Article

Evaluating the Impact of Green Roof Evapotranspiration on Annual Building Energy Performance

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Abstract

The performance of the building envelope predominantly determines the ultimate energy performance throughout the lifecycle of a building. A sustainable alternative to enhance roof performance while limiting heat flux through a roof is integrating passive techniques such as green roof. Particularly, green roof performance is sensitive to local climate. The main objective of this study was to evaluate the evapotranspiration effect of an extensive green roof on annual energy consumption of an office building in relation to the humid continental climate of Republic of Korea. The dynamic behavior of green roof and building energy performance were investigated through a parametric simulation method using green roof module in EnergyPlus coupled with jEPlus. Structural data of the reference building and ASHARE 90.1-2007 operational schedules were used as inputs for baseline building model while inputs for the green roof module were based on experimental data sets. Due to the influence of the humid conditions and local wind current on the evapotranspiration process, it was generally found that high leaf area index (LAI) reduced cooling energy demand and somewhat reduced heating energy demand as well; corresponding to the highest daily evapotranspiration fluxes of 4.79 mm day⁻¹ in summer and 1.80 mm day⁻¹ in winter. Increasing LAI from 20% to 100% cover increased evapotranspiration flux by 10.4% in summer and 80.2% in winter. Thus to minimize energy losses in winter, foliage cover must be carefully considered. Within limitations specified, the overall annual building energy consumption deceased by 90.9 GJ (3.7%).

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... Köppen classification Weather Season Type of study Feng et al. [52] Cfa -Summer Modelling Jim and Peng [49] Cwa Sunny-cloudy-rainy Summer Experimental Jim and Tsang [47] Cwa Sunny-cloudy-rainy Whole year -Lazzarin et al. [50] Cfa -Summer-winter Modelling He et al. [53] Cfa Clear-cloudy-rainy Summer Modelling Tabares-Velasco and Srebric [54] --Summer Experimental Tabares-Velasco and Srebric [46] --Summer Modelling Ouldboukhitine et al. [55] Cfb -Summer Experimental Coutts et al. [48] Cfb Sunny Summer Experimental Schweitzer and Erell [56] Csa -Summer-winter Experimental Ouldboukhitine et al. [57] Cfb -Summer Experimental Tan et al. [58] A f -Summer-winter Experimental Tian et al. [59] Cfa -Summer Modelling Hodo-Abalo et al. [60] -Sunny -Modelling Tsang and Jim [61] Cwa Sunny-cloudy Summer Modelling Ouldboukhitine et al. [62] -Sunny Summer Modelling Boafo et al. [63] Dwa -Summer-winter Simulation Silva et al. [64] Csa -Summer-winter Simulation Vera et al. [65] Bsk Csc Cfb - ...
... This section shows the ET results obtained by using EnergyPlus [63][64][65] dynamic simulation software. ...
... Boafo et al. (2017) [63] investigated the potential contribution of the evapotranspiration in green roofs on the annual energy consumption of an office building located in Incheon, Republic of Korea. So this study could be representative of the Dwa climate according with the Köppen classification (2006) [102]. ...
Article
Previous research has shown that most of the green roof benefits are related to the cooling effect. In the literature available, however, it is still not clear how and how much the evapotranspiration affects the performance of a green roof. In order to fill the gap in this research topic, this study carries out a review on the cooling effect due to the evapotranspiration process of green roofs. First of all, an overview of the evapotranspiration phenomenon in green roofs, as well as the equipment and methods used for its measurement are presented. Then, the main experimental results available in literature, the physical-mathematical models and the dynamic simulation software used for the evaluation of the latent heat flux are also analysed and discussed among the available literature. Moreover, this review proposes a classification of the results carried out by previous studies as function of the main parameters affecting the evapotranspiration process (e.g. volumetric water content, stomatal resistance, Leaf Area Index, solar radiation, wind velocity, relative humidity, soil thickness, and substrate composition). Additionally, a sensitivity analysis of the results obtained from the literature allowed underlining the correlation among the main factors affecting the evapotranspiration. Finally, a vision of the world area where green roof studies were performed is provided. From the results, it is possible to emphasize that most of the studies that evaluated the evapotranspiration used high precision load cells. Furthermore, all the heat transfer models of green roofs considered in this review took into account the latent heat flux due to evaporation of water from the substrate and plants transpiration, however, only few of them were experimentally validated.
... Refahi et al. (2015) claim that green roofs are one of the most effective approaches to reducing energy use in buildings. Boafo et al. (2017) define green roofs as a passive technique, representing a sustainable alternative to enhance roof performance while limiting heat flux through it. ...
... Besides water management and retention, the most studied benefit of green roofs is their contribution to low-energy building projects (Jaffal et al., 2012;Feng & Hewage, 2014;Langston, 2015). Thermal performance of green roofs has been widely studied both by experiments (Emilsson 2008;Coma et al., 2016;Scharf & Zluwa, 2017) and through simulations (Sailor, 2008;Jaffal et al., 2012;Boafo et al., 2017). Results have shown a good response regarding a reduction of mechanical cooling and heating needs in several climates. ...
... Results have shown a good response regarding a reduction of mechanical cooling and heating needs in several climates. This literature review reveals advantages especially for the summer season when green roofs provide a decrease for the cooling requirements inside buildings (Jaffal et al., 2012;Skelhorn et al., 2016;Boafo et al., 2017). ...
... They both found that cities in hot desert climates, which are indicated by the BWh sub-group, had the most positive results relative to those in other locations. It was also determined that the GRs in continental climates (Dfa or Dwa) achieved the poorest performance with regard to ∆T s [30,79,81]. Shanghai, China (Dfa) was found the most-appropriate location to implement GRs, as the greatest ∆T s was recorded in this city [78,80,82]. ...
... More precisely, the T s of a non-vegetated roof was higher than that of a GR at night-time, following Morakinyo, Dahanayake, Ng and Chow [26] and Cascone, Catania, Gagliano and Sciuto [21]. A warmer roof deck underneath the GR was observed in winter at daytime, following Boafo, Kim and Kim [81] and Cai, Feng, Yu, Xiang and Chen [85]. A combined effect of great heat storage and thermal inertia of GR components is likely to explain a warmer skin temperature of outer roof decks at night [18]. ...
Article
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Water-sensitive urban design (WSUD) has been widely used in cities to mitigate the negative consequences of urbanization and climate change. One of the WSUD strategies that is becoming popular is green roofs (GR) which offer a wide range of ecosystem services. Research on this WSUD strategy has been continuously increasing in terms of both quantity and quality. This paper presents a comprehensive review quantifying the benefits of GRs in papers published since 2010. More precisely, this review aims to provide up-to-date information about each GR benefit and how they have improved over the last decade. In agreement with previous reviews, extensive GRs were considerably researched, as compared to very limited studies on intensive and semi-intensive GRs. Each GR ecosystem service was specifically quantified, and an imbalance of GR research focus was identified, wherein urban heat- and runoff-related benefits were outstandingly popular when compared to other benefits. The results also highlight the recent introduction of hybrid GRs, which demonstrated improvements in GR performance. Furthermore, limitations of GRs, obstacles to their uptake, and inconsistent research findings were also identified in this review. Accordingly, opportunities for future research were pointed out in this review. This paper also recommends future studies to improve upon well-known GR benefits by exploring and applying more innovative GR construction techniques and materials. At the same time, further studies need to be undertaken on inadequately studied GR benefits, such as reduced noise and air pollution. In spite of the existence of reliable modelling tools, their application to study the effects of large-scale implementations of GRs has been restricted. Insufficient information from such research is likely to restrict large-scale implementations of GRs. As a result, further studies are required to transform the GR concept into one of the widely accepted and implemented WSUD strategies.
... Besides water management and retention, the most studied benefit of green roofs is their contribution to low energy buildings (e.g., [74,73,75]. Thermal performance of green roofs has been widely studied both by experiments [72,71,77] and simulations [50,74,70]. Results have shown a reduction of cooling and heating needs in several climates. ...
... Results have shown a reduction of cooling and heating needs in several climates. This literature review reveals advantages especially for the summer season when green roofs provide a decrease of the cooling requirements inside buildings [74,59,70]. ...
Article
Full-text available
A comprehensive understanding of the effect of green roofs on the indoor thermal comfort, under different microclimates, will help to identify key design aspects. In this study, which is the first of its kind in Brazil, the indoor thermal comfort for two different types of roofs, under different microclimates in Porto Alegre in Southern Brazil, have been compared. Coupled simulations using ENVI-met and EnergyPlus linked calculations of outdoor microclimate and indoor thermal comfort. The site was approximately 100 m by 100 m with 24 one-story, naturally ventilated semi-detached houses with an area of 39 m². One of the houses, located approximately in the middle of the site, represented the building scale. In the original site (with no tree shadings), the substitution of the ceramic by the green roof led to an increase of 9.1 % of the time within the thermal comfort zone. This study helps to bridge the current gap between thermal simulations in different scales. Moreover, this investigation concluded that green roofs performed better when in a green environment: for the summer season, with trees partially shading the roof, the green roof resulted in a reduction of the maximum operative temperature by 4.3 °C, whereas for the site without trees, the reduction was 2.8 °C.
... Both in the case of cooling and heating of the building, the reduction in energy demand owing to the green roof means a reduction in CO 2 emission from generating power or heat [49,59,61]. However, studies have shown that in the case of energy-efficient or passive buildings, the impact of a green roof on the thermal parameters of the building interior is much lower than in the case of energy-intensive buildings [43,[63][64][65][66]. Experimental research is required to analyze the permeation of heat through green roofs of different constructions in the climatic conditions of Central and Eastern Europe because there has not been much research on this type done in this region. ...
... Air pollution is a major problem in city centers and heavily urbanized areas [65][66][67][68][69]. Factors such as the concentration of transportation, local boiler houses, and industries in urbanized areas are all responsible for the presence of CO 2 , NO x , SO 2 , heavy metals, and suspended particulate matter in city centers [69][70][71]. ...
Article
Full-text available
This study presents the results of a review of publications conducted by researchers in a variety of climates on the implementation of 'green roofs' and their impact on the urban environment. Features of green roofs in urban areas have been characterized by a particular emphasis on: Filtration of air pollutants and oxygen production, reduction of rainwater volume discharged from roof surfaces, reduction of so-called 'urban heat islands', as well as improvements to roof surface insulation (including noise reduction properties). The review of the publications confirmed the necessity to conduct research to determine the coefficients of the impact of green roofs on the environment in the city centers of Central and Eastern Europe. The results presented by different authors (most often based on a single case study) differ significantly from each other, which does not allow us to choose universal coefficients for all the parameters of the green roof's impact on the environment. The work also includes analysis of structural recommendations for the future model green roof study, which will enable pilot research into the influence of green roofs on the environment in urban agglomerations and proposes different kinds of plants for different kinds of roofs, respectively.
... Roof insulation: 0.95, 1.2 and 3.4 W/m 2 K. Vegetation scenarios: one semi-intensive and three extensive types. Boafo et al. (2017) 3.7% Four-story office building in Incheon, South Korea. Roof insulation 0.25 W/m 2 K. Vegetation LAI 2. Substrate depth 8 cm. ...
Article
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Green roofs are often claimed to provide a range of environmental, economic and social benefits, or ‘ecosystem services’. These reported benefits, suggests that green roofs could play a significant role in sustainable urban development, and consequently green roofs are now widely used as tools in urban planning strategies. Accordingly, it is relevant to assess whether the benefits of green roofs and comparative advantages over conventional roofs rest on a robust evidence base. A considerable number of studies of the ecosystem services delivered by green roofs have appeared over the last few decades, but a rigorous assessment of the overall level of evidence is lacking. Using a systematic review approach, this study seeks to evaluate the documentation relating to three selected green roof ecosystem services: reduction of the urban heat island effect, reduction of urban air pollution, and reduction of building energy consumption. The number of studies quantifying effectiveness with original data was found to vary significantly from service to service: 17 studies reported cooling at street level ranging between 0.03–3 C°, four reported pollution removal at roof level e.g. removal of small particles, PM10, ranging between 0.42–9.1 g/m² per year, and 41 reported on building energy consumption, of which 20 were comparable and claimed changes in annual consumption ranging between an increase of 7% to a 90% decrease. The large spans in documented effectiveness are ascribed to heterogeneity in context and design parameters of the identified studies. Analysis of the identified studies suggests that some parameters are of key importance for the effectiveness but further research is needed to clarify the complex relation between ecosystem service effectiveness and the parameters influencing it.
... Because of the difficulty in measurement of the evapotranspiration process, the rate (or flux) of evaporation was defined to indicate the degree of evapotranspiration [66]. Figure 4 compares the average monthly evapotranspiration rate for all four selected cities at two different levels of LAI (5 and 2). ...
Article
Full-text available
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.
... The construction and usage of infrastructure also influence the environment through fragmentation, pollution, microenvironment alternation and so on (Jim, 2004;Losasso, 2016). In turn, the environment may also influence infrastructure through effects such as weathering, building foundation provision, usage intensity, biodegradation, bio-remediation, protection, etc. (Ryan, 1985;Boafo et al., 2017), while also serving people by providing various ecosystem services, such as water regulation, air purification, soil retention, noise reduction, recreation, etc. (Gómez-Baggethun and Barton, 2013). The magnitudes of these relationships are reflected by corresponding indicators in the evaluation framework. ...
... Relative humidity control (I 8 ) was another indicator that only affected the green roof, since it depended on the evapotranspiration produced by vegetation. Based on several studies consisting of onsite measurements [74][75][76][77], values of 3, 3.5 and 2.5 mm/day were assigned to this indicator under the Mediterranean, Oceanic and Continental scenarios. Similarly, the green roof was the only alternative capable of providing a suitable space for biodiversity and agricultural growth (I 9 ), resulting in a binary indicator as shown in Table 5. ...
Article
The sustainability of cities is being influenced by their roofs, which cover a high proportion of built-up areas and whose design is crucial to control their economic, environmental and social impacts in a context of urban sprawl and Climate Change. For this reason, this research developed a Multi-Criteria Decision Analysis (MCDA) methodology combining the Analytic Hierarchy Process (AHP) and the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) to support the selection of four representative flat roof types (self-protected, gravel finishing, floating flooring and green) according to their contribution to sustainability, based on their performance across a list of indicators aligned to the United Nations Sustainable Development Goals (SDGs). The analysis was carried out under three different climate scenarios (Mediterranean, Oceanic and Continental) and relied on the judgments provided by a panel of experts in the building sector to both refine and weight the proposed indicators. The results proved that green roofs were the most sustainable alternative for all the scenarios evaluated, by virtue of their insulation, recycling, cost, energy, water and ecosystem-related benefits. Consequently, this type of roof emerges as a multifunctional solution to be strongly considered in the design of planning strategies seeking urban regeneration.
... However, studies have found certain irregularities with the "advanced" method [25]. The EnergyPlus vegetated roof model has been used in several green roof studies [16,35,[110][111][112] and has been validated by other authors [23,113,114]. Another vegetated roof model [71] has been integrated in TRNSYS [115] and further validated with field data for vegetated walls and roofs in mock-up buildings; however, this model is not part of the official TRNSYS package/type. ...
Article
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.
... O comportamento higrotérmico de coberturas vegetadas tem sido estudado internacionalmente há vários anos, tanto em experimentos, por exemplo os realizados por Emilsson (2008), Coma et al. (2016) e Scharf e Zluwa (2017); como em simulações computacionais feitas por Sailor (2008), Jaffal, Ouldboukhitine e Belarbi (2012) e Boafo e Kim (2017). ...
Article
Full-text available
Este artigo apresenta o desempenho térmico de diferentes coberturas vegetadas aplicadas em um edifício de escritórios na cidade de Pelotas-RS, Zona Bioclimática Brasileira 2, observando, a partir do comportamento dos fechamentos opacos e transparentes, a contribuição das diferentes soluções vegetadas para o plano horizontal. O edifício condicionado artificialmente possui 187,50 m², configurando seis zonas térmicas, e foi simulado no software Energy Plus 8.4.0. Como alternativas às coberturas vegetadas – configuradas em quatro alturas de substrato – foram utilizados outros três modelos de cobertura: fibrocimento com laje de 10 cm em concreto – com e sem isolamento térmico de poliestireno extrudado – e fibrocimento com superfície externa pintada de branco. O estudo buscou determinar qual dessas coberturas é a mais eficiente energeticamente, através da avaliação dos resultados do consumo de energia e da análise do fluxo térmico no edifício. A cobertura vegetada de maior espessura de substrato (50 cm) apresentou melhor resultado, com consumo energético de 84,3 kWh/m2.ano. Já a cobertura de laje com telha de fibrocimento convencional foi responsável pelo maior dispêndio energético: 103,5 kWh/m2.ano. As coberturas vegetais apresentaram melhor desempenho que as demais em função das elevadas capacidade e resistência térmica e dos aspectos voltados a evapotranspiração e consequentes trocas de calor latente. Este trabalho almeja contribuir no melhor entendimento do desempenho termoenergético das coberturas vegetadas.
... The main result obtained by this study is that the higher the LAI, the greater the reduction in cooling loads due to the evapotranspiration of vegetation-substrate system and the canopy's shading effect. Boafo et al. (2017) evaluated the evapotranspiration effect of an extensive green roof on annual energy consumption of an office building in relation to the humid continental climate of Republic of Korea. Due to the influence of the humid conditions on the evapotranspiration process, it was found that high leaf area index reduced cooling energy demand and somewhat reduced heating energy demand as well. ...
Article
Green roofing is a sustainable solution for building energy saving, urban heat island mitigation, rainwater management and pollutant absorption. The effectiveness and performance of green roofs depend on layer composition and properties. The uncertainties surrounding green roof performance modeling are mainly related to the vegetation and substrate layer, which are subjected to surrounding climatic conditions. Energy simulation software typically does not use validated models encompassing all possible combinations of vegetation layers and substrates. Therefore, the objective of this research is to investigate different extensive green roof solutions for assessing thermal performance and to provide information on vegetation and substrate layer design. Different simulations executed in EnergyPlus were carried out based on realistic literature data drawn from previous experimental tests conducted on plants and substrates. Several combinations (30 plant-substrate configurations, six vegetative species and five types of substrates) were defined and evaluated. Furthermore, indexes based on the surface temperatures of green roofs were used. Finally, a comprehensive ranking was created based on the scores to identify which extensive green roof combinations offered the highest performance. Greater plant heights, LAI values and leaf reflectivity values improve green roof energy performance in the summer more significantly than substrate modification. During the winter, thermal performance is more heavily dependent on the substrate if succulent vegetation is present, regardless of the substrate used. These results could provide designers with useful data at a preliminary stage for appropriate extensive green roof selection.
... The rooftop usually represents the top elevation of an urban valley and receives the intensive sunshine without much shade, so planting rooftops tends to provide effective cooling benefit. A study based on EnergyPlus simulations found that green roofs could reduce the annual building energy consumption by 3.7% [41]. The cooling effect depends on the green roof coverage and climate zones. ...
... A number of studies (e.g., Refs. [90,112,128,131,144,152]) agree that vegetation LAI is crucial in decreasing building cooling energy use in hot and warm climates. Olivieri et al. [109] monitored the summer thermal behavior of a fully vegetated green roof and of a bare soil rooftop in the coastal Mediterranean climate, finding out that the plants' activity on the fully vegetated green roof decreases the heat gains by 60%. ...
Article
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.
... Extensive green roofs with sedum, grasses, and forbs plants. (Boafo et al., 2017) 3.7% ...
... Despite a large number of studies on the temperature and humidity of enclosing structures [8-12], the vast majority of studies on the design of internal roof drain systems are devoted to their organization and streamflow calculations [13][14][15], as well as to thermal efficiency of the roof itself [16][17]. Less attention is paid to the issue of condensation process, namely, the issues of the effectiveness of roof aerators or deflectors are studied, as well as waterproofing and insulating properties of membranes [18][19]. ...
Article
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A field survey of roof structures of several administrative buildings in the temperate climatic zone showed the presence of condensate in the zone of the internal drain. The fact of overmoistening of the roof structure raises doubts about the operability of the roof aerators installed on these coatings, designed to remove condensate from the roof layers. The inefficiency of using roof aerators can be explained by the process of condensed moisture freezing in the structure during the cold season thus cannot be removed by aeration. Two types of structures of the internal roof drain system used in construction from the point of view of condensate formation are revealed. The difference between the types is the degree of water vapor permeability of the junction layer between the pipe and the coating plate. An impermeable solution can be made by mounting a steel flange at the junction of the pipe and the coating plate. The vapor-permeable solution is made in the form of a simple sealing of the gap with polyurethane foam or other permeable materials. A calculated analysis of the temperature fields and the humidity conditions of the two types of internal roof drain structures showed that the use of polyurethane foam or its analogs in the gap is not enough to protect the roof structure from condensation. This solution leads to condensation inside the structure at positive outside temperatures (less than 2 °C). The design with steel flange at the junction of the pipe and the coating plate is free from these drawbacks and can be used at lower outdoor temperatures.
... The latter situation might occur in arid climates with cold winters (Coma et al., 2016), (Refahi & Talkhabi, 2015). Overall, the efficiency of GRs on reducing heating energy demand in cold and snowy climates tends to be very low, and sometimes negligible (Berardi, 2016), (Boafo et al., 2017), (Feng & Hewage, 2014) (Appendix A Table A5). ...
Article
Climate change and urban heat islands (UHIs) pose mounting threats to built-up areas. In this regard, photovoltaic panels and green roof systems (PV/GR) can offer numerous benefits towards promoting environmentally sustainable cities. This review examines the benefits of GR systems, integrated PV/GR systems and their optimal design factors; research gaps in urban scales and building scales in hot climates are highlighted. A systematic review was undertaken on published papers from the Scopus database that investigated the effect of GR (157 papers) and PV/GR systems (28 papers) that addressed UHI mitigation and how Energy-Saving and Indoor Thermal Comfort (UH-ES-ITC) was achieved in urban buildings. It has been found that GR and GR/PV systems have a positive impact on improving dominant parameters in hot arid climates, especially on the building scale. Unfortunately, there are not many studies that investigate GR/PV systems on coupling scales. This review highlights the research gaps concerning the method, scale, climate, target, factors and parameters of this integration in different climate zones. The results would be valuable for researchers and urban planners to guide research implementation and future research.
... Energy demand is everlastingly escalating every day due to increased consumption patterns in various domestic and industrial needs (Boafo, Kim, and Kim 2017;Karthick et al. 2020a). The energy is needed for different applications such as heat, transport, lighting, and air-conditioning in our day to day life. ...
Article
This work explores the opportunities to address the setback in thermal energy storage of solar-based water heaters by uniting it with a suitable hybrid-nano composite phase change material (HNCPCM) in a static mode of operation. The experiments were conducted on a natural circulation all-glass evacuated solar water heating system (AGSWH). The investigation was steered in five cases such that the first case without any phase change material (PCM), the second with pure paraffin as PCM, and remaining three cases with three different mass percentage of HNCPCMs (0.5%, 1.0%, and 2.0% mass fraction of hybrid nanoparticles within PCM) in real-time solar exposure. The system was analyzed based on the first and second law of thermodynamics to assess the performance in all the five cases. Erstwhile, the hybrid nanoparticles were prepared by blending equal mass of SiO2 and CeO2 nanoparticles and characterized to gauge its thermal storage properties. The achieved results substantiated that the thermal conductivity had boosted with the accumulation of hybrid nanoparticles within the paraffin matrix, and maximum enhancement of 65.56% was attained with 2.0% mass fraction. The first law and second law investigations revealed that the incorporation of hybrid-nano composites improved the energy and exergy content of the system, distinctly. Among the experimented cases, HNCPCM with 1.0 mass% of hybrid nanoparticles remarkably yielded a better result of 19.4% and 1.28% improvement in energy and exergy efficiencies, respectively. Besides, it evidenced the necessity of choosing the right quantity of nanoparticles for achieving better overall results.
... Some studies characterized Sedum genus evapotranspiration (Berretta et al., 2014;Berghage et al., 2007;Ayata et al., 2011) by means of weighing lysimeters or by using volumetric water content sensors in the substrate layer, under controlled or uncontrolled environmental conditions. They have shown that evapotranspiration rates differ between seasons, with high values during summers and low values during winter cold conditions (Berretta et al., 2014;Poë et al., 2015;Boafo et al., 2017), suggesting that the best performance of green roofs in stormwater control can be achieved in warm periods. ...
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In this study a long-term field experiment evaluating evapotranspiration rates from irrigated and non-irrigated green roof modules, as well their impacts on stormwater control was accomplished. Six green roof modules (3 irrigated and 3 non-irrigated) vegetated with S. rupestre were monitored throughout 8 months in southern Brazil. Four non-vegetated modules (2 irrigated and 2 non-irrigated) were simultaneously assessed to understand the role of the vegetation in the whole process. The average evapotranspiration under water-stress (ETr) was 2.6 mm.day-1, while mean evapotranspiration under water-abundance (ETp) was 2.8 mm.day-1. Higher evapotranspiration rates were observed during summer, increasing the substrate storage capacity, although ETr amount along the seasons was very similar, mainly affected by climatic conditions. The long-term analysis showed that 47% of the total rainfall was converted into runoff, 21% was retained in the green roof modules and 32% was released through evapotranspiration, reinforcing the importance of vegetation as a mechanism for improving stormwater control benefits. The results of this research also allowed the establishment of a crop coefficient (Kc) time series, with a monthly average of 0.9 which permits the S. rupestre evapotranspiration to be preliminarily estimated by using equations developed for reference culture without the need of monitoring.
... In fact, between two consecutive rainfall events, a green roof uses ET to create water storage capacity. However, the measurement and modeling of green roofs' ET processes have been performed by a limited number of researchers (DiGiovanni et al., 2010;Voyde et al., 2010, Cascone et al., 2019, Levallius, 2005Schweitzer and Earl, 2014;Boafo et al., 2017). Limited researchers (e.g. ...
Article
Despite the significance of urban landscapes, there are limiting factors like spaces and water resources to expand them across the world. These limitations necessitate the development of water-conserving strategies in vertical infrastructures such as green roofs. One water-conserving strategy is precise irrigation regimes based on the plant species’ water needs. We investigated the water need of Carpobrotus edulis and Aptenia cordifolia under treatments with different soil-containing and soil-less water-absorbing substrate amenders and humic acid applications. The experiment was factorial based on a randomized complete block design with three replications and was conducted from May to September 2020. The first factor was the substrates with different green roof substrate compositions including soil-containing and soilless substrates with varying bentonite percentages. The second factor was humic acid levels (zero, 100, and 200 mg/l), which were applied as fertigation every 15 days during the experiment. Water needs were determined using the lysimetric method. The results showed that despite the soil-containing substrate with bentonite, the soilless substrate alone could not lead to optimal plant growth. The highest water use efficiency and the least evapotranspiration were obtained from the substrate containing 20%Soil +20% leca +20% perlite +20% mineral pumice +20% leaf litter plus 12% w bentonite, combined with A. cordifolia. This plant species showed a better performance compared with C. edulis. During the spring and summer months, the soil-containing substrate with bentonite and A. cordifolia can create a sustainable green roof system by creating better coverage, more water conservation, and a more aesthetic appearance. Based on the results, the application of the highest concentration level of humic acid (200 mg/l) increased the water use efficiency by about 40% after the establishment of the plants. Also, using this level of humic acid reduced the evapotranspiration rate in A. cordifolia up to 10 ml/day and in C. edulis up to 15 ml/day.
... A study focused on the analysis of the ET in an extensive green roof in Incheon (Republic of Korea) was analysed by Boafo et al. (2017). The effect on ET given by high and low foliage cover area and irrigated and non-irrigated soil media were evaluated. ...
Thesis
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Nature-Based Solutions (NBS) are crucial to achieving the goals of the United Nations Agenda 2030 for sustainable development and other global agendas, such as the Paris Agreement on Climate Change. In the last decade, the NBS umbrella concept has become more relevant intending to contribute to urban resilience and to address the climate change challenges. NBS are living solutions inspired by nature that use or mimic natural processes intending to face several societal challenges, from the perspective of resource-efficient use and the promotion of economic and environmental benefits. Currently, cities are encouraged to understand and measure the NBS contribution to identify adequate strategies for enhancing resilience and prioritize investments accordingly. The objective of the present thesis is to promote and enhance the NBS implementation in cities, focused on solutions for stormwater management and control. Based on the analysis of their contribution to urban resilience, the potential to meet environmental, social, and economic challenges and to adapt across diverse urban scales and contexts is demonstrated. In this sense, a Resilience Assessment Framework (RAF) to assess the NBS contribution to urban resilience was developed. This framework aims to assess the NBS contribution to urban resilience. Moreover, a Guidance for the RAF application in cities with different resilience maturity was developed, which involved the RAF validation by seven cities (from a national and international context), that participated voluntarily in this phase. In this context, the developed RAF is comprehensive and multidimensional. It is driven by the definition of objectives, criteria, and metrics, according to the proposed structure for assessing the water supply and wastewater system service performance in the framework of the ISO 24500 standards of the International Organization for Standardization. For an oriented assessment of the criteria, qualitative and quantitative metrics were defined, considering data from different sources and complexity. Reference values were also identified and metrics’ classifications were defined. In this classification, each answer is associated with a resilience development level, intending to assess the NBS contribution to urban resilience on a normalized scale. To support the RAF application to cities with different resilience maturity (in terms of resilience and available information), three analysis degrees (essential, complementary, and comprehensive) and a set of metrics were proposed, which are pre-defined in the guidance for the RAF application. To support the selection of the analysis degree more adequate to any city, a structure to characterize the city’s profile was developed. This complementary profile also supports the interpretation of the RAF results, both at the city and at the level of specific NBS.
... Because of the variation in the thermal conductivity of the layer, the resulting thermal transmittance of the green roof is dynamic [58], and simulation techniques can be used to understand the behaviour on a yearly basis [59]. The effect of this variation on the annual energy performance balance [60] is determined by the previously specified factors (precipitation, irrigation, evapotranspiration). The effectiveness of green roofs in reducing energy consumption in various climates has recently been reviewed [61], indicating how green roofs perform well in multiple conditions, showing particular benefits in terms of cooling load reduction [62]. ...
Chapter
This research project, undertaken by the University of Southampton, investigates the impact that climate change will have on roofs covering the existing stock of buildings across the UK. It was commissioned by the NFRC Charitable Trust under the Trust’s ‘Sustainability’ charitable aim.
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Green roof technology has been established through research and in-situ monitoring to provide good potential for stormwater retention, mitigation of urban heat island (UHI) effect, reduction of local air pollution, increase local biodiversity and most importantly, passive energy savings both for new buildings and as a retrofit option for older buildings. However, even with this existing wide range of benefits, green roof technology research and markets in terms of implementation and widescale commercial adoption is relatively non-existent in temperate climates of the world such as the UK, compared to other regions with different prevailing climatic characteristics. This research investigates the causative factors and barriers for this relatively slow rate of adoption both from technological and economic perspectives with the United Kingdom as a case study. A number of experimental papers on energy savings benefits from green roofs were compiled; and from the analysis of collated data, it was found that green roofs tend to perform better from an energy savings perspective in hotter climates of the world or during the summer season in colder climates when temperatures are higher such as seasonal heatwaves. Further research into the energy savings behaviour during winter in temperate regions is required to assert the all-season suitability of green roofs for implementation in new builds within the United Kingdom. Government legislation and incentives could potentially increase wide-scale adoption. The performance of green roofs is however found to be largely climate dependent, meaning the performance varies across different regions of the world, therefore increased local research and quantification into metrics will lead to better understanding and potential adoption of green roofs and how to best optimise their design according to the region in which they are to be installed.
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Under the many available strategies for the adoption of sustainable practices, the urban agriculture emerges as a relevant alternative. Urban naturation is the vegetative treatment of built surfaces, using plants adapted to the local environmental conditions. The vegetation is a highly relevant element to the regulation and balance of extreme climatic conditions. It also affects buildings thermal comfort and energy use, when assuming functions of control regarding solar radiation, air relative humidity and air movement. Besides the role of climate control, the vegetation can also play a role in food production. The growing of vegetable crops, spices and medicinal herbs has gained the urban spaces of Brazilian cities. The growth of plants at home or in the urban environment, described as productive landscape, becomes one of the few ways of contact with the elements of nature. Therefore, the urban agriculture can create natural spaces in the urban centers, thus, promoting the comfort into two scales: the urban scale and the building scale. On the other hand, the addition of vegetation for food production on built surfaces assumes a multidisciplinary effort. It is needed to technically respond to the suitable choice of substrate and plant species, to the nutrition values of the cultivated foods and, therefore, to the building physics that supports the food production. The aims of this investigation project are: (i) to increase international partnerships in the subject (the Federal University of Pelotas, in Brazil; the Lund and the ALNARP Universities, in Sweden; the Polytechnic University of Madrid, in Spain; and the Arizona State University, in the United States); (ii) to bring information on both the building energy efficiency and the outdoor microclimate as a consequence of the green roof establishment; (iii) to generate a cultivation guide for food production on rooftops. Thus, this paper presents the first step of the research interdisciplinary approach, which deals with the construction of the Cultivation Guide for Rooftop Farmings. Through a literature review, data from 19 food plant species were compiled to inform their proper growth and management. Additionally the same data will be used as the inputs for the modelling of the outdoor microclimate and indoor thermal comfort provided by those species. Exemplifying results in the form of synthesis tables, this paper shows the data of substrate and vegetation for two vegetable species: lettuce and tomato.
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Urban Heat Island (UHI) effect relates to the occurrence of a positive heat balance, compared to suburban and extra-urban areas in a high degree of urbanized cities. It is necessary to develop effective UHI prevention and mitigation strategies, one of which is blue-green infrastructure (BGI). Most research work comparing impact of BGI parameters on UHI mitigation is based on data measured in different climate zones. This makes the implication of nature-based solutions difficult in cities with different climate zones due to the differences in the vegetation time of plants. The aim of our research was to select the most statistically significant quality parameters of BGI elements in terms of preventing UHI. The normative four-step data delimitation procedure in systematic reviews related to UHI literature was used, and temperate climate (C) zone was determined as the UHI crisis area. As a result of delimitation, 173 publications qualified for literature review were obtained (488 rejected). We prepared a detailed literature data analysis and the CVA model-a canonical variation of Fisher's linear discriminant analysis (LDA). Our research has indicated that the BGI object parameters are essential for UHI mitigation, which are the following: area of water objects and green areas, street greenery leaf size (LAI), green roofs hydration degree, and green walls location. Data obtained from the statistical analysis will be used to create the dynamic BGI modeling algorithm, which is the main goal of the series of articles in the future. Keywords: urban heat island mitigation strategy; blue-green infrastructure effectivity factors; blue-green infrastructure parameterization
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Greenery systems are sustainable ecosystems for buildings. Many studies on greenery systems, such as green roofs and green walls, have demonstrated that greenery systems support energy saving and improve thermal conditions in the building sector. This paper summarizes, discusses, and compares greenery systems and their contributions to the reduction of the urban heat index, the reduction of internal and external buildings' wall temperatures, and the reduction of the energy consumption of buildings. The fundamental mechanisms of greenery systems, which are thermal insulation, evapotranspiration, and shading effect, are also discussed. The benefits of greenery systems include the improvement of stormwater management, the improvement of air quality, the reduction of sound pollution, the reduction of carbon dioxide, and the improvement of aesthetic building value. The summarized materials on the greenery systems in the article will be a point of references for the researchers, planners, and developers of urban and rural areas, as well as the individual's interest for future urban and rural plans.
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Green roofs are an effective nature-based solution to eco-environmental problems arising from climate change and rapid urbanization because they provide multiple ecosystem services and can have a significant positive impact on human well-being. To explore state-of-the-art research, deficiencies, and development trends related to green roof ecosystem services, the “Bibliometrix” R package and “CiteSpace” were used to conduct a quantitative analysis of 1623 English language sources published in Scopus before 2020. Results show that since 1981, the amount of research on green roofs has steadily increased with approximately 40.9% of the articles focusing on regulating services in the contexts of water, 30.0% on the thermal environment, and 3.5% on and air quality. Green roofs have proved effective at reducing urban stormwater management pressures, mitigating the urban heat island effect, reducing energy consumption, and improving air quality. However, no standard assessment methods and tools exist to value green roof ecosystem service delivery; a balance and coordination between different service values are lacking. Future research should focus on customizable low-cost and innovative green roof designs, increasing the number of quantitative case studies, and conducting multi-perspective evaluations. Considering how environmental, social, economic, and other benefits can be achieved on a larger scale is also necessary. Overall, this review helps advance research on green roofs and guide wide-spread implementation in urban areas in response to environmental challenges.
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Research suggests that—relative to conventional roofs—green roofs can significantly reduce rooftop heat exchange in moderate climates; however, limited research exists on the performance of green roofs in colder climates. This paper analyzes the comparative performance of two side-by-side roof assemblies: a conventional roof and a green roof located in the temperate climate of Ottawa, Canada. Using two years’ worth of temperature and solar radiation data, we analyze variations in the incremental thermal benefit of the green roof relative to the conventional roof. We discuss factors contributing to these variations, such as precipitation and ambient temperature. Our results indicate that the green roof under investigation reduced thermal transmittance by 31.5% on average across two years. Although the percent benefits were much higher during the summer months, reductions in thermal transmittance were consistently above 7.7% throughout both years, indicating green roofs may be an appropriate alternative to conventional roofs in climates with hot, humid summers and cold, snowy winters.
Thesis
Sustainable roofs are an important element in environmentally sustainable architecture, as they are an effective and practical way to increase the efficiency of thermal performance in building spaces and thus achieve energy conservation in them, and what this concept contribute to reduce the consumption of electrical energy which is depends mainly on fossil fuels especially in Iraq. In fact that the administrative buildings, consume large amounts of energy because of the functional nature, higher occupancy throughout the day period, especially in Iraq with the hot dry climate, which is characterized by long summer, frequent solar radiation, high temperatures, and a large amount of the thermal loads on the envelop of building, specially the roof which is a bears a large amount of it and it has become necessary to use a sustainable roofs on administrative buildings, specially university administrative buildings, to achieve energy conservation for indoor environment of buildings, as well as improve air quality ,and increase thermal comfort ranges in them The general problem is to look for: the lack of a holistic perception of knowledge about the patterns and the role of the sustainable roof in energy conservation according to the climate of the region and the pattern of buildings. While the special problem: there is a lack of knowledge about the utilize the efficient sustainable roofs in the field of energy conservation for university administrative buildings in Iraq. Then, the general aim of the research is: To clarify the most comprehensive strategies related to utilize the sustainable roofs for energy conservation in hot dry regions such as Iraq. As for the secondary aims of the research, they are defined as: • Clarifying the types of sustainable roofs and the importance of each type to increasing the efficiency of thermal performance, and then achieving the concept of energy conservation for indoor spacing of university administrative buildings . • Finding practical strategies to explore the most efficient sustainable roofs in the field of energy conservation for each type of them, while clarifying the possibility of its application in contemporary Iraqi university administrative buildings. • Providing a hypothetical application to test a university administrative building block that is identical in design, with different sustainable roofs and in line with Baghdad's hot dry climate in order to enrich the architectural experience in general, and the university administrative buildings in particular. The research lays the following basic hypothesis: “Sustainable roofs are considered one of the efficient design solutions and one of the most effective ways to achieve energy conservation within administrative buildings in general, and Iraqi university administrative buildings in particular.” The general hypothesis of the research included a set of secondary hypotheses, which included the following: • the roofs effect on overall of thermal performance, and as a result, on achieving energy conservation for university administrative building. • Contributed all of types of the Sustainable roofs and the results of their applications a fundamental role in achieving the concept of energy conservation in the university administrative buildings. • using the environmental simulation programs to recognize the most efficient sustainable roofs which it's achieving conservation energy in university administrative buildings. The research is based in its methodology for the purpose of achieving its goals, on a theoretical study supported by a practical application of a university administrative building in the hot and dry city of Baghdad. Many sources related to the main concepts of the research were reviewed and discussed in three chapters, namely: The first chapter dealing with the concept and strategies of achieving "Energy conservation in the building", and the second chapter discussed: requirements, importance and advantages of "university administrative building and energy conservation", then the third chapter dealt with: all types of roofs that achieve energy conservation, which are "sustainable roofs". After extracting the theoretical indicators from the previous chapters, from Then the practical aspect was implemented in the fourth semester: "Application of sustainable roofs in university administrative buildings" using a computer program for environmental simulation. As a result, the research reached a number of conclusions, the most important of which are: Energy conservation is a concept that is applicable in the hot and dry climate of Iraq sustainable roofs, and the high efficiency of the Intensive Green Roof and the Ponds roofs in improving the internal environment of the university administrative building in Baghdad is specifically by reducing the energy consumed for Cooling and heating, which is reflected positively in reducing energy demand and then saving it.
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Bioclimatic design strategies are among the most promising sustainable approaches for improving energy efficiency of buildings. However, their contributions to reducing the energy consumption and carbon footprint of buildings are largely dependent on the alignment of building design with climatic conditions. The objective of this paper is to investigate the effect of key bioclimatic design strategies, namely green roof and walls, tree shading, natural ventilation, glazing system, blinds, building orientation and Trombe wall on the energy performance of a typical residential building in the three most dominant climates worldwide. These strategies are analyzed in Riyadh, Tetouan and Montreal cities, selected to represent those climates, viz. arid, temperate and cold climates, respectively. To this end, numerous dynamic thermal simulations were performed using EnergyPlus software. The findings of this research revealed that, individually, green roof and walls, and Trombe wall strategies have the highest performance in terms of energy savings and greenhouse gas (GHG) emissions mitigation for all selected locations. Moreover, blinds and tree shading strategies are too recommended for arid and temperate climates, while natural ventilation is advisable only for the last one. Additionally, significant energy saving could be achieved by optimizing the building orientation, especially in arid and cold climates. However, the greatest energy savings and GHG emissions mitigation were achieved (i) by combining green roof and walls, Trombe wall, blinds and tree shading techniques for arid climates, (ii) by adding natural ventilation to the last combination for temperate climates, and (iii) when green roof and walls design is combined with an optimal building orientation for cold climates, with a share of 33%, 58% and 19%, respectively. This work is intended to be a reference to help building designers and engineers to select the appropriate bioclimatic design strategies according to the building's climate.
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Actual evapotranspiration is a key process of hydrological cycle and a sole term that links land surface water balance and land surface energy balance. Evapotranspiration plays a key role in simulating hydrological effect of climate change, and a review of evapotranspiration estimation methods in hydrological models is of vital importance. This paper firstly summarizes the evapotranspiration estimation methods applied in hydrological models and then classifies them into the integrated converting methods and the classification gathering methods by their mechanism. Integrated converting methods are usually used in hydrological models and two differences exist among them: one is in the potential evaporation estimation methods, while the other in the function for defining relationship between potential evaporation and actual evapotranspiration. Due to the higher information requirements of the Penman-Monteith method and the existing data uncertainty, simplified empirical methods for calculating potential and actual evapotranspiration are widely used in hydrological models. Different evapotranspiration calculation methods are used depending on the complexity of the hydrological model, and importance and difficulty in the selection of the most suitable evapotranspiration methods is discussed. Finally, this paper points out the prospective development trends of the evapotranspiration estimating methods in hydrological modeling.
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Green roofs and other urban green spaces can provide a variety of valuable benefits linked to evaporative processes, including storm-water management, reduction of urban heat island, and carbon sequestration. Accurate and representative estimation of urban evapo- transpiration (ET) is a necessary tool for predicting such benefits. However, many common ET estimation procedures were developed for agricultural applications, and thus carry inherent assumptions that may not be applicable to urban green spaces, including green roofs. The objective of this paper is to evaluate the performance of two combination methods for the prediction of ET from a green roof. Two ETestimation methodologies were compared, using on-site and regionally available data sets for daily time steps, to weighing lysimeter measurements of actual ET at a green roof site in the Bronx, New York. Regionally available estimates of potential ET did not accurately predict lysimeter measured actual ETon 30 nonconsecutive, non-water-limited days in months from September through December. Over the same period, the ASCE Standardized Reference Evapotranspiration Equation performed well in predicting actual ET with an RMSD of only 0 . 03 mmd − 1 . Additionally, the ET equation for short reference types, using on-site climatic data and coupled with a variation of the Thornthwaite-Mather approximation, which accounts for variable media moisture conditions, gave reasonable predictions of actual evapo- transpiration for 89 days analyzed (representing months from June through January) with an aggregate underestimation of 10.1%. However, this method was highly sensitive to input parameters, specifically media field capacity. Further on-site data collection is necessary to fully evaluate the performance of the equations over different seasons at this location, and monitoring of supplementary urban green spaces and green infrastructure sites will also lend further insights regarding urban evapotranspiration.
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The crop coefficient during the initial period K c ini varies with wetting frequency, evaporative demand, and water-holding capacity of the upper soil layer. It is possible to develop a semitheoretical integrated function to predict the average K c ini representing the initial period of a growing season when the soil is mostly bare and that incorporates these three factors. The function is based on a two-stage evaporation function as used in the Food and Agriculture Organization Irrigation and Drainage Paper No. 56 (FAO-56) dual crop coefficient method. Parameters in the integrated equation are soil based and can be calculated a priori without field measurements. The procedure can be used to produce graphical figures similar to that introduced in FAO-24 for K c ini . Similar to FAO-24, the function utilizes the mean time between wetting events and reference evapotranspiration. In this paper, the development of the procedure and figures for K c ini are described. Comparisons with measured evaporation and K c ini in southern California indicate relatively good perfor-mance by the function without calibration.
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Green roofs can be classified as intensive and extensive roofs based on their purpose and characteristics. Depending on the roof type and weather conditions, green roofs are built with different physical layers with variable thicknesses. Common basic layers of green roofs, from bottom to top, are root barrier, drainage, filter, growing medium, and vegetation layer. There are many environmental and operational benefits of vegetated roofs; however weight and cost is a challenge to the industry. New technology enabled the use of low-density polyethylene and polypropylene (polymers) materials to reduce the weight and improve the performance of green roofs. The objective of this paper is to evaluate the socio-environmental benefits of green roofs by comparing emissions of NO2, SO2, O3 and PM10 in polymers manufacturing process, with the green roof's pollution removal capacity. Additionally, a probabilistic analysis was conducted to estimate the public economic public benefits of green roofs air pollution removal. The analysis demonstrated that green roofs are sustainable products in long-term basis. On average, green roofs can balance air pollution due to the polymer production process in 25 years. Nevertheless, the manufacturing process of low-density polyethylene and polypropylene has many other negative impacts to the environment than air pollution.
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Although the evapotranspiration (ET) process has historically received limited attention, it is an important factor for assessing the health and behavior of urban green spaces, including green roofs. In this study, common potential evapotranspiration (PET) models, which assume non-water-limited substrate moisture conditions, and actual evapotranspiration (AET) models, which account for water-limited substrate moisture conditions, are used to predict ET from local climate conditions at two extensive Sedum green roof sites in New York City (NYC); one a vegetated mat system (termed W118) and the other a built in place system (termed USPS). Results from the predictions are compared to 12,000. h of on-site ET measurements obtained using a dynamic chamber system. Among the Hargreaves, Priestley-Taylor, Penman, and American Society of Civil Engineers Penman-Monteith PET models, results from the Priestley-Taylor model, which was developed to predict ET from a wet vegetated surface with minimal advection, best correlate with the dynamic chamber measurements (r-squared = 0.96 for W118, 0.82 for USPS). Nonetheless, a systematic error is seen whereby the Priestley-Taylor model overestimates the low ET fluxes observed during the winter months and underestimates the high ET fluxes observed during the summer months. This error is only exaggerated by the inclusion of an advective ET term. To estimate green roof ET under water-limited conditions, a storage model, antecedent precipitation index (API), and advection-aridity model are applied to the Priestley-Taylor formulation to calculate AET. Results indicate that only the API model, which is based on precipitation history alone, can improve upon the Priestley-Taylor PET predictions ( r-squared = 0.96 on W118, 0.85 on USPS). Use of a more-physically based, substrate moisture storage greatly over-estimates ET reduction during dry periods. The work provides insight into which common ET models best capture the behavior of full-scale, extensive green roofs, and points to the need for better estimates of green roof ET under climate conditions typical of NYC's winter and summer months.
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Sustainability trends for buildings require new construction systems to foster energy efficiency and environmentally friendly buildings. Green roofs are interesting construction systems because they provide both aesthetic and environmental benefits. This paper continues a long-term research in order to evaluate and improve the thermal behaviour and sustainability of extensive green roofs. Simultaneously this research provides experimental data for specific Mediterranean continental climate conditions. The experiment consists in evaluating the energy consumption and thermal behaviour of three identical house-like cubicles located in Puigverd de Lleida (Spain), where the only difference is the roof construction system. The roof consists of a conventional flat roof with insulation in the reference case, while in the other two cubicles the insulation layer has been replaced by a 9 cm depth extensive green roof (comparing recycled rubber crumbs and pozzolana as drainage layer materials). The electrical energy consumption of a heat pump system was measured for each cubicle during 2012 and part of 2013. Both extensive green roof cubicles show less energy consumption (16.7% and 2.2%, respectively) than the reference one during warm periods, whereas both extensive green roof systems present a higher energy consumption (6.1% and 11.1%, respectively) compared to the reference cubicle during heating periods.
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The aim of this study is to investigate the thermal behaviour and the energy efficiency of an Intensive Green Roof System composed of indigenous aromatic plants with low irrigation needs, installed in the 10000 m2 roof of a fully insulated, low energy office building in Athens, Greece. It consists of almost 16000 Mediterranean plants of at least 14 different kinds and a running track of a stabilized ceramic floor. The urban heat island mitigation potential of the green roof as well as its energy contribution is investigated using experimental and theoretical methodologies. The surface temperature of the green roof is found to be up to 15 K lower than that of a conventional roof. Plants having a low absorptivity to solar radiation together with a dense foliage are found to present a much lower surface temperature and a higher mitigation potential. The surface temperature of the plants is found to be highly influenced by the ambient air temperature. Using simulation techniques it is calculated that such a type of green roofs can decrease the average indoor temperature of a non air conditioned building up to 0,7 K, while it may decrease substantially its annual cooling and heating needs.
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Heating and cooling of residential and commercial buildings account for approximately 40 percent of world's total energy consumption [1]. This considerable amount of energy consumption have made scientist to search for every possible way to reduce it. Among the most effective approaches is the use of green roof for buildings. Although the positive effects of using such roofs are well proven, the amount of energy reduction which can be achieved by this method is another issue that this paper is trying to investigate. In this study, three different climates of Iran are chosen for the analysis. The results demonstrate that using green roof in Very Hot Dry (Bandar Abbas), Warm Dry (Isfahan), and Mixed Dry (Tabriz) climates causes energy consumption to decrease by approximately 8.5, 9.2 and 6.6 percent, respectively. Considering the reduction of energy consumption as the only desirable benefit of green roof, the payback period would be 25-57 years (depending on the climate).
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Given the large amount of worldwide energy use associated with buildings' life cycle, in recent years various energy efficient strategies have been proposed to reduce buildings' environmental impact, e.g. green and cool roofs. The purpose of this work is to analyze an innovative type of green roof, named Cool-Green roof combining the features of both green and cool roofs. In fact, it is characterized by a specific vegetative layer able to optimize the quote of short-wave radiation reflected by the selected vegetation. After the analytical dissertation of the system, the developed solution is studied when applied in a case study building represented by a multifamily XVI century building in central Italy, characterized by cement based roof ceiling needing to be retrofitted. Both in-lab and infield experimental analyses were carried out for evaluating the building thermal-physics and the solar reflectance and thermal emittance of the selected plant compared to other flat roof materials and greeneries. Additionally, the year-round performance of Cool-Green roof is assessed through calibrated and validated dynamic thermal-energy simulation. Main findings of the study show how the Cool- Green roof is able to reduce the number of indoor overheating hours in summer by 98.2%, with negligible penalties in winter, given its high insulation capability, typical of green roof solutions. Therefore, the Cool-Green roof could be considered as (i) a strategy for roof retrofitting in existing (even historic) buildings, as (ii) a solution for improving urban environment. Finally, the Cool-Green Roof could represent a promising mitigation strategy against urban heat island phenomenon, suitable for application even in those dense historical cities where other invasive mitigation techniques are unlikely applicable.
Article
Given the large amount of worldwide energy use associated to buildings' life cycle, in recent years various energy efficient strategies have been proposed to reduce buildings' environmental impact, e.g. green and cool roofs. The purpose of this work is to analyze an innovative type of green roof, named Cool-Green roof combining the features of both green and cool roofs. In fact, it is characterized by a specific vegetative layer able to optimize the quote of short-wave radiation reflected by the selected vegetation. After the analytical dissertation of the system, the developed solution is studied when applied in a case study building represented by a multifamily XVI century building in central Italy, characterized by cement based roof ceiling needing to be retrofitted. Both in-lab and infield experimental analyses were carried out for evaluating the building thermal-physics and the solar reflectance and thermal emittance of the selected plant compared to other flat roof materials and greeneries. Additionally, the year-round performance of Cool-Green roof is assessed through calibrated and validated dynamic thermal-energy simulation. Main findings of the study show how the CoolGreen roof is able to reduce the number of indoor overheating hours in summer by 98.2%, with negligible penalties in winter, given its high insulation capability, typical of green roof solutions. Therefore, the Cool-Green roof could be considered as (i) a strategy for roof retrofitting in existing (even historic) buildings, as (ii) a solution for improving urban environment quality. Finally, the CoolGreen Roof could represent a promising mitigation strategy against urban heat island phenomenon, suitable for application even in those dense historical cities where other invasive mitigation techniques are unlikely applicable.
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Currently, there is no clear and unified understanding about the status quo of China's energy consumption in the building sector. In addition, a considerable underestimation of energy associated with buildings has impeded the effective implementation of measures to improve building energy efficiency of China. Thus, in this paper, we seek to identify the building sector's energy consumption of China by establishing an estimation model of building energy consumption from a life cycle perspective. On the basis of macro-level statistical data and relevant literature, we analyze the activities in each phase and calculate associated energy consumptions throughout buildings’ whole life cycle in China from 2001 to 2013. The results show that China's energy consumption associated with buildings has reached 1.66 billion tons coal equivalent in 2013, with a stable growth rate of 7% annually since 2001. Buildings’ life-cycle energy has approximately accounted for 43% of China's total energy consumption for recent three years (2011–2013). What's more, energy consumption in buildings’ operation phase has been salient, accounting for over 20% of China's total energy consumption. More focus should be drawn on energy efficiency in building material production phase and energy consumed in China's rural residential buildings as both have been significantly neglected.
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Many cities have inadequate green infrastructures and cannot benefit from ecosystem services brought by greenspaces. Global warming and urban heat island (UHI) effect impose a dual warming impact on cities, especially compact ones. Green roofs offer a plausible solution for climate adaptation. In compact humid-tropical Hong Kong, two green-roof and a control bare-roof plots were installed on a high-rise building. Precision sensors were installed along a holistic vertical temperature profile extending from outdoor air to roof surface, green-roof material layers, and indoor ceiling and air. Three apartments under the plots were kept vacant to monitor air-conditioning energy consumption. The comprehensive-systematic data allowed in-depth analysis of thermal performance of vegetation (Sedum and Perennial Peanut) and weather (sunny, cloudy and rainy) in summer. Intense solar radiation at Control plot triggered significant material heating, which in turn warmed near-ground air to intensify UHI effect and indoor space to lift energy consumption. Sedum plot with incomplete plant cover, sluggish transpiration and limited substrate moisture storage had feeble evapotranspiration cooling. The warmed roof passed heat to near-ground air and subsurface layers to impose a small indoor cooling load. Peanut plot with high transpiration rate can significantly cool foliage surface and near-ground air to ameliorate UHI. Its high moisture-holding capacity, however, can generate an appreciable heat-sink to push heat downwards and increase indoor cooling load. Practical hints on green roof design and management were distilled from the findings for application in Hong Kong and beyond and to contribute to climate-resilient cities.
Article
The effectiveness of cool and green roofs to improve thermal comfort could be strongly dependent on the U-value of the roof itself and on the way it has been constructed (ventilated or unventilated, lightweight or massive, etc.). Recent strict limits on the U-values of building envelopes run the risk of reducing the effectiveness of cooling strategies in roofs which could be employed in warm and temperate climates to reduce surface temperatures and consequently to cool internal environment. In this paper, we experimentally analyse some roof systems (a high-albedo membrane and a green roof) compared to traditional ones in a Nearly Zero Energy Building, in order to provide new information concerning their effect on the internal comfort and the air temperatures of the surrounding environment. Experimental results confirm that, while the effectiveness of green and cool roofs for the mitigation of the Urban Heat Island effect is well established, the use of high-albedo materials on roofing systems with very low U-value is of little effectiveness for internal comfort. The green roof is distinguished by its passive cooling ability due to the evapotranspiration phenomena of the vegetation and the storage capacity of the substrate.
Article
Insulation properties of glass wool (GW) and opacified fumed silica (OFS) as fillers of vacuum insulation panel are experimentally investigated for variable pressing load and vacuum level. Density change of the specimen as a function of the pressing force is measured. The thermal conductivity at center of panel is measured under various vacuum levels and pressing loads. To evaluate the radiative conductivity separately, the diffusion approximation is adopted and the extinction coefficient is measured by an FT-IR apparatus. As the density increases, the solid conductivity increases, while the radiative conductivity decreases to have their sum increased. Pore size is inversely proportional to the density of the material; however, the relation is not consistent in the case of OFS at very low density because of the highly heterogeneous porous structure at that density. Comparing the materials in terms of initial insulation per, formance at center of panel, we find that GW is superior at low pressing load and the other one is better at high pressing load. Also, OFS turns out to have a longer service-life.
Article
Quantifying green roof evapotranspiration (ET) in urban climates is important for assessing environmental benefits, including stormwater runoff attenuation and urban heat island mitigation. In this study, a dynamic chamber method was developed to quantify ET on two extensive green roofs located in New York City, NY. Hourly chamber measurements taken from July 2009 to December 2009 and April 2012 to October 2013 illustrate both diurnal and seasonal variations in ET. Observed monthly total ET depth ranged from 0.22 cm in winter to 15.36 cm in summer. Chamber results were compared to two predictive methods for estimating ET; namely the Penman-based ASCE Standardized Reference Evapotranspiration (ASCE RET) equation, and an energy balance model, both parametrized using on-site environmental conditions. Dynamic chamber ET results were similar to ASCE RET estimates; however, the ASCE RET equation overestimated bottommost ET values during the winter months, and underestimated peak ET values during the summer months. The energy balance method was shown to underestimate ET compared the ASCE RET equation. The work highlights the utility of the chamber method for quantifying green roof evapotranspiration and indicates green roof ET might be better estimated by Penman-based evapotranspiration equations than energy balance methods.
Article
The establishment of a methodology for the calculation of the cost-optimal insulation thickness of building elements has been a subject of interest for some years. Many studies have been conducted on the ideal insulation thickness and been based on specific assumptions and approaches. The introduction of the Energy Performance of Buildings Directive recast (2010/31/EC) in May 2010, leads to the compulsory implementation of a specific methodology for this purpose by all European Union member states (Article 5, EPBD recast). Therefore, a study on this subject was conducted, to evaluate the results of previous studies and the strengths and weaknesses of the previous methodologies and to determine how the methodologies should be further developed to provide more reliable results. Additionally, a derived model was validated by a parametric study that examined all possible aspects that could potentially affect the end results. The minimum requirements of the insulation thickness for three selected European cities were also compared to the results of the proposed model applied to these cities. The results show that the proposed model provides a better compromise between simplicity and accuracy, leading at the same time to significantly lower U-values and therefore to improved energy efficiency of the buildings.
Article
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.
Article
This study develops a thermal performance metric for vegetated roof systems. The Dynamic Benefit of Green Roofs (DBGR) is the ratio of Heating, Ventilation and Air-Conditioning (HVAC) energy use for a building with a conventional roof to that of a building with a green roof. If the green roof results in lower energy use than a conventional roof with the same level of thermal resistance the value of DBGR is greater than unity.Data from a field study in Portland Oregon were used to validate the green roof model incorporated within a whole-building energy simulation program. This model was then used to estimate the DBGR for a new construction office building in four climates: Portland, Oregon; Chicago, Illinois; Atlanta, Georgia; and Houston, Texas. Results suggest that a green roof in Atlanta and Houston would provide net annual HVAC energy savings compared with a traditional roof. The Chicago case, with severe winter and mild spring/summer/fall, resulted in a smaller energy savings. The DBGR for Portland was less than unity, suggesting a net energy consumption penalty associated with the green roof. This was due, in part, to the undesirable evaporative cooling in the shoulder seasons which led to increased building heating loads.
Article
DOE-2 energy simulation program was used to determine the effects of rooftop garden on the annual energy consumption, cooling load and roof thermal transfer value (RTTV) of a five-story hypothetical commercial building in Singapore. The thermal resistances (R-values) of turfing, shrubs and trees were estimated using data from site measurements, and the effects on the building energy consumption of a rooftop garden with these three types of plants were simulated. Two soil types with different soil thickness on the building roof were also simulated. The results showed that the installation of rooftop garden on the five-story commercial building can result in a saving of 0.6–14.5% in the annual energy consumption, and shrubs was found to be most effective in reducing building energy consumption. The results also revealed that the increase of soil thickness would further reduce the building energy consumption and the moisture content of soil can affect the outcome quite substantially.
Article
The cooling effect of various kinds of greenery cover was investigated by both experimental model and computer simulation. Four concrete roof models were constructed and different coverings were arranged for each: bare concrete, soil layer, soil layer with turf, and soil layer with ivy. Temperature profiles, including air temperature in the air space under the roof were measured along with other environmental parameters to calculate the cooling effect. A computer model to simulate the systems and to evaluate cooling load was constructed using the simulation language CSMP. The simulated results matched reasonably well with the measured ones, and the cooling effect increased with increase in leaf area per unit roof area (LAI).
Article
A detailed and integrated presentation of the green roof systems is provided in the present paper. Aiming to analyse a specific urban case study, we describe the basic architectural and scientific principles that characterize its performance and efficiency. Furthermore, a state of the art presentation of the system is provided, including the presentation of several case studies as well as a selection and description of plants that usually are extensively used in the green roof system all over the world.Energy and environmental investigation data of the green roof system performance in an office building located in the greater Athens area are provided. The energy efficiency was examined by calculating the energy savings through an accurate dynamic mathematical model. The thermal performance investigation showed a significant reduction of the building's cooling load during the summer period arriving at approximately 40%. Moreover, the influence of the green roof system in the building's heating load was fount insignificant, and this can be regarded as a great advantage of the system as any interference in the building shell for the reduction of cooling load leads usually to an increase of its heating load.
Article
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.
Article
Green roofs have several environmental benefits, such as improving building energy efficiency. The present paper provides a comprehensive study of the impact of a green roof on building energy performance. A model of green roof thermal behavior was coupled with a building code to allow the evaluation of green roof foliage and soil surface temperatures. Simulations were conducted for a single-family house with conventional and green roofs in a temperate French climate. In the summer, the fluctuation amplitude of the roof slab temperature was found to be reduced by 30 °C due to the green roof. The heat flux through the roof was also evaluated. In the summer, the roof passive cooling effect was three times more efficient with the green roof. In the winter, the green roof reduced roof heat losses during cold days; however, it increased these losses during sunny days. The impact of the green roof on indoor air temperature and cooling and heating demand was analyzed. With a green roof, the summer indoor air temperature was decreased by 2 °C, and the annual energy demand was reduced by 6%. The present study shows that the thermal impact of green roofs is not functionally proportional to the leaf area index parameter. It also shows the high dependency of this impact on the roof insulation. Finally, the simulations suggest that green roofs are thermally beneficial for hot, temperate, and cold European climates.
Article
This paper presents a mathematical model yielding a sensible, albeit simplified representation of the dynamic thermal behaviour of actual green roofs. Several parametric sensitivity analyses have been carried out to assess the cooling potential of green roofs in summer. The main conclusion of these analyses is that green roofs do not act as cooling devices but as insulation ones, reducing the heat flux through the roof. A relatively small set of parameters have been identified as relevant for green roof design: the leaf area index (LAI) and the foliage geometrical characteristics, the soil apparent density, its thickness, and its moisture content.
Article
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.
Article
Green roof utilisation has been known since ancient times both in hot and cold climates. Nowadays, it has been reconsidered at issue of energy saving and pollution reduction. In this paper, some measurement sessions on a green roof installed by the Vicenza Hospital are described. A data logging system with temperature, humidity, rainfall, radiation, etc. sensors surveyed both the parameters related to the green roof and to the rooms underneath. The aim is to evaluate the passive cooling, stressing the evapotranspiration role in summer time. Furthermore, the enhanced insulating properties have been tested during winter time. A predictive numerical model has been developed in a building simulation software (TRNSYS) to calculate thermal and energy performances of a building with a green roof, varying the meteorological dataset for a specific geographic zone.
Article
A physically based model of the energy balance of a vegetated rooftop has been developed and integrated into the EnergyPlus building energy simulation program. This green roof module allows the energy modeler to explore green roof design options including growing media thermal properties and depth, and vegetation characteristics such as plant type, height and leaf area index. The model has been tested successfully using observations from a monitored green roof in Florida. A preliminary set of parametric tests has been conducted on prototypical 4000 m2 office buildings in Chicago IL and Houston TX. These tests focus on evaluating the role of growing media depth, irrigation, and vegetation density (leaf area index) on both natural gas and electricity consumption. Building energy consumption was found to vary significantly in response to variations in these parameters. Further, this response depended significantly on building location (climate). Hence, it is evident that the green roof simulation tool presented here can serve a valuable role in informing green roof design decisions.
Article
Evapotranspiration (ET) calculations were made on a daily basis throughout 1988 for two locations near Menemen, Turkey. Calculations used the FAO-56 “dual” crop coefficient approach that includes separate prediction of evaporation from soil. Two days were drawn from the data set to correspond with Landsat flyovers to provide for comparison with remote sensing estimates of ET.One study site was a cotton field in a relatively flat, irrigated region. The second study site was an integrated area in the Gediz River Basin where the farm and field sizes are small, of the order of 3–5 ha, and about ten different “crops” are grown. Predicted ET (ETc act) for the cotton site was 3.1 and 5.3 mm/day for 26 June and 29 August, and was 4.9 and 4.3 mm/day for the integrated crops in the Gediz valley. Total calendar year ETc act was predicted to be 800 for cotton and 940 mm for the Gediz valley. Evaporation during the crop growing periods averaged 9% of total evapotranspiration for cotton and 14% for the mixed crops.The predictions of ETc act were within 20% of predictions by the Landsat-based SEBAL remote sensing method at only one site and date. Predictions were within 20% of ET based on an energy feedback remote-sensing application using NOAA-AVHRR and Landsat data for both sites on one of the two dates. Before comparison, the predictions of ETc act by the FAO-56 procedure were reduced by 15%, to account for less than pristine crop establishment, growth and water management in the area.
Article
Green roofs are a passive cooling technique that stop incoming solar radiation from reaching the building structure below. Many studies have been conducted over the past 10 years to consider the potential building energy benefits of green roofs and shown that they can offer benefits in winter heating reduction as well as summer cooling.This paper reviews the current literature and highlights the situations in which the greatest building energy savings can be made. Older buildings with poor existing insulation are deemed to benefit most from a green roof as current building regulations require such high levels of insulation that green roofs are seen to hardly affect annual building energy consumption.As over half of the existing UK building stock was built before any roof insulation was required, it is older buildings that will benefit most from green roofs. The case for retrofitting existing buildings is therefore reviewed and it is found there is strong potential for green roof retrofit in the UK.
Article
This paper attempts to evaluate the positive effects of vegetation with a multi-scale approach: an urban and a building scale. Monitoring the urban heat island in four areas of New York City, we have found an average of 2 °C difference of temperatures between the most and the least vegetated areas, ascribable to the substitution of vegetation with man-made building materials. At micro-scale, we have assessed the effect of surface albedo on climate through the use of a climatological model. Then, using the CO(2) equivalents as indicators of the impact on climate, we have compared the surface albedo, and the construction, replacement and use phase of a black, a white and a green roof. By our analyses, we found that both the white and the green roofs are less impactive than the black one; with the thermal resistance, the biological activity of plants and the surface albedo playing a crucial role.
Vegetation for extensive and biodiverse green roofs
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Quantifying evapotranspiration from urban green roofs: A comparison of chamber measurements with commonly used predictive methods
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