Thermal performance and energy savings of white and sedum-tray garden roof: A case study in a Chongqing office building

This study presents the experimental measurement of the energy consumption of three top-floor air-conditioned rooms in a typical office building in Chongqing, which is a mountainous city in the hot-summer and cold-winter zone of China, to examine the energy performance of white and sedum-tray garden roofs. The energy consumption of the three rooms was measured from September 2014 to September 2015 by monitoring the energy performance (temperature distributions of the roofs, evaporation, heat fluxes, and energy consumption) and indoor air temperature. The rooms had the same construction and appliances, except that one roof top was black, one was white, and one had a sedum-tray garden roof. This study references the International Performance Measurement and Verification Protocol (IPMVP) to calculate and compare the energy savings of the three kinds of roofs. The results indicate that the energy savings ratios of the rooms with the sedum-tray garden roof and with the white roof were 25.0% and 20.5%, respectively, as compared with the black-roofed room, in the summer; by contrast, the energy savings ratios were −9.9% and −2.7%, respectively, in the winter. Furthermore, Annual conditioning energy savings of white roof (3.9 kWh/m2) were 1.6 times the energy savings for the sedum-tray garden roof. It is evident that white roof is a preferable choice for office buildings in Chongqing. Additionally, The white roof had a reflectance of 0.58 after natural aging owing to the serious air pollution worsened its thermal performance, and the energy savings reduced by 0.033 kWh/m2·d. Evaporation was also identified to have a significant effect on the energy savings of the sedum-tray garden roof

Climate Mitigation and Adaptation Strategies for Roofs and Pavements. A Case Study at Sapienza University Campus

The progressively emerging concept of urban resilience to climate change highlights the importance of mitigation and adaptation measures, and the need to integrate urban climatology in the design process, in order to better understand the multiple effects of combined green and cool technologies for the transition to climate responsive and thermally comfortable urban open spaces. This study focuses the attention on selected mitigation and adaptation technologies; two renovation scenarios were designed and modeled according to the minimal intervention criterion. The study pays attention to the effect on surface temperature and physiological equivalent temperature (PET) of vegetation and high albedo materials characterizing the horizontal boundaries of the site. The Sapienza University campus, a historical site in Rome, is taken as a case study. These results highlight the importance of treed open spaces and the combination of permeable green pavements associated with cool roofs as the most effective strategy for the mitigation of summer heatwaves and the improvement of outdoor thermal comfort

uhi effects and strategies to improve outdoor thermal comfort in dense and old neighbourhoods

Abstract Modelling techniques have received growing attention as a tool to investigate the thermal comfort within a city, on the basis of which decision makers can set-up appropriate mitigation strategies. This research aims at studying the effectiveness of strategies for reducing the urban heat island-associated effects in dense and old neighborhoods considering, in particular, green roofs, cool roofs, cool pavements, green areas and urban renewal actions. Computer simulation was selected as the major methodology in this research; ENVI-met software was used under different scenarios for a case study consisting in an old neighborhood in the city of Avola. The investigation focused on evaluating the efficacy of each strategy for a condition corresponding to a typical summer heat wave. The results highlight that the cool pavements allow relevant improvements at the height of 1.50 m, with a temperature decrease up 1.15°C, whereas the other scenarios, given the relatively high density of the buildings, are able to improve outdoor conditions only at higher elevations. Reported results represent a guideline for the choice of UHI mitigation method that can help stakeholders involved in new urban assessment of old neighborhoods in Mediterranean climate

Effectiveness of Green Roofs and Green Walls on Energy Consumption and Indoor Comfort in Arid Climates

Increased urbanization have many negative effects on human well-being, city infrastructure, electricity usage and the increase of indoor temperatures. A solution may be to retrofit existing buildings, with implementing a vegetated layer to roofs and walls, this may enhance building performance, reduce consumption and improve indoor comfort. Cities with tall buildings may be more adequate to implement a green-wall as it have more area to make impact. This paper examines the energy reduction advantages of adding greenery on buildings in the hot arid climate of Egypt by considering three typical types of residential buildings in the city of Cairo as a case study. Designbuilder software was selected to stimulate the buildings chosen in this research. The results shows that an extensive soil thickness of 15cm performs better in the arid climates. electricity consumption for the base case is 52 kWh/m2 annually when used a traditional external envelop and dropped to 43 kWh/m2 when a vegetated layer added to the whole building (roof & wall), annual electricity consumption reduced by 17% to 25% per annum when added a vegetated layer. In addition to enhancing the indoor thermal comfort by 3 PMV values and indoor air temperature by 5°C

The evapotranspiration process in green roofs: a review

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.This work is partially funded by the Spanish governmentENE2015-64117-C5-1-R (MINECO/FEDER). The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2017 SGR 1537). GREiA is certified agent TECNIO in the category of technology developers by the Government of Catalonia. Julià Coma would like to thank Ministerio de Economia y Competitividad de España for the Grant Juan de la Cierva, FJCI-2016-30345. This research is also funded by “the Notice 5/2016 for financing the Ph.D. regional grant in Sicily” as part of the Operational Programme of European Social Funding 2014–2020 (PO FSE 2014–2020)

Multifunctional vegetated wall for thermal insulation and gray water treatment of buildings

People are beginning to understand sustainable natural solutions in the last several decades to reduce floods and temperature in metropolitan areas, which have been rising owing to many factors like urbanisation and climate change.The population of cities has been growing as a result of fast urbanisation, which has also caused an increase in buildings and other man-made structures, which has contributed to an increase in urban heat. Recently, multifunctional walls and roofs have gained popularity as a means of combating urban heat and flood mitigation. Grey water is regarded as one type of wastewater and is the waste water produced by showers, kitchen sinks, and washing machines in residential, commercial, and industrial settings. Untreated wastewater discharge into the ecosystem has many negative repercussions, and grey water treatment is on the rise. The creation, analysis, and optimization of a model are the main topics of this study in order to enhance the functioning of a multifunctional vegetated wall.Incomin

Effect of vegetation biomass structure on thermal performance of tropical green roof

The passive cooling effect of green roofs in humid, tropical Hong Kong was investigated with reference to three vegetated plots, grass, groundcover herb, and shrub, with contrasting growth form and biomass structure and a bare control plot. Temperature was monitored at 15-min intervals for a year at seven levels: high (H) at 200 cm, middle (M) at 60 cm, low (L) at 20 cm, surface, soil, rockwool (water storage), and roof-tile surface. The findings indicated the crucial roles played by biomass quantity and structural complexity in passive cooling functions. Temperature variations of vegetated roofs occurred mainly during the day, with lower maximum and minimum than the control, but they did not cool air at night better than the control. Control and grass surfaces were warmed above the ambient temperature, but groundcover and shrub surfaces followed the ambient. Despite complex biomass structure, shrub created the most extreme diurnal air temperature regime. Despite simple biomass structure, grass cooled air more effectively than groundcover and shrub. Four anomalies in the vertical temperature profile were detected. First, the grass roof cooled daytime near-ground air to create a suspended temperature inversion. Second, the stagnant air within the shrub biomass trapped heat to generate a daytime canopy temperature inversion. Third, the elevated branch-foliage biomass of groundcover and shrub brought passive cooling to form a perched thermal discontinuity. Fourth, the air gap of the plastic drainage layer arrested downward heat transmission in all vegetated plots to form a subsurface thermal discontinuity. The findings provide hints on species choice and design of green roofs. © 2011 The Author(s).published_or_final_versionSpringer Open Choice, 21 Feb 201

Evaluating the Hydrologic and Thermal Performance of a Green Roof in Syracuse: Measurements and Modeling of a Full-Scale System

Climate change and urbanization have increased the risk of flooding and combined sewer overflows as well as other stormwater related problems. Given the high costs of traditional infrastructure rehabilitation, green infrastructure, which mimics natural systems, has become a popular solution. Green roofs are one prominent example of green infrastructure. These are engineered vegetative systems positioned on the top of roof structures have been widely adopted around the world, owing to an abundance of roof area in urban neighborhoods. However, their hydrologic performance and thermal properties are unclear, due to a lack of qualitative and quantitative analyses on monitored full-scale green roofs. In particular, few studies have focused on factors that impact the hydrologic performance of green roofs, such as soil properties which change as the roof ages, and evapotranspiration (ET) which dries the soil and enables the green roof to store water from the next storm. Understanding water exchange on a green roof also requires investigation into the thermal properties of the system. To quantify thermal impacts, field measurements and a model that couples energy with soil moisture would be of value. My study aims to fill these gaps by advancing understanding of green roof behavior, including the aging effect of soil media, ET, and heat transfer, and by developing methods to predict the hydrologic performance and related thermal properties of green roofs. In this research, rainfall, runoff, soil moisture content, and meteorological data have been measured in a green roof system at the Onondaga County Convention Center in Syracuse, NY (OnCenter) since 2015. This study included controlled laboratory experiments for soil characterization, monitoring the OnCenter green roof under a variety of weather conditions, and use of computer modeling to predict green roof performance. In the first phase of the study, in which I investigated the effects of aging on green roof functions, virgin and 7-year-old growth media were characterized and the impact of the observed changes on hydrologic performance was assessed. Differences in structure (particle size distribution, porosity, organic content, density) and some hydrologic properties were observed. The aged growth medium experienced a shift to finer particles and smaller pores with a 60% increase in the organic content. An increase in water filled porosity indicated more water can be stored in aged growth medium than in the original medium. The observed aging effects on hydrologic performance were modelled using HYDRUS-1D. Five 24-hour design storms were applied to predict the retention and detention performance. A 4% improvement in retention performance was calculated for 7-year-old growth medium for significant storms over the original medium. Runoff was detected around an hour later in simulations in aged growth medium compared to original medium. Better retention and detention performance of the green roof was suggested from both monitored data and simulated data from HYDRUS-1D. The second phase of the study focused on evapotranspiration (ET), a vital component of the water balance and also an important term in the soil surface energy balance of green roofs. Quantifying ET for green roofs helps quantify the thermal and hydrologic benefits of green roof systems, enabling informed design and installation decisions. In this work, a soil water balance method was applied to quantify ET using continuous field monitoring for the period May through November during 2015, 2016, and 2017. Results show daily ET ranged from 0 to 5.4 mm/day with an average of 0.76 mm/day. No clear seasonal variation of ET in the seven-month period was observed. The ET rate was significantly influenced by initial soil moisture content and solar radiation. The ET measurements were also compared to fourteen potential ET models together with soil moisture extraction functions (SMEF), the Thornthwaite-Mather (T-M) equation, and antecedent precipitation index (API). The crop coefficient (Kc) was obtained through backward least squares optimization. When soil moisture data are available, the Blaney-Criddle model and the Priestley-Taylor model together with SMEF and monthly Kc values are recommended for predicting ET for the northeastern U.S. due to their limited data input requirements. When soil moisture data are not available, the modified API model with monthly Kc is recommended. In the third phase of the study, the focus shifted to energy storage and transfer. Green roofs have the potential to improve thermal performance of building systems through evapotranspiration, thermal mass, insulation and shading, thus decreasing the cooling energy consumption in summer. A combined energy and moisture model for the retrofit green roof at the OnCenter was developed in CHAMPS software with a hourly time step. Reasonable agreement was observed between the simulated output and monitored data. From the simulated data, the green roof demonstrated the ability to significantly reduce the temperature fluctuations of the roof membrane. In summer, the green roof moderated the heat flow through the roofing system and reduced the air conditioning cost. In winter, under the accumulation of snow, the protection provided by the growth medium was negligible compared with the protection provided by the snow. The temperature of the growth medium on the Convention Center remained slightly above freezing and was relatively steady when heavy snow coverage was present, even during extremely cold air temperatures. Heat flux is dominated by the temperature gradient between interior space and the snow layer. Overall, this research provides valuable understanding on the hydrologic and thermal behavior of green roofs, especially extending knowledge of the effect of soil aging, quantification of the ET process, and prediction of energy flows. The methods and results in this study are valuable for informing future green roof design, planning, retrofit, maintenance, and policy decision making

Roof-Integrated Green Technologies, Energy Saving and Outdoor Thermal Comfort: Insights from a Case Study in Urban Environment

Green urban infrastructures have a significant impact on urban climate mitigation, on indoor and outdoor thermal comfort and on energy performance of buildings. In this paper, outdoor thermal comfort conditions and energy saving for space heating and cooling were investigated before and after the use of roof-integrated green technologies. Existing urban energy and climate models and tools were applied to an urban area located in a Turin (Italy). CitySim, ENVI-met and SOLWEIG tools and a GIS-based model were used to evaluate the mean radiant temperature and the thermal comfort of outdoor spaces before and after the use of vegetated roofs and green surfaces such as the predicted mean vote (PMV), the physiological equivalent temperature (PET) and the universal thermal climate index (UTCI). A GIS-based engineering model and CitySim tool were used to evaluate the energy saving and energy independence index for space heating and cooling after the use of green roofs and solar technologies. According to the shape and the suitability of rooftop elaborated with GIS tools, some roofs were identified as potential green roofs other as potential solar roofs for installing solar thermal collectors and photovoltaic panels. According to the results it is possible to confirm that the use of green roofs and urban greenery can decrease the mean radiant temperature until about 10℃ during summer season, improving outdoor thermal comfort conditions and energy savings with a reduction of 12% for space cooling energy consumption