LAI based trees selection for mid latitude urban developments: A microclimatic study in Cairo, Egypt

To study the leaf area index, LAI, based thermal performance in distinguishing trees for Cairo's urban developments, ENVI-met plants database was used as platform for a foliage modeling parameter, the leaf area density, LAD. Two Egyptian trees: Ficus elastica. and Peltophorum pterocarpum were simulated in 2 urban sites with one having no trees, whilst the second is having Ficus nitida trees. Trees LAD values were calculated using flat leaves' trees LAI definition to produce maximum ground solid shadow at peak time. An empirical value of 1 for LAI is applied to numerically introduce LAD values for ENVI-met. Basically, different meteorological records showed improvements for pedestrian comfort and ambient microclimate of the building using E elastica. About 40-50% interception of direct radiation, reductions in surfaces' fluxes around trees and in radiant temperature T-mrt in comparison to base cases gave preferability to E elastica. The lack of soil water prevented evapotranspiration to take place effectively and the reduced wind speeds concluded negligible air temperature differences from both base cases except slightly appeared with the F elastica. Results show that a flat leaves tree if does not validate LAI of 1, the ground shading would not fulfill about 50% direct radiation interception and this value can be used as a reference for urban trees selection. Further simulations were held to investigate LAI value of maximum direct radiation interception. Performing additional simulations, F elastica of LAI of 3 intercepted almost 84% of direct radiation and revealed implications about urban trees in practice and its actual LAI. (C) 2009 Elsevier Ltd. All rights reserved

Effects of street design on outdoor thermal comfort

The paper deals with the dependence of outdoor thermal comfort on street design with emphasis on summer conditions in hot and dry climate. The effects of the height-to-width ratio (H/W) and street orientation, the asymmetry of the vertical profile, the use of galleries, overhanging facades, as well as the use of rows of trees were investigated. The study was conducted by means of the three dimensional model ENVI-met, which simulates the microclimatic changes within urban environments in a high spatial and temporal resolution. Thermal comfort is assessed by means of the physiologically equivalent temperature PET. The results reveal that the vertical profile and orientation of the urban canyon have a decisive impact on the human thermal sensation at street level, as well as all other design details studied. This is mostly because affecting the sun exposure and so the heat gained by a human body. Shading appeared as the most important condition of comfort in the summertime, which can be reached by an appropriate combination of all those urban design describers

A multi-dimensional energy-based analysis of neighbourhood sustainability assessment tools: are institutional indicators really missing?

Neighbourhood Sustainability Assessment Tools (NSATs) have become the modern day template for urban planners to achieve sustainable development in their communities, districts and cities. The popularity of the pioneering NSATs led to the creation of other tools in different regions. Also, with the popularity and replication of these tools came the replication of their limitations. The most notable limitation and motivation for this study is the inadequate recognition of the complexities of institutional dimensions (i.e. policies, laws and regulation) that contribute to mainstreaming and operationalising sustainable neighbourhood development. Studies that have investigated NSATs generally argue lack of coverage of the institutional dimension. However, there has been little consistent and explicit mention of the precise indicators and criteria sought out to make this claim. Also, there is a clear confusion as to what institutional indicators actually are, what characteristics they possess and how best they can be identified. This study, via the lens of energy-based indicators, expands on the role of the institutional indicator and its associated dimensions. This study also utilises a multi-dimensional approach to indicator analysis and draws out current trend or characteristics of institutional indicators in 15 currently existing NSATs. The results show a limited view on the classification of institutional indicators. The study also demonstrates that there are more institutional indicators than previously reported in prior studies. Additionally, this study confirms that an institutional indicator cannot be a single entity or identity but rather it must operate under the linkage of the other dimensions (environment, social and economic). Finally, this study, based on the analysis of 15 NSATs provides a definition of what can be considered an institutional indicator. In conclusion, it is recommended that future development of NSATs should ensure a constant institutional link to indicators, as this could provide an enhanced alternative to the development of NSATs, particularly for regions that are looking into developing their own assessment tools

Numerical evaluation of thermal comfort in traditional courtyards to develop new microclimate design in a hot and dry climate

The growing interest in thermal comfort of outdoor environments yields in different analysis on courtyards as a common space between urban and architectural scales. However, there is a limited knowledge regarding the microclimatic behavior of such spaces. Using ENVI-met simulations, this paper aims to numerically discuss the thermal performance of different configurations of traditionally designed courtyards in Shiraz, Iran, which experiences hot summers and cold winters. The geometrical effects such as orientation and H/W (height to width ratio) of courtyards are considered as potential parameters to improve the microclimatic conditions. In this paper, PMV and UTCI are used as thermal comfort indices. The obtained results indicate mean radiant temperature and wind speed as the most effective parameters for thermal comfort of courtyards. In addition, the aforementioned geometrical parameters might not be able to solely create a desirable condition, but they could significantly improve the thermal comfort of courtyards during summer and winter. To achieve a desirable thermal comfort level, the results suggest using configurations of a high H/W rate and southward orientation in order to obtain better shading during summer as well as allowing the solar radiation in while regulating the wind speed in winter

Evaluating the Efficacy of BREEAM Code for Sustainable Homes (CSH): A Cross-sectional Study

AbstractThere is now a substantial body of evidence suggesting that climate change is occurring as a result of human activities. Bottom-up approaches have been encouraged to enhance sustainability agenda. Assessment methods have been developed to ensure an incessant decrease in carbon footprint of buildings. It has long been discussed that many of such assessment methods systematically lack dedicated criteria to assess building beyond its physical boundaries. This paper focuses on Code for Sustainable Homes (CSH) and attempts to map it against LEED and CASBEE with an aim to encourage assessment beyond physical boundaries of a building and into its immediate context and surrounding environment. A critical review of the latest literature was conducted to establish the general concepts and principles behind the CSH's method of assessment in comparison with CASBEE and LEED. Following this, differences, positive and negative aspects of the three assessment method were established through in-depth review of their official documents and by cross-referencing the different components, methodologies and assessment criteria of each. This led to a comparative analysis using a critical evaluation of findings of The Building Environmental Quality Evaluation for Sustainability through Time (BEQUEST), The European Sustainable Development Strategy (ESDS) and The Freiburg Charter (FC). Expert interviews were conducted to consolidate the findings of this study. This added technical in-depth expert opinions to the preliminary findings of this research and helped pave the way for providing practical suggestions for possible areas of improvement for the CSH

The impact of increasing urban surface albedo on outdoor summer thermal comfort within a university campus

The impact of increasing urban surface albedo on outdoor thermal comfort was studied in two phases: Firstly, the thermal conditions of three locations with different ground surface materials were compared. The study used CFD modelling followed by a measurement campaign to validate the control simulation. It was observed that the physiological equivalent temperature (PET as the outdoor thermal comfort index) in the campus park (covered with grass) was 11.0 °C lower than the parking lot (paved with concrete) at 16:00 CET. As the next step, the albedo of the roofs and walls were increased from 0.2 (control) to 0.3, 0.4, 0.5 and 0.6. It was found that increasing the albedo made the open space of the courtyard uncomfortable due to the higher reflectivity of high-albedo materials. An increase of every 0.1 albedo of the surfaces led to 1.2 °C higher mean radiant temperature, and consequently, 0.8 °C higher PET. The study also showed that the increase of albedo radiated more sun to the ground surface. This increased average ground surface sensible heat flux (6.7 W/m2) and surface temperature (0.4 °C) during the day. This finding shows that the position and orientation of high albedo materials can significantly affect pedestrians' thermal comfort in urban open spaces