Seasonal and Diurnal Thermal Performance of a Subtropical Extensive Green Roof: The Impacts of Background Weather Parameters

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Substrate moisture effect on water balance and thermal regime of a tropical extensive green roof

Green-roof thermal and hydrological performance has been extensively studied, but the specific effect of substrate moisture has received little attention. This study investigates the substrate moisture effect on evapotranspiration (ET), water balance and subaerial and subsurface temperatures of an extensive tropical green roof. Firstly, three weather types (sunny, cloudy and rainy) in conjunction with three substrate moisture states (wet, moist and dry) generate nine permutations for a scenario analysis. Secondly, the correlation analysis explores the relationship between substrate moisture and thermal performance indicators. The major finding is that substrate moisture is effective in regulating substrate thermal behavior, but less so in enhancing ET and associated cooling. Substrate moisture can notably cool the soil, rockwool and concrete tile on sunny days, and warm them on cloudy and rainy days. In contrast, substrate moisture has limited effect on ET, which is largely dependent on solar radiation, relative humidity and wind speed. The dry substrate on sunny day demonstrates an aberrant behavior of high ET which contradicts with previous studies. This unusual phenomenon is explained by the limited substrate mass effect of the thin extensive green roof. The vegetation surface and air temperatures show little variations between different soil moisture states, and their correlations with substrate moisture are insignificant. The findings could provide an additional substrate moisture dimension to enhance the design and management of green roofs with reference to water and thermal behavior. © 2012 Elsevier B.V.link_to_subscribed_fulltex

Weather effect on thermal and energy performance of an extensive tropical green roof

This study investigated the weather effect on thermal performance of a retrofitted extensive green roof on a railway station in humid-subtropical Hong Kong. Absolute and relative (reduction magnitude) ambient and surface temperatures recorded for two years were compared amongst antecedent bare roof, green roof, and control bare roof. The impacts of solar radiation, relative humidity, soil moisture and wind speed were explored. The holistic green-roof effect reduced daily maximum tile surface temperature by 5.2°C and air temperature at 10cm height by 0.7°C, with no significant effect at 160cm. Green-roof passive cooling was enhanced by high solar radiation and low relative humidity typical of sunny summer days. High soil moisture supplemented by irrigation lowered air and vegetation surface temperature, and dampened diurnal temperature fluctuations. High wind speed increased evapotranspiration cooling of green roof, but concurrently cooled bare roof. Heat flux through green roof was also weather-dependent, with less heat gain and more heat loss on sunny days, but notable decline in both attributes on cloudy days. On rainy days, green roof assumed the energy conservation role with slight increase instead of reduction in cooling load. Daily cooling load was 0.9kWhm -2 and 0.57kWhm -2, respectively for sunny and cloudy summer days, with negligible effect on rainy days. The 484m 2 green roof brought potential air-conditioning energy saving of 2.80×10 4kWh each summer, equivalent to electricity tariff saving of HK$2.56×10 4 and upstream avoidance of CO 2 emission of 27.02t at the power plant. The long-term environmental and energy benefits could justify the cost of green roof installation on public buildings. © 2011 Elsevier GmbH.link_to_subscribed_fulltex

Environmental, health and equity effects of urban green space interventions

As populations become increasingly urbanised, the preservation of urban green space becomes paramount. Despite the potential from cross-sectional evidence, we know little about how to design new, or improve or promote existing, urban green space for environmental, health and well-being benefits. This chapter highlights aspects to be considered when designing and evaluating urban green space interventions that aim to maximize environmental, social and health benefits, and address equity issues. Based on a review of international research evidence and a compilation of European case studies, the chapter addresses the variety of green space intervention approaches and their related impacts. There was strong evidence to support park-based and greenway/trail interventions employing a dual-approach (i.e. a physical change to the urban green space and promotion/marketing programmes particularly for park use and physical activity); strong evidence for the greening of vacant lots for health, well-being (e.g. reduction in stress) and social (e.g. reduction in crime) outcomes; strong evidence for the provision of urban street trees and green infrastructure for storm water management for environmental outcomes (e.g. increased biodiversity, reduced air pollution, climate change adaptation). Urban green space has an important role to play in creating a culture of health and well-being. Results show promising evidence to support the use of certain urban green space interventions for health, social and environmental benefits. The findings have important implications for policymakers, practitioners and researchers

The valuation of public and private benefits of green roof retrofit in different climate conditions

Green roofs represent a suitable option for industrial buildings refurbishment, providing private and social benefits. Nowadays, in Italy green roof technology is still uncommon, because of high installation cost that drives the choice towards more traditional performing solutions, such as cool roofs (CRs). Thus, a thorough valuation of green roofs benefits in urban contexts is required to encourage their diffusion. This paper aims to valuate private and social costs and benefits generated by extensive green roofs (EGRs) compared with cool roofs in three Italian cities: Trieste, Ancona and Palermo. These contexts are characterized by different Mediterranean climate conditions (North, Centre and South Italy); moreover, residential areas overlooking industrial settlements take place in each of them, so it is possible to hypothesize a potential enhancement of landscape value in these properties, allowing to compare aesthetic benefits due to green roofs upon industrial buildings. The study has been based on literature review and on simulation of energy performances of EGR and CR alternatively considered as refurbishment solution for a reference industrial building taking place in each industrial settlement. For the social side, the externalities deriving from EGRs and CRs, such as aesthetic enhancement, biodiversity preservation and natural habitat provision, carbon reduction, air quality improvement, stormwater control, have been monetized according to available data for the cases of study. The analysis demonstrates that a private investor has a poor convenience to implement EGR rather than CR. On the other, a positive Net Present Value (NPV) derives from social cost-benefit analysis comparing EGR and CR, due to the EGR positive externalities. The valuation of the positive externalities let the calculation of economic incentives amount to promote the diffusion of green roofs in the Mediterranean area. On this basis, an annual reduction of local property tax has been considered as incentive form. Further, a sensitivity analysis with Monte Carlo simulation of both private and social benefits evaluation has been performed for each of three case studies. This technique properly evaluates the final effects on private investments in the presence of random unpredictable variables, depending either on climate conditions or on market observation, that influence their economic affordability. Finally, through the comparison of the three contexts, an overall discussion about of the influence of climate and urban conditions on the economic analysis has been conducte