Green roofs are artificial ecosystems that provide a nature-based solution to environmental challenges such as climate change and the urban heat island. Green roofs aid in the conservation of both ...cooling and heating energy; deposition of particulates and mitigation of air pollution; control of runoff and water pollution; promotion of biodiversity; and provision of aesthetic and health benefits. This research is a holistic review of the green roof literature and provides a global perspective of the subject with a classification of modelling studies; and an extensive review of contributions to energy conservation, carbon sequestration, mitigation of air pollutants, runoff control; and urban noise reduction. The review covers the system's thermal performance modelling through several methodologies; experimental studies; parametric studies to assess the impact of various parameters on the system's energy efficiency using several configuration parameters such as leaf area, foliage height and density, plant coverage, roof insulation, soil thickness, and irrigation; energy benefits; and environmental benefits including air pollutants mitigation, carbon sequestration, runoff control and urban noise reduction. Finally, review was complemented with a life cycle assessment study of green roofs, which examined the extraction of raw materials, manufacturing and construction, transportation, and disposal.
Green roofs can reduce the cooling load by up to 70%, decrease the indoor temperature achieving an indoor air temperature reduction up to 15 °C, and provide a significant improvement of thermal comfort conditions. The environmental benefits of green roofs were focused on decreasing pollutants concentrations (e.g. PM2.5, PM10, O3, NO2), sequestering carbon and reducing urban noise.
•A nature-based approach of green roofs is provided.•A critical perspective as regards green roofs improving urban sustainability is adopted.•Green roof systems may reduce the cooling load up to 70%.•Coupling green roof systems with life cycle assessment.•There is significant potential for energy savings for green roof systems.
Growing and densifying cities set a challenge for preserving and enhancing green spaces to cool urban spaces. Green roofs, involving the planting of vegetation on rooftops, are regarded as an ...alternative approach to enhancing urban greenery and urban cooling. For better cooling performances, it is essential to reasonably configure green roofs, especially in real and complex neighborhoods. Therefore, the aim of this paper is to investigate the impact of morphological characteristics of green roofs on pedestrian cooling in real and complex neighborhoods. In specific, based on an ENVI-met model, we studied the effect of greening layout, coverage ratio, vegetation height, and building height on pedestrian air temperature reduction in the tropical city of Hangzhou, China. Results indicate green roofs could generate moderate effects on pedestrian air temperature reduction (around 0.10⁻0.30 °C), while achieving a cooling performance of 0.82 °C. Green roofs in upwind zones were able to generate the most favorable cooling performance, while green roofs in downwind zones made slight differences to pedestrian thermal environments. Green roofs with a low coverage ratio were not useful for lowering pedestrian temperature, and a greening coverage ratio of 25⁻75% in upwind zones was cost-effective in real neighborhoods. Locations that were horizontally close to green roofs enjoyed better cooling performances. Increasing vegetation height could strengthen cooling effects of green roofs, while an increase in building height weakened the cooling performance. Nevertheless, higher building height could enhance pedestrian cooling performances because of building shading effects. In addition, because of wind effects and building shading, building height limits for the cooling performance of green roofs could be higher than 60 m.
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•An integrated model of EnergyPlus and ENVI-met was employed for this study.•We studied energy saving and cooling potential by different green-roof types.•Both models’ results show a ...good agreement for hourly roof surface temperature.•Lower electricity peak and temperature was found with green-roof types.•The observed lowered energy and temperature varies per urban density and climate.
This paper presents a parametric study on the effect of four green-roof types on outdoor/indoor temperature and cooling demand under four different climates and three urban densities using co-simulation approach with ENVI-met and EnergyPlus. Results reveal an outdoor nighttime warming effect of not more than 0.2°C which is most obvious with the semi-extensive while the outdoor and indoor cooling effect ranges between 0.05–0.6°C and 0.4–1.4°C, respectively depending on the green-roof type, urban density and time of the day. These daytime temperature reductions also vary per prevailing climates and follow this order: hot-dry, hot (or warm)-humid, and temperate which can be explained by the interplay between solar intensity/air temperature and relative humidity between the regions. In a hot-humid region, the evaporative cooling potential of greenery is dampened when compared to hot-dry region. This is also true for region with low solar intensity and humidity like the temperate region. In terms of cooling demand reduction, 5.2% was observed in hot-dry climate on the hottest day of the year with full-intensive green-roof while the least saving of 0.1% was found with semi-extensive green-roof in temperate climate. In general, for both outdoor temperature and cooling demand reduction, semi-intensive green-roof was found more effective than its full-extensive counterpart while the higher spatial green-roof is most important for indoor temperature reduction irrespective of the leaf density of the greenery. Therefore, the intent of green-roof installation should be a determining factor for the type and spatial extent to be implemented.
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•A comprehensive review of 145 research articles on photovoltaic-green roofs was conducted.•The benefits of photovoltaic-green roofs are summarized from six different ...perspectives.•Research challenges and the difficulties of existing research are shown; future research directions are identified.
Photovoltaic (PV)-green roofs, a new development integrating the PV system with a green roof, provide additional benefits for renewable electricity production as compared to the green roof. This study provides a systematic review of the published literature in Scopus and Web of Science regarding PV-green roof technologies, to identify the benefits and challenges associated with PV-green roofs in practice, and its future directions. A total of 145 published documents were reviewed, revealing that the PV-green roof is an effective strategy for producing clean energy on the building scale. However, there are still various challenges that hinder the large-scale implementation of PV-green roofs, including high initial costs, limited experimental data, and lack of awareness about the long-term benefits. These challenges can be overcome through the new cost-effective design of PV-green roofs and the adoption of the most appropriate materials, which can perform more effectively over a longer period. In addition, more real large-scale experimental studies are needed to evaluate the long-term performance of PV-green roofs in urban areas. Suggestions for further improvements include: providing the optimal design of PV-green roofs for each climatic region; improving laws and regulations; evaluating life-cycle assessment including social, environmental, and economic benefits over a longer period; and establishing interagency collaboration and cooperation tools for the wider adoption of PV-green roof projects. This review draws an overall picture of the benefits and limitations of the PV-green roof around the world. Findings provide a useful reference for the enhancement of the PV-green roof design for their broader application in the building industry.
Green infrastructure (GI) strategies, including green roofs, have become a common, decentralized, nature-based strategy for reducing urban runoff and restoring ecosystem services to the urban ...environment. In this study, we examined the water quality of incident rainfall and runoff from a green roof installed on top of the Jacob K. Javits Convention Center in New York City. Since the 2014 installation of this green roof, one of the largest in North America, a colony of nesting herring gulls grew to approximately 100 nesting pairs in 2018 and 150 nesting pairs in 2019. Water quality monitoring took place between September 2018 and October 2019. Except for phosphorus on some occasions, we found concentrations of nitrate, nitrite, chlorine, sulfate to be below federal drinking water standards. Levels of the fecal indicator bacteria (FIB), total coliform, E. coli, and Enterococcus, were consistently higher in runoff samples than rainwater, ranging from 150 to over 20,000 CFU/100 mL for E. coli and 100 to over 140,000 CFU/100 mL for total coliform. Quantitative polymerase chain reaction (qPCR) methods were used to search for potential opportunistic pathogens, including Legionella spp., Mycobacterium spp., Campylobacter spp., and Salmonella spp. Discovery of the presence of Catellicoccus marimammalium, a gull-associated marker in runoff water indicates that herring gulls are the likely source of contamination. Due to habitat loss, herring gulls, and other Larus gull species are increasingly nesting on urban roofs, both green (such as at the Javits Center) and conventional (such as on Rikers and Governors Islands). Habitat creation is one of the target ecosystem services desired from GI systems. Although the discharge from the green roof of the Javits Center is directed to the city's sewer system, this study demonstrates the need to treat runoff from green roofs with nesting gull populations if its intended use involves reuse or human contact.
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•Javits Center green roof runoff met tested chemical US EPA drinking water standards.•High fecal contamination exceeded regulatory limits for various water uses.•Gull presence contributed to fecal contamination on the green roof.•Runoff from gull-populated green roofs may require treatment before use.
The authors regret that some funding information was missing from the Acknowledgements section in their original paper and apologise for any inconvenience caused. The full Acknowledgements are given ...below and the online version of the paper has been updated.
A significant portion of the total primary energy is consumed by today's buildings in developed countries. In many of these buildings, the energy consumption can be significantly reduced by adopting ...energy efficiency strategies. Due to environmental concerns and the high cost of energy in recent years there has been a renewed interest in building energy efficiency. This article strives to make an exhaustive technical review of the building envelope components and respective improvements from an energy efficiency perspective. Different types of energy efficient walls such as Trombe walls, ventilated walls, and glazed walls are discussed. Performance of different fenestration technologies including aerogel, vacuum glazing and frames are presented. Advances in energy efficient roofs including the contemporary green roofs, photovoltaic roofs, radiant-transmittive barrier and evaporative roof cooling systems are discussed. Various types of thermal insulation materials are enumerated along with selection criteria of these materials. The effects of thermal mass and phase change material on building cooling/heating loads and peak loads are discussed. Application of thermal mass as an energy saving method is more effective in places where the outside ambient air temperature differences between the days and nights are high. Air tightness and infiltration of building envelopes are discussed as they play a crucial role in the energy consumption of a building. Energy efficiency approaches sometimes might not require additional capital investment. For example, a holistic energy efficient building design approach can reduce the size of mechanical systems compensating the additional cost of energy efficiency features.
The evapotranspiration process in green roofs: A review Cascone, Stefano; Coma, Julià; Gagliano, Antonio ...
Building and environment,
January 2019, 2019-01-00, 20190101, 2019-01-01, Volume:
147
Journal Article, Publication
Peer reviewed
Open access
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.
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•Nature-based solutions (NBS) are a viable option for greywater (GW) treatment.•Review of case studies provided numerical thresholds for hydraulic design of NBS.•Life cycle assessment ...studies demonstrated the benefits of NBS for GW treatment.
Recognizing greywater as a relevant secondary source of water and nutrients represents an important chance for the sustainable management of water resource. In the last two decades, many studies analysed the environmental, economic, and energetic benefits of the reuse of greywater treated by nature-based solutions (NBS). This work reviews existing case studies of traditional constructed wetlands and new integrated technologies (e.g., green roofs and green walls) for greywater treatment and reuse, with a specific focus on their treatment performance as a function of hydraulic operating parameters. The aim of this work is to understand if the application of NBS can represent a valid alternative to conventional treatment technologies, providing quantitative indications for their design. Specifically, indications concerning threshold values of hydraulic design parameters to guarantee high removal performance are suggested. Finally, the existing literature on life cycle analysis of NBS for greywater treatment has been examined, confirming the provided environmental benefits.
•Collembolan communities on 15 green roofs have been investigated in the Paris region (France).•Extensive and productive green roofs exhibited the same taxonomic diversity.•Compost inputs lead to ...higher abundances of euedaphic collembolan on productive green roofs.•Wind dispersal is a probable way of Collembola settlement.
Green roofs, especially productive ones (e.g. of edible biomass), are urban ecosystems developed in response to the scarcity of arable areas in urban environments. Their installation is also perceived as a possible way to preserve biodiversity in cities. However, the effectiveness of green roofs in supporting biodiversity, especially soil biodiversity, has rarely been studied. In order to orient the ecological engineering of green roofs, it is crucial to understand the resulting biodiversity patterns. We hypothesised that a functional trait-based approach could be used to investigate different ways of colonisation. We investigated collembolan communities in both extensive and productive green roofs. Surprisingly, no difference was observed in either taxonomic or functional structures of collembolan diversity between extensive and productive green roofs. Conversely, according to the functional composition, two ways of colonisation are suggested: a passive wind dispersal − the “flying” collembolans − and a settlement through compost inputs. We conclude that stakeholders should take into account the spatial connections of green roofs with other green spaces in order to support soil biodiversity. Further studies are needed to more accurately elucidate the importance of green roof types for collembolan communities and associated ecological networks.
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