Thesis document - Jana Milosovicova - Urban Design English

Impact of the street orientation on insolationThe streets’ orientation affects the solar exposure of open areasand buildings as well as the comfort of people walking in the streets.In moderate climates, the objectives on this subject are rather complicated:To provide maximum shade in summer and maximum impingingsolar radiation in the winter. These requirements are difficult to satisfy,as in the summer, the sun stands high on the sky and thus reaches thestreet level easier than in winter, when the radiation angle is considerablylower and the street better protected by buildings from directsolar radiation. There is only deciduous vegetation in form of robust,solar-friendly trees that is able to oblige the human physical comfortdemand, providing shade in summer and letting insolation penetratethrough the thin branches in the winter. In this case, the South-Northorientation of the streets would prove to be most convenient, allowingsunlight reaching the streets’ ground level in the winter.When aiming to alleviate the impacts of the summer heat waves, however,the heating-up effect of the urban canyons must be considered.A study by Herrmann & Matzarakis (2010, p. 525-526) showed that aNorth-South oriented street reaches very high temperatures, while inthe case of East-West oriented urban canyons, the temperatures wereconsiderably lower. 24 Although this study has been conducted on anidealized canyon model, it implies that East-West oriented streetcanyons (and canyons oriented in a small angle to this direction)are optimal in moderate climate. What additionally affects thetemperatures in street canyons is the ventilation, discussed below.VentilationStrong airflow in the streetThe air circulation is essential in mitigation of extremely high temperatures,due to the ability of the wind to transfer cool air from vegetatedareas in the direction of urban cores, pushing the hot air in the centreupwards. Thus, considerable attention will be given to ventilationaspects in this Thesis. The main urban design features that affect thewind conditions are 25 :0 - ca. 10°Fig. 28 Streets parallel or in an small angle (ofup to 10°) to the prevailing wind direction.1.2.3.4.The overall urban density;Combined impact of street orientation and width of the streets;Ventilation channels, open spaces and green shelter belts – theiravailability, size distribution and design details.Height and shape of the individual buildings and the existence ofhigh-rise buildings;Downwind street side with stronger air flowUpwind street side with gentler air flow1. The urban density affects the ventilation conditions in the streets,as well as the potential for natural ventilation of buildings. This effect,however, depends greatly on the details of the urban physical structure.Even in dense urban areas, it is possible to obtain a wide range ofwind conditions by applying different urban design approaches. For ex-The higher street width, the better air circulationFig. 29 Streets oriented oblique to the prevailingwind direction.24 Canyons rotated in between the two main directions showed step-wise modificationin the temperatures, North-South and East-West orientations being the twoextrema.25 Givoni 1998, p. 261; modified and completed26Climate Sensitive Urban Design in Moderate Climate Zone: Responding to Future Heat Waves. Case Study Berlin Heidestrasse/Europacity