Article

Fundamental green roof performance of residential building in desert climate: In terms of sustainability and decrease in energy consumption

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Abstract

In modern times, the majority of the world's energy consumption is attributable to the heating and cooling of residential buildings. Because of this, the development of sustainable energy sources has increased dramatically, particularly in residential buildings, with the goal of reducing the amount of energy that is consumed within buildings. An extensive green roof system is one of the most effective ways to save energy. Not only does this lessen the impact that humans have on their surroundings, but it also has positive effects on people's health and the way their homes look. The purpose of this study was to investigate the thermal characteristics of green roofs installed on residential buildings in Qatar's hot and dry climate in order to assess their viability and determine how best to minimize energy usage. In the course of this investigation, five distinct heights ranging from 10 to 50 cm were taken into consideration to assess the energy efficiency of the roof. Of these heights, the height of 10 cm was found to be the most suitable height for planting in this environment. In addition, in order to evaluate the performance of roof energy, five plant leaf area indices with values ranging from one to five have been taken into consideration. Of these, the results indicate that the plant leaf area index is the plant planting index that works best in this environment. The larger the plant's leaves, the more protection they will provide from the sun and the higher the yield will be. In addition, to evaluate the effectiveness of the roof energy system, four height dimensions of 8, 13, 18, and 23 cm were considered for the cultivation layer. According to the findings, the height of the plant substrate layer is 23 cm, and the height of the cultivation layer is 18 cm. The cultivation layer that yields the best results for green roofs in this environment.

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... The results showed that the developed 2-D finite element model was able to accurately predict the exterior and interior surface temperatures of both models. Yuan et al. [12] investigated the thermal characteristics of green roofs installed on residential buildings in Qatar's hot and dry climate in order to assess their viability and determine how best to minimize energy usage. The results indicated that the plant leaf area index is the plant planting index that works best in this environment, and the height of the plant substrate layer is 23 cm, and the height of the cultivation layer is 18 cm. ...
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... Though infrastructure development undoubtedly leads to economic growth and advancement in diverse spheres, it has been noted to be a major contributor to carbon emissions through industrial and construction activities (Yuan et al. 2022). This demands the production of low carbon infrastructure, which generates fewer carbon emissions and promotes resilience against the climate. ...
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span>Green roof system is one of sustainable approach for energy consumption reduction and improving the aesthetic value of the built environment. The system has been adopted by most of developed countries; and in Malaysia, research on green roof studies are quite evolving however the implementation of the system is slow due to some perceptions and obstacles. Green roof has potential on providing benefits such as reduction on the urban heat island effect, reduces temperatures, pollution and improves the attenuation of stormwater. This paper will highlights on a preliminary review of the implementation green roof system in Malaysia and explores the performances of Malaysian green roof in order to highlight the performance of green roof under tropical climatic conditions using local configurations.</span
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The efficiency of photovoltaic cell is highly temperature‐dependent; therefore, the performance of these solar panels would be increased by decreasing the temperature. In this research, a novel integration of coupling thermal photovoltaic panels with thermoelectric generator module (PVT‐TEG) is investigated for possible application in reducing cell temperature in order to increase output electrical power, thermal efficiency, and overall efficiency of the integrated PVT‐TEG system. Initially, component validation is performed by experimental data with equipment in the energy laboratory for high reliability. In the hybrid system (PVT‐TEG), one‐third of a monocrystalline PV panel backside was equipped with thermoelectric generators (TEG), while aluminum water blocks were attached to the cold side of TEGs for cooling aim, then tested and compared with a simple panel at the same environment condition (Shahrood city in Iran) from August until September 2020. In this study, the influence of water velocity and its temperature are studied simultaneously. In addition, mathematical modeling is based on thermal resistance, whereas the impact of the thermal resistance of adjacent layers, TEGs, and the upper heat loss thermal resistance on the PVT‐TEG system and simple panel properties are investigated, respectively. Experimental and theoretical data are validated with obtained results from MATLAB and showed acceptable deviation error with less than 18%. The electricity generated in the PVT‐TEG panel is 8.5% more than a simple panel. TEG power generation has a small share of total power generation, so economic assessment is essential for industrial production. Finally, parametric analysis in PVT‐TEG estimates 70% higher total efficiency compared with conventional simple panel.
Article
In this investigation, a hybrid energy conversion system is proposed and evaluated for energy, exergy, and environmental criteria for generating power and freshwater. The system comprises of a Humidifier Dehumidifier Desalination (HDD) system for producing freshwater, an organic Rankine cycle system for generating electric power, and a solar Parabolic Trough Concentrator for absorbing solar energy as the desalination heat source. Different working fluids including Al 2 O 3 , Cu, CuO, TiO 2 , and MWCNT nanoparticles in oil as the base fluid are examined. The influence of different nanofluids on the performance of the system is investigated as the main goal of this study. Environmental impacts of the suggested system are studied. Results show that the thermal efficiency of the Parabolic Trough Concentrator was with the application of Cu/oil nanofluid as about 62.4%. It is illustrated that the amount of freshwater production can be increased by raising the nanofluid concentration. The freshwater production varies between nearly 15.28 kg/h to 15.46 kg/h with the application of nanofluid. The organic Rankine cycle net work and total efficiency improved with increasing nanofluid concentration. Also, it can be concluded that the application of MWCNT/oil with a concentration of 5% volume fraction has shown the highest exergy efficiency of 4.7%. It was concluded the suggested desalination system with application of the solar organic Rankine cycle system, in addition to producing fresh water and power, significantly reduced amounts of CO 2 emissions in the environment. Finally, it should be mentioned that the ideal system was analyzed and the gains from the use of nanofluids are very small.
Article
Agriculture and energy are inextricably connected; many energy systems can be driven by biomass supplied from agricultural waste products. In this study, a combined biomass/natural gas fed multi-generation system, prodcuing cooling, heating, and power is investigated from exergetic and thermo-economic standpoints. The system consists of four susbsystems, encompassing a gasification cycle, a gas cycle, a Rankine steam cycle, and a double effect absorption refrigeration cycle. To increase the lower heating value of the fuel injected into the combustion chamber, natural gas is mixed with syngas. Also, to exploit the exhaust gas from the stack of the gas turbine, the flue gas is divided into two streams by a spliter,providing the required heat for the Rankine steam and absorption refrigeration cycles. The effects of parameters such as the gas turbine inlet temperature , combustion chamber inlet pressure, the amount of natural gas mixed with syngas, and split ratio of the exhaust gas from the gas turbine on the thermodynamic and thermo-economic outputs are studied. The results show that the gas cycle with 61% and the double-effect absorption refrigeration cycle with 6% exergy destruction rates have the largest and lowest shares of the total exergy destruction rate, respectively. By changing the mixing ratio of the natural gas injected into the cycle from 0.5 to 1, the system's net work is seen to increase by 90.77%, while the modified ecological coefficient of the system performance boosts by 9.49%. In addition, such a change leads to 53.45% increase in the net present value of the total cost over the defined economic life, and also an increase of 90.25% in the net present value of the total output of the cycle equivalent to electricity over the economic life. Moreover, it brings about 19.36% decrease in the system's levelized cost of energy.
Article
Phase change materials (PCMs) have received substantial interest for their ability to store and release latent heat for energy conservation and thermal control purposes. PCMs are available in a variety of latent heat and melting points but their performance is low due to low value of thermal conductivity which limits its usage. The addition of highly thermal conductivity nanoparticles, porous metal foams and encapsulation methods have been used to address this issue and try to fix the low thermal conductivity of PCMs which is broadly discussed in this manuscript. The ability of PCM to store and release the thermal energy prompted the researchers to use it in potential applications. The energy retained and emitted by PCMs may be used for a variety of purposes, such as in photovoltaic (PV) panels, thermoelectric generators, building air-conditioning, air and water heating systems, heat exchangers, desalination solar stills, textiles, thermal management of electronic equipment and batteries and food packaging. Therefore, in this review, first the advancements in thermal properties of PCMs are thoroughly discussed in terms of enhancement in melting and solidification rates. After that, the use of PCMs in various applications is then explored, and conclusions are drawn accordingly. Based on analysis of recent literature, it was discovered that the phase transition temperature, phase transition enthalpy and thermal conductivity are three important parameters for the selection of an appropriate PCM for use in various applications. The current status of these advanced energy storage materials is also presented in this review. Lastly, some challenges and future recommendation are also proposed for future researchers which will bring a revolution in thermal management field.
Article
Urban green spaces can provide habitat and resources for urban dwelling fauna. Suburban green spaces occur most commonly as parks and roadside vegetation, but as human populations grow and space in cities becomes increasingly limited, space-efficient green solutions like green roofs and walls in metropolitan areas are becoming increasingly common. However, knowledge of the efficacy of these forms of green infrastructure in attracting and promoting biodiversity remains limited. To address this, we compared arthropod, gastropod, and avian species richness and diversity between green and conventional roofs on neighbouring and identical buildings in metropolitan Sydney, Australia. By monitoring local biodiversity using motion sensing camera traps and regular insect surveys, we found that the green roof supported four times the avian, over seven times the arthropod, and twice the gastro-pod diversity of the conventional roof. Only the green roof attracted locally rare species including blue banded bees (Amegilla Cingulata) and metallic shield bugs (Scutiphora pedicellata). Our results suggest that green roofs, like other urban green spaces, can have ecological significance by attracting and supporting urban fauna that may then add important functional capacities to previously depauperate spaces. This study demonstrates the potential for the widespread adoption of green roofs to create more biologically diverse cities.
Article
Green roofs are increasingly popular as a result of their ability to provide local ecosystem services in the urban landscape. The number and intensity of the services provided is a function of the abiotic and biotic design elements chosen for a given green roof design. We manipulated experimental semi-intensive green roof plots in order to uncover which combinations of design choices created the system most capable of providing ecosystem services with the lowest number of trade-offs. We monitored performance of planted vegetation, weeds, soil carbon, and stormwater runoff in a complete factorial experiment involving three different green roof system types (conventional green roof, blue-green roof, and quasi-traditional green roof), two plant community types (restoration and horticulture), and two arbuscular mycorrhizal fungal treatments (inoculated or non-inoculated). We hypothesized that more natural designs (i.e., less engineered systems) had the potential to provide a greater amount of ecosystem services with fewer trade-offs. However, our results showed that natural design elements did not consistently perform better than engineered design choices, which does not support the idea that habitat templates should guide green roof design. We found system type to be most impactful on ecosystem services. In particular, the blue-green roof provided the most services with the lowest number of trade-offs and may represent the ideal intermediate worthy of further investigation.
Article
Green roofs are an interesting technology that has attracted worldwide attention because of the multi-disciplinary benefits, involving the improvement of stormwater management, the mitigation of the urban heat island effect, the prolonged lifespan of the roof membrane, the enhancement of urban aesthetic, the creation of recreational spaces, and the possibility to generate energy savings for building heating and cooling. Several papers dealt with green roofs, spacing from quantification of runoff quality and quantity, to the evaluation of plant and substrate intrinsic characteristics, to the social aspects related to the installation of vegetated surfaces in densely populated cities. A big share of research has investigated the thermal performances of different green roof solutions in the attempt to assess the effect on the building energy demand. A lot of studies have been conducted through experimental research on properly instrumented green roofs or by numerical simulations implemented in different environments or even by developing and validating thermo-physical models that describe the interaction between the green roof and the surrounding environment. Although the relevant number of papers dealing with the thermal performance of vegetated roofs in the literature, quantitative estimations of the reduction of building energy consumption due to green roofs are not easily found. The paper presents a comprehensive literature review to summarize the relevant findings in terms of energy savings produced by a green roof to offer a suitable answer to the question of the energy effectiveness of such a solution and quantitatively report the results obtained across different climates.
Article
Green roofs, as part of urban green structures, have been pointed out as the solution to pursuit the goal of healthy cities. This study aims to investigate the direct, focused on meteorological changes, and indirect, related to both meteorological and emissions changes, impacts of green roofs on air quality (PM10, NO2 and O3). For that, the numerical modelling system composed by the WRF-SLUCM-CHIMERE models was applied to a 1-year period (2017), having as case study the Porto urban area. The EnergyPlus model was also applied to estimate the green roofs impacts on the building's energy needs and related impacts on air quality and atmospheric emissions. The analysis of the direct impacts showed that green roofs promote a temperature increase during the autumn and winter seasons and a temperature decrease during the spring and summer seasons. Both negative - concentrations increase - and positive - concentrations decrease - impacts were obtained for the primary, PM10 and NO2, and secondary, O3, air pollutants, respectively, due to changes in the dynamical structure of the urban boundary layer. The indirect effects of green roofs showed their potential to enhance the buildings energy efficiency, reducing the cooling and heating needs. These changes in energy consumption promoted an overall decrease of the environmental and economic indicators. Regarding air quality, the impact was negligible. The obtained results highlight the need for a multipurpose evaluation of the impacts of green roofs, with the different effects having to be traded off against each other to better support the decision-making process.
Article
Municipal activities are one of the most important water users worldwide; thus, the treatment and reuse of greywater for non-potable purposes helps to reduce a remarkable amount of consumed water within urban communities. To achieve greywater reuse standards, and remove surfactants, micropollutants, organic matters, microorganisms and other pollutants various methods including physical, chemical and biological processes have been used. Treated greywater can be used on site for different purposes: carwash, toilet flushing, fire protection, green roofs, green walls, non-food irrigation etc. Among them, the use of greywater is very important in the expansion of the green roofs. Green roofs offer many benefits to urban areas such as decreasing air pollution, reducing building cooling needs, promoting mental health of habitants, noise reduction and aesthetics improvement. Therefore, this article provides an overview mainly from two aspects, the possibilities of greywater reuse by studying the characteristics and available options for greywater treatment and its benefits toward the developing green roofs.
Article
Green roofs are widely considered as a promising nature-based solution for urban stormwater management. In this study, the stormwater retention and detention performance of 6 green roof modules with different types and depth of substrates at Beijing, China was investigated through 3-year continuous monitoring. The Hydrus-1D was applied to further explore the stormwater management performance of green roofs under extreme storms. The average event-based stormwater retention and detention rates of the green roofs with 10 cm substrates ranged between 81% and 87%, and 83%–87%, respectively; and the average time delays in runoff generation and peak discharge ranged between 82 and 210 min, and 63–131 min, respectively. Green roofs with 15 cm depth of substrates offered higher stormwater retention and peak runoff attenuation rates than those with 10 cm substrates. However, due to the high frequency (55 out of total 92) of light rainfall events (<10 mm) and short antecedent dry weather periods (3.8 days in average), no significant difference was found on stormwater control performance of those green roofs. The Hydrus-1D simulations revealed that green roof stormwater retention rate decreases exponentially with return periods of extreme storms but increases with substrate depth. There exists a critical depth of substrates and further increases in substrate depth beyond this critical value could not bring much improvement in stormwater retention performance of green roofs. The application of extensive green roofs with 10–15 cm substrates provides promising stormwater retention and detention performance in highly urbanized area of Beijing.
Article
Rainfall-runoff (r-r) modeling at different time scales is considered as a significant issue in hydro-environmental planning. As a first hydrological implementation, for one-time-ahead r-r modeling of two watersheds with totally distinct climatic conditions, Genetic Algorithm (GA, as a global search technique) and Emotional Artificial Neural Network (EANN, as a new production of Artificial Intelligence (AI) based methods that simulated based on the brain neurophysiological structure) was combined. Determining the optimal architecture of AIbased networks is vital for increasing the accuracy of prediction by the network and also to reduce run-time. In the current study, GA has been implemented to choose the important features candidate as EANN input and automatically diagnose the optimal number of hidden nodes and hormones simultaneously. The acquired results indicated a better representation of the proposed hybrid GA-EANN model compared to the sole ANN and EANN. Numerical identification of obtained results revealed that the proposed hybrid GA-EANN model might enhance the better results than the EANN model up to 19% and 35% in terms of testing suitability criteria for Aji Chai and Murrumbidgee catchments, respectively.
Article
The global popularity of green roofs (GRs) rises as urban runoff becomes a primary environmental concern in both developed and developing countries. Although a growing number of studies have measured the runoff retention (RR) performance of GRs and investigated the underpinning factors, a systematic and quantitative understanding is lacking. This study applies a statistical approach on a dataset of 2375 original experimental samples associated with the RR performance of GRs observed across 21 countries, consolidated from 75 internationally peer-reviewed studies published in 2005–2020. The results show that the sampled RR rates (i.e., the proportion of rainfall retained on a per-event basis) range widely (0–100%), with an average of 62%. Rainfall intensity, substrate depth, GR surface coverage, climate type, vegetation type, and season type partially explain the variances in retention performance. Moreover, the effects of some factors (e.g., rainfall intensity) are not isolated but contingent on other factors (e.g., vegetative cover). This global synthesis shows few samples emanate from Africa, Central America, and Central Asia, highlighting the need of more GR research and applications in these regions. The average GR RR rate appears lower than some specified in green building standards, which implies the need to further improve the RR performance of GRs or combine GRs with other RR measures. Contingent effects of GR RR incluencing factors demonstrate the need to leverage design parameters and to account for local weather and climate characteristics in the optimization of GR performance.
Article
At nearly 27,500 m², the Jacob K. Javits Convention Center (JJCC) located in New York City, hosts one of the largest extensive green roofs in the United States. This paper explores three years of fine scale microclimate data collected at the JJCC green roof and its potential ability to reduce the urban heat island intensity (UHII). Surface energy fluxes and microclimate parameters on four different surfaces are analyzed before and after installation of the southern section of the green roof, offering a unique before/after, test/control study. The results indicate that the temperatures of the air above the green roof, and its exterior surface are different (e.g. lower) than those measured above and on, respectively, the black roof that preceded it. Differences in the maximum daytime air and surface temperature between the black and green roof were 1.80 °C and 18.4 °C, respectively. Installation of the green roof increased evapotranspiration, modifying the roof's surface energy balance, and reduced the median summer nighttime UHII (compared to the pedestrian level station) by 0.91 °C. Though microclimatic conditions on two sections of the green roofs vary somewhat, the research findings generally support the statement that green roofs are an effective strategy for mitigating the UHI effect.
Article
In the current century, climate change, air pollution, and the depletion of energy resources are big threats to our society, especially in urban areas. It is an inevitable fact that we need to develop the green building concept and produce innovative solutions in our quest to design structures that are compatible with nature, sustainable, environmentally friendly, aesthetic and use natural resources efficiently. Roofs are the most efficient and promising building surfaces for the combination of photovoltaic panel applications and green roofs considering their locations and inclination angles. This research focuses on how carbon emission can be reduced via both green roofs and solar energy while producing electricity in OSTIM, one of Turkey's most prominent industrial zones located in the capital. The long-term detailed analysis of photovoltaic-green roof application in terms of economics and carbon emission is discussed. Although the rooftop option of a combination of solar panels and a green roof design costs higher than a standard photovoltaic system, it opens up new prospects for urban lighting in smart cities with exciting aesthetic effects. This combination of two sustainable features can become a model of green technology and opens up a wide range of research applications.
Article
Three of the primary functions of green roofs in urban areas are to delay rainwater runoff, moderate building temperatures, and ameliorate the urban heat island (UHI) effect. A major impediment to the survival of plants on an unirrigated extensive green roof (EGR) is the harsh rooftop environment, including high temperatures and limited water during dry periods. Factors that influence EGR thermal and hydrologic performance include the albedo (reflectivity) of the roof and the composition of the green roof substrate (growing media). In this study we used white, reflective shading structures and three different media formulations to evaluate EGR thermal and hydrologic performance in the Pacific Northwest, USA. Shading significantly reduced daytime mean and maximum EGR media temperatures and significantly increased nighttime mean and minimum temperatures, which may provide energy benefits to buildings. Mean media moisture was greater in shaded trays than in exposed (unshaded) trays but differences were not statistically significant. Warmer nighttime media temperatures and lack of dew formation in shaded trays may have partially compensated for greater daytime evaporation from exposed trays. Media composition did not significantly influence media temperature or moisture. Results of this study suggest that adding shade structures to green roofs will combine thermal, hydrologic, and ecological benefits, and help achieve temperature and light regimes that allow for greater plant diversity on EGRs.
Article
Rail transit system has been considered to have a large energy harvesting potential, and to be usable to achieve self-powering for rail-attached electrical installations. Dowty retarder is a key device installed on the side of rails to assist train braking, which can be used as a carrier for kinetic energy harvesting. In this paper, a high-efficiency kinetic energy harvester (KEH) based on a railway Dowty Retarders (DRs) is investigated. This new KEH can accumulate the kinetic energy of a decelerating train using a novel vibration rectification mechanism. The current study comprises four main components: energy input module, motion transmission module, generation module, and energy storage module. The energy input module has a screw-nut mechanism that can convert linear vibration into rotational motion. As a core component of the entire device, the motion transmission module contains a special closed-loop shaped gear train that converts the two-way rotary motion into a unidirectional rotation. The final unidirectional rotation is transferred to the generation module for power generation and the generated energy is stored in the energy storage module. Finally, both experimental and simulation approaches were performed to verify the dynamics response of the KEH mechanism. The maximum efficiencies of 55.4% and 51.9% are obtained during the simulation and experimental analyses. It is validating that the KEH mechanism is promising and practical in self-powered applications for the heavy haul railway.
Article
Green roofs are among the most popular type of green infrastructure implemented in highly urbanized watersheds due to their low cost and efficient utilization of unused or under-used space. In this study, we examined the effectiveness of green roofs to attenuate stormwater runoff across a large metropolitan area in the Pacific Northwest, United States. We utilized a spatially explicit ecohydrological watershed model called Visualizing Ecosystem Land Management Assessments (VELMA) to simulate the resulting stormwater hydrology of implementing green roofs over 25%, 50%, 75%, and 100% of existing buildings within four urban watersheds in Seattle, Washington, United States. We simulated the effects of two types of green roofs: extensive green roofs, which are characterized by shallow soil profiles and short vegetative cover, and intensive green roofs, which are characterized by deeper soil profiles and can support larger vegetation. While buildings only comprise approximately 10% of the total area within each of the four watersheds, our simulations showed that 100% implementation of green roofs on these buildings can achieve approximately 10–15% and 20–25% mean annual runoff reductions for extensive and intensive green roofs, respectively, over a 28-year simulation. These results provide an upper limit for volume reductions achievable by green roofs in these urban watersheds. We also showed that stormwater runoff reductions are proportionately smaller during higher flow regimes caused by increased precipitation, likely due to the limited storage capacity of saturated green roofs. In general, green roofs can be effective at reducing stormwater runoff, and their effectiveness is limited by both their areal extent and storage capacity. Our results showed that green roof implementation can be an effective stormwater management tool in highly urban areas, and we demonstrated that our modeling approach can be used to assess the watershed-scale hydrologic impacts of the widespread adoption of green roofs across large metropolitan areas.
Article
Over the last twenty years, Cairo experienced a great rise in temperature by 4-5 K due to the high urban density and lack of vegetation. These factors led to increased air conditioning and electricity usage. This study therefore seeks to evaluate the effect of green roofs on reducing outdoor air temperature and lowering buildings’ cooling energy demand in different urban densities. Group A consisted of the same aspect ratio areas H/W = 1 and different building heights of 12 m, 18 m, and 30 m. Group B contained areas of the same building heights (12 m) and different aspect ratios of H/W = 1, 2, and 3. ENVI-met v.4.4.4 was used to study each area by simulating the reference case and two scenarios: extensive and intensive green roofs. Then, a DesignBuilder model was used to calculate the buildings’ energy demand. This study found that intensive green roofs achieve the maximum reduction in air temperature and buildings’ cooling energy. However, the economic aspect favors using extensive green roofs as they were able to reduce air temperature and buildings’ cooling energy in Group A by 0.1–0.5 K and 1.3–3.2% and in Group B by 0.1–1.7 K and 3.2–13.3%.
Article
People migration to urban region have created dense opaque urban landscape which generates high volume of storm water runoff and frequent flash flood episodes. This has caused tremendous damages and loss to the nation. Local authority has to spend greatly to repair damages caused by this disaster. Studies have proven that green roof acts as an efficient green infrastructure to control storm water runoff and hindrance flash flood occurrences. However, the worth of implementing green roof for the local authority remains unrevealed. This study prompts to assess the economic worth of implementing green roof for the local authority using costs benefits analysis. Overall, extensive green roof provides better cost benefits ratio than intensive green roof whereby the benefit is 1.2–3.5 times larger than green roof cost. Roof slope contributes the highest benefit ratio for intensive green roof at 2 times higher than minimum cost. Meanwhile, vegetation provides the largest benefit ratio for extensive green roof at 4.2 times larger than minimum cost. Green roof has proven to be worthy for local authority from the economic and environment aspects. This is significant in creating a new pathway to encourage sustainable practice among local authority thus serve national sustainable development agenda.
Article
Coconut fibre insulators represent an insulating material considered as ‘‘exotic”, which clashes with the scepticism of his thermo-hygrometric behaviour, particularly in the case of covering technology such as green roofs, which is a technological solution often adopted in the case of sustainable buildings or nearly zero energy building. Green roofs represent a valid constructive solution with high thermal performances, adopted both in existing and new buildings. The purpose of the research regards the study of the thermo-hygrometric behaviour of the concrete (CLS) and Cross-Laminated Timber (CLT) slabs, insulated with coconut fibreboards (CF) such as an alternative of synthetic insulator, referred to 10 different green roofs scenarios. The results show that coconut fibre insulations are equally comparable to natural and synthetic materials, and the doubts for their applications, including the green roofs, are related to technological solutions for the implementation in the market and their diffusion between the buildings materials, rather than their hygrothermal features.
Article
Urban temperature increase is a critical problem for many cities. Green roofing is an approach to mitigating urban temperature increase, while the maintenance of the green roof for stable cooling potential has been less studied. Therefore, this study aims to investigate the cooling performance of prefabricated green roofs for maintenance purposes. Focusing on the cooling and humidifying performance of the green roof, this study is to understand the influence of (i) vegetation species, (ii) weather condition and (iii) watering. This study was experimentally performed in the subtropical city of Hangzhou, China in the summer season, with three local vegetation species including Pomegranate, Bermuda grass and Sedum lineare. Results indicate that under sunny conditions, the Pomegranate roof was favourable with the best diurnal cooling and humidifying effects, the Bermuda grass roof could be acceptable while the Sedum lineare roof is not suggested. In comparison, all green roofs could maintain diurnal cooling and humidifying effects under cloudy conditions. Watering is critical to green roof cooling and humidifying effects. Without watering, all green roofs could elevate air temperature and dry surrounding environment and could die. The Pomegranate should be watered before 15:00 under sunny condition, while both Bermuda grass and Sedum lineare roofs should be watered before noon. Moreover, nocturnal watering makes slight differences to green roof cooling and humidifying effects. Overall, this study helps understand the green roof cooling and humidifying effects and it can instruct green roof management and maintenance.
Article
Green roofs and cool roofs are commonly used to improve indoor thermal environment, reduce air-conditioning load and mitigate the Urban Heat Island (UHI) effect. This study aimed to quantify the differences in thermal and energy performance between the two different roof types under the climate of Shanghai. Firstly, field experiment was conducted in the Shanghai area. Thermal performance of green roof, cool roof and common roof in summer and winter were measured. Results showed that, compared to common roof, the cool roof had an average cooling effect of 3.3 °C on the outer roof deck surface in summer, while the green roof only had a cooling effect of 2.9 °C. In winter, the green roof provided good insulation, and could improve outer surface temperature of the roof deck by an average of 3.3 °C compared to the cool roof. A hygrothermal transfer model for green roof was coupled with a dynamic building thermal performance simulation software (THERB) and validated using measured data. The coupled model was used to predict the effect of both roof types on energy performance of a public building. Simulation results showed that green roof could reduce the cooling and heating loads of the top floor by 3.6% and 6.2%, respectively. The cool roof could reduce cooling load by 3.6% and increase heating load by 10.4%. Finally, a parametric analysis was implemented. The functional mechanism of the main parameters of green and cool roof as well as their impacts on thermal and energy performance of public buildings were analyzed in detail. Conclusions drawn from this paper could provide guidance for the design optimization and application of green roof and cool roof in Shanghai area.
Article
To face the consequences of climate change and unsustainable urbanization, green roofs are currently widely implemented in urban environments. Despite their benefits to restore ecosystem services are quite well established at the roof scale, green roofs need to be widely and appropriately distributed to perform efficiently at larger scales. However for now, this scale-factor is not considered to guide and conduct green roof implementation policies. Here we show that a multi-scale analysis based on fractal theory is helpful in providing information for green roof implementation and in assessing the relevance of these policies. Computed for 9 European cities, green roofs fractal dimensions are sparse, ranging 0.49 to 1.35, and illustrate some different degrees of progress in urban greening. These results demonstrate some significant inconsistencies between political ambition and their in situ realization, and the necessity to better take into account the spatial distribution of green roof implementations in order to optimize their performances.
Article
Green roofs appear to be an appealing solution for sustainable constructions because they could produce different advantages for the building, especially at an energy level. Nevertheless, usually dynamic models adopted for the simulation of the green roof performances require the knowledge of several parameters, which are often difficult to estimate, in order to properly define the thermal exchanges with the external environment. In this paper, in order to overcome this limitation, dynamic hourly simulations were performed by means of TRNSYS software, employing experimental climatic data and the monitored temperatures in an experimental green roof. In order to contemplate the overall effect of the vegetated roof, the temperature at interface with the structural roof was provided as the boundary condition in the building model. Simulation results have shown that, at annual level in the considered climatic context, a non-insulated green roof provides the best results due to the significant reduction of the cooling energy demand, with annual savings of 34.9% in continuous operation and of 34.7% in intermittent operation. The effect of the green roof was also detected in the second to last floor of the investigated building. The results further highlighted the capability of the green roof to consistently improve the indoor thermal comfort in both winter and summer season.