications are from China and all are from developed countries; A large-scale collaborative network has not yet formed among authors. (2) Through keyword clustering analysis, it was found that “green roof,” “performance,” and “UHI” were the three keywords with the highest frequency. The research direction of this theme mainly includes five primary themes: rainwater management, urban biodiversity, building energy efficiency, alleviating urban heat islands and improving air quality, sustainable development, and public health. Through keyword hot words, it is found that the frequency of occurrence is relatively high, mainly involving energy conservation, alleviating urban heat islands, biodiversity, and sustainable development. The research on sustainable development, its impact on urban microclimate, and air quality remains a hot topic through keyword highlighting. (3) Co-citation analysis was used to identify the most influential journals, highly cited publications, and authors. (4) Three potential study objectives have been identified: synergistic development with other green infrastructures from an urban planning standpoint, localized research on green roofs, and photovoltaic green roofs.
... The analysis was performed in a probabilistic fashion to embrace the variety of cost and benefit values that were elicited from the academic literature reviewed. In fact, scientific knowledge represented by the published CBA results has become subject to debate (Vijayaraghavan, 2016), whereby studies can be found contradicting one another (see for instance, Jim and Tsang, 2011;Santamouris et al., 2007;Zhao and Srebric, 2012). Such a context of uncertainty and disagreement over cost and benefit values in CBAs has traditionally been dealt with probabilistic CBAs (Nassar and Al-Mohaisen, 2006). ...
... Green roofs' ability to provide thermal protection may help buildings to use less energy and experience less thermal load [1][2][3][4]. Also, the configuration (thickness) of drainage and substrate layers and their materials' thermal and physical properties can affect the insulation performance and water-holding capacity of green roof systems [5][6][7]. ...
This study conducted a sensitivity analysis and assessed the effects of long-term weather conditions on green roof models, including recycled and artificial materials. Climate conditions can affect the hygrothermal performance of green roof materials, but this important issue has hardly been evaluated for drainage and substrate layers made of recycled and artificial materials. Climate change makes it unclear how well green roofs will perform hygrothermally. Moreover, the heat flux sensitivity to the thickness and physical characteristics of green roofs with artificial and recycled materials has received less attention. This study applied three weather scenarios on green roof models with artificial and recycled materials: the beginning, middle, and end of the 21st century. As per the results, at the beginning and middle of the 21st century, substrate layers’ water content was roughly nine times more than the drainage layers’. At the end of the 21st century, the comparable difference was 6.5 times larger. During the summer and the beginning of autumn, the green roofs’ thermal performance with recycled and artificial materials was improved until the end of the 21st century. The entire parameter change demonstrated the scatter of thermal conductivity, density, and thickness effectively influenced the dispersion of heat flux for the green roof layers. Also, the density scatter was more effective in heat flux dispersion for the substrate layer than the drainage layer.
... On the other hand, the building's design with a green roof leads to increased stability and proper management of torrential rains and rainwater [25,26]. Studies illustrate that green roofs generally reduce energy consumption throughout the year, but this amount is more significant in hot seasons than in cold seasons [27]. The impact of green roofs on energy consumption in the Mediterranean region shows that energy consumption decreases by 33% and 6% in hot and cold seasons, respectively [28,29]. ...
This paper presents a novel study on the multi-objective energy audit and management of a proposed plus-ZEB covered by a green roof in Tehran’s climate. The planning impact of changing a proposed plus-ZEB to an intensive plus-ZEB is also evaluated. The planning is performed for one year based on Tehran’s accurate urban climate data. The plus-ZEB consists of renewable and non-renewable resources like CHP, boiler, furnace, photovoltaic, solar water heater, wind turbine, air to the water heat pump, electric heat pump, and chiller boiler units in addition to energy storage to supply diverse electrical, thermal, and cooling demands of the presented building. The planning’s functions are included in the total cost and emission of the plus-ZEB. The objective function prioritization is also participated to show the planner’s decision on the function. Also, diverse solvers are implemented to evaluate and compare and validate results. The problem is simulated in energy plus to assess the amount of demands, construction materials, and energy audit issues; then, the results transfer to the GAMS software for energy management of the proposed plus-ZEB by utilizing a green roof. The problem in GAMS is modeled as a real mixed-integer programming (RMIP) and solved using the augmented epsilon constraint method (AEC). The final results show the significant effect of the proposed planning on reducing the cost and emission of the plus-ZEB, in which the total cost and pollution are decreased by about 7.4 % and 10.6 %, respectively.
... In addition, the two roofs in [7] showed similar performance during the shoulder seasons and during times of snow cover. [8] concluded that the presence of snow diminished the capability of a green roof to save on building energy expenditure. A more recent study by [9] found that snow cover stabilized growth substrate temperatures and thus heat flux through the green roof, demonstrating that snow cover may help isolate the outer-most layer of the green roof from ambient temperatures. ...
Research suggests that—relative to conventional roofs—green roofs can significantly reduce rooftop heat exchange in moderate climates; however, limited research exists on the performance of green roofs in colder climates. This paper analyzes the comparative performance of two side-by-side roof assemblies: a conventional roof and a green roof located in the temperate climate of Ottawa, Canada. Using two years’ worth of temperature and solar radiation data, we analyze variations in the incremental thermal benefit of the green roof relative to the conventional roof. We discuss factors contributing to these variations, such as precipitation and ambient temperature. Our results indicate that the green roof under investigation reduced thermal transmittance by 31.5% on average across two years. Although the percent benefits were much higher during the summer months, reductions in thermal transmittance were consistently above 7.7% throughout both years, indicating green roofs may be an appropriate alternative to conventional roofs in climates with hot, humid summers and cold, snowy winters.
... Changing materials (Doulos et al., 2004;Carnielo and Zinzi, 2013) and adding vegetation (Oliveira et al., 2011;Ng et al., 2012;Morakinyo and Lam, 2016;Morakinyo et al., 2017;Sun et al., 2017) are two common strategies. Using highly reflective materials in buildings and urban spaces (Synnefa et al., 2007;Akbari and Levinson, 2008), integration of high-tech materials (Zhu and Wu, 2001;Karlessi et al., 2011), increasing the amount of vegetation in buildings in the form of green roofs and green facades (Niachou et al., 2001;Santamouris et al., 2012;Zhao and Srebric, 2012) and increasing the area of urban greenery in urban parks and green streets (Taha et al., 1991;Shashua-Bar and Hoffman, 2000;Chen et al., 2012;Georgi and Zafiriadis, 2006;Lobaccaro and Acero, 2015) are some of these proposed techniques. Rosenfeld believes that three strategies are important in mitigating the UHI effect: a. cool roofs, b. cool pavements, and c. vegetation for evapotranspiration (Rosenfeld et al., 1995;Alexandri and Phil, 2008;Dvorak and Volder, 2013). ...
Given the role of open spaces in quality of living environment and the importance of climatic comfort for effective usage of such spaces, this research examines the impact of vegetation in producing thermal comfort in the hot arid Sistan Province, southeast Iran. For this purpose, 29 points were selected in Zabol University in two different locations—adjacent to buildings and vegetation; or solely surrounded by vegetation. The climatic parameters were then measured 3-hour intervals for these points during the warmest summer days of August 2016 at three microclimate, local and city levels. The parameters measured were air temperature, relative humidity, wind velocity, etc. These measurements were then used to calculate the Wet Bulb Globe Temperature (WBGT) as the main comfort criteria in open spaces.The results indicate that vegetation can bring all climatic parameters to comfort levels in their immediate proximity. These parameters are not affected in their vicinity, however. Therefore, mean climatic comfort was higher at microclimatic level as compared with local or city levels. Furthermore, the parameters most affected by vegetation were found to be wind velocity and average radiant temperature.
... The only exception from the general pattern of larger temperature fluctuations for the black roof occurs on winter days with snow cover and during snowmelt. In the snow-covered winter months, the surface temperatures of the black and the green roof sections were nearly identical, confirming findings reported for other cold snowy climates that the snow acts as an equalizer (Getter et al. [14]; Zhao and Srebric [27]; Lundholm et al. [28]). This also indicates that different snow depths due to snowdrifts or different snow accumulation patterns for the black and the green roof surfaces had little effect on the surface temperatures. ...
Green roofs are complex systems, with a vegetation layer covering the outermost surface of the building shell. An effective design may confer environmental and energy benefits. Most field studies evaluating green roof performance have been conducted in warmer climates with few studies of full-scale green roofs in cold regions. No study has so far evaluated the energy performance of a green roof in a sub-arctic climate. This study demonstrates the heat flow and thermal effect of an extensive green roof versus a black bare roof area on a highly insulated building in the sub-arctic town of Kiruna, Sweden, for the period from November 2016 to February 2018. Measured temperature and heat flux values were consistently higher and more variable for the black roof than the green roof, except during the snow-covered winter months when the responses were similar. The cumulative heat flux showed that the net heat loss was greater through the black than the green roof, but the values remained low. Overall, the study confirms that the energy benefit of a green roof on a highly insulated building in a subarctic climate is low.
... The roof slope and media depth helps in minimizing runoff quantity by increasing time duration than actual rainfall [38].Green roof shows energy efficiency reducing cooling load and heating load of the buildings in summer and winter season respectively [16]. Green roofs affects thermal performance minimizing heat flow and heat energy of the buildings especially in winter season [39]. It keeps indoor air cool, enhances air quality and helps in noise conservation [40]. ...
Green roofs have emerged as an alternative in mitigating outdoor thermal environment, reducing air pollution, minimizing noise and enhancing green stock of the nature. The technology is beneficial as it helps in the proper regulation of carbon cycle and managing greenhouse gases, slowing down energy consumptions, along with light and thermal defects in the environment. Besides, these structure also contribute in managing stormwater runoff and increasing lifespan of roof membranes. The installation of
green roof for minimizing the impact of urbanization is based on historical climatology, and geographical conditions of the region. This paper emphasizes new innovations and researches on green roofing technology, mainly its designing and management, along with improvement and exploring new concepts for a safer environment and public health.
... Increasing substrate thickness has a positive effect on heating load as its value decreases compared to the baseline due to increased insulation. This finding agrees well with results reported from cold climate regions (22,23) where it was found that reduction of heating load is achieved by increasing substrate thickness and associated insulation. In contrast, cooling loads slightly increase due to greater thermal mass which reduces the cooling effect of the green roof occurring near the green roof surface was observed by La Roche and Berardi (24). ...
Three experimental green roofs in Melbourne with depth of 100, 150 and 300 mm have been assessed to quantify their thermal performance. To evaluate the benefit of substrate depth, temperature was recorded every 50 mm along a vertical profile. Green roofs consisted of scoria substrate and a mix of three species of plants: Lomandra longifolia, Dianella admixta and Stypandra glauca. Statistical analyses applying the hierarchical partitioning technique showed that solar radiation is the main driver affecting the green roof surface temperature, air temperature has strong correlations with the variations of the temperatures recorded below the surface, while moisture content has the least influence. Temperature profiles of the green roof show that the first 50 mm do reduce the heat flowing through the green roof substrate regardless the total green roof substrate depth. Differences in thermal performance arise at deeper points, where thicker green roofs are able to delay the change of substrate temperatures. Similar effects were found for the heat fluxes measured at the interface between the green roof and building roof. These results confirmed that green roofs may be used as a sustainable passive technology to reduce building energy consumptions for South-East Australia climate.
... Regarding green roofs, an observational study in Hong Kong found that green roofs offer passive and effective warming of indoor space in winter [22]. Additionally, a field experiment in Pennsylvania found that green roofs reduce the heat flow through the roof and keep the indoor temperature at a certain level during the winter [23]. All these studies confirm that cool/green roofs will impact not only extreme heat in summer but also other seasonal temperature conditions, such as cold in winter. ...
Many cities are developing mitigation plans in an effort to reduce the population health impacts from expected future increases in the frequency and intensity of heat waves. To inform heat mitigation and adaptation planning, information is needed on the extent to which available mitigation strategies, such as reflective and green roofs, could result in significant reductions in heat exposure. Using the Weather Research and Forecasting (WRF) model, we analysed the impact of green and cool (reflective) roofs on the urban heat island (UHI) and temperature-related deaths in the Greater Boston area (GBA) and New England area (NEA) in summer and winter. In the GBA, green and cool roofs reduced summertime population-weighted temperature by 0.35 °C and 0.40 °C, respectively. In winter, green roofs did not affect temperature, whereas cool roofs caused a temperature reduction of 0.40 °C. In the NEA, the cooler summers induced by green and cool roofs were estimated to reduce the heat-related mortality rates by 0.21% and 0.17%, respectively, compared to baseline. Cool-roof-induced temperature reduction in winter could increase the cold-related mortality rate by 0.096% compared to baseline. These results suggest that both green and cool roofing strategies have the potential to reduce the impact of heat on premature deaths. Additionally, the differing effects in winter suggest the need for a careful consideration of health trade-offs in choosing heat island mitigation strategies.
... Solar Energy 202 (2020) 485-497 ventilation could save up to 26.7% of the energy used. Some of the studies (Imran et al., 2018;Köhler et al., 2002;Lin et al., 2013;Zhao and Srebric, 2012;Ziogou et al., 2017) indicated that the energy-saving performance of the green roof depends on various factors (e.g., building and climatic conditions). Green roofs perform more effectively in the regions (e.g., Spain) where the summer is hotter . ...
... Changing materials (Doulos et al., 2004;Carnielo and Zinzi, 2013) and adding vegetation (Oliveira et al., 2011;Ng et al., 2012;Morakinyo and Lam, 2016;Morakinyo et al., 2017;Sun et al., 2017) are two common strategies. Using highly reflective materials in buildings and urban spaces (Synnefa et al., 2007;Akbari and Levinson, 2008), integration of high-tech materials (Zhu and Wu, 2001;Karlessi et al., 2011), increasing the amount of vegetation in buildings in the form of green roofs and green facades (Niachou et al., 2001;Santamouris et al., 2012;Zhao and Srebric, 2012) and increasing the area of urban greenery in urban parks and green streets (Taha et al., 1991;Shashua-Bar and Hoffman, 2000;Chen et al., 2012;Georgi and Zafiriadis, 2006;Lobaccaro and Acero, 2015) are some of these proposed techniques. Rosenfeld believes that three strategies are important in mitigating the UHI effect: a. cool roofs, b. cool pavements, and c. vegetation for evapotranspiration (Rosenfeld et al., 1995;Alexandri and Phil, 2008;Dvorak and Volder, 2013). ...
... Thermoregulation in warm and cool seasons has a demonstrable impact on green roof cooling and heating load, respectively (Jim and Peng, 2012a;Zhao and Srebric, 2012). For example, Liu and Minor (2005) found in an experimental study in Toronto, that green roofs reduced heat flux from the roof substrate to the indoor environment by up to 90% during summer, and indoor heat loss by up to 30% during the winter compared to conventional bare roof surfaces. ...
The thermoregulation of buildings and cities by green roofs is a primary driver of their integration into urban environments. In warm seasons, green roofs cool buildings (thereby reduce interior air conditioning costs), and cities (impervious surfaces contribute to urban heat islands and vegetation mitigates contributions by conventional roof surfaces). In cool seasons, green roofs insulate buildings by reducing heat flux through the roof surface. Here we investigate thermoregulation services provided by extensive green roofs in warm and cool seasons from temperature data points recorded at 5-minute intervals over a four-year period, and from modules containing either Sedum or perennial grasses and herbaceous flowers, mineral- or organic-based substrate, 10 cm or 15 cm substrate depth, and supplemental irrigation or none. We demonstrate that Sedum outperformed a mixture of perennial grasses and herbaceous flowers over the total inter-annual survey period. The meadow mixture was more dependent on supplemental irrigation than Sedum, but more susceptible to inter-annual climate variability. Our findings point to the durability of Sedum as a plant for extensive green roof cooling, as well as the importance of plant selection and identifying traits that match not just microclimatic conditions in summer, but also in winter.
... In addition, most validated models from warm temperate (climate zone C) or snow/boreal (climate zone D) zones exclusively used data from the summer period, missing the winter season, and only two had validation on winter [80,81]; however, these models were not validated in the summer period. Note that the benefits of a green roof could be affected by the presence of snow on the roof because it would change the heat flows through the system and freezing of the substrate [81,121,122]. ...
Vegetated or green roofs are sustainable roofing systems that have become increasingly widespread across the world in recent decades. However, their design requires accurate numerical modeling to fully realize the benefits of this technology at the building and larger scales. For this reason, several heat and mass transfer models for vegetated roofs have been developed over the last 36 years. This paper provides a critical review of more than 23 heat transfer vegetative roof models developed between 1982 and 2018 that have been used for building energy or urban modeling purposes. Findings of the study include the following: (i) more than 55% of the vegetated roof models have been developed and validated using data from warm temperate climate zones; (ii) green roof validation efforts vary and do not follow a common verification and validation framework; (iii) four of the reviewed models have not been subjected to any simulation process; (iv) no model has been validated for semi-arid conditions or cold climates or during cold winter conditions; (v) the most common variable reported for validation (in more than half of the models) is substrate surface temperature; however, surface temperature does not fully test the accuracy of a model to represent all heat and mass transfer phenomena; (vi) practitioners access to these models is limited since only five of the 23 models have been implemented in whole-building energy models, such as EnergyPlus, TRNSYS, ESP-r, and WUFI; finally, (vii) despite the extensive studies on the impacts of vegetative roofs on building energy performance and urban temperature reduction, no studies have validated the model using whole-building energy data or at larger scales.
... The difference of 14°C, 16°C, and 18°C in 24 hour period for three types of green roof assembly was significantly lower comparing to the conventional roof where difference of 40°C in 24-hour period was consequential and could induce serious damage over time. In extreme climates with high snow in winters, implementing the green roof, significant reduction of the heat losses was recorded [14]. ...
Altering the surface cover of an area causes the change in the environment. By erecting buildings change in the flow of energy and matter through the urban ecosystems occurs creating multiple environmental problems. Built areas exert considerable influence over their local climate, amplifying problems such as heat waves, air pollution, and flooding. Greening the building envelope these problems can be partially mitigated. By combining nature and built areas in their designs, architects and urban planners can respond to these serious human health and welfare issues and restore the environmental quality of dense urban areas. Green living systems are not the only solution for new designs. Retrofitting existing buildings by altering the buildings' surficial properties can reduce buildings' energy consumption in case of older buildings with poor existing insulation. Implementation of green living systems in the building envelope, greening horizontal surfaces with intensive and extensive green roofs or using vegetation in vertical greening systems for façades, is a strategy that provides ecological, economic, and social benefits. This review paper presents collected evidence of effects and explores the important role that the green living systems can play in the dense urban areas. Benefits such as heat island amelioration, reduction of buildings energy consumption, air quality and indoor and outdoor comfort conditions improvement, stormwater management and improved water run-off quality, will be mainly considered. [Project of the Serbian
Ministry of Education, Science and Technological Development, Grant no.
III42008]
... 23% compared to a conventional roof, but the difference is only 5% with a layer of snow on top. Preliminary results from the same measurements were also described in a 2012 article [70]. Tang and Qu [71] examine the effect of the phase change of water on the thermal properties of green roofs. ...
Green and blue-green roofs are emerging as an increasingly popular feature of rooftops, particularly in urban areas. Particular problematic conditions render their usage complex in the Nordic countries. In order to ensure that green roofs are built durable and with the service life expected of them, it is important to know all the relevant factors surrounding their construction and operation. A scoping study was conducted in order to gain an overview on green roof research and available scientific literature. One hundred articles of particular interest for Nordic climates were retrieved and their findings summarized. It is found that the vast majority of green roof research has been conducted on a theoretical basis, or with practical measurements on green roof test beds or isolated components. There is scarcely any literature on the operation of full-scale, building-implemented green roofs, and no articles were found on the building technical performance of aged green roofs. These knowledge gaps indicate a major risk factor in green roof operation, as their performance and integrity over time has not been documented. This despite the fact that green roofs have been implemented and in operation worldwide for decades.
... For instance, during the winter, the green roof acts as an insulator and decreases the heat flow, although this benefit has been often-debated. Some studies have claimed that a green roof saved energy [31], some identified that a green roof had no influence on energy consumption during the winter [32], while still others viewed it as the cause of increased energy consumption [33]. Researchers in Japan found that the peak sensible heat fluxes (Q H ) were small for the white roof (153 W/m 2 ) during a summer day, but the Q H of the green roof was twice as much as that of the white roof [34]. ...
This study presents the experimental measurement of the energy consumption of three top-floor air-conditioned rooms in a typical office building in Chongqing, which is a mountainous city in the hot-summer and cold-winter zone of China, to examine the energy performance of white and sedum-tray garden roofs. The energy consumption of the three rooms was measured from September 2014 to September 2015 by monitoring the energy performance (temperature distributions of the roofs, evaporation, heat fluxes, and energy consumption) and indoor air temperature. The rooms had the same construction and appliances, except that one roof top was black, one was white, and one had a sedum-tray garden roof. This study references the International Performance Measurement and Verification Protocol (IPMVP) to calculate and compare the energy savings of the three kinds of roofs. The results indicate that the energy savings ratios of the rooms with the sedum-tray garden roof and with the white roof were 25.0% and 20.5%, respectively, as compared with the black-roofed room, in the summer; by contrast, the energy savings ratios were −9.9% and −2.7%, respectively, in the winter. Furthermore, Annual conditioning energy savings of white roof (3.9 kWh/m²) were 1.6 times the energy savings for the sedum-tray garden roof. It is evident that white roof is a preferable choice for office buildings in Chongqing. Additionally, The white roof had a reflectance of 0.58 after natural aging owing to the serious air pollution worsened its thermal performance, and the energy savings reduced by 0.033 kWh/m²·d. Evaporation was also identified to have a significant effect on the energy savings of the sedum-tray garden roof.
... In cold regions, such as Canada, green roofs have been reported to reduce daily surface temperature fluctuation significantly due to the absorption of solar radiation by green roofs [13]. Additionally, green roofs demonstrated the reduction of the heat flow in extreme climates with highly snowy winters [14], and other researchers reported that the impact of the green roofs on the surface temperature and the heat flux were low in winter (12% on average) [15]. ...
... Recent studies in the Mediterranean climate found that with higher plant density, green roofs may provide a reduction in the cooling energy consumption of 50% when compared to a conventional roof [10,18]. The benefits of green roofs in cold climates have also been acknowledged [19][20][21]. However, contrasting results have been found in climates with different weather conditions during the year. ...
Green roofs have been proposed for energy saving purposes in many countries with different climatic conditions. However, the energy saving potential of green roofs depends on several aspects, such as the climate characteristics or the building loads. For this reason, the authors have been working on ways to modify the thermodynamic behavior of green roofs through passive low energy systems operating according to rules based on the relationships between the indoor and outdoor temperatures. This paper discusses the improvements in indoor thermal comfort which can be obtained by adopting water-to-air heat exchangers and indirect evaporative and radiant cooling strategies in buildings with green roofs. The study specifically looks at the effect of combining a simple evaporative/radiant system that cools the water pond where the water-to-air heat exchange occurs. Ad-hoc built test cells were investigated in southern California for over a year. Overall, the water-to-air heat exchangers proved to cool the indoor air in the test cells by almost 10 °C when the exterior temperatures were above 35 °C. In this system, the heat from the interior of the cells that could not be absorbed by the green roof, was transferred to the coupled water sink, and then dissipated into the atmosphere. This study shows that the benefits of the water-to-air heat exchange and of the evaporative cooling system are promising, while the water consumption is limited. Finally, the experimental investigation summarizes the benefits of combining green roofs and evaporative and radiant cooling of a water-to-air heat exchanger as a solution for building cooling and proposes simple equations to anticipate their temperature cooling effects.
... As a proof that the selection of substrates and plants is essential to maximise the green roof thermal performance for cold climates (Zhao et al., 2014), it was found that in summer a thick and light substrate offers higher insulating thermal mass and retention of moisture for evaporative cooling than a thin dark substrate (Liu, 2003). In winter, the thermal advantage is considerably smaller than in summer, because the extra snow layer facilitates the heat loss from indoor to outdoor and drastically reduces the insulation properties of the green roof (Liu, 2003;Zhao and Srebric, 2012). Even doubling the thickness of substrate from 75 to 150 mm, has no significant impact in enhancing the thermal performance in winter (Lundholm et al., 2014). ...
In Australia, there is an increasing interest in using extensive green roofs to make buildings more sustainable and provide a number of social, ecological, aesthetic and thermal benefits to cities. The potential of green roofs to reduce building energy consumption has been extensively studied overseas in a variety of different climates. However, in Australia the green roof industry is relatively new. There is still very little information on the thermal properties of Australian green roofs and their performance. Further, as a relatively new industry, there is a general lack of specific policies and initiatives to promote green roofs. In this paper, we briefly review the research investigating green roof thermal performance in various climates and analyse policies and actions that have been implemented internationally to foster green roofs with an emphasis on their thermal performance.
The results showed that most policies were focused on ecological benefits, such as stormwater runoff reduction, rather than thermal benefits. Many green roof policies had difficulty interpreting the thermal performance of green roofs, because of the dynamic nature of green roof R-values. In this study, the effectiveness of overseas green roof policy is discussed and recommendations how they could be adapted for Australian cities are provided.
... Zhao and Srebric acknowledged the significant reduction of the heat flow thanks to green roofs in extreme climates with highly snowy winters [51]. In Toronto, an experimental study on two extensive green roofs (soil depth between 75 mm to 100 mm) found that the roof heat gain reduced by 70-90% in summer while the heat loss reduced by 10-30% in winter [52]. Temperature measurements using thermocouples placed in the roof measured how the internal temperatures were delayed thanks to the presence of the thermal mass of the soil. ...
... The authors also identified that maximum energy savings depend strongly upon the plant species as well as type and thickness of growth medium. During winter, green roof act as insulators decreasing heat flow; however this benefit is often under debate as some studies claimed green roof as a medium to save energy [35], others identified that green roof has no influence during winter [36] and some viewed it as a cause of more energy consumption [37]. Considering these controversial results, it is suggested to conduct more research on impact of seasonal variations on thermal performance of green roofs. ...
With the shortage of energy and the promotion of environmental protection awareness, building energy saving (BES) has caused great concern in the world, the research related to BES is more and more. It is vital for interested researchers to get the full picture of global research. However, the current research review in the field of BES mainly focuses on the application summary of single BES technology, and there is a lack of summary of other latest research progress in this field, which makes it difficult for new researchers to clarify the development status and future research direction in the field of BES. Based on a review of the literature on BES published from 2010 to 2020, combined with bibliometric analysis and science mapping, this paper discusses the research trend in the field of BES in the past decade, as well as the co-authorship and influence of countries or regions, authors. This paper summarizes the main trend and deficiency of the current research on BES around three themes: energy saving design methods, energy simulation and optimization, energy measures drive and barrier. Future potential research directions are proposed, including: focus on the life cycle assessment of BES measures, the research about accuracy of energy performance evaluation, the intelligent integration of energy simulation software and cost evaluation, the research about influence factors of energy saving measures drive and barrier as well as the quantitative research of interaction relationship.KeywordsBuildingEnergy savingBibliometric analysisScience mappingFuture direction
Urban green infrastructures (UGI) have been suggested as a natural solution to tackle the problem of human thermal comfort as well as to reduce energy consumption in buildings under the pressures of rapid urbanization and global warming. However, the acceptance of UGI to mitigate the urban heat effect is not yet universal. The development of such an infrastructure is also not consistent across the regions, emphasizing the different objective parameters and methodologies. A systematic review has been conducted to analyze the published research work on UGI, targeting thermal comfort, in the past decade to identify the trends of UGI development around the world. The result shows that most of the studied locations were situated around the Mediterranean Sea region in a temperate climate, and most of the studied cities are within countries with a high gross domestic product, large urban area and urban population, primary energy consumption, and high greenhouse gas and carbon dioxide emissions. Extensive green roofs are the most popular type of UGI and mostly use Sedum plants. In the published studies, experimental setups are the most common methods by which to collect data. EnergyPlus is the most popular software used to conduct energy analysis for buildings, whereas ENVI-met is more commonly used for microclimate analysis. These results indicated that the direction of UGI studies is driven by climate characteristics and the socioeconomic factors of geographical location, which favor low construction cost and maintenance needs, with a minimal irrigation requirement for small-scale UGI projects. Understanding the trend of UGI approaches for thermal comfort allows researchers to standardize practices that help the decision-making process for future researchers while recognizing the limitations and potential of current UGI practices. It is recommended that future studies should include arid and equatorial climate regions, with more focus on large-scale projects including high-rise building environments to comprehensively evaluate the effectiveness of UGIs.
Effectively controlling and reducing the energy consumption of buildings is the global focus. A considerable variety of research on building energy saving (BES) had been raised in the past. However, most of the previous reviews focus on a single topic within the area, and systematic review and objective analysis are lacking. This study comprehensively reviews 2569 papers on BES published between 1974 and 2020 through bibliometrics, network mapping analysis and in-depth content analysis to fill this research gap. This paper discusses the development evolution and research trends in the field based on the analysis results, and the following three major research themes are identified and discussed: (1) influence factors of building energy consumption (BEC), (2) implementation of BES and (3) barriers and drivers of BES. Lastly, the current study indicates the possible potential research direction in the future; for example, intelligent integration of energy management and control system, quantitative and qualitative analyses of the interaction of BESM and comprehensive summary and quantitative analysis of the driving and hindering factors of BES. The contribution of this study is that it can help scholars and practitioners to have a comprehensive cognition of the research status and trends in the field of BES.
Green roofs are an interesting technology that has attracted worldwide attention because of the multi-disciplinary benefits, involving the improvement of stormwater management, the mitigation of the urban heat island effect, the prolonged lifespan of the roof membrane, the enhancement of urban aesthetic, the creation of recreational spaces, and the possibility to generate energy savings for building heating and cooling. Several papers dealt with green roofs, spacing from quantification of runoff quality and quantity, to the evaluation of plant and substrate intrinsic characteristics, to the social aspects related to the installation of vegetated surfaces in densely populated cities. A big share of research has investigated the thermal performances of different green roof solutions in the attempt to assess the effect on the building energy demand. A lot of studies have been conducted through experimental research on properly instrumented green roofs or by numerical simulations implemented in different environments or even by developing and validating thermo-physical models that describe the interaction between the green roof and the surrounding environment. Although the relevant number of papers dealing with the thermal performance of vegetated roofs in the literature, quantitative estimations of the reduction of building energy consumption due to green roofs are not easily found. The paper presents a comprehensive literature review to summarize the relevant findings in terms of energy savings produced by a green roof to offer a suitable answer to the question of the energy effectiveness of such a solution and quantitatively report the results obtained across different climates.
This study investigated the impacts of extensive and semi-intensive green roofs on both building insulation and surface urban heat island effect under winter conditions. To this aim we compared measurements of surface and building envelope temperatures as well as conductive heat fluxes reaching the external building envelope with those measured on a conventional bituminous roof under identical climatic conditions. The main effect of green roofs was to decrease daily fluctuations of external building envelope temperatures and as a consequence to reduce fluctuations of conductive heat fluxes reaching the building envelope. This effect is all the more important that the substrate is deep, in link with its heat capacity and thermal inertia. Yet, no significant effect of the green roofs on surface urban heat island has been observed on average despite a surface cooling during daytime. It is concluded that the green roofs can be suitable urban greening solutions since they do not have negative effect on surface urban heat island during winter, provide cooling during summer, and contribute to building insulation inducing therefore building energy savings.
As two of the highest trending green technologies, photovoltaic panels and green roofs are proven to be effective practices for energy generation and energy saving. The achievable impact from the widespread installation of such technologies is, however, not clearly established. This is mainly because the degree of this impact highly depends on the inherently uncertain environmental and climate factors, as well as the unknown adoption rates of these technologies, which in turn depend on different characteristics of decision makers and interactions among them. To that end, this study aims to investigate the diffusion rate of these green technologies under uncertainties caused by climate change, characteristics of adopters, and their interactions. An integrated framework is developed to capture the interplay between financial and attitudinal aspects, as well as the uncertainties due to both the stochastic nature of system parameters and the interactions among agents involving human beings. Specifically, this framework consists of a integer programming model to optimize the green roof and/or photovoltaic panel installation settings for a given building under climate change uncertainty, and an agent-based model to factor in the role of human behavior and interactions. A case study for the city of Knoxville, TN, is presented to evaluate the effects of different policies on the diffusion rate of the green technologies of interest. The results show that the affordability of green technologies and public awareness are the key drivers of the adoption of these technologies, which highlight the important role of the decision makers in impacting the diffusion rate.
As urban green space, green roof has been increasingly installed in cities mainly for amenities, temperature regulation and energy conservation. Nevertheless, in subtropical urban setting and during winter, the thermal and radiation behaviours of green roofs, especially the intensive type, have remained poorly understood. This paper examined the effect of a woodland-type intensive green roof (IGR) on the roof-level microclimate by comparing temperature and radiation parameters against a reference bare roof (BR). In-situ microclimatic monitoring was conducted on an IGR and BR pair in subtropical Hong Kong throughout a winter. Using objective selection criteria, 30 sampled days with representative winter weather, namely sunny, cloudy and rainy conditions, were identified for statistical analyses of interactions among key factors. The results showed that the woodland canopy intercepted about 90% of incoming solar radiation regardless of weather, thus substantially suppressing the energy source of passive warming, and instead creating undesirable cooling of ground surface and canopy-enclosed air. Surface and air temperatures on IGR were lower than BR, with the highest mean difference reaching 2.77 °C and 2.27 °C respectively in sunny daytime. The vegetation canopy retained some but insufficient outgoing thermal radiation to counteract the observed cooling. Limited solar inputs could only slightly warm the soil which experienced heat loss in cloudy weather to raise indoor heating load. The empirical findings provided the basis to recommend changes in landscape and soil designs to allow IGR to yield thermal benefits in winter and to improve building energy efficiency.
Urban heat island (UHI) significantly affects the thermal-energy performance of the buildings. Moreover, urban materials absorb solar and infrared radiation, heat accumulation is dispersed in the atmosphere, a fact which increases air temperature. In this context, green roofs are the most suitable solution to resolve these vital issues. The expanding benefits of a green roof, such as energy saving, thermal insulation, and mitigating heat island effect emphasize the key role of this structure in overall thermal performance of buildings and microclimate conditions of indoor spaces. The main objective of the study is to analyse the influence of extensive green roof on the heat flow, in the thermal bridges developed structurally in buildings where they might replace the classical terrace roof. The influence is analysed through the comparison of the thermal impact of a classical terrace roof and that of an extensive green roof, through thermal characteristics of their components. The first part of the paper presents the structures of each type of roof and their thermic characteristics established and evaluated according to the normative regulation in force. In this context, the classical terrace roof and extensive green roof are examined from a thermic point of view, analysing the parameters of the types of thermal bridges usually met, in order to establish if the extensive green roof might have an influence on the overall heat flow. In conclusion, the unpredictable results obtained for the analysed thermal parameters let conclude that the extensive green roof solution presents a favourable environmental impact, promoting a “beautiful” added value to a building, in terms of both sustainability and aesthetics.
In the past decade, many studies have proposed tree species selection guidelines for “greening” the urban open spaces as a method to mitigate the rising temperatures and urban heat island effect making the cities into Climate “Hotspots”. The cooling effect of tree species can be divided into two components; cooling intensity and cooling extension. These two components are affected by different factors. This review of the literature reveals the impact of tree species on temperature and on the immediate surrounds. Based on this review, two components that have an effect on cooling intensity and cooling extension were identified: internal factors and external factors which is imperative in the effectiveness of microclimatic comfort in urban open spaces for human activity and well-being. The internal factors or indexes, extracted are as follows; Size index, Shape index, Tree species and Tree canopy coverage are the most common indexes in most of the studies. The external factors can be divided into climate and local environmental parameters. A discussion of the reviewed studies reflects the impact of each index on the cooling intensity and cooling extension. The existing methods and techniques for determining these indexes have also been considered in this paper from various peer reviewed technical papers, journals and reports from 1950 to 2018. Further, this study has identified the gap and the way forward for future research in landscape architecture and other related disciplines on heat mitigation through cooling effect of native trees on microclimatic comfort in urban open spaces, making Cool the climate “Hotspots” in tropical Indian cities.
Keywords: Tree, heat mitigation, cooling extension, cooling intensity, microclimatic comfort
The urban heat island (UHI) phenomenon and the dependency of buildings on
fossil fuels were the two main issues that formed this dissertation. UHI results in higher air temperatures in dense urban areas compared with their suburbs and rural surroundings. This phenomenon affects human health through thermal discomfort. Furthermore, in the Netherlands, it is estimated that by 2050 the air temperature could be up to 2.3°C warmer as compared to the period of 1981-2010. Besides, the energy consumption of buildings is responsible for 30 to 45% of CO2 emissions. 31% of this consumption belongs to residential buildings. Residential buildings can play a major role in reducing the CO2 emissions caused by fossil fuel consumption.One of the passive architectural design solutions is the courtyard building form. Courtyards have been used for thousands of years in different climates in the world. In hot climates they provide shading, in humid climates they cause a stack effect helping ventilation, in cold climates they break cold winds and protect their microclimate. In temperate climates (such as of the Netherlands), the thermal behaviour of courtyards has been studied less. In this dissertation, low-rise residential courtyard buildings were therefore studied among (and along) different urban block types in the Netherlands.As the first step, computer simulations were done as a parametric study for indoor and outdoor thermal comfort. Field measurements were done in actual urban courtyards and in dwellings alongside urban courtyards in the Netherlands (and in a similar temperate climate in the US). A scale model experiment later followed the simulations. Some of these field measurements were used to validate the simulation models. These efforts answered the two main research questions:1) To what extent is a dwelling alongside an urban courtyard more efficient and thermally comfortable than other dwellings?2) To what extent do people have a more comfortable microclimate within an urban courtyard block on a hot summer day than within other urban fabric forms?To answer the first question, the energy performance of and thermal comfort inside dwellings in three types of urban blocks in the Netherlands (each with 1, 2 and 3 stories) were analysed (with an identical floor area). The main objective of the research was to clarify the effect of building geometry on annual heating energy demand, thermal comfort, heat loss, solar gains through external windows and on overheating in summer. The buildings had different surface to volume ratios owing to different shapes: single, linear and courtyard shape. The single shape model is more exposed to its outdoor environment and has the highest surface to volume ratio. The linear models consist of a row of dwellings, which leads to a smaller area exposed to the outdoor environment, and this amount is the lowest for the courtyard models. The single dwelling has a higher surface to volume ratio and this model has the highest solar gains. The average amount of energy demand for heating in a year for the single shape is the highest among the models. However, the lighting energy demand for the single shape is the lowest. The linear and courtyard models are very similar in lighting energy demand. The courtyard shape has the lowest energy demand for heating
since it is more protected. Considering thermal comfort hours in free running mode, the courtyard shape has the lowest number of discomfort hours among the models. Reducing the external surface area exposed to the climatic environment leads to higher energy efficiency and improved summer thermal comfort performance. Therefore, this analysis showed that the courtyard shape proves to be more energy efficient and thermally comfortable than other dwellings.For the second research question, the microclimate within the urban block forms previously studied (singular, linear and courtyard) were simulated, each with two different orientations (E-W and N-S, except for the courtyard). To explore their microclimates the simulations were done for the hottest day in the Netherlands (19th June 2000) according to the temperature data set provided in NEN5060. The results showed that the singular forms provide a long duration of solar radiation exposure for the outdoor environment. This causes the worst comfort situation among the models at the centre of the canyon for a hot summer day. In contrast, the courtyard provides a more protected microclimate which has less solar radiation in summer. Considering the physiological equivalent temperature (PET), the courtyard has the highest number of comfortable hours on a summer day. Regarding the different orientations of the models and their effect on outdoor thermal comfort, it is difficult to specify the differences between the singular E-W and N-S forms because they receive equal amounts of insolation and are equally exposed to wind. Nevertheless, the linear E-W and N-S forms are different in their thermal behaviour. The centre point at the linear E-W form receives sun for about 12 h. In contrast, this point at the linear N-S form receives 4 h of direct sunlight in that day. Therefore, in comparison with the E-W orientation this N-S orientation provides a cooler microclimate.To sum up the above findings, it should be said that this study showed that courtyard buildings as a passive design solution (originally from hot and arid climates) can improve energy efficiency and thermal comfort for Dutch dwellings. This building archetype can reduce energy demands for cooling, as a result being a good alternative form for the expected warmer future of the Netherlands. Designing small scale courtyards (single- family house) needs attention in winter. Courtyards provide more indoor and outdoor comfort in comparison with linear and singular forms. With this knowledge, it could be said that design strategies taken from one climate may be applicable in other climates but with serious attentions and modifications. Different disciplines and sciences can perform valuable roles to make this transition beneficial for the fragile ecosystem and people.
The urban heat island (UHI) phenomenon and the dependency of buildings on
fossil fuels were the two main issues that formed this dissertation. UHI results in higher air temperatures in dense urban areas compared with their suburbs and rural surroundings. This phenomenon affects human health through thermal discomfort. Furthermore, in the Netherlands, it is estimated that by 2050 the air temperature could be up to 2.3°C warmer as compared to the period of 1981-2010. Besides, the energy consumption of buildings is responsible for 30 to 45% of CO2 emissions. 31% of this consumption belongs to residential buildings. Residential buildings can play a major role in reducing the CO2 emissions caused by fossil fuel consumption.One of the passive architectural design solutions is the courtyard building form. Courtyards have been used for thousands of years in different climates in the world. In hot climates they provide shading, in humid climates they cause a stack effect helping ventilation, in cold climates they break cold winds and protect their microclimate. In temperate climates (such as of the Netherlands), the thermal behaviour of courtyards has been studied less. In this dissertation, low-rise residential courtyard buildings were therefore studied among (and along) different urban block types in the Netherlands.As the first step, computer simulations were done as a parametric study for indoor and outdoor thermal comfort. Field measurements were done in actual urban courtyards and in dwellings alongside urban courtyards in the Netherlands (and in a similar temperate climate in the US). A scale model experiment later followed the simulations. Some of these field measurements were used to validate the simulation models. These efforts answered the two main research questions:1) To what extent is a dwelling alongside an urban courtyard more efficient and thermally comfortable than other dwellings?2) To what extent do people have a more comfortable microclimate within an urban courtyard block on a hot summer day than within other urban fabric forms?To answer the first question, the energy performance of and thermal comfort inside dwellings in three types of urban blocks in the Netherlands (each with 1, 2 and 3 stories) were analysed (with an identical floor area). The main objective of the research was to clarify the effect of building geometry on annual heating energy demand, thermal comfort, heat loss, solar gains through external windows and on overheating in summer. The buildings had different surface to volume ratios owing to different shapes: single, linear and courtyard shape. The single shape model is more exposed to its outdoor environment and has the highest surface to volume ratio. The linear models consist of a row of dwellings, which leads to a smaller area exposed to the outdoor environment, and this amount is the lowest for the courtyard models. The single dwelling has a higher surface to volume ratio and this model has the highest solar gains. The average amount of energy demand for heating in a year for the single shape is the highest among the models. However, the lighting energy demand for the single shape is the lowest. The linear and courtyard models are very similar in lighting energy demand. The courtyard shape has the lowest energy demand for heating
since it is more protected. Considering thermal comfort hours in free running mode, the courtyard shape has the lowest number of discomfort hours among the models. Reducing the external surface area exposed to the climatic environment leads to higher energy efficiency and improved summer thermal comfort performance. Therefore, this analysis showed that the courtyard shape proves to be more energy efficient and thermally comfortable than other dwellings.For the second research question, the microclimate within the urban block forms previously studied (singular, linear and courtyard) were simulated, each with two different orientations (E-W and N-S, except for the courtyard). To explore their microclimates the simulations were done for the hottest day in the Netherlands (19th June 2000) according to the temperature data set provided in NEN5060. The results showed that the singular forms provide a long duration of solar radiation exposure for the outdoor environment. This causes the worst comfort situation among the models at the centre of the canyon for a hot summer day. In contrast, the courtyard provides a more protected microclimate which has less solar radiation in summer. Considering the physiological equivalent temperature (PET), the courtyard has the highest number of comfortable hours on a summer day. Regarding the different orientations of the models and their effect on outdoor thermal comfort, it is difficult to specify the differences between the singular E-W and N-S forms because they receive equal amounts of insolation and are equally exposed to wind. Nevertheless, the linear E-W and N-S forms are different in their thermal behaviour. The centre point at the linear E-W form receives sun for about 12 h. In contrast, this point at the linear N-S form receives 4 h of direct sunlight in that day. Therefore, in comparison with the E-W orientation this N-S orientation provides a cooler microclimate.To sum up the above findings, it should be said that this study showed that courtyard buildings as a passive design solution (originally from hot and arid climates) can improve energy efficiency and thermal comfort for Dutch dwellings. This building archetype can reduce energy demands for cooling, as a result being a good alternative form for the expected warmer future of the Netherlands. Designing small scale courtyards (single- family house) needs attention in winter. Courtyards provide more indoor and outdoor comfort in comparison with linear and singular forms. With this knowledge, it could be said that design strategies taken from one climate may be applicable in other climates but with serious attentions and modifications. Different disciplines and sciences can perform valuable roles to make this transition beneficial for the fragile ecosystem and people.
Green roof monitoring is critical to understand and improve the design, implementation, and management of green roof ecosystems. Creating resilient, less resource intensive living roofs fitting their larger eco-regional context, specific local setting, and unique project objectives means understanding inputs and outputs. This chapter addresses monitoring abiotic inputs and outputs related to green roof hydrology
(precipitation and irrigation, storage, outflow, and evapotranspiration), water quality, energy fluxes, temperatures, meteorological conditions (wind), and gas/carbon exchange. This chapter presents monitoring approaches and equipment needs from literature and researcher interviews detailing several relevant examples. Important design, educational, and management opportunities relating to effective monitoring programs are discussed.
Snow plays an important role in determining heat and moisture exchanges between the underlying surface and atmosphere in winter. However, the effect of snow cover is not considered or assumed to be negligible in existing urban canopy energy balance models. In this paper, a one-dimensional snow model that accounts for heat transfer within snow cover is developed, and the model is implemented into an urban canopy energy balance model to simulate energy and moisture exchanges in cold urban areas with stable snow cover. The numerical methods of the snow model and the urban canopy model are demonstrated first, and the urban canopy model is subsequently used to simulate the thermal climate of a residential area dynamically in Yichun, China during winter. The results indicate that the existence of snow cover decreases the outdoor air temperature by 0.15 °C on average and 1.16 °C at maximum. In addition, the outdoor mean SET* increases 0.43 °C with the removal of snow cover, indicating that the thermal comfort of people outside decreases due to the presence of snow cover.
In the last five years, the term green roof has taken on ecological and social significance beyond its seemingly simplistic description, this term has become an epithet for the reduction of pollution and improving urban environment, for large scale mitigation of storm water runoff, and for maximum utilization of urban land. Erbil the capital city of Kurdistan region is facing a lot of environmental problems such as waste water treatment, water supply, land preservation, air and noise pollution due to the increasing number of cars, in addition, interestingly recent statistics suggested that the percentage of green areas in Erbil is approximately 6.5%, while according to international standards 30% of urban areas should be green. Green roofs infrastructure on the other hand promises to become an increasingly important solution for building owners and community planners which provides a significant numbers of social, environmental and economic benefits that are both public and private nature. Research problem is the ambiguity of green roofs implementation techniques in the region and the goal is initiated to determine the obstacle and challenges of green roofs implementations in Erbil city as case field by analyzing international experiences and concluding Erbil's green roofs criteria.
Tins study explores effects of green roof materials on green roof thermal performance based on simulated heat transfer through a roof assembly. A case study for a commercial building with a green roof located in Chicago, IL compares heat fluxes and net radiation for different plant and substrate materials. The investigation included a total of 35 cases based on combinations of seven types of plants and five types of substrates used in extensive green roofs. The green roof performance during one week in July was simulated employing a validated green roof model. ANOVA statistical analyses provide direct comparison of simulated heat fluxes and net radition with different plant and substrate types. The results show that both plant and substrate types are statistically important to the total heat fluxes, while only plant types affect the simulated net radiation. The alteration effect of plant and substrate types is not statistically important. Specifically, the combination of a plant and a substrate with the highest albedo was chosen as the base case, and comparative analyses were conducted between the base case and other cases. The base case shows the best thermal performance in most simulated conditions. Therefore, in this case study it was sufficient to measure the thermal properties of selected green roof plants and substrates to determine the assembly with best expected thermal performance.
Snow on the ground is a complex three-dimensional porous medium consisting of an ice matrix formed by sintered snow crystals and a pore space filled with air and water vapor. If a temperature gradient is imposed on the snow, a water vapor gradient in the pore space is induced and the snow microstructure changes due to diffusion, sublimation, and resublimation: the snow metamorphoses. The snow microstructure, in turn, determines macroscopic snow properties such as the thermal conductivity of a snowpack. We develop a phase-field model for snow metamorphism that operates on natural snow microstructures as observed by computed x-ray microtomography. The model takes into account heat and mass diffusion within the ice matrix and pore space, as well as phase changes at the ice-air interfaces. Its construction is inspired by phase-field models for alloy solidification, which allows us to relate the phase-field to a sharp-interface formulation of the problem without performing formal matched asymptotics. To overcome the computational difficulties created by the large difference between diffusional and interface-migration time scales, we introduce a method for accelerating the numerical simulations that formally amounts to reducing the heat- and mass-diffusion coefficients while maintaining the correct interface velocities. The model is validated by simulations for simple one- and two-dimensional test cases. Furthermore, we perform qualitative metamorphism simulations on natural snow structures to demonstrate the potential of the approach.
Although green roofs (also called garden roofs) provide many benefits such as reducing heating/cooling requirements and stormwater runoff, adoption has been low in Canada due to a lack of awareness among building professionals and the general public. This project developed objective technical data and analyses to demonstrate the benefits of green roofs.
An interesting approach to reduce building energy consumption is to use green roofs as a part of building envelope. However, many building designers ignore this opportunity as it is quite difficult to estimate the resulting energy saving. This paper provides results from an ongoing experimental research project that focuses on the thermal performance of extensive green roofs when buildings are in the cooling mode. The paper discusses the importance of green roofs and reviews previous research studies. In particular, this paper focuses on the role of plants for the heat flux reduction through the roof structure. The performance of the plant material was assessed in an environmental chamber by experiments with two samples, one with the plant material, and another one without the plant material. Overall, plants reduced the measured heat flux through the green roof sample by 40-50% compared to the roof sample without plants. In conclusion, plants have an important role in reducing the heat flux by regulating: (I) latent heat flux through better water management and additional water storage in the plant leaves/roots, and (2) sensible heat flux through additional shading provided by the plant leaves. Based on these results, future research will focus on thermal modeling of green roof including the role of plants.
This paper presents the results of a numerical study of the effects of snow cover on long-term, periodic, steady-state equilibrium ground temperatures. It is shown that mean annual ground temperatures decrease with depth when the soil thermal conductivity is greater in the frozen than in the unfrozen phase. For permafrost conditions the increase in mean annual ground temperatures due to seasonal snow cover is augmented significantly when soil latent heat is present. In seasonal frost cases the calculated depth of frost penetration is extremely sensitive to details of the snow cover buildup. In permafrost cases calculated mean annual temperatures are extremely sensitive to the assumptions made in treating the snow cover. In either case, because it is difficult to model snow cover accurately, the reliability of ground thermal regime computations is adversely affected. Keywords: ground thermal regime, ground temperatures, soil temperatures, numerical model, finite difference, snow cover.
Green roofs have entire roof tops covered with vegetation as opposed to shingles, bitumen, cement or gravel in conventional roofs. During the previous four years, the number of extensive green roofs (which are characterized by a relatively shallow depth of the growing medium) in the United States has grown at the rate of about 50% each year. Even then the total coverage area for green roofs in the US remains insignificant as compared with Germany, where green roofs have grown steadily over the past 25 years. The future of green roofs in the US depends not only on right incentives, which are more or less non-existent at this time, but also on the establishment of national performance standards, research facilities and test methods. The need for test standards and performance criteria is especially urgent for synthetic materials such as waterproofing membranes, root barrier layers, geocomposites and geotextiles, where many competing products can quickly flood the market, making it almost impossible to distinguish between what works and what does not. Given the right conditions, it is not unlikely that the size of green roof market in the US could far exceed that in Germany in eight years, and perhaps sooner.
MEETING. The archival version of this paper along with comments and author responses will be published in ASHRAE Transactions, Volume 115, Part 2. ASHRAE must receive written questions or comments regarding this paper by August 3, 2009, if they are to be included in Transactions. ABSTRACT An interesting approach to reduce building energy consumption is to use green roofs as a part of building enve-lope. However, many building designers ignore this opportu-nity as it is quite difficult to estimate the resulting energy saving. This paper provides results from an ongoing experi-mental research project that focuses on the thermal perfor-mance of extensive green roofs when buildings are in the cooling mode. The paper discusses the importance of green roofs and reviews previous research studies. In particular, this paper focuses on the role of plants for the heat flux reduction through the roof structure. The performance of the plant mate-rial was assessed in an environmental chamber by experiments with two samples, one with the plant material, and another one without the plant material. Overall, plants reduced the measured heat flux through the green roof sample by 40-50% compared to the roof sample without plants. In conclusion, plants have an important role in reducing the heat flux by regu-lating: (1) latent heat flux through better water management and additional water storage in the plant leaves/roots, and (2) sensible heat flux through additional shading provided by the plant leaves. Based on these results, future research will focus on thermal modeling of green roof including the role of plants.
A new experimental apparatus, “Cold Plate”, was designed and built to quantify heat and mass transfer processes for green roof samples inside an environmental chamber. The “Cold Plate” apparatus addressed shortcomings in the existing data sets available for green roof energy balance calculations. Experimental data collected in this apparatus show that evapotranspiration controlled the intensity of all other heat fluxes, depending on the plant and environmental conditions. Also, under the described laboratory conditions, the uninsulated green roof samples with plants showed an average heat flux reduction of 25% compared to samples without plants. This reduction was due to the plants providing extra shading, additional water storage and better water control mechanisms.
Vegetation can play an important role in the topoclimate of towns and the microclimate of buildings too. It is different according to the macroclimatic circumstances, but in any case vegetation can give a significant contribution to the climatic conditions.Local climate is determined by atmospheric elements, such as net radiation, advection and convection, and by geographical fators, especially longitude and latitude, oceanity and aridity, the relief graduations and the factors of the urban surface and structure. Those factors ‘stress’ the atmospheric elements and form the urban topoclimate and microclimate.The urban structures, volume and special surfaces alter the near-surface conditions of the atmosphere. They form special climatotopes. These urban types can be organized as poleotopes of different density and structures which build— more or less — their own topoclimate: therefore we call them ‘poleoclimatotopes’.Each poleoclimatotope, industrial, commercial/city, residential/urban/suburban, and different kinds of open spaces in towns, has its own mean structure and percentage of vegetation surface. But also in the ‘choroclimatotopes’ — the climatotopes of the open landscape — as wood, grove, heath, farmland greenery, arable land, and open water surfaces — special styles of vegetation surface and structure can be found.With buildings, some vegetative climatic effects can be made by combining green cover on walls, roofs, and in open spaces in the vicinity of buildings. According to the environmental conditions the different climatotopes show the effect of vegetation on the urban topoclimate and microclimate, regarding different styles of greenery at and around buildings.
The presence of seasonal snow cover during the cold season of the annual air temperature cycle has significant influence on the ground thermal regime in cold regions. Snow has high albedo and emissivity that cool the snow surface, high absorptivity that tends to warm the snow surface, low thermal conductivity so that a snow layer acts as an insulator, and high latent heat due to snowmelt that is a heat sink. The overall impact of snow cover on the ground thermal regime depends on the timing, duration, accumulation, and melting processes of seasonal snow cover; density, structure, and thickness of seasonal snow cover; and interactions of snow cover with micrometeorological conditions, local microrelief, vegetation, and the geographical locations. Over different timescales either the cooling or warming impact of seasonal snow cover may dominate. In the continuous permafrost regions, impact of seasonal snow cover can result in an increase of the mean annual ground and permafrost surface temperature by several degrees, whereas in discontinuous and sporadic permafrost regions the absence of seasonal snow cover may be a key factor for permafrost development. In seasonally frozen ground regions, snow cover can substantially reduce the seasonal freezing depth. However, the influence of seasonal snow cover on seasonally frozen ground has received relatively little attention, and further study is needed. Ground surface temperatures, reconstructed from deep borehole temperature gradients, have increased by up to 4°C in the past centuries and have been widely used as evidence of paleoclimate change. However, changes in air temperature alone cannot account for the changes in ground temperatures. Changes in seasonal snow conditions might have significantly contributed to the ground surface temperature increase. The influence of seasonal snow cover on soil temperature, soil freezing and thawing processes, and permafrost has considerable impact on carbon exchange between the atmosphere and the ground and on the hydrological cycle in cold regions/cold seasons.
To model the impacts of ecoroofs on building envelope heat transfer accurately, thermal property data for ecoroof soils are needed. To address this need we have measured thermal conductivity, specific heat capacity, thermal emissivity, short wave reflectivity (albedo) and density for ecoroof soil samples over a range of moisture states. To represent a wide range of commonly used ecoroof soils we created eight test samples using an aggregate (expanded shale or pumice), sand, and organic matter in varying volumetric composition ratios. The results indicate significant variability in properties as a function both of soil composition and soil wetness. Thermal conductivity ranged from 0.25 to 0.34W/(mK) for dry samples and 0.31–0.62W/(mK) for wet samples. Specific heat capacity ranged from 830 to 1123J/(kgK) for dry samples and 1085–1602J/(kgK) for wet samples. Albedo was consistently higher for dry samples (0.17–0.40) decreasing substantially (0.04–0.20) as moisture was added. Thermal emissivities were relatively constant at 0.96±0.02 regardless of soil type or moisture status. These results are discussed in the context of their impacts on building energy consumption and the importance of including daily and seasonal property variation within models of the ecoroof energy balance.
Over the years, the concept of total building performance and its application to commercial and residential buildings has been of great interest among researchers in this field. In a country such as Singapore, whose society is paying increasing attention to paper qualifications, the evaluation of academic institutions using this concept may provide a gateway to critical issues related to the learning environment.In an attempt to understand the conduciveness of classroom environments towards learning, a study is done to investigate the performance of classrooms in a typical secondary school in Singapore. Performance is indicated by the measurement and evaluation of six mandates, namely thermal, spatial, visual, acoustic, indoor air quality, and building integrity. The usage of both objective and subjective methods gave rise to interesting and sometimes conflicting results with regards to the classrooms’ performance.
This paper deals with the experimental investigation and analysis of the energy and environmental performance of a green roof system installed in a nursery school building in Athens. The investigation was implemented in two phases. During the first phase, an experimental investigation of the green roof system efficiency was presented and analysed, while in the second one the energy savings was examined through a mathematical approach by calculating both the cooling and heating load for the summer and winter period for the whole building as well as for its top floor. The energy performance evaluation showed a significant reduction of the building's cooling load during summer. This reduction varied for the whole building in the range of 6–49% and for its last floor in the range of 12–87%. Moreover, the influence of the green roof system in the building's heating load was found insignificant, and this can be regarded a great advantage of the system as any interference in the building shell for the reduction of cooling load leads usually to the increase of its heating load.
Vegetation strategically placed on roofs and walls can be considered as a complement of urban greens. It is actually an ecological solution to the concrete jungle in cities. The benefits of green roofs are unquestionable from the thermal point of view. But some quantitative data on this subject are still needed in the context of tropical climate. Therefore, a field measurement was conducted in Singapore to investigate the thermal impacts of rooftop garden. From the derived data, it has been confirmed that rooftop gardens contribute thermal benefits to both buildings and their surrounding environments.
Although green roofs (also called garden roofs) provide many benefits such as reducing heating/cooling requirements and stormwater runoff, adoption has been low in Canada due to a lack of awareness among building professionals and the general public. This project developed objective technical data and analyses to demonstrate the benefits of green roofs. Bien que les toits verts (également désignés toitures-terrasses) procurent de nombreux avantages, comme une réduction des exigences énergétiques en matière de chauffage et de climatisation, et de la décharge des eaux de ruissellement, leur adoption au Canada a été jusqu'ici peu marquée, en raison d'un manque de reconnaissance chez les professionnels du bâtiment comme dans le public en général. Dans le cadre de ce projet, on a développé des données techniques objectives et mis au point des analyses en vue de démontrer les bienfaits des toits verts. RES
Observations were made on the mean daily air temperature and on soil temperature at depths 5 and 10 cm below the surface during the period 23 December 1956 to 31 October 1962. Average annual temperatures were calculated for the observation levels at intervals of one-seventh of a year. The average annual air temperature was observed to vary between 4.90 and 7.37 degrees C; the average annual 10-cm soil temperature between 7.86 and 9.00 degrees C; and the difference between them between 1.27 and 3.25 C degrees. The analysis indicated that the snow cover was the principal reason for the difference between average annual air and soil temperatures at the Ottawa site. The partitioning of surface heat between convection and evaporation or evapotranspiration, and the variation with time of the surface heat transfer coefficients probably contributed between 0 and 1 C degree to the difference. Des observations ont été faites sur la température journaliè re moyenne de l'air et sur la température du sol à des profondeurs de 5 et 10 cm sous la surface durant la période allant du 23 décembre 1956 au 31 octobre 1962. Les tempé ratures annuelles moyennes ont été calculées pour les niveaux d'observation à des intervalles d'un septième d'anné e. On a constaté que la température moyenne annuelle de l' air varie entre 4.90 et 7.37 degrés C; que la température moyenne annuelle du sol à 10 cm varie entre 7.86 et 9.00 degrés C et que la différence entre elles varie entre 1.27 et 3.25 degrés C. L'analyse a montré que la couverture de neige a été la principale raison de la différence existant entre les températures moyennes annuelles de l'air et du sol à la station d'Ottawa. Le cloisonnement de la chaleur de surface entre la convection et l'évaporation ou l'é vaportranspiration et la variation selon le temps des coefficients de transfert de la chaleur de surface ont probablement ajouté jusqu'à 1 degré C à la différence. RES
Vegetation, primarily forests, has been identified as an important component of any strategy to reduce greenhouse gas (GHG) emissions, through the sequestration of carbon in the woody biomass of trees. Given the limited space available for additional trees in many North American metropolitan cities, new adaptation strategies such as placing the vegetation directly on building roofs (rooftop gardens) become especially attractive. Rooftop gardens or green roofs are found throughout Europe. Germany, in particular, has carried out a significant amount of technical research to improve the various roofing components. Here at home, Canada has agreed to reduce GHG emissions by six per cent relative to 1990 levels by 2008-2012. Rooftop gardens may be a part of the solution. Il a été reconnu que la végétation, essentiellement forestière, est une composante importante de toute stratégie visant la réduction des émissions de gaz à effet de serre (GES) via la séquestration du carbone dans la biomasse ligneuse des arbres. Étant donné l'espace limité qui est disponible pour la plantation d'arbres supplémentaires dans de nombreuses métropoles d'Amérique du Nord, les nouvelles stratégies adaptatives telles que la mise en place de végétation directement sur les toitures-terrasses de bâtiment (terrasses-jardins ou jardins suspendus) deviennent tout particulièrement attrayantes. Les terrasses-jardins ou toits verts se rencontrent dans toute l'Europe. L?Allemagne, plus particulièrement, a mené un grand nombre de recherches techniques visant à améliorer les divers éléments constituants des toitures. Chez nous, le Canada a consenti à réduire de 6 p. 100, entre 2008 et 2012, ses émissions de GES par rapport aux niveaux de 1990. Et les terrasses-jardins pourraient bien constituer une partie de la solution au problème visé. PRAC
Green roof is a specialized roofing system that supports vegetation growth on rooftops. This technology is rapidly gaining popularity in North America as a sustainable design option. Green roofs offer multiple benefits to urban areas such as reduction of heating/cooling needs for the building, urban heat island and stormwater runoff for the region. In this study, the performance of two extensive green roofs located in the City of Toronto, Ontario, Canada was monitored. The green roofs varied in system components, types and depths of growing medium, vegetation coverage and types of roofing systems. The green roofs were instrumented with sensor networks to provide thermal performance data. Observations from the first year of monitoring showed that the green roofs reduced the heat flow through the roofs, thus lowering the buildings'heating/cooling energy demand, independent of the roofing systems the green roofs were installed on. Although the plant coverage was relatively low in the first year, the green roofs reduced the annual heat flow through the roofs and they were more effective in the summer than in the winter. Energy efficiency varied slightly with growing medium depth and system design. Le toit vert est un système de couverture spécialisé qui permet et entretient la croissance végétale. Cette technologie gagne rapidement en popularité en Amérique du Nord comme option de conception durable. Les toits verts offrent de multiples avantages dans les régions urbaines, tels qu?une réduction des besoins en chauffage et en refroidissement pour les bâtiments, des îlots thermiques urbains et du ruissellement des eaux de pluie dans la région. Dans le cadre de cette étude, la performance de deux (2) toits verts de grande ampleur situés dans la ville de Toronto (Ontario), au Canada, a fait l'objet d'une surveillance. Ces toits verts étaient différents l'un de l'autre en termes de composants de système, de type et de profondeur du milieu de croissance, de nature de la couverture végétale et de type de système de couverture. Ces couvertures ont été instrumentées avec des réseaux de capteurs afin de produire des données liées à la performance thermique. Les observations réalisées la première année du programme de surveillance ont révélé que les toits verts réduisent la perte thermique à travers la toiture, abaissant ainsi la demande en énergie du bâtiment pour le chauffage / le refroidissement, et ce, quel que soit le système de couverture formant support au toit vert. Bien que les couvertures végétales aient été d'une hauteur relativement faible la première année de la plantation, les toits verts ont néanmoins réduit dès le début l'écoulement de la chaleur à travers la toiture, en présentant toutefois une plus grande efficacité en été qu?en hiver. L?efficacité énergétique variait légèrement selon la profondeur du milieu de croissance et la conception du système. RES
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