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Effects of Plant and Substrate Selection on Thermal Performance of Green Roofs during the Summer
... Albedo is increased by selecting light or silver colored plant species, including: many grasses (albedo ranging from 0.25 to 0.30 [161]), light colored Sedums such as Sedum tomentosum (0.23) or sexangulare (0.22) [162], Stachys byzantia [30], or others found in Ref. [26,163]. Ensuring high vegetation coverage can increase albedo since plants generally have higher albedo than substrate (ranging from 0.08 to 0.13 [162]). ...
... Albedo is increased by selecting light or silver colored plant species, including: many grasses (albedo ranging from 0.25 to 0.30 [161]), light colored Sedums such as Sedum tomentosum (0.23) or sexangulare (0.22) [162], Stachys byzantia [30], or others found in Ref. [26,163]. Ensuring high vegetation coverage can increase albedo since plants generally have higher albedo than substrate (ranging from 0.08 to 0.13 [162]). However, albedo decreases with higher soil moisture content [164] and with increased plant height (taller plants can trap radiation) [97,130]. ...
... Wong et al. (2003) found that a green roof on an uninsulated building decreased energy consumption for cooling by 15%, but a green roof over an insulated roof decreased consumption by less than 2% [108]. Thicker insulation layers dampen the benefit of a green roof to reduce energy flows into the building [108,162], especially in winter. In summer, Vera et al. (2017) found that ET and shading from the vegetation could be more effective at reducing heat fluxes into the building than increasing roof insulation [170]. ...
Green roofs have the potential to offer numerous ecosystem services; however, they are rarely designed to achieve them. Instead, design is restricted by perceived structural and maintenance constraints, which consequently diminish the achievable benefits. For green roofs to improve sustainability and resilience of cities, their design should match their promised multi-functional application using performance-based design. The first step towards a comprehensive performance model is to synthesize design recommendations across disciplines to identify synergies and trade-offs in design objectives for multiple benefits. This study discusses design strategies that could alter the energy and water balance in the green roof in order to attenuate urban stormwater, increase building energy performance, mitigate urban heat, and improve the output of solar panels placed on top of green roofs. These benefits are mathematically linked to quantifiable processes (discharge rate, water content, evapotranspiration, sensible heat, net radiation, insulation, and thermal mass), forming the foundation for a performance-based design model. Design recommendations are then summarized for each process, followed by a discussion of synergies, trade-offs, and research needs that arise when green roofs are designed to achieve multiple functions. Selecting vegetation with high leaf area and albedo improves multiple benefits without affecting structural constraints, whereas choosing plants with low stomatal resistance leads to trade-offs between higher evapotranspiration and higher irrigation requirements. Trade-offs in substrate depth and properties including organic matter and moisture are also apparent. Interdisciplinary collaborations are needed to simulate and optimize design parameters based on stakeholder preferences related to co-benefits and constraints.
... However, it is widely known that there are highly non-linear processes occurring in this system [2,19]. Sailor and Hagos [18] and Zhao et al. [20] incorporated how compaction affects the substrate thermal properties. However, their model did not account for the effect of water flow on the energy balance. ...
... Soil compaction has been typically investigated without considering its impact on the coupled water and heat transport in porous media [22,23]. There are many investigations that deal with the impact of compaction on water fluxes [21,[24][25][26], as well as many studies that investigate how compaction affects heat fluxes in soils [18,20]. Nonetheless, there is a lack of studies that have investigated the effect of substrate compaction on the combined water and heat transport in green roofs. ...
... In general, for a specific moisture level, as compaction occurs the thermal conductivity of the substrates increase. This behavior is consistent with the findings of other investigations [18,20] and occurs because as the substrate is compacted, there is more physical contact between the solid particles, which increase thermal conduction [20,24,25,35]. Also, the magnitude of the thermal conductivity is similar to that presented in the literature [15,20]. ...
Although compaction affects water and heat transport processes in porous media, few studies have dealt with this problem. This is particularly true for substrates, which are artificial porous media used for engineering and technological solutions, such as in vegetated or green roofs. We propose a methodology to study the effect of substrate compaction on the characterization of physical, hydrodynamic and thermal properties of five green roof substrates. The methodology consists in a parametric analysis that uses the properties of a substrate with known bulk density, and then modifies the substrate properties to consider how compaction affects water and heat fluxes. Coupled heat and water transport numerical simulations were performed to assess the impact of the changes in the previous properties on the hydraulic and thermal performance of a hypothetical roof system. Our results showed that compaction reduced the amplitude of the fluctuations in the volumetric water content daily cycles, increasing the average water content and reducing the breakthrough time of the green roof substrates. Compaction changes the thermal behavior of the green roof substrates in different ways for each substrate due to the dependence of the air, water and soil fraction of each substrate.
... [26,92]), but when installed on well-insulated rooftops the effect of green roofs can be negligible or even detrimental (e.g., Refs. [93][94][95][96][97][98][99][100][101][102]). The thermal insulation provided by soil-that depends on its thickness and water storage capacity [90,103]-can entail a decrease in heating and cooling energy-demand in cold and hot climates, respectively [104]. ...
... Green roofs can be effective, to different extents, on UHI mitigation, depending on climate [69,87,104,[158][159][160], plants' evapotranspiration [126,[161][162][163], plants' density foliage [108], solar reflectivity [96], coverage [103], and evaporation from the growing medium [142,161,163]. Simultaneously, the aforementioned parameters assume a different importance depending on the environmental conditions. ...
... In particular, plants with low absorptivity and high-density foliage keep surface temperature lower than plants with high absorptivity and limited foliage [108]. Zhao et al. [96] investigated the role played by plants' reflectivity and substrate in decreasing the net solar radiation in summer in four American cities: Austin, Texas; Sacramento, California; Nashville, Tennessee; Chicago, Illinois; representative of hot, warm, mixed and cool climates, respectively. It resulted that, in all the investigated cities, solar reflectivity is crucial in decreasing summer net solar radiation; whereas, variations in substrate are ineffective. ...
In the next decades, the increase in global population will lead to further urbanization determining,
on the one hand, an increase in building energy use and, on the other hand, a surge in urban temperature,
which, in turn, affects building energy demand. Since the building sector greatly contributes to the
use of energy globally, the amelioration of this sector is an urgent issue to contribute to climate
stabilization.
Published literature shows that green roofs affect both directly and indirectly building energy use, delivering
the message that green roofs are fit-all solutions. However, the efficacy of the deployment of green roofs varies
depending on climate and on their specific design.
The present study contains a geographically explicit review of the potential building energy benefits deriving
by the installation of green roofs depending on their specific design aiming at answering to the following research
questions:
- Are green roofs fit-all solutions for decreasing building energy use in diverse climates?
- How insulation, growing media, and plant selection of green roofs should be calibrated in different climates
to maximize their effect on building energy use?
- How green roofs can contribute to urban heat island-mitigation in different climates?
Answering these research-questions, this study provides urban decision-makers and planning agencies useful
insights to, not only prioritize strategies, but also efficiently design by-laws and local regulations to maximize the
potential positive effect of urban-wide green roof deployment on building energy use.
... As a component of green infrastructure, green roofs have become more relevant in recent years because of the ecosystem services they provide, including the reduction of energy consumption in buildings (Tabares-Velasco and Srebric 2011; Zhao et al. 2014) and Urban Heat Island (UHI) (Gill et al. 2007). The cooling service of green roof vegetation relies on the abilities of different species to transpire, provide shade, reflect radiation back to the atmosphere or absorb it through photosynthesis (Cook-Patton and Bauerle 2012; Blanusa et al. 2013;Vaz Monteiro et al. 2017). ...
... The r s values obtained in this study were compared to those reported by Sailor (2008) and Zhao et al. (2014), which were derived from studies on desert plants by Tabares-Velasco and Srebric (2011). ...
... When comparing the r s values obtained on this study with those proposed in the heat and mass transfer models from green roofs to buildings of Sailor (2008), only the mean r s values at 20:00 of the herbaceous White and Pink Verbena sp. and Sedum spurium red were within the range. On the other hand when comparing the r s values obtained with the ones proposed for desert plants by Zhao et al., (2014), all species had values within that range. Pink, at 8:00 h, 12:00 h, 16:00 h and 20:00 h. ...
Current modelling approaches for energy simulations in green roofs use a range of values for parameters such as stomatal resistance (r s) of the vegetation. r s reflects the capability of a plant to transpire, thus it has a direct relation to the cooling potential of green roofs in buildings. Therefore, r s values need to be revised based on differences among species and contrasting environmental conditions, considering anatomical and physiological characteristics among species and their changes throughout the day. In order to provide real data on species commonly used for green roofs in semiarid climates, this paper aims to evaluate the stomatal resistance of nine species of groundcovers and to compare this data with current models. r s was measured for each species at 8:00 h, 12:00 h, 16:00 h and 20:00 h during day and night-time in winter in a leaf located at the middle of the stem. The results of this study showed that r s varies significantly among species, throughout the day and between the side of the leaf (adaxial or abaxial). The lowest r s values for species was at noon ranging from 264 to 807 s m-1 and the highest r s was at night ranging from 568 to 973 s m-1. Sedum spurium red, Sedum hybrid, and white and pink Verbena sp. had the largest r s variation in the day-night cycle. The results of r s are higher than those values recommended for some energy simulation models.
... Thermal insulation also plays an important role in the performance of vegetated roofs. Numerical and field studies showed lower heating and cooling energy savings from insulated green roofs (2-10%) than from uninsulated green roofs (up to 48%) because insulation decouples the cooling capabilities of vegetated roofs [25,30,32,[34][35][36][37][38]. ...
... For example, typical conductivities for soil vary from 0.2 W/m K for dry soil to 2.0 W/m K for wet soil [97]. The thermal conductivity reported in three green roof studies varied between 0.18 and 0.4 W/m K [37,98,99], whereas for a saturated substrate the thermal conductivity ranged from 0.5 to 1.0 W/ m K [37,98,99]. ...
... For example, typical conductivities for soil vary from 0.2 W/m K for dry soil to 2.0 W/m K for wet soil [97]. The thermal conductivity reported in three green roof studies varied between 0.18 and 0.4 W/m K [37,98,99], whereas for a saturated substrate the thermal conductivity ranged from 0.5 to 1.0 W/ m K [37,98,99]. ...
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.
... Although Sailor's (2008) model assumes that thermal properties depend on the substrate moisture, it considers that moisture within the green roof diffuses at a constant rate. Jaffal et al. (2012) developed another thermal model with similar assumptions to those of Sailor's model, while Sailor and Hagos (2011) and Zhao et al. (2014) included the effect of compaction on the thermal properties of the substrate. The assumption of constant moisture diffusion can seriously impair model estimations because the interplay between vegetation water demands, time-dependent atmospheric conditions, and the building internal temperature dynamics can introduce abrupt spatial and temporal changes in the moisture profile across the substrate. ...
... The specific objectives were, first, to characterize a set of five green roof substrates in terms of their hydrodynamic and thermal properties: water retention curve, hydraulic conductivity curve, thermal conductivity, and specific heat capacity. The substrates investigated had organic matter contents that ranged between 4 and 35% and were chosen due to their common use in green roofs (Pianella et al., 2016;Zhao et al., 2014) and their local availability. Secondly, we aimed to evaluate the impacts of these properties on water and heat transport through the green roof substrates using numerical simulations and including the effect of irrigation or drainage. ...
... Substrates S1 and S3 are >80% sand, which prevents the reduction of the saturated hydraulic conductivity with compaction (Fassman-Beck et al., 2015). The use of perlite (S2) in green roofs was analyzed by Zhao et al. (2014), while crushed bricks (S3) have been studied by Pianella et al. (2016) due to their high porosity and lightness. Note that these substrates were acquired in the local market and no efforts to change their mixture or composition were made. ...
Core Ideas
Hydrodynamic and thermal properties of five green roof substrates were determined.
Coupled heat and water transport in a hypothetical roof was simulated.
The green roof substrates showed a large capacity to store and transport water.
Water retention, storage, and organic matter control substrate hydraulic behavior.
Green roofs integrate vegetation into buildings, thereby minimizing energy requirements and water runoff. An understanding of the processes controlling water and heat fluxes in green roofs under site‐specific climatic conditions is needed to optimize their benefits. The hydrodynamic and thermal characteristics of substrates and vegetation layers are the primary controlling factors determining water and heat fluxes on green roofs. We characterized the physical, hydrodynamic, and thermal properties of five green roof substrates. We performed coupled heat and water transport numerical simulations to assess the impact of these properties on the hydraulic and thermal performance of a hypothetical roof system. The five substrates showed a large capacity to store and transport water, while their ability to conduct heat was similar to other green roof substrates. Under unsaturated conditions, water retention, storage capacity, and organic matter (OM) content of the substrates controlled the hydraulic and thermal response of each substrate. Our simulation results show that the substrate with the best capacity to store water and to reduce the heat flux through the substrate layer was composed of perlite and peat and had large OM content (30.7%) and saturated water content (0.757 cm ³ cm ⁻³ ). This substrate outperformed the others, probably due to its low thermal conductivity and its large pore space. The dynamic modeling presented in this study can represent the complexity of the processes that are occurring in green roof substrates, and thus it is a tool that can be used to design the configuration of a green roof.
... (2) Soil layer: the growth substrate characteristics are crucial GR parameters [52]. (3) Filter layer: separates soil and drainage material [53]. ...
... Latent heat transfer due to water evaporation (latent heat flux) should be considered, as evaporative cooling would contribute significantly to GR energy performance, while simultaneous heat and mass transfer due to soil moisture migration should not be disregarded [31,58,59]. Also, long-wave radiation exchange between the soil surface, foliage, and ambient air may play a significant role in the thermal behavior of GRs, particularly under clear sky conditions, when the atmospheric window operates effectively and radiative cooling can be achieved via the GR system [52]. Due to its high thermal capacity and time lag effect, soil is also capable of functioning as a thermal storage mass [19]. ...
... Regarding the thermal performance of green roofs in summer, a two-sample study with minimum and maximum spectral reflectivity values shows that in these two roofs, the net radiation fluxes and the peak net radiant flux are different from each other by 20% and 16%, respectively. But, the heat flow of the substrate is the same in different green roofs [36]. ...
... [35] 2014 Provides strict requirements for plants used in green roofs and also offers a list of resistant and stable plants. [36] 2014 Bed heat flow is the same on different green roofs, but the radiation fluxes values vary by up to 20% due to their different spectral reflectivity values. [41] 2014 ...
The increasing desire for urban development has led to numerous environmental problems. Environmentally friendly design of building components is one of the most appropriate solutions for sustainable urban development. Roofs make up a significant portion of the total area of urban areas. Although green roofs are increasingly being implemented worldwide, there is still a lack of knowledge about choosing the best vegetation for a particular climate that can lead to optimal green roof performance. This study aims to develop a model of selecting the most suitable green roof vegetation under the cold semi-arid climatic conditions of Qazvin city in Iran. In this study, vegetation selection and climatic criteria were identified separately and were approved, weighted and prioritized based on experts' opinions using Likert and AHP questionnaires. Then the data were analyzed using SPSS statistical software. Findings show that among the vegetation selection criteria, economic, energy and environmental criteria, and among climatic ones, the normalization of sundials and temperature regime, are more important, respectively. Finally, the appropriate vegetation was selected for the desired climate.
... This probably occurred because of the pressure variation applied by the plunger in the bed samples, which may have rearranged the particles of the materials, reducing the porosity and density over the entire depth tested. This behavior is consistent with the findings of other investigations [48] and occurs because as the material is dynamically compacted, there is more physical contact between the solid particles, which increase thermal conduction [49]. Additionally, the magnitude of the thermal conductivity is similar to that presented in the literature [48][49][50]. ...
... This behavior is consistent with the findings of other investigations [48] and occurs because as the material is dynamically compacted, there is more physical contact between the solid particles, which increase thermal conduction [49]. Additionally, the magnitude of the thermal conductivity is similar to that presented in the literature [48][49][50]. ...
Among animal facilities, compost-bedded pack (CBP) barns have attracted a lot of attention from milk producers and the scientific community. Systematic investigation of the main thermal properties utilizing sawdust in CBP barns is of environmental and economic relevance. In this paper, the aim was to (a) develop predictive equations for the thermal conductivity (k) of compost bedding as a function of moisture content (MC), the degree of compaction (DCo), and particle size (PS); and (b) investigate the links between k and depth within bedding material. Samples of compost bedding materials were collected from 42 commercial CBP barns distributed throughout Kentucky (USA). From these predictive equations, it was possible to understand how the MC, DCo, and PS of the bedding materials may influence the behavior of k. These results are very useful for solving obstacles to simulate and predict the variable outcomes of the compost bedding materials process in CBP barns, allowing for its optimization, consequently reducing the time and energy spent on their optimization and allowing for simulation and assessment of compost bedding process modifications. The results of the current study may have important implications in the design and management of bedded pack barns.
... As stated by Djedjig et al. [24], the shading effect of foliage decreases substantially the surface temperature of the building envelope. Additional studies corroborate a direct relationship between LAI and the thermal performance, showing a significant influence of foliage density on the thermal behaviour of green roofs [27][28][29][30][31]. ...
... Previous work by Wilkinson and Castiglia Feitosa [45] where only the influence of green roofs on temperature attenuation was considered, found similar results to Pandey et al. [22]. Several works have shown the potential of green roofs to attenuate indoor temperature [10,20,23,25,[27][28][29][30][31][32][33]36,39,41,50,51]. According to Fioretti et al. [51] this occurs due to the attenuation of solar radiation through the vegetation layer, as well as to the thermal insulation performance of the green roof structure. ...
The process of rapid urbanisation is becoming problematic due to the reduction in, and lack of compensation of, previously vegetated areas. With a combination of green roofs and green walls, adopted on a large scale, it is possible to attenuate the urban heat island effect and internal temperatures in buildings. Tall buildings are becoming a common housing type in many cities, and considering the role of external walls in heat gain, it is expected that the combination of green roofs and green walls have great potential to improve thermal performance. As only 1-2% is added to the total stock of buildings annually, the focus should be on the retrofit of existing buildings to deliver maximum thermal benefits. In the present work lightweight, modular vegetated systems were adopted for roofs and walls. Instead of considering only the temperature influence in heat stress, this research adopted the use of heat index that encompasses the combined effect of temperature and relative humidity. For this purpose, the thermal benefits of green roof and green wall retrofit is evaluated in two small scale experiments, where identical prototypes (vegetated and non-vegetated) are compared using block work and timber framed drywall structures for Rio de Janeiro, Brazil and Sydney, Australia, respectively. The results show a different understanding in heat stress evaluation regarding heat index rather than temperature itself, especially under high levels of relative humidity. This evidence demonstrates green roof and green wall retrofit offer a proven role in heat stress attenuation in residential buildings.
... Taking all of the above into consideration [59][60][61], the substrate to be used will be a mixture of 20% compost from the Faculty of Engineering canteen waste, 30% perlite, 20% vermiculite, 10% sand, and 20% gravel from reclamation. This mixture will be spread around the selected perimeter of the roof to be landscaped by pouring, raking, and lightly compacting. ...
Green roofs are artificial ecosystems that provide a nature-based solution to environmental problems such as climate change and the urban heat island effect by absorbing solar radiation and helping to alleviate urban environmental, economic, and social problems. Green roofs offer many benefits in terms of heat and water conservation as well as in terms of energy costs. This work proposes the design of an extensive and environmentally sustainable green roof for the Faculty of Engineering building in Bilbao. The green roof will be made from the composting of food waste generated in the building’s own canteen. Therefore, the main objective of this study is to calculate the solar efficiency of a sustainable green roof, evaluate its thermal performance, and quantify the impact that its implementation would have on energy consumption and the thermal comfort of its users. The results obtained confirm that an environmentally sustainable green roof has a positive effect on summer energy consumption and that this effect is much greater when there is water on the roof, as shown by the difference in energy savings between the dry (−53.7%) and wet (−84.2%) scenarios. The data show that in winter the differences between a green roof and a non-vegetated roof are not significant. In this case, the estimated energy consumption penalty (0.015 kWh/m2) would be 10% of the summer gain.
... That's why the success of green roofs depending on choosing an appropriate substrate. Water quality enhancement, peak flow reduction, thermal advantages, and sound insulation are all affected by the growth substrate (Zhao & Cesar, 2014). That's why no one material can possess all characteristics that constitute green roof substrate. ...
People face a critical problem with the gradual increase in temperature due to climate change as well as being in Egypt, a hot arid climate zone. Most of the construction companies supply their buildings with manufactured heating and cooling systems like air conditioners with different types and variations. Although these systems are well designed to achieve their goal which is internal thermal comfort, they heavily rely on electricity to function which results in huge power
consumption. So, green roofing is considered as a solution that can solve these problems and incorporate sustainable development principles in building features. Green roofs have a lot of other environmental advantages such as improving the management of stormwater, reducing the effects of urban heat islands, decreasing air and noise pollution, and increasing wildlife ecosystems as well as social and economic benefits. The aim of this thesis is to investigate how green roof technology can improve the thermal behavior and energy usage of educational buildings in Egypt as compared to a traditional roof. The research adopts a quantitative approach towards investigating and comparing the green roof with the conventional roof. The simulation working mechanism is by building a digital model, measure and compare the effect of this alternative roof design on temperature and energy demand, to determine if the green roof minimizing heat gain through the roof. This method is applied in building A in the British university in Egypt. The research results proved that green roofs could enhance thermal performance and reduce energy demand in buildings in summer and winter by decreasing indoor air temperature to be able to reach thermal comfort.
... This means that increasing the substrate layer thickness increases the energy consumption in these climate types. This is due to the thermal inertia provided by the substrate layer, that acts as insulation and delays the heat flux curve during the day (Zhao et al. 2014), making the energy consumption for cooling higher for locations that require cooling in the hours around sunset. In this way, the substrate reduces the heat flux from the interior to the exterior of the building. ...
The objective of this study was to investigate the cooling energy-saving potential of a green roof under different climates comparing green roofs with concrete slabs in Brazil. Eight cities were chosen to represent distinct conditions, according to the Köppen-Geiger climate classification. A numerical simulation was carried out to analyze the roof energy-saving potential for an office building, based on Sailor’s vegetated rooftop model. A sensitivity analysis was performed using a paired t-test and multivariate factorial analysis and considering the leaf area index (LAI) and substrate layer thickness. The results showed that significant annual cooling energy savings were achieved by the green roof for 6 of the 8 climate classifications analyzed. Since the substrate layer thickness was not as relevant as the LAI, the green roof strategy could also be used for building retrofits, with the optimal composition being a substrate layer thickness of 5 cm and LAI equal to 5.00. As a key finding of this investigation, the cooling energy-saving potential of the green roof strategy was verified under all distinct climates tested in Brazilian territory. Through these results, its performance and benefits were highlighted and quantified, considering the most important design parameters that could achieve this goal.
... The substrate is also important for water drainage and retention capacity [16] and provides additional thermal inertia to the roof [17,18]. Previous studies have shown that the thermal conductivity of substrates varies between 0.10 and 0.25 W/(m· • C) and 0.30 and 0.60 W/(m· • C) for dried and saturated states, respectively [19][20][21][22][23]. Although only a few experimental studies explore the specific heat of substrates, this is an important parameter to evaluate the dynamic thermal behaviour of green roofs. ...
Green roofs are made up of several components, including those belonging to the waterproofing and drainage layers, substrate, and vegetation. Of these, the substrate is undoubtedly one of the most important layers of a green roof, contributing not only to the healthy growth of vegetation but also to the water retention capacity and thermal behaviour of the whole solution. Although green roofs are widely recognized as sustainable solutions, it is possible to further improve their environmental performance by developing more ecological substrates that contain industrial by-products. Bearing this objective in mind, sixteen newly developed substrates were characterized in terms of thermal conductivity, specific heat, emissivity, water vapour transmission, hygroscopic sorption, and water retention/drainage capacity. These properties are extremely relevant when solving heat and mass transfer problems as well as for water management prediction. Two reference substrates were also studied for comparison purposes. The results showed that the new ecological substrates have properties that make them comparable to conventional substrates already available on the market. Additionally, the results showed that temperature, moisture content, and density play an important role in the behaviour of substrates of this kind and have a significant influence on many of the studied properties.
... from 0.11 to 0.30 and leaf emissivity ranges from 0.95 to 1.0 in the relevant literature [190,[202][203][204][205][206]. ...
In order to address the increased urban heat island (UHI) effects and energy demand caused by global urbanization, it is imperative to seek sustainable urban design solutions. It is widely acknowledged that urban green infrastructure (UGI), which includes site-scale vegetation and building-integrated vegetation, influences the energy consumption of urban buildings. In the planning and design phases of UGI, numerical simulations are essential tools for evaluating and optimizing design strategies. However, the methodology for the simulation at various scales is still unclear, necessitating a comprehensive review of relevant studies. This review examined the research conducted on UGI modeling in numerical simulations of building energy consumption over the past 35 years and outlined the general workflow of these simulations. The numerical methods and tools for each step, as well as the coupling and validation methods for these tools, were described in detail. Thus, this study equips researchers with the knowledge necessary to analyze the impact of UGI on the energy consumption of buildings using numerical simulations. According to the review, existing building energy model (BEM) tools have not yet integrated modeling of site-scale vegetation for microclimate and shading. Future collaboration between urban climatologists and building physicists should be encouraged to improve the integration of climate and UGI shading simulations with BEM in order to simplify the use of numerical simulation tools.
... from 0.11 to 0.30 and leaf emissivity ranges from 0.95 to 1.0 in the relevant literature [190,[202][203][204][205][206]. ...
Smart metering and the internet of things (IoT) accumulate massive time-series building data. Mining operation patterns from time-series data have huge potential to provide extra information for improving energy efficiency. Previous studies mainly focused on mining control patterns of the heating, ventilation, and air-conditioning system (HVAC). Mining operational patterns from time-series data can help building managers identify energy-wasting operations. This study proposes three methods of mining the operation hours on the time-series data of hundreds of buildings. A key performance indicator (KPI) of facility hours is proposed to indicate the discrepancy between occupants’ requirements and facility hours. The study is carried out on the 240 office buildings of building data genome project 2 (BDG2). The proposed methods are evaluated by comparing mined hours with annotated hours. The impacts of eight operational KPIs are quantified with correlation coefficients and ensemble learning. The practicality of the proposed methods is evaluated on three case buildings. The results show that the cumulative histogram method is effective in mining operation hours. The regression results indicate that mined KPIs can improve the energy prediction accuracy (R²) from 0.35 to 0.41. The impacts of operational KPIs reveal that the KPI of weekends has a tremendous impact on energy consumption. The case study results show that reducing unnecessary facility hours can save from 2.9% to 10.6% energy. This study verifies that operational KPIs mined from time-series data can provide building managers with intuitive knowledge for improving operations.
... Vaz Monteiro et al. [240] 2017 Functional green roofs: importance of plant choice in maximizing summertime environmental cooling and substrate insulation potential Vera et al. [241] 2017 Influence of vegetation, substrate, and thermal insulation of an extensive vegetated roof on the thermal performance of retail stores in semiarid and marine climates Kumar and Mahalle [242] 2016 Investigation of the thermal performance of green roof in a mild warm climate Virk et al. [243] 2015 Microclimatic effects of green and cool roofs in London and their impacts on energy use for a typical office building Vox, Blanco and Schettini [244] Zhao et al. [260] 2014 Effects of plant and substrate selection on thermal performance of green roofs during the summer Zheng and Weng [261] 2020 Modeling the effect of green roof systems and photovoltaic panels for building energy savings to mitigate climate change Zheng, Dai and Tang [262] 2020 An experimental study of vertical greenery systems for window shading for energy saving in summer Ziogou et al. [263] 2018 Implementation of green roof technology in the residential buildings and neighborhoods of Cyprus ...
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.
... To optimize the benefits to thermal environment on green roofs, it is important to choose appropriate green roof components. The energy balance for a green roof depends mostly on the selection of plants and substrates suitable for the building's location (Coma et al., 2017;Zhao et al., 2014). For example, Blanusa et al. (2013) showed that leaf morphology influenced leaf temperature. ...
Vegetation plays a key role in many of the ecosystem services provided by green roofs. Green roofs reduce the amount of heat flux through the building envelope but most existing research has focused on hot season cooling functions and not on cold season benefits which can also result in building energy savings. This study examined the effect of different types of native vegetation on heat flux during winter conditions in two locations with different climates in Japan. We established replicated trays (modular green roof system; n = 5 per treatment) with five monoculture treatments and one plant species mixture treatment and an unplanted control treatment on rooftops in Ishikawa and Tokyo. Each tray was fitted with a heat flux sensor at its base and heat flux values were logged every 30 min from December 2015 to March 2016. There were no significant differences in heat flux between the sites for the unplanted controls, indicating that the tray and soil behaved similarly at both sites, however, the relative impact of the different vegetation types was not consistent across the sites. The Tokyo location had more sun and less snow and plants that had relatively low heat flux in Ishikawa showed the opposite pattern in Tokyo. This is consistent with other studies that suggest that in winter conditions with frequent sunny conditions, plants can result in lower energy savings than unplanted controls. Thus, this result addressed the importance of selecting plants in consideration of climate to optimize energy saving with green roofs.
... The soil and plant canopy characteristics of the green roof are based on Table 3 of Yaghoobian and Srebric (2015) (also provided in Appendix 2 here). The green roof properties are based on the construction assembly of an extensive type green roof installed on a commercial building in Chicago, Illinois Zhao et al. 2014). The reflective roof assembly follows Akbari and Konopacki (2005) for post-1980 buildings, while the asphalt roof has the same characteristics as that of the reflective roof, but with an asphalt material outer layer. ...
We investigate the understudied role of diurnally variable urban surface heating in transport phenomena within an idealized urban environment. We also explore whether heating from different roof materials (asphalt, reflective, and green roofs) at different times of the day affects pollution dispersion and ventilation mechanisms. Results show that the ventilation capacity of urban canyons varies diurnally and is influenced by the buoyancy forces from differentially heated urban surfaces, indicating the highest values in the afternoon and the lowest in the evening. The mechanism of canyon ventilation also varies diurnally. In the morning, the pollutant outflux at the roof level is the principal route of ventilation, while in the evening, lateral outfluxes are dominant and pollutant escape at the roof level is damped because of a local stable air layer. In the afternoon, both vertical and horizontal pollutant outflows contribute similarly to the canyon ventilation. In general, lateral turbulent (rather than mean) fluxes from the side canyon boundaries are the main contributors to the canyon pollutant ventilation throughout the day for all roof-type cases, but their significance slightly decreases from morning to evening. Results reveal that different roof types influence the canyon ventilation mechanism and capacity based on their diurnally-varying surface temperatures and their temperature gradients with respect to other urban surfaces. The existence of the green roof type mainly leads to the generation of a local stable layer and suppression of pollutant escape at the roof level.
... The growing medium provides water and nutrients to the plants and contributes to water retention (Soulis et al., 2017) and thermal performance (Zhao et al., 2014). Generally, such a layer is composed of organic matter and porous minerals with low weight, such as lapillus, pumice, zeolite, expanded clay and perlite. ...
Green roofs offer several environmental and social benefits to urban life. However, such roofs require a greater amount of materials than conventional roofs. The life cycle assessment (LCA) is an appropriate tool that has been used to obtain the potential environmental impacts associated with green roofs throughout their life cycle. This paper aims to review the literature related to the LCA of green roofs, responding: which materials and layers were used in green roofs in LCA studies; which processes were considered in each life cycle phase; which types of roofs have already been compared to green roofs through LCA; which measures are taken to reduce the environmental impacts of green roofs; which methods were used to assess the economic feasibility of green roofs over their life cycle and what were the purposes of such analyses; and which LCA studies included public perceptions about the green roofs. Our findings indicate that the materials used in the green roof layers vary among the articles. However, polymeric materials are usually used for all the layers, except for the substrate. Cradle to grave is the most common approach. Within this approach, more than half of the articles considered cooling and heating energy, which may significantly influence the life cycle analysis results. Most studies reviewed agreed that green roofs cause less environmental impacts than conventional and white roofs. The use of byproducts or recycled materials may further improve the performance. In most studies, public perception is not included in the analysis. Regarding the economic approach, both life cycle cost and life cycle cost-benefit are used to compare green roofs economic viability with other roof systems. In addition to discussing studies reported in the literature, this article also recommends future research to improve the performance of green roofs.
... Table 2 summarizes the climatic characteristics of the selected cities according to the Köppen-Geiger [43] and ASHRAE climate classifications [44]. Weather data files (.epw format) used in the simulations were downloaded from Energyplus.net [45]. ...
Recently, living walls and vegetative roofs have emerged as envelope technologies that can save energy owing to the cooling effects of the building envelope. However, simulation models are required as part of the design support tools available for sizing greenery systems according to architectural constraints and climate. In this study, a green roof heat and mass transfer (GRHMT) model was adapted to develop a novel pot-based living walls heat and mass transfer (LWHMT) model to assess the cooling potential of living walls. The LWHMT model is validated using climate data for Santiago (Chile), which demonstrated a close agreement between the experimental data and the simulated foliage and substrate temperatures and substrate volumetric water content. Along with a previously established GRHMT model, the proposed LWHMT model was coupled to EnergyPlus® through the MLE+® toolbox to simulate the heat transfer between a building and several vegetative surfaces simultaneously. Finally, a prototype retail building was simulated, using climatic conditions for Santiago, to evaluate the impact of wall and roof insulation on the performance of the greenery system, with additional simulations performed for three cities in the USA (Atlanta, GA; Tucson, AZ; Tampa, FL) using different greenery system configurations. The living walls show cooling load reductions of 19.7–24.9%, while the green roofs show much lower reductions of 9.6–15.1%. Moreover, the highest cooling load reductions were obtained by combining green roofs and living walls, achieving a maximum reduction of 36.8% compared with the base case building. In the future, the LWHMT model should be extended to continuous growing media such as pocket felts. In addition, GRHMT and LWHMT models should be integrated into building energy modelling software to develop the full potential of a parametric tool for greenery systems performance simulation.
... Moreover, Blanusa et al., (2013) suggested that plant species Stachys as an ideal alternative to replace Sedum that was widely used in rooftop greening. It was a significant finding for tropical green roof planting as some of the Sedum plant varieties are growing well only on temperate climate conditions (Zhao et al., 2014). The Stachys plant species have been proved that the presence of hairs on the leaves of Stachys plants works on preventing the infrared radiation falling on leaf surfaces by reflecting the incoming irradiance. ...
The interest towards green roof implementation has highly boosted in tropical cities as a means of mitigating high daytime temperatures and thermal discomforts experienced by urban dwellers. This scientific review plans to evaluate the impact of plant species and growing substrates to enhance the thermal comfort of roof greening through a comprehensive overview of the existing literature. Accounting for plant species selection, height, morphology, thickness of leaves, size of leaves, and color of leaves were identified as the decisive factors in mitigating thermal stress. Sedum, Ipomea pescaprae, Nephrolepis spp and Euphorbiaceae family plants were identified as suitable species for integrating into tropical rooftops. The impact of the substrate media is another significant factor that determines the heat mitigation potentials of rooftop greeneries. Depth and composition of the substrate, water holding capacity and porosity properties were the key factors that determine the thermal performance of a specific substrate. Burned sludge, perlite and peat mixture were revealed as ideal substrates to rooftops of urban landscapes owing to their high thermal performance indices. Hence, the appropriate plant species and substrate selection are vital to optimize the thermal benefits associated with roof greening in the tropical context.
... Other studies have underlined that aspects that need to be adequately considered during the GR design phase are those regarding the link between the achievable energy savings and the plants species growing on the roof [49] and those concerning the impact that the selected substrate has on the thermal [50][51][52], environmental [53,54] and energy [55,56] performance of GRs. A few relevant parameters concerning the energy modelling of GRs have also been investigated, specifically referring to the role played by plant species and solar radiation in the thermal exchanges between the vegetated layers and the surrounding environment [57][58][59]. ...
The effects of climate change on the built environment represents an important research challenge. Today, green roofs (GRs) represent a viable solution for enhancing energy and urban resilience in the face of climate change, as they can have a positive impact on the building's indoor thermal comfort and energy demand, as well as inducing various environmental benefits (easing urban heat island effects, improving the management of runoff water, reducing air pollution, etc.). Thus, it is important to be able to assess their effectiveness, both today and under future climate conditions, in order to evaluate whether they can also provide a valid long-term solution. In this paper, a simulation approach is proposed to evaluate the energy and indoor-comfort efficacy of GRs installed on a cluster of buildings with respect to climate change and demographic growth. To illustrate the proposed methodology, it has been applied to two European urban environments characterized by very different climatic conditions (Esch-sur-Alzette in Luxembourg and Palermo in Italy) considering their behaviour over a period of 60 years (2020, 2050, 2080). Results showed that, with respect to standard existing roofs (i.e., without the presence of green coverage), and considering the rising temperatures due to climate change, during cooling seasons GRs enabled significant energy savings (ranging from 20% to 50% for Esch-sur-Alzette and from 3% to 15% for Palermo), improvement of the indoor comfort (reduction of the average predicted mean votes − PMVs) and attenuation of the ceiling temperatures (2–5 °C for both contexts) of the buildings' top floors.
... Due to the effect of materials characteristics on the heat resistance of green roof systems [8,18,47], the properties of substrate with coarse recycled materials and IMSWA were obtained as presented in Table 1. The bulk density of substrate in wet and dry states was equal to 1000.95 kg/m 3 and 944.1 kg/m 3 , respectively. ...
A green roof is composed of a substrate and drainage layers which are fixed on insulation material and roof structure. The global heat resistance (Rc) within a green roof is affected by the humidity content of the substrate layer in which the coarse recycled materials can be used. Moreover, the utilization of recycled coarse aggregates such as incinerated municipal solid waste aggregate (IMSWA) for the drainage layer would be a promising solution, increasing the recycling of secondary resources and saving natural resources. Therefore, this paper aims to investigate the heat transfer across green roof systems with a drainage layer of IMSWA and a substrate layer in-cluding recycled tiles and bricks in wet and dry states according to ISO-conversion method. Based on the results, water easily flows through the IMSWAs with a size of 7 mm. Meanwhile, the Rc-value of the green roof system with the dry substrate (1.26 m2 K/W) was 1.7 times more than that of the green roof system with the unsaturated substrate (0.735 m2 K/W). This means that the presence of air-spaces in the dry substrate provided more heat resistance, positively contributing to heat transfer decrease, which is also dependent on the drainage effect of IMSWA. In addition, the Rc-value of the dry substrate layer was about twice that of IMSWA as the drainage layer. No sig-nificant difference was observed between the Rc-values of the unsaturated substrate layer and the IMSWA layer.
... In case the green roof includes foliage, it can also act as a shading device, by absorbing part of the thermal energy for photosynthesis, and lowering heat exchange under the foliage (Coma et al., 2016). The choice of the types of plants has also an influence on cooling performances (Monteiro et al., 2017;Peri et al., 2016;Zhao et al., 2014), with plants like Salvia and Stachys to be preferred to succulent plants for summertime environmental cooling and substrate insulation (Monteiro et al., 2017). Finally, soil and vegetation create cooling effects through evapotranspiration (Berardi et al., 2014) and the vegetation acts on the albedo of the roof, increasing it from values of 0.1-0.2 ...
Embedding nature-based solutions (NBS) in cities is expected to bring quantifiable benefits, including resilience to flooding, drought, and heatwaves, and air quality improvement. Among NBS, green roofs have an important role in temperature regulation in buildings and in lowering the damaging effects of heatwaves on human health. In this paper a spatial microsimulation model is implemented to simulate temperature impacts of green roofs installations in cities and their capacity to attenuate the effects of heatwave episodes. Particularly vulnerable to heatwaves are elderly people with limited mobility, who have limited means to seek cooling and create cooler indoor environments. The model, implemented using the Netlogo platform (version 6.0.4), considers as agents the elderly citizens in a city area and simulates the heatwave-related health impacts, which are measured in mortality likelihood. In particular, the model simulates a generalised 1.5 °C to 3 °C indoor temperature reduction range induced by green roofs (based on inferences from green roof literature) in four different European cities: Szeged (Hungary), Alcalá de Henares (Spain), Metropolitan City of Milan (Italy) and Çankaya municipality (Turkey). The simulation utilises a ceteris paribus modelling approach, meaning that the relationships of the observed phenomenon (mortality induced by heatwaves) with other possible influencing factors (e.g. level of sport and physical activities practiced by people) are not taken into account. In the case of Szeged, Alcalá de Henares, and Çankaya municipality a substantial reduction in mortality is found to occur associated with green roofs roll out. In the case of the Metropolitan city of Milan, green roofs installations show a low mitigation effect in some scenarios. The underlying factor is the temperature threshold parameter of the model, above which heatwave mortality occurs. This parameter was inferred from the literature (Baccini M., et al., 2008) and it resulted to be substantially higher in the Metropolitan city of Milan (31.8 °C) than in the other cities. The simulation helps in obtaining results which are specific to a given city and particular scenarios therein, and provides additional insights, such as expected temperature mitigation effect induced by green roofs under climate change conditions, or the indoor temperature reduction targets that are needed for a particular city to have a maximum desired heatwave mitigation impact. However, the model parameters have to be carefully selected, after an accurate study of the domain literature.
... Other studies have underlined that additional issues would probably need more attention regarding plants growing on the roof, especially their influence on the thermal performance of green roofs [56,57], and the influence of the evapotranspiration component on the green roof heat and mass transmission [50,58]. ...
In the line of pursuing better energy efficiency in human activities that would result in a more sustainable utilization of resources, the building sector plays a relevant role, being responsible for almost 40% of both energy consumption and the release of pollutant substances in the atmosphere. For this purpose, techniques aimed at improving the energy performances of buildings’ envelopes are of paramount importance. Among them, green roofs are becoming increasingly popular due to their capability of reducing the (electric) energy needs for (summer) climatization of buildings, hence also positively affecting the indoor comfort levels for the occupants. Clearly, reliable tools for the modelling of these envelope components are needed, requiring the availability of suitable field data. Starting with the results of a case study designed to estimate how the adoption of green roofs on a Sicilian building could positively affect its energy performance, this paper shows the impact of this technology on indoor comfort and energy consumption, as well as on the reduction of direct and indirect CO2 emissions related to the climatization of the building. Specifically, the ceiling surface temperatures of some rooms located underneath six different types of green roofs were monitored. Subsequently, the obtained data were used as input for one of the most widely used simulation models, i.e., EnergyPlus, to evaluate the indoor comfort levels and the achievable energy demand savings of the building involved. From these field analyses, green roofs were shown to contribute to the mitigation of the indoor air temperatures, thus producing an improvement of the comfort conditions, especially in summer conditions, despite some worsening during transition periods seeming to arise.
... Similarly, the energy reductions for well-insulated, moderately insulated and uninsulated green roofs for an office building in the Mediterranean climate of Athens (Greece) were 2%, 7% and 48%, respectively [41]. An experimental and simulation study in four U.S. climates concluded that the green roof with insulation was less effective in reducing energy consumption [42]. Pablo in his study proved that the green roof without insulation could have appropriate performance in the summer but not in the winter, as a lower heat transfer coefficient was needed for reducing the heating load [43]. ...
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.
... In the long term, one of the most important factors influencing the GRs performance is the vegetation layer (Cook-Patton and Bauerle, 2012; Raimondo et al., 2015;Young et al., 2014;Zhao et al., 2014). Several researchers have indicated that what enhances GRs' performance and lifetime in urban areas is the selection of suitable plants (Dvorak and Volder, 2010;MacIvor and Lundholm, 2011;Schindler et al., 2019). ...
... Plant species of varying heights, colors, biomass structures, and physiological properties may exhibit distinct thermal behaviors. Zhao et al. [21] studied 3 types of sedum plants and found a 20% range in net radiation flux, in association with different spectral reflectivity values. Silva et al. [1] assessed the energy savings of 3 green roofs with plant heights of 0.05, 0.5, and 1 m and associated leaf area indices (LAIs) of 1, 2.5, and 5 to be 20%, 60%-70% and 45-60%, respectively. ...
This study evaluated and compared the longterm thermal and energy performance of two distinct large-scale green roofs in a humid subtropical city of China. One is an extensive sedum roof (EGR), and the other is an intensive one (IGR) with much deeper soil layer, higher plant diversity and more complex biomass structure. Roof surface temperature (Ts), air temperature at heights of 10 and 150 cm (T10, T150), roof heat flux, and cooling/heating load were analyzed for the green roofs and a control bare roof on hourly, daily, and seasonal basis over an entire year. The two green roofs displayed a similar and consistent performance pattern across the year, characterized by cooling of the roof surface during the day and warming of it at night, and, conversely, warming of the ambient air during the day and cooling of it at night. IGR was more effective than EGR in decreasing daytime and nocturnal Ts, cooling the ambient air, and cutting the summer cooling load, but it added more heating load to the building in winter. Findings from the research suggest that green roofs do not always function in favorable ways for urban heat island (UHI) mitigation and energy conservation but may actually have adverse impacts under certain weather conditions. Despite having a much more complex structure, IGR did not seem to outperform EGR commensurately in thermal benefits. The results can shed light on green-roof design and management for optimization of thermal and energy performance in subtropical areas.
... It should be more important to consider the heat characteristics and selection of plants in order to improve the thermal characteristics of green roofs. Adapting the application of green roof technology to the most diverse climatic conditions and the proper selection of plants are key elements of success [30,31]. Green roofs can reduce outside temperature growth by about 42% and increase the internal temperature by 8% during the day. ...
The need for primary energy has almost tripled in the past 30 years [1]. Energy-efficiency of buildings is the most demanding sector in Serbia, but also the largest energy resource, especially through the potential possibility of renovating existing buildings. The school buildings sector is high on the priority list related to energy savings and represents an important sector that needs to be rehabilitated and improved. The current state of energy efficiency in Serbia in the field of public buildings is worrying, giving a lot of opportunities for improving and saving energy. The aim of this study is to develop and determine an optimal model of energy rehabilitation in the process of comprehensive revi-talization of existing primary school building Ćele Kula in Niš by implementing passive solar design strategies, as well as their application in local climatic conditions. In addition to the literature review, this research used a modeling method based on a computer simulation of a representative existing elementary school building. With the implementation of concrete interventions of passive solar design principles, new models of energy rehabilitation and reduction of annual needs for cooling and heating energy have been developed. The results of energy consumption of the primary school Ćele kula in Niš before and after implementation of the passive design strategies were obtained by simulations using SketchUp and EnergyPlus software packages.
... Solcerova et al. [19] suggested that extensive sedum-covered green roofs in Utrecht (Netherlands) reduced the temperature at night but increased it at daytime, suggesting that the availability of water in the substrate may play an important role in the cooling behavior of the green roof. Other studies [20,21] demonstrated that plant coverage, floristic composition, and plant and substrate selection on the green roof can also influence its thermal behavior. In addition to the urban heat island mitigation, storm water run-off reductions of 60% and 90% were observed for extensive and intensive green roofs, respectively, in Pittsburgh (U.S.A) [22]. ...
Green roofs have become popular in urban areas as a solution to restore green space in cities and mitigate urban problems. In this study, the economic and environmental sustainability of using green roofs for rooftop agriculture (i.e., roof farms) is evaluated and compared with that of using green roofs as extensive gardens of flowers and non-edible plants with low maintenance (i.e., roof gardens) based on these two green roofs that were installed and operated for over five years in a university building in Seoul, Korea. The life cycle cost analysis results show that the total cost of the roof garden is 38.9% lower than the flat roof whereas the total cost of the roof farm is 68.3% higher than the roof garden. The environmental impacts of both the roof garden and farm were 2.4–35 times as high as those of the flat roof. The need to frequently replenish the lightweight soil over its lifetime was the main contributor to both the economic cost and environmental impacts of the roof farm, suggesting a need to develop cost-effective and environmentally benign lightweight soil materials. A survey was also conducted to investigate public preferences and perceptions of these two green roof options. Over 80% of the respondents expressed the necessity for green roofs in urban areas, and 79.3% preferred roof gardens over farms. Our results show that roof farms have several merits in urban areas, especially social benefits, but future research should focus on improving their economic and environmental sustainability.
... One special group of green roof plants are succulents, among which different species of Sedums are most often used. Stomatal resistance values reported for Sedums are in the range from 340 s/m to 1000 s/m or higher [29,30]. ...
This paper presents a study of the thermal response of lightweight extensive green roofs with lightweight mineral wool growing media in wintertime in water-freezing conditions. A model of green roof heat and mass transfer was developed, which considers sensible as well as latent heat accumulation in plants and lightweight mineral wool growing media using an apparent heat capacity method. The model was validated with in-situ experiments. The influence of latent heat storage on the thermal response of a green roof was studied for different climatic conditions. The results of numerical analyses showed that the process of water freezing further improves the energy efficiency of green roofs, because the peak heat flux at the inner surface of the roof is up to 30% lower in comparison to the non-vegetated roof. It is shown that latent heat storage significantly contributes to decreasing heat losses during wintertime, which are approximately 5% to 20% lower in comparison to non-vegetated roofs.
... This leads to a trade-off between the cost of increasing substrate thickness and the benefits of improved ecosystem function (Dusza et al., 2017;Feitosa and Wilkinson, 2016). Plant choice can influence the provision of many key services of extensive green roofs (Jim, 2015;Williams, 2015;Zhao et al., 2014) but laborious testing of hundreds of available plant species is logistically challenging. Consequently, ecologists have attempted to use species-level morphological and ecophysiological traits to predict performance of important ecosystem properties and services including drought tolerance , temperature moderation in hot (Monteiro et al., 2016;Williams, 2015) and cold seasons , stormwater capture (Farrell et al., 2013;Nagase and Dunnett, 2012;Starry et al., 2014), and nutrient uptake . ...
Plant selection and diversity can influence the provision of key ecosystem services in extensive green roofs. While species richness does predict ecosystem services, functional and phylogenetic community structure may provide a stronger mechanistic link to such services than species richness alone. In this study, we assessed the relationship between community-weighted trait values from four key leaf and canopy functional traits (plant height, leaf area, specific leaf area, dry leaf matter content), functional diversity, and phylogenetic diversity to ten different green roof functions, including ecosystem multifunctionality, in experimental polycultures. Functional traits of dominant plant species were a major driver for indicators of multiple green roof functions, such as substrate nitrate-N, substrate phosphorus, aboveground biomass and ecosystem multifunctionality. In contrast, functional diversity alone increased substrate organic matter. Moreover, both functional/phylogenetic diversity and identity predicted canopy density, substrate cooling. This study highlights the first line of evidence that distinct aspects of phylogenetic and functional diversity play a major role in predicting multiple green roof services. Therefore, we provide further evidence that to maximize green roof functioning, a very careful selection of plant traits and polycultures are needed.
... Os estudos de simulações com modelagem são comparados com experimentos e coleta de dados observados e referem-se tanto para avaliação da capacidade de retenção do escoamento (LOCATELLI et al., 2014), como para predizer o desempenho do arrefecimento por perda de calor latente, que está condicionada a espessura do substrato (METSELLAR, 2012). Independentemente das zonas climáticas, o resultado das simulações mostrou que o tipo de vegetação influencia significativamente no saldo de radiação (ZHAO et al., 2014). ...
O efeito direto da temperatura, da radiação solar e da precipitação nas cidades pode provocar impactos como as ilhas de calor e as inundações urbanas. O objetivo deste artigo é avaliar a influência de fatores e elementos meteorológicos no comportamento de telhados verdes instalados em mais de 100 países a partir da classificação climática de Köppen-Geiger. Foram mapeados mais de 170 artigos científicos publicados em periódicos nacionais e internacionais com estudos experimentais e de modelagem aplicados em telhados verdes. Os resultados indicam predominância de 70% de estudos com telhados verdes em áreas de clima temperado, sendo 65% das pesquisas relacionadas ao conforto térmico e à quantidade e qualidade da retenção do escoamento superficial. As pesquisas revelam relativa influência de fatores geográficos que condicionam os elementos climáticos de temperatura e precipitação na capacidade de retenção do escoamento superficial em telhados verdes, entretanto são capazes de condicionar sistemas de arrefecimento à medida que delimitam efeitos térmicos provocados por variações de temperatura presentes nas superfícies de telhados verdes.
Extensive green roof system is widely used due to its lightweight, thin growing media, limited or no maintenance, low cost, and high potential application for use over the new or existing lightweight structures. This study is focused on the energy performance and rainwater retention performance of extensive green roofs when coupled with highly insulated roof deck. In this experimental study, three roof systems: conventional roof (CR) and two extensive green roofs with plants (GR) and with no plants (GM) are constructed, instrumented and their responses to real environmental conditions are monitored for over a year and analyzed. The experimental results suggest that during wet period, the rainwater retention potential of green roof is only about 21%, while in the summer the rainwater retention capacity increases as high as 100%. Plants play an important role in rainwater interception, growing media wetness, rain runoff and the green roof's thermal performance by modifying short- and long-wave radiation and as well as convective heat exchanges. Installation of green roofs on highly insulated roof decks yields a mixed performance in a mild and wet climate. The heat loss through the green roof during the heating months is about 2% higher than a similar roof without green roof. Whereas during the cooling months the green roof is able to reduce the heat gain by 66%. This substantial heat gain reduction can help to reduce overheating problems in highly insulated buildings.
Green roof is an environment-friendly structure developed globally as a result of increasing urbanization. In this review paper we first tried to collect classification, structure and materials of green roofs. Increasing water availability of substrate using water retention additives is also collected and studied in this paper. Accordingly, different materials are applied in green roofs, among which polymers have attracted a lot of attention. Polymer materials are widely used in different layers of green roofs due to their characteristics like light weight, which is an important concern about green roofs. So, in the next step, we gathered different polymeric materials that are used in different layers of green roof or can be used in this structure. For example, low density polyethylene (LDPE) or polyethylene (PP) material use as physical barriers. Therefore, this article provides an opportunity to review and compare different polymeric materials that have been studied in different articles in various layers.
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.
Global warming is a harsh reality of today’s century. All human and animals are facing challenges for survivals. Sometimes challenges are very big. According to the environment and nature’s role all of us make the arrangement for the leaving comfort. Undoubtedly, as the ambient temperature increases, the inside and outside temperature of the building also increases. This increase in the temperature affects the living condition of human being as well as other biota. Those who can afford they can use a mechanical system called as Refrigeration and air conditioning system. The green roof top is an idea where the cost cutting is done in the energy consumption and increases the comfort level of the biota. Thus, the overall objective of the paper is to investigate the impact of green roof on thermal performance for Indian climate. The thermal performance of the green roof over conventional roof has been compared for the results. The temperatures, cooling potential parameters have been compared for the results.
Green roofs are components of the building envelope that have become increasingly popular in urban contexts because other than providing numerous environmental benefits they are also capable of reducing building energy consumption, especially in summer. However, despite all these advantages, green roofs are still affected by some limitations. Specifically, there are some gaps affecting the energy modelling consisting in the absence of a proper database, information (growth stage, leaf area index, and coverage ratio) relative to the different green roof plant species, which technicians could use in case of lack of actual field data to perform energy analysis of buildings equipped with green roofs. These gaps concern also environmental and economic assessments of such technology. In fact, the currently available green roof LCA and LCC studies seem to underestimate the role of the substrate on the overall environmental impact and the role of the disposal phase on the life cycle cost of the green roof. In this chapter, all these aspects are addressed, and contributions to their solution, which arose from both experimental and modelling research, carried out by the authors are presented.
Green roofs represent a well-consolidated solution for new or existing buildings to achieve considerable energy savings. Theoretical and experimental analyses have shown that in summer the interface temperature between green and structural roofs decreases considerably when compared with traditional roofing solutions, producing a limitation of the thermal energy entering the indoor environment. Experimental measurements carried out on a green roof in a Mediterranean location showed cooling peak powers noticeably reduced and cooling requirements 37.9% lower than for a bituminous black building roof. On a large scale, green roofs have been proven to help in the mitigation of urban heat islands (UHIs) thus contributing to improvement of livability in cities.
HIGHLIGHTS - SNAPSHOT & ADDITIONAL ANALYSIS
Experiment 1 - Glasshouse
• Under glasshouse conditions there was no significant difference between germination in green roof substrate media and nursery seed raising media; with synchronous emergence of diverse species in both media.
• (Additional) Recommendation to use of green roof substrate in nursery production for green roof landscape planting as having potential to minimise transplant shock by eliminating water potential differential between nursery stock and the green roof substrate.
Experiment 2 – Green Roof Modules
• Seed sowing establishment of Australian grassland forb only meadow is suggested as a cost-effective method of installation with minimal weed maintenance and possibly advanced resilience to disturbance, comparative to planting establishment on green roofs; having on ground and conservation application.
• (Additional) Diverse species rich rapid high cover of Australia grassland forb meadow establishment occurred even under extreme temperatures of green roof substrate and ambient air conditions with irrigation.
• A seed sowing density of 200seeds and 400 seeds /metre square at surface to 10 mm depth, in green roof module conditions under irrigation, will rapidly produce a diverse species rich high cover.
• With 400 seeds /meter square providing the most rapid cover, this density is recommended for weed suppression.
• Seed length and width were not indicated as predictors of forb seed germination under irrigated green roof module conditions.
The University of Melbourne’s research repository for excellence in academic and post-grad research, Minerva Access. The below permanent URL to the thesis is provided for citing and linking purposes.
Thesis: Direct seeding onto green roof substrate supports species rich, high cover novel grassland
Permanent URL: http://hdl.handle.net/11343/148396
Access: Open Access
The urban environment becomes a place of extremely high population density, which has such environmental defects as high risk of infectious and chronic diseases, air pollution, vulnerability to climate change, etc. On account of that, the problem of energy-efficient and safe construction methods development that would mitigate the effects of air pollution (to create areas for health recovery, increase the length of working period of human life) becomes especially important. As a tool for solving these problems, the technology of «green roof» is proposed. To confirm the theoretical studies on the energy efficiency of roofing with natural landscaping, a test stand was created, and an experiment to determine the thermal properties of a «green roof» was conducted in a laboratory of NRU MGSU (Moscow, Russia). The results of the experiment are presented. The energy efficiency of a public building roof was tested on three models of «green roof» with different composition and thickness. The results were compared with theoretical calculations.
Low Impact Development (LID) techniques have been drawing an increasing attention in recent years as efficient ways of stormwater management. These methods try to mimic nature by providing pervious area which has been decreased due to urbanization. One of the most efficient practices of LID is the use of Green Roof (GR) systems. Although GRs have been traditionally used in the past, their engineering design and construction is a recent trend. Since GR systems, similar to other LID techniques, are supposed to endure local climate and environmental conditions, their design should be accomplished regarding the conditions of the area where they will be installed. In order to systematically examine, design, and construct various LID techniques for Korean climate and environment, the LID & GI Center of Korea is built in Pusan National University. This center tries to hire hardware and software facilities to study and design LID practices; Hydrological Performance Tester for Green Roof (HPT-GR) and Korea Low Impact Development Model (K-LIDM) are made for this purpose. In order to examine the performance of a Green Roof (GR) system composed of layers with different material and size, five trays were made at LID & GI Center of Korea. The size and composition of these trays were: (A) plant + soil + drainage mat with total depth of 15 cm, (B) plant + soil + sand with total depth of 15 cm, (C) plant + soil + sand with total depth of 9 cm, (D) a bare soil with total depth of 15 cm, and (E) a concrete with total depth of 15 cm. All the trays were examined under different uniform precipitations with rates of 50, 80, 100 and 150 mm/h using HPT-GR. The results showed that the use of drainage mat in tray A could significantly improve the performance of the GR by increasing its storage capacity up to 40% of the rainwater, decreasing its saturation rate, and reducing its discharge peak value. Then, as the first use of K-LIDM for simulating a green roof, all the experimental GRs were numerically simulated using this model; the numerical hydrographs were compared to those achieved from the experiment. The results showed that K-LIDM can be used for performance prediction of GR systems with slightly conservative but acceptable results. With an increase in the rainfall intensity, the discharge peak values increased and their times decreased in both numerical and experimental scenarios; however, the peak values were slightly higher in simulation results than those of the corresponding experimental ones.
A remarkable advantage of clay tiles roof coverings in hot climates is the realization of a ventilated air layer between them and the roofing underlay that allows a natural and forced convection through the tiles joints and the channel from eaves to ridge, thus cooling the roof materials. However recently, in many countries, regulatory developments on buildings energy efficiency or buildings sustainability certification protocols are increasingly encouraging the use of alternative strategies, with the aim of reducing the urban heat island (UHI) effect and the buildings’ cooling consumptions. Among them, the use of ‘cool’ materials for roof covering. These mandatory or voluntary measures de facto push the construction products market towards specific directions, risking penalizing traditional components such as clay tiles. This article reports the results of experimental and numerical activities carried out in order to extensively characterize the optical properties of clay tile materials and investigate their impact, also coupled with above sheathing ventilation, on the thermal performance of a ventilated roof under warm-temperate climate. In the first phase of the research, the main optical properties of over 30 different clay products have been experimentally characterized in order to get a clear and extensive picture of such properties for the materials spread in the market. In a second phase, starting from the thermal data collected on an experimental real-scale building, a dynamic energy analysis tool was calibrated and used to perform simulations by varying the optical properties of the roof covering thus assessing the impact on the roof temperatures, also in comparison to a clay tiles roof. The results underline that the use of the above sheathing ventilation obtained through clay tiles is an effective strategy to reduce roof temperatures, even if covering materials are not qualified as ‘cool’, thus impacting on both UHI and indoor comfort.
As envoltórias verdes são um meio de tornar a vegetação parte integrante da edificação e de seus sistemas, tais como o de resfriamento passivo. No entanto, as dinâmicas que sustentam o bom desempenho térmico destas envoltórias dependem de diversas variáveis. O objetivo deste artigo foi identificar, através de revisão sistemática da literatura recente sobre o tema, o comportamento térmico de ambientes construídos internos sob a influência das envoltórias verdes e verificar quais são as possíveis variáveis de desempenho térmico, conforme suas características. Os trabalhos analisados mostram que a redução de temperatura do ambiente interno é significativa, sendo mais acentuada no caso de paredes verdes. O desempenho térmico das envoltórias verdes depende de variáveis como o tipo de vegetação, densidade de folhagem, composição do substrato, etc., destacando as características climáticas, apesar da maioria das pesquisas focar em resultados de outras variáveis. Foi possível, também, verificar pontos frágeis do conhecimento atual, como as lacunas a respeito do peso da umidade do substrato no resfriamento de coberturas verdes e da falta de estudos que comparem o desempenho de coberturas verdes com coberturas de telhas cerâmicas ou de fibrocimento. A análise das variáveis identificou que estas exercem entre si relações multifacetadas, o que tornou evidente que determinar hierarquias entre estas não é possível e nem prudente. A análise da coerência entre as variáveis é mais importante do que a determinação de hierarquia entre as mesmas, bem como esta ação deve preceder a definição das características de uma determinada envoltória verde a ser implantada em dado lugar.
Thermal discomfort, increased energy consumption, and heat related stress are some of the most prominent consequences of urban warming. Instances of heat related deaths have been reported; the elderly and the poor remain especially vulnerable. Urban greening has often been cited as an economically efficient method for inducing ambient cooling. Consequently, increased impetus is given to provision of public green spaces. However, a general increase in urban green cover especially in the form of parks and green spaces may be inadequate to achieve desired results. This article serves to highlight the thermal heterogeneity of landcape elements and stresses on the need for strategic shade provision. The originality of this study lies in the fact that it provides a comparative review of energy conservation potential of public and private green spaces. It is found that large parks may not have substantial cooling effect on the indoor built environment. Moreover, people tend to spend more time indoors than outdoors. Thus the need for greening of private areas has become an undeniable climatic necessity. The potential of shade trees, green walls, and roof gardens for cooling of built environment are discussed with quantitative evidences of their thermal and economic benefits. Parameters incurring cost expenditure and weaknesses of the greening strategies are enumerated for enabling prudent selection/implementation of strategies. Proposals are generated to improve climatic resilience to urban warming and for diligent planning of cities.
The unsaturated soil hydraulic properties are often described using Mualem-van Genuchten (MVG) type analytical functions. Recent studies suggest several shortcomings of these functions near satura- tion, notably the lack of second-order continuity of the soil water retention function at saturation and the inability of the hydraulic conductivity function to account for macroporosity. We present a modified MVG formulation that improves the description of the hydraulic conductivity near saturation. The modified model introduces a small but constant air-entry pressure (hs) into the water retention curve. Analysis of the UNSODA soil hydraulic database revealed an optimal value of 24 cm for hs, more or less independent of soil texture. The modified model uses a pressure dependent piece-wise linear cor- rection to ensure that deviations between measured and fitted conduc- tivities between pressure heads of 0 and 240 cm were eliminated. A small correction was found necessary between 24 and 240 cm, and a much larger correction was needed between 0 and 24 cm. An average RMSE in logKof only 0.26 remained for a data set of 235 samples. The resulting modified MVG model was found to have small systematic errors across the entire pressure range. The modified model appears well suited for large-scale vadose zone flow and transport simulations, including inverse modeling studies.
A green roof is a vegetated roof or deck designed to provide urban greening for buildings, people, or the environment. Made popular across Europe over the past few decades, green roofs are now becoming more familiar to North Americans as some cities have built green roof pilot projects and adopted incentives for using green roofs or even require their use. Green roof standards and guidelines are also emerging to be used for governance and project specification. Although much is known about the application of green roofs across Europe, much less is known about their application across North America's diverse ecological regions. When considering the many decisions required in applying green roof technology to a specific place, there are few choices more critical to their success than the selection of appropriate vegetation. We conducted a review of green roof research to investigate what is known about the application of plants on green roofs across North America and their ecological implications. Results indicate that investigation sites across ecoregions begin to reveal differences in plant survival. Although ecological investigations are limited, their results show improved plant performance and ecological services with diverse green roofs. We conclude that as green roofs continue to become regulated and adopted in policy, further development of standards and guidelines is needed. To date, there is no common ground for reporting of green roof research, and we make recommendations for facilitating such efforts for improved research, policy development and their management across North America's diverse ecological regions.
Of several available methods for the measurement of the thermal resistivity of soils, the thermal needle method and the Shannon and Wells method are considered most suitable, because of their relative simplicity and the short measurement time required. The thermal needle method is the simpler of the two, and it offers the added advantage that knowledge of the specific heat of the soil is not required for calculation of the thermal resistivity from the test data. A special thermal needle design and simple test procedures have been developed which make possible the determination of thermal resistivity in both the radial and axial directions and the specific heat for a given sample.
A new edition of the bestseller on convection heat transfer A revised edition of the industry classic, Convection Heat Transfer, Fourth Edition, chronicles how the field of heat transfer has grown and prospered over the last two decades. This new edition is more accessible, while not sacrificing its thorough treatment of the most up-to-date information on current research and applications in the field. One of the foremost leaders in the field, Adrian Bejan has pioneered and taught many of the methods and practices commonly used in the industry today. He continues this book's long-standing role as an inspiring, optimal study tool by providing: Coverage of how convection affects performance, and how convective flows can be configured so that performance is enhanced How convective configurations have been evolving, from the flat plates, smooth pipes, and single-dimension fins of the earlier editions to new populations of configurations: tapered ducts, plates with multiscale features, dendritic fins, duct and plate assemblies (packages) for heat transfer density and compactness, etc. New, updated, and enhanced examples and problems that reflect the author's research and advances in the field since the last edition A solutions manual Complete with hundreds of informative and original illustrations, Convection Heat Transfer, Fourth Edition is the most comprehensive and approachable text for students in schools of mechanical engineering.
Studies of heat and mass exchange between leaves and their local environment are central to our understanding of plant-atmosphere interactions. The transfer across aerodynamic leaf boundary layers is generally described by non-dimensional expressions which reflect largely empirical adaptations of engineering models derived for flat plates. This paper reviews studies on leaves, and leaf models with varying degrees of abstraction, in free and forced convection. It discusses implecations of finding for leaf morphology as it affects – and is affected by – the local microclimate. Predictions of transfer from many leaves in plant communities are complicated by physical and physiological feedback mechanisms between leaves and their environment. Some common approaches, and the current challenge of integrating leaf-atmosphere interactions into models of global relevance, are also briefly addressed.
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.
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.
Green roof technology has been adopted in the United States as a specialized roofing system and as a sustainable technology capable of saving energy. Most of the previous thermal performance models for green roofs have had the main goal of quantifying these energy savings. However, until recently, none of the models had been fully validated with laboratory and experimental data including both heat flux and surface temperature data. A recently developed green roof thermal performance model was validated with detailed experimental data from a new experimental apparatus called a Cold Plate, which is specifically designed and built for that purpose. In order to further examine the accuracy of the model, this paper describes the dynamic validation of the model using field data from a green roof installed on a commercial roof in Chicago. The dynamic validation consists of comparing substrate surface temperature, heat flux through the roof, and net radiation. The validated results show that the green roof thermal model predicts the heat and mass transfer appropriately as long as the long-wave radiation data from a weather station are used to reduce a possible bias resulting from the sky condition.
A summary is given of some of the main features associated with the thermal properties of soils in cold regions as described in a USACRREL monograph and report. The main effects of the freezing process in soils are noted and its analogy with the drying process is emphasized. It is shown that the unfrozen water present in frozen fine-grained soils plays an important and effective role in facilitating heat transfer. The influence of the degree of saturation is described and the concept of a “critical” degree of saturation introduced.The methods for calculating the thermal conductivity of frozen soils are compared and some of their trends indicated. The results of an evaluation of these methods show which gives the best agreement with measured thermal conductivity values under certain conditions.
Thermophysical parameters of cohesive soil are important properties in the design of the ground source heat pump system and the ventilation system of subway. In this paper, the more precise measurements are taken to study the thermophysical parameters of cohesive soil based on the transient heat flow probe method by KD2 pro. The results show that the thermal conductivity and capacity increase obviously as water content enhances. The higher the temperature, the higher the thermal conductivity. So the temperature effect of thermal conductivity should be taken into consideration under some certain temperatures. The modification of Johansen's equations indicates the good applicability for the same type of cohesive soil, which can be used for predicting the thermal conductivity of cohesive soil with different water content and dry densities.
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.
This study explores the complex and interacting physical mechanisms that lead to building energy use implications of green roof design decisions. The EnergyPlus building energy simulation program, complete with an integrated green roof simulation module, was used to analyze the effects of roof surface design on building energy consumption. Simulations were conducted for both black and white membrane control roofs and nine variations of green roofs. The investigation included a total of eight buildings – new office and new multi-family lodging buildings, each in four cities representing diverse climatic conditions: Houston, Texas; New York City, New York; Phoenix, Arizona; and Portland, Oregon. Building energy performance of green roofs was generally found to improve with increasing soil depth and vegetative density. Heating (natural gas) energy savings were greatest for the lodging buildings in the colder climates. Cooling energy (electricity) savings varied for the different building types and cities. In all cases, a baseline green roof resulted in a heating energy cost savings compared to the conventional black membrane roof. In six of the eight buildings, the white roof resulted in lower annual energy cost than the baseline green roof. However, a high vegetative cover green roof was found to outperform the white roof in six of the eight buildings.
Emphasizing the integration of mathematical expressions with clear physical associations, this textbook on convective heat and mass transfer reviews the laws of thermodynamics and fluid motions, behavior of laminar and turbulent flows in a variety of conditions, natural free convection in space, and flows through porous media.
The book focuses on solar radiation characteristics, solar radiation
available for practical applications, heat transfer, radiation
characteristics of opaque materials, theory of flat-plate collectors,
and concentrating collectors. Also discussed are solar process
economics, solar water heating, solar heating system design, solar
cooling, conversion to mechanical energy, evaporative processes, and
selfgradient ponds.
The coupled heat and mass transfer in soil can be analysed by examining the temperature dependence of thermal conductivity. We have measured the thermal conductivity of two kinds of soil (Ando soil and Red Yellow soil) as a function of both temperature (5–75°C) and water content by the twin heat probe method. From our results we concluded that the thermal conductivity resulting from the latent heat transfer can be separated from the apparent thermal conductivity by subtracting the thermal conductivity at a temperature near 0°C from that at a higher temperature. The relation between the phenomenological enhancement factor (β) and the volumetric air-filled porosity was divided into two parts: β increases linearly as the volumetric air-filled porosity increases from zero (that is, water saturation), to the point at which soil water potential corresponds to −320 J kg−1; from that point to oven-dry condition, β decreased logistically with the volumetric air-filled porosity. From these results, we could generalize the behaviour of β.
The advantages of the planned roofs are undoubtedly numerous from both the ecological and the social point of view. They act positively upon the climate of the city and its region, as well as upon the interior climate of the buildings beneath them. They give protection from the solar radiation, which is the main factor in passive cooling. By reducing thermal fluctuation on the outer surface of the roof and by increasing their thermal capacity, they contribute, to the cooling of the spaces below the roof during the summer and to the increase of their heat during the winter. Due to the decrease of the thermal losses, the green roofs save the energy consumption.This paper refers to the analysis of the thermal properties and energy performance study of the green roof. The investigation were implemented in two phases: during the first phase, extended surface and air temperature measurements were taken at the indoor and outdoor environment of the buildings where the green roof had installed and during the second phase of the study, the thermal properties of the green roof, as well as, the energy saving were examined, through a mathematical approach.
From measurements of surface heat transfer on the roofs of two commercial buildings in Northern California we have developed a correlation that expresses the outside convective air-film coefficient for flat, horizontal roofs as a function of surface-to-air temperature difference, wind speed, wind direction, roof size, and surface roughness. When used in detailed building energy analysis programs, this correlation is expected to give more accurate calculation of roof loads, which are sensitive to outside surface convection. In our analysis, about 90% of the variance of the data was explained by a model that combined standard flat-plate equations for natural and forced convection and that took surface roughness into account. We give expressions for the convective air-film coefficient: (1) at an arbitrary point on a convex-shaped roof, for a given wind direction; (2) averaged over a strip along the wind direction; and (3) averaged over a rectangular roof for a given wind direction.
This review paper addresses the role of green roofs in urban drainage considering both management of water quantity and quality. Results from investigation of full scale installations as well as from laboratory models are reviewed. The following factors affecting runoff dynamics from green roofs are discussed: type of green roof and its geometrical properties (slope); soil moisture characteristics; season, weather and rainfall characteristics; age of green roof; vegetation. Design parameters as suggested by different authors are also reviewed. Factors which affect influence of a green roof on runoff water quality are discussed in general terms followed by the review of data regarding concentrations of phosphorus, nitrogen, and heavy metals in green roof runoff, its’ pH, and first flush effect. Linking among fertilization, runoff pollution and vegetation development is given a particular focus. The review indicates clearly that there is a need for more research into a green roof performance in an urban environment. The differences measured by few existing studies between the early years performance of green roofs and the later years indicate a need for long term monitoring of green roofs.
This study was conducted to examine possible errors in the use of the instantaneously heated infinite line source (IHILS) theory by comparing the IHILS model with three other models that account for different characteristics of the heat pulse apparatus. For typical probe geometry and heating times, estimates of volumetric heat capacity (ρc) obtained from the IHILS theory were within 1% of the estimates obtained by using the more rigorous models. A generalized error analysis is presented that permits direct graphical estimation of errors for different probe geometries, different heating times, and different soil thermal properties. First-order error analysis was also used to examine potential error in ρc as a result of errors in probe spacing, temperature maximum, and heat input. -from Authors
An efficient time-dependent equation for predicting ground surface
temperature devised by Bhumralkar (1975) and Blackadar (1976) is tested
against a 12-layer soil model and compared with five other approximate
methods in current use. It is found to be generally superior if diurnal
forcing is present and very much superior to the use of the insulated
surface assumption. An analogous method of predicting ground surface
moisture content is presented which allows the surface to become moist
quickly during rainfall or to become drier than the bulk soil while
evaporation occurs. These improved methods are not of much relevance
unless the main influences of a vegetation layer are included. An
efficient one-layer foliage parameterization is therefore developed that
extends continuously from the case of no shielding of the ground by
vegetation to complete shielding. It includes influences of both ground
and foliage albedos and emissivities, net leaf area index, stomatal
resistance, retained water on the foliage, and several other
considerations. When it is tested against data for wheat measured by
Penman and Long (1960), it appears quite adequate despite the many
simplifying assumptions. The parameterization predicts that errors of up
to a factor of 2 in evapotranspiration can be incurred by ignoring the
presence of a vegetation layer.
Garden roof systems (GRS) are specialized roofing systems that support vegetation growth on rooftops. GRS not only add aesthetic appeal to the unused roof space that is available in most urban areas; they also provide multiple benefits in an urban context. From a building's point of view, the plants and soil protect the roofing membrane from exposure to ultra violet radiation, extreme temperatures and physical damage, thus contributing positively to the roof's service life. Le système de terrasse-jardin (STJ) est un système de toiture spécialisé qui favorise la croissance de végétation sur les terrasses. Le STJ ne fait pas qu'ajouter à l'esthétique des nombreuses terrasses non utilisées des agglomérations; il leur apporte divers autres avantages dans un univers urbain. Les plantes et la terre végétale protègent le revêtement des toitures des rayons ultraviolets, des températures extrêmes et d'une détérioration physique, contribuant ainsi positivement à leur durée de vie. RES
Contenido: Elementos de transferencia de calor; Ecuación de conducción del calor; Conducción constante del calor; Conducción transitoria del calor; Métodos numéricos en la conducción del calor; Fundamentos de convección; Convección externa forzada; Convección interna forzada; Convección natural; Evaporación y condensación; Fundamentos de radiación térmica; Transferencia de calor por radiación; Intercambiadores de calor; Transferencia de masa; Enfriamiento de equipo electrónico; Apéndices.
Comparison of solar radiation and simulated net radiation during five days of July in Austin, TX. Fig. 14. Comparison of simulated net radiation difference between cases during five days of
- Fig
Fig. 13. Comparison of solar radiation and simulated net radiation during five days of July in Austin, TX. Fig. 14. Comparison of simulated net radiation difference between cases during five days of July in Austin, TX. Fig.
KD2 pro specifications
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Building and Environment xxx (2014) 1e13 10 Please cite this article in press as Effects of plant and substrate selection on thermal performance of green roofs during the summer
- Ca M Sacramento
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Comparison of solar radiation and simulated net radiation during five days of July in Sacramento, CA. M. Zhao et al. / Building and Environment xxx (2014) 1e13 10 Please cite this article in press as: Zhao M, et al., Effects of plant and substrate selection on thermal performance of green roofs during the summer, Building and Environment (2014), http://dx.doi.org/10.1016/j.buildenv.2014.02.011
Green roof design and implementation in Florida
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Florida; 2004. Presented at the The Second Annual Greening Rooftops for
Sustainable Communities Conference.
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Predictive green roof model for assessment of heat transfer through a roof assembly in summer weather conditions
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ASHRAE. ASHRAE standard 90.1. Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.; 2007. M. Zhao et al. / Building and Environment xxx (2014) 1e13 13 Please cite this article in press as: Zhao M, et al., Effects of plant and substrate selection on thermal performance of green roofs during the summer, Building and Environment (2014), http://dx.doi.org/10.1016/j.buildenv.2014.02.011
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Presented at the The Second Annual Greening Rooftops for Sustainable Communities Conference
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- C Miller
- M Lohr
Livingston EH, Miller C, Lohr M. Green roof design and implementation in
Florida; 2004. Presented at the The Second Annual Greening Rooftops for
Sustainable Communities Conference.
Experimental study on the thermophysical parameters of Cohesive soil by the transient method
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