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A hygrothermal model of green walls and a model of mass flows in street canyons have been proposed and implemented in a building simulation program (TRNSYS). The coupled models allow the study of the hygrothermal interaction of green walls at the interface of the detailed building model and the urban microclimate of the street. Its use highlights the effects on both urban microclimate and buildings energy loads, especially in the summer period. While reducing anthropogenic heat release, green walls set up on west or east façades mitigate the street air temperature and reduce building cooling loads depending on streets’ aspect ratio. Some of the canyon model parameters were calibrated through numerical comparison with experimental data on a reduced scale mockup. This mockup has been designed specifically to assess the green walls hygrothermal impact and to evaluate the developed numerical tools. This experimental calibration made simulating the green walls interactions with street canyons of different aspect ratios possible. The experimental and numerical results obtained with green façades underline the advantage of this modeling approach for the design of passive cooling for buildings and mitigation of excessive thermal conditions within street canyons in dense cities in warm climates. [ABSTRACT FROM AUTHOR]

Since some years, dense cities and compact buildings are promoted as sustainable and energy efficient designs. Nevertheless, urban planning strategies should take into account the interactions between buildings and the microclimate because the Urban Heat Island (UHI) phenomenon can increase the cooling load of buildings and is strongly influenced by urban morphology, urban landscaping and the thermal properties of buildings and soil. The modification of these parameters, such as building density, can mitigate UHI, with direct and indirect improvement of building energy performances. The case study presented in this paper concerns a new district in La Rochelle (France) named Atlantech. Currently at the design stage, the goal is to transform this old military camp into a zero carbon district. This study was performed in parallel with urban planning using EnviBatE and SOLENE-Microclimate simulation. Two building densities are compared through the impacts on solar irradiance, wind airflows, building indoor temperatures and energy demand. Analysis of reference and densified district highlights various impacts such as the wind velocity decrease, up to 80%, and the effect on an existing nearby building solar irradiation, reduced by 7%. These results underline the potential usefulness of these simulation tools for urban planners at the design stage. [ABSTRACT FROM AUTHOR]

This study carried out in late 2013 for the French Ministry of Ecology, Sustainable Development and Energy (MEDDE), aims primarily to make a situational analysis of the awareness and consideration level of the UHI constraints, by organizations that influence on the location and the design of building hosting sensitive people to high temperature (nursery, retirement homes). This assessment was performed by a national survey which was conducted in 10 French cities which are likely to be affected by the phenomenon of UHI, among 75 local stakeholders who were likely to be involved in the choice of construction or location of this kind of establishment. The UHI mitigation and adaptation practices applied in each city have also been analyzed. These practices are mainly vegetation (green spaces, green screens and roofs) and specific coatings on facades and roofs (variation of radiative properties by using different colors and materials). Among the other main conclusions of this investigation, it appears that only 11% of the total panel questioned considers UHI in decisions and only 17% of the influential stakeholders believe that there has been an evolution in their decision making since the introduction of the PNACC plan in France. These most influential stakeholders in the decision-making process are the designers (prime contracting: thermal and design engineering, architect, etc.). To complete this study, some operational suggestions are proposed to improve the consideration of UHI constraints in decision process, concerning the implementation or the refurbishment of the targeted building. [ABSTRACT FROM AUTHOR]

This paper presents the design and the results of a reduced-scale experimental bench to study the effect of green roofs and green facades on local urban microclimate. An analysis of experimental data was carried out on three street canyons: one reference street, one street between two buildings with green roofs and one with a green wall to the west. The results show a hygrothermal effect of green envelopes on buildings on urban heat island mitigation. In the detailed analysis of these green coating techniques, we highlighted that green facades modify strongly the radiative balance of the street and improve the hygrothermal comfort in urban canyons through reducing the overheating in the street in hot summer days. [ABSTRACT FROM PUBLISHER]

Abstract: Energy performance of air conditioned buildings and summer comfort can be improved with high solar reflectance and high emittance of building envelopes. Widely used for roofs, this technique known as cool roof, has a direct impact on the external surface temperatures peaks which reduces both heat transfer to the building and to the environment. In this paper, this technique used with façades is experimented in a confined environment similar to a typical urban scene. This reduced-scale of 4 street canyon rows is designed in order to give realistic measurements of thermal confinement. Then, the temperatures of a street canyon with brown cool selective paint façades are compared with a standard brown coating on another street façades, and with an asymmetrical configuration. The analysis of thermal effects on both buildings and outdoor environments gives interesting prospects for urban heat island mitigation. [Copyright &y& Elsevier]

We developed and studied key performance indexes and representations of energy simulation heat fluxes to evaluate the performance of the evaporative cooling process as a passive cooling technique for a commercial building typology. These performance indexes, related to indoor thermal comfort, energy consumption and their interactions with their surrounding environments, contribute to understanding the interactions between the urban climate and building for passive cooling integration. We compare the performance indexes for current and future climates (2080), according to the highest emission scenario A2 of the Special Report on Emission Scenario (SRES). Specific building models were adapted with both green roof and wetted roof techniques. The results show that summer thermal discomfort will increase due to climate change and could become as problematic as winter thermal discomfort in a temperate climate. Thanks to evapotranspiration phenomena, the sensible heat contribution of the building to the urban heat island (UHI) is reduced for both current and future climates with a green roof. The performance of the vegetative roof is related to the water content of the substrate. For wetted roofs, the impacts on heat transferred to the surrounding environment are higher for a Mediterranean climate (Marseille), which is warmer and drier than the Paris climate studied (current and future climates). The impact on indoor thermal comfort depends on building insulation, as demonstrated by parametric studies, with higher effects for wetted roofs. [ABSTRACT FROM AUTHOR]

In this paper, we propose a practical approach for decision-making regarding passive cooling design for buildings in dense urban contexts. For non-cooled buildings under temperate climates, assessment of summer thermal discomfort determines the usual passive cooling design together with fossil energy and GHG savings at earth scale. However, passive cooling techniques for indoor climate can be also valuable for local environment impacts, especially urban heat islands’ mitigation. Lack of simple representative criteria and complexity of simulation outputs constitute a barrier for the development of passive cooling. Based on a study of a generic commercial building, we analyzed several designs with Sankey diagram and we developed two performance indexes. This chart synthesis of complex output data allows a direct comparison of design solutions. This analysis gives hints for better designer understanding of urban climate and building interactions for the studied passive cooling solutions: cool roofing, nocturnal natural ventilation and rooftop PV system as shading device. Our results show that nocturnal natural ventilation is efficient to moderate indoor overheating compared to the "cool roof". In addition, cool roofs reduce anthropogenic heat transferred to urban environment. PV panels as shading device mitigate summer discomfort and produce energy that increase building energy efficiency through the year. We defined two Key Performance Indexes (KPIs) to define cooling potential of both indoor and urban environment. These KPIs obtained for different temperate climates highlight new prospects for the design of efficient urban designs with controlled environmental impacts and decision process of stakeholders. [ABSTRACT FROM AUTHOR]