Influence of urban geometry on outdoor thermal comfort in a hot dry climate: A study in Fez,Morocco

There are few studies on the microclimate and human comfort of urban areas in hot dry climates. This study investigates the influence of urban geometry on outdoor thermal comfort by comparing an extremely deep and a shallow street canyon in Fez, Morocco. Continuous measurements during the hot summer and cool winter seasons show that, by day, the deep canyon was considerably cooler than the shallow one. In summer, the maximum difference was on average 6 K and as great as 10 K during the hottest days. Assessment of thermal comfort using the PET index suggests that, in summer, the deep canyon is fairly comfortable whereas the shallow is extremely uncomfortable. However, during winter, the shallow canyon is the more comfortable as solar access is possible. The results indicate that, in hot dry climates a compact urban design with very deep canyons is preferable. However, if there is a cold season as in Fez, the urban design should include some wider streets or open spaces or both to provide solar access.     

Evaluation of effects of windows installed with near-infrared rays retro-reflective film on thermal environment in outdoor spaces using CFD analysis coupled with radiant computation

Recently, windows with low-e double-glazing or heat-shading films often have been installed to the exterior surfaces of buildings to reduce the cooling load of the buildings. These windows specularly reflect solar radiation into pedestrian spaces. It has been pointed out that the increase in the incident solar radiation reflected at the windows degrades the thermal comfort levels of pedestrians. The installation of near-infrared rays retro-reflective film to window surfaces may both reduce the cooling load of the building and reduce the impacts on the thermal environment in outdoor spaces. Hence, it is expected that the installation of this film will counteract this problem and have positive effects. To assess the feasibility of installing retro-reflective materials to the exterior surfaces of the building walls and ground forming part of a city block, for improving the thermal environment in outdoor spaces, computational methods could serve as a powerful tool for analyzing the radiant environment in urban and building spaces. In this paper, a computational method is outlined for considering the directional reflections from the exterior surfaces of building walls and windows. The method is used to estimate the effects on the outdoor thermal comfort of pedestrians in the summer season.     

Pedestrian level winds and outdoor human comfort

Outdoor human comfort in an urban climate may be affected by a wide range of parameters, including wind speed, air temperature, relative humidity, solar radiation, air quality, human activity, clothing level, age, etc. Several criteria have been developed in the wind engineering community for evaluating only the wind-induced mechanical forces on the human body and the resulting pedestrian comfort and safety. There are significant differences among the criteria used by various countries and institutions to establish threshold values for tolerable and unacceptable wind conditions even if a single parameter, such as the wind speed is used as criterion. These differences range from the speed averaging period (mean or gust) and its probability of exceedance (frequency of occurrence) to the evaluation of its magnitude (experimental or computational). The paper addresses the progress made towards the computational evaluation of pedestrian level winds. All existing criteria for wind and thermal comfort are absolute criteria, which specify the threshold values or comfort ranges for respective weather parameters. The paper will outline an approach towards the establishment of an overall comfort index taking into account, in addition to wind speed, the temperature and relative humidity in the area.     

Study of wind towers with different funnels attached to increase natural ventilation in an underground building

Finding ways to cool buildings by natural, passive techniques is crucial in the context of global warming. For centuries, wind towers (traditional windcatchers) have been used in the Middle East for cooling purposes. In this study, the use of funnels at the openings of wind towers for wind ingress and egress is proposed primarily to increase the mass flow captured by the wind tower. The use of funnels in the wind ingress openings increases the inlet area, improving the capture of wind. In parallel, the use of funnels in the egress openings modifies the wake of the tower, which aims to ease the exit of the flow from inside the building. Several design configurations are presented, where the length and width of the funnels are changed and tested separately by computational fluid dynamics (CFD). Results of over 120 CFD simulations are presented and compared. The volumetric flow entering the wind towers increases by 10.7% in several cases. These results indicate that adding funnels to wind towers could positively influence their performance. Changing the dimensions of the funnels affects their efficacy and can increase or decrease the airflow entering the tower.     

A holistic approach to energy efficient building forms

Minimizing energy consumption in buildings has become an important goal in architecture and urban planning in recent years. Guidelines were developed for each climatic zone aiming at increasing solar exposure for buildings in cold climates and at reducing solar exposure for buildings in hot climates. This approach usually plans for the season with the harshest weather; often forgetting that temperatures in cities at latitude 25° can drop below thermal comfort limits in winter and that temperatures in cities at latitude 48° often rise above thermal comfort limits in summer. This paper argues that a holistic approach to energy efficient building forms is needed. It demonstrates a generic energy efficient building form derived by cutting solar profiles in a conventional block. Results show that the proposed building form, the Residential Solar Block (RSB), can maximize solar energy falling on facades and minimize solar energy falling on roofs and on the ground surrounding buildings in an urban area in winter; thus maximizing the potential of passive utilization of solar energy. The RSB also supports strategies for mitigating the urban heat island through increased airflow between buildings, the promotion of marketable green roofs and the reduction of transportation energy.     

On the development of an urban passive thermal comfort system in Cairo,Egypt

This paper investigates how urban form can be designed to act as a passive thermal comfort system in Cairo. The system utilizes two main elements, the urban fabric form, with its green structure, and thermal comfort adaptation by introducing urban green scene stimulation with the time of exposure to the urban environment. The courtyard form on a large scale is used to study comfort levels, the effect of compactness on solar access and the local radiant heat island potential in a theoretical neighborhood design using a medium population housing concept as required by Egyptian urban planning laws. Urban canyons in a grid network, with three mid latitude orientations 15°, 45° and 75° from the E–W axis, were examined, with one canyon having virtually no shade. Other canyons had a green structure containing two types of native Egyptian trees. Numerical simulations using ENVI-met were performed for hot climate conditions. Although some very hot conditions were recorded, there were evident examples of more acceptable comfort levels and cooling potential for some orientations and degrees of urban compactness due to the clustered form with green cool islands and wind flow through the main canyons. Some design guidance on how to form urban passive cooling systems is presented.     

Wind comfort in a public urban space—Case study within Dublin Docklands

Open public spaces provide venues for cultural, recreational events and promote informal social contact between citizens. Successful outdoor spaces promote comfort and invite people to stay outdoors. Provision of thermal comfort outdoors present a challenge, as an extended range of environmental conditions must be dealt with. The present study examines whether climatic characteristics in Dublin facilitate exercising long-term outdoor activities during summer, and investigates the extent to which urban planning and the resulting urban morphology of the built environment influences microclimates created, from the viewpoint of wind environment. Microclimates at Grand Canal Square have been simulated by ENVI-met. Wind velocity has been expressed in relation to that of the ‘‘background’’ climate in order to verify if the site has a wind protecting character or to the contrary, it enhances airflow. The results show for the dominant wind directions (W, SW, S) that 60% higher wind velocity than at Dublin Airport can occur around buildingcornersandatrestrictedflowsections—preventing any kind of long-term outdoor activity during a ‘‘typical’’ day. S and SW winds cause 15%-20% acceleration at the W waterfront area. Windy urban environment can call forth a limited frequentation of urban space.     

Measurement and evaluation of the summer microclimate in the semi-enclosed space under a membrane structure

This study aims to clarify the summer microclimate in membrane structure buildings with semi-outdoor spaces and develop a computational simulation tool for designing a comfortable urban environment using membrane structures. Field measurements were conducted in a membrane structure building with a semi-outdoor space during a summer period. The present paper describes analysis results of measurement data for vertical distributions of air temperature and velocity under the membrane structure on clear sunny days. The following subjects were also discussed: (1) the effect of solar transmission on the warming of air temperature by the floor under the membrane structure; (2) the temperature reduction effect of ventilation by wind; (3) evaluation of thermal comfort in the living space under the membrane structure in terms of a thermal comfort index (new standard effective temperature: SET*).     

湿热地区步行商业街夏季室外热环境实测分析

我国湿热地区夏季空气温度和湿度相对较高,太阳辐射强烈,人们在此种气候条件下的室外步行商业街区活动可能会造成身体不适,甚至是中暑。因此,高品质的室外热环境既对于步行商业街区在吸引人流方面扮演了重要角色,同时也为城市公共空间提供活力。通过对南宁市典型步行商业街区夏季室外热环境变量进行测试,从而得出热环境与周围材质和建筑类型有关,遮阳形式是决定人在步行通道空间中是否感到舒适的重要因素。     

A design supporting simulation system for predicting and evaluating the cool microclimate creating effect of passive evaporative cooling walls

As a passive cooling strategy to control increased surface temperatures and create cooler urban environments, we have developed a passive evaporative cooling wall (PECW) constructed of pipe-shaped ceramics that possess a capillary force to absorb water up to a level higher than 130 cm. The current paper presents a simulation system to predict and evaluate microclimatic modifying effects of PECWs in urban locations where PECW installation is under consideration at the design stage. This simulation system is composed of a CFD simulation tool and a 3D-CAD-based thermal simulation tool. Simulation methodology of coupling the two simulation tools was developed and described in this paper. Numerical models for simulating surface temperatures and evaporation of PECWs were proposed based on analysis results of experimental data. Validation of the proposed numerical models was confirmed by comparing simulated results with measured data. In order to demonstrate the applicability of the proposed simulation system, a case study was then performed to predict and evaluate the microclimate in a rest station where PECWs were assumed to be installed. Spatial distributions of air temperature, airflow, moisture and surface temperature in the rest station were simulated under a sunny weather condition in the summer of Tokyo. Furthermore, thermal comfort indexes (mean radiant temperature and new standard effective temperature) were used to evaluate thermal comfort in the human activity spaces of the rest station. Simulation results show that this simulation system can provide quantitative predictions and evaluations of microclimatic modifying effects resulting from the application of PECWs.     

Computational evaluation of building physics—The effect of building form and settled area,microclimate on pedestrian level comfort around buildings

Wind discomfort and the dangers that the wind may lead can be harmful in terms of comfort conditions of both indoor and outdoor environment of the building/buildings to be constructed or just completed. The wind effects on a site can be divided in two as: mechanical wind effects and thermal wind effects. This study is specifically about mechanical wind stress and pedestrian wind comfort. Typically, the cause of frequent occurrences of strong wind at pedestrian area is primary related to the configuration of building structures and/or topography in the vicinity of the pedestrian area. Depending on the characteristics of the wind including magnitude, uniformity, ambient temperature, etc., the level of disturbance to users of pedestrian areas can be different. In this context, the regions where Necmettin Erbakan University (N.E.U.) temporary education buildings are located have a fairly intensive topography in terms of wind. Therefore, detailed analyses of the inside regions and the surrounding areas of education buildings in particular are performed in terms of microclimatic comfort and indoor energy recovery. Especially, the topography where the university campus temporary educational buildings are located has very high wind climate conditions comparing to the city of Konya, Turkey, climate conditions. In this study pedestrian level wind conditions around N.E.U. campus buildings and in urban areas and campus buildings settlements topography are analyzed by CFD FloEFD. The aim of the study is to analyze causes of wind nuisance in campus site area and around temporary education buildings, and compare and evaluate remedial measures. The results show that current campus settlement, around the buildings and amphi classes are seen to reach very discomforting levels in terms of in classroom comfort. Draft architectural campus temporary education buildings projects proposed by the author can improve on existing wind conditions where possible, and as a minimum, can not significantly degrade wind conditions especially when considering the safety criteria.     

Outdoor thermal comfort: Analyzing the impact of urban configurations on the thermal performance of street canyons in the humid subtropical climate of Sydney

The quality of outdoor space is becoming increasingly important with the growing rate of urbanization. Visual, acoustic, and thermal balance degradation are all negative impacts associated with outdoor comfort in dense urban fabrics. Urban morphology thus needs assessment and optimization to ensure favorable outdoor thermal comfort (OTC). This study aims to evaluate the thermal performance of streets in residential zones of Liverpool, NSW, Australia, and tries to improve their comfort index (Physiological Equivalent Temperature) to reveal optimum urban configurations. This evaluation is done by investigating the following urban design factors affecting OTC using computational simulation techniques: street orientation, aspect ratio, building typology, and surface coverage. Our findings reveal that street canyon orientation is the most influential factor (46.42%), followed by aspect ratio (30.59%). Among the influential meteorological parameters (air temperature, wind speed, humidity and solar radiation), wind velocity had the most significant impact on the thermal comfort of the outdoor spaces in this coastal region, which typically experiences intense airflow. The results of our analysis can be utilized by multiple stakeholders, allowing them to understand and extract the most vital design factors which contextually influence the thermal comfort of outdoor spaces. Outdoor thermal comfort has a direct effect on the health and wellbeing of occupants of outdoor spaces.     

当代MOMA工程高层多塔楼、高位悬挑及连体结构设计与施工关键技术研究

首次对多塔楼复杂连体的滑动连接进行了研究,应用了摩擦摆式防震支座,保证了连体和塔楼抗震安全;通过对高层复杂结构体系、高位大悬挑结构、大跨度复杂连体结构等进行综合性的研究,成功地解决了当代MOMA工程复杂结构的设计与施工技术难题;首次对整体建筑群风环境和行人舒适度进行研究,提供了风荷载合理取值,并对行人的舒适度问题提出了改进措施。     

Refining the use of evaporation in an experimental down-draft cool tower

Direct evaporative cooling has long been recognized as an energy-efficient and cost-effective means for space conditioning in hot dry areas. In order to extend the use of evaporative cooling to include exterior or semi-enclosed spaces, a down-draft evaporative ‘cool tower’ was integrated in the project of a 500 m² glazed courtyard located at the heart of a building complex in the arid Negev Highlands of southern Israel, designed by the authors. The present article describes the development of the cooling tower system, undertaken in three phases: (i) Prototype analysis. Performance of a small-scale tower was monitored, and comparisons were drawn between varying rates and mechanisms of water and air supply. The results indicated a potential for substantial temperature reduction in the order of 10 °C under summer daytime conditions, but a meager cooling output when using a natural draft system. Mechanical-forced air flow was thus utilized in the actual tower. (ii) Field monitoring. The cool tower, approximately 10 m in height and 10 m² in cross-sectional area, was operated and monitored during a summer season; its performance was analyzed using a series of water supply mechanisms and operating modes. The system produced a peak cooling output of just over 100 kW, with a wet bulb temperature depression of close to 85–95% during all hours of operation, and a water consumption rate of approximately 1–2 m³/day. (iii) Refinement. Potential improvement in the system's operation was investigated through the development of a wind capture mechanism for increasing inlet pressure and air flow to the space. Both fixed and dynamic capture units were investigated, with wind speed and direction as well as internal air speeds measured in the small-scale prototype tower. The wind capture unit with the simplest configuration and best performance is recommended for future integration in the full-scale tower.     

夏热冬冷地区近零能耗建筑技术途径探索

近年来近零能耗建筑的关注度愈来愈高,我国在这一领域的探索与实践较多集中于严寒地区与寒冷地区。夏热冬冷地区面积大、人口密集、冬夏两季气候差异大,不足以满足建筑舒适的要求,耗能巨大。如何在这一地区发展近零能耗建筑技术值得探索和研究。文章从被动式节能技术、外围护结构的保温性能、太阳能资源的一体化利用、人的行为特征与被动控制体系等方面出发,探索其在具体案例中的应用。希望这一探索能对近零能耗建筑在夏热冬冷地区的发展提供参考和帮助。     

The effect of Urban Heat Island mitigation strategies on outdoor human thermal comfort in the city of Baghdad

Todays, most Iraqi cities suffer from extremely hot-dry climate for long periods throughout the year. However, most urban patterns that exist inside these cities are not suitable for this harsh conditions and lead to an increase in the value of the Urban Heat Island (UHI) index. Consequently, this will increase outdoor human thermal discomfort as well as energy consumption and air pollution in cities. This study attempts to evaluate the effect of UHI mitigation strategies on outdoor human thermal comfort in three different common types of urban patterns in the biggest and most populated city in Iraq, Baghdad. Three different mitigation strategies are used here – vegetation, cool materials, and urban geometry – to build 18 different scenarios. Three-dimensional numerical software ENVI-met 4.2 is utilised to analyse and assess the studied parameters. The input data for simulations process are based on two meteorological stations in Baghdad: Iraqi Meteorological Organization & Seismology, and Iraqi Agrometeorological Network. All measurements are taken in a pedestrian walkway. The results of different scenarios are compared based on their effect on human thermal comfort. Outdoor thermal comfort is assessed according to Predicted Mean Vote index, as mentioned in ISO 7730 standard. This study provides a better understanding of the role of UHI mitigation strategies on human thermal comfort in the outdoor spaces of Baghdad's residential neighbourhoods. This can help generate guidelines of urban design and planning practices for better thermal performance in hot and dry cities.     

Mitigation of wind‐induced motion of Milad Tower by tuned mass damper

With a height of 435 m, Milad Tower, situated in north‐west of Tehran, Iran, would be the fourth highest telecommunication tower of the world. This tower has the largest head structure among its counterparts. Preliminary studies demonstrate that the upper part of the tower has excessive wind‐induced acceleration‐related vibrations beyond human comfort limit during wind events. In this paper, the effectiveness of tuned mass damper (TMD) on the suppression of wind‐induced motion of Milad Tower is examined through mathematical analyses. The tower is modelled as a vertical linear cantilever beam, with 57 degrees of freedom. The fluctuating wind speed is assumed to be a stochastic process which is identified by an appropriate power spectral density function. Random vibration analyses were carried out to determine response statistics. The possible application of TMDs in suppressing wind‐induced motions of the tower was investigated, and a TMD was designed to be installed at the sky dome. The results clearly show that the designed TMD has a considerable influence on the suppression of the structural response of the tower below human comfort limits. The authors believe that Milad Tower can be considered as a benchmark control problem for television and telecommunication towers by the structural control community. Copyright © 2008 John Wiley & Sons, Ltd.     

Simulation of the urban thermal comfort in a high density tropical city: Analysis of the proposed urban construction rules for Dhaka, Bangladesh

The thermal comfort in urban canyons of a high density city is a very challenging issue for urban planners and designers, especially in hot humid tropical zone. The present study aims to evaluate the effects of a newly promulgated building construction rules in respect of thermal climate for Dhaka, Bangladesh, a region characterized by high density area with tropical climate. Three different urban canyons from three areas were considered which almost represents the whole city. Measurements were carried out to assess the existing thermal climate in the city canyons. Further, three model canyons were configured according to the new rules of ground coverage, floor area ratio (FAR) and site setback. A three-dimensional numerical model with high spatial and temporal resolution was used to investigate the microclimatic changes within the urban environments. Model calculations were run for a typical summer day. The thermal climate was evaluated based on air temperature T _a, surface temperature T _s, relative humidity RH, and wind speed in the existing and model canyons. For thermal comfort assessment the temperature humidity index (THI) was considered in this study. The results showed that the outdoor spaces of the study areas are thermally uncomfortable and the new building construction rules hardly improve the conditions in general. However, THI decreases in a canyon where sky view factor (SVF) decreases in the model canyon than the existing one. In addition, the surface temperature T _s and air temperature T _a do not show the same picture. Furthermore, the wind speed increases in all the model canyons as the site setback allows wind flow uniformly inside the canyons.     

Analysis of the microclimatic and human comfort conditions in an urban park in hot and arid regions

Urban parks have complex surface structure that produces an environment with specific microclimatic qualities. These qualities affect the balance of energy of the human body and are applicable to an individual’s thermal perception. They have impacts on using outdoor spaces especially in hot and arid regions. This study investigates users’ thermal comfort in an urban park in Cairo, Egypt. The investigation was carried out during the hot and cold months using subjective surveys and field measurements. The campaign consisted of a subjective survey using questions on the perception of the thermal environmental applying seven-point ASHRAE 55 thermal sensation votes (TSV) in nine different zones in the urban park. At each zone, the thermal environment parameters – air temperature, solar radiation, air relative humidity and wind speed were measured. Through these data, the values of the Physiologically Equivalent Temperature (PET) were calculated in each zone using the RayMan model. The current people clothing and metabolic rate were recorded. The results of the field measurements were compared with judgements about the thermal environment. Results demonstrate that differences in the PET index among these zones due to different sky view factors (SVF) and wind speed. Results revealed an alteration in human comfort sensation between different landscape zones. This paper suggests that the thermal requirements of visitors and qualities of the local climate should be carefully considered when designing landscapes for the future urban parks in the hot and arid regions.     

An experimental investigation of the wind tower-assisted by the underground passive cooling system

Wind towers have been used for the buildings passive cooling, in warm and dry regions. The wind towers are employed to capture the wind from the external air stream and direct it into the buildings and facilitate the circulation of the air from ambient through the building. The wind towers are not able to decrease the air temperature. In some locations of Iran such as Bam, the wind tower outlet was first directed into an underground channel, before being introduced into the building. The channel was built under the garden to employ the humidly of soil to cool down the air. In this paper, a small scale model of underground air-earth heat exchanger is employed to assess the system performance. The paper reports the effect of the garden irrigation time, humidity and temperature diurnal variations of the ambient air on the channel performance. The results show that when the garden is irrigated, and soil moisture content is at the higher level, the maximum average cooling performance of the channel is achieved, 51.30%. The temperature drop of the air inside the channel is due both the evaporation of moisture from the channel wall and the lower temperature of the soil than air.