Thesis document - Jana Milosovicova - Urban Design English

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ample, it is better to have an urban area of higher density, witha mixture of high and low buildings, to obtain good ventilationconditions than an area of lower density, with buildings of the sameheight (Givoni 1998, p. 284).The other physical details of urban space that influence the airflowin an urban area more than building density are the orientation ofstreets and buildings with respect to the wind direction and the levelof compactness (Givoni 1998, p. 284), where higher compactnessimplies hindered ventilation.2. Combined impact of street orientation and widthIn the urban environment, different situations emerge according to thestreets’ orientation:Streets free from robust tree vegetation, oriented parallel (or in a smallangle) to the wind direction, create obstacle-free ventilation lanes. Thewider are the streets, the less is the airflow resistance from the buildings,thus improving the urban ventilation (fig. 28) (Givoni 1998, p. 290).When the streets are angled in an oblique wind direction, the windcomponents create different situations in the streets: the first componentflows in the direction of the street, but is concentrated mainlyof the downwind side of the street; the second causes pressure in theupwind side of the buildings. On the upwind side of the street, theairflow is gentler and a low-pressure zone surrounds the building. Thesame rule applies here: the wider the streets, the better the ventilationconditions (fig. 29) (Givoni 1998, p. 290).Streets perpendicular to the wind direction, with buildings of the sameheight, cause the first row of buildings divert the approaching windupwards, making the principal air current flow above the buildings. Therest of the buildings, as well as the streets canyons behind, are in thewind shadow (Givoni 1998, p. 290). Especially in this case it is importantto note, that when the street H/W ratio is higher than 2, the airflow above building height will become highly difficult to reach the pedestrianlevel where the buildings are tightly packed to form a narrowstreet (Kam-Sing et al. 2009). In these circumstances, suitable placementof high-rise buildings creates vertical currents that help stirringthe urban air mass, achieving higher near-ground wind speeds (fig. 30)(Givoni 1998, p. 290, 293).90°“Wind shadow”, ventilation significantly reduced“Wind shadow”, ventilation significantly reducedStrong airflow at the urban edgeCarefully placed higher buildings enhance the air turbulenceon the street level and thus enhance ventilationFig. 30 Streets perpendicular to prevailingwind direction (above - section, middle- ground plan; below - section with adjustedbuilding height).3. Ventilation channels, open spaces and green shelter belts.In the dense city centres, the hot air rises gradually, and a near-ground,cooler air flows from the surrounding lower density areas, green areasor water bodies towards the center (fig. 31) (Givoni 1998, p. 285).The cooling wind masses however can only be transported into thesettlements if there are obstacle-free ventilation channels that enablewind streaming. Already in the 19th century, climate researchers werecalling for wedge-formed open space ventilation systems that wouldprovide ventilation of urban cores (Fritsch 1895).Such ventilation channels can be introduced by urban design to supportthe transfer of cooling air masses between the city center and theoutskirts as well as between the inner city green areas and denselyThe cooling effect ofgreen areas depends onthe presence andcharacter of airflowchannels-°CThe heat island effect is mostsignificant in the urban core+°C+°CFig. 31 Air flow characteristic in urban areasCooling effect 50 -300 m from the bodyof water (depends onthe permeability ofthe built waterfrontand presence ofairflow channels)-°C2 Literature review: The impact of built structures on climate, energy flow and the water cycle27
Emergingof fresh andcold air100-200 mObstacle-freeventilation channelsleading towards theurban coreFig. 32 Wedge-formed open space system thatprovides ventilation of the urban core via ventilationchannels reaching from the outskirts.populated areas. On the level of the whole city, a radial, wedge-formedopen space system is considered being the most effective to providesufficient ventilation (Hahn-Herse 1997, Section ‘Climate’, p. 60) (fig.32). In cities with non-concentric density patterns, the pattern of theUHI and the associated air current are irregular. The topography alsoinfluences the thermally induced air currents (Givoni 1998, p. 285).In these cases, the desired design of the ventilation channels is nonconcentric,adjusted according to given conditions. Within the city itself,these can be open parks free from robust trees, wide avenues orflowing water bodies with little air flow resistance.The ventilation channels are commonly divided into two categories(Matzarakis 2001, p. 220):• Fresh air ventilation channels, producing and transportingpollutant-free “fresh air” that is rich with moisture evaporated fromnatural surfaces and from vegetation (such as grassy, bushy areas,or areas with higher but compact tree vegetation);• Cold air ventilation channels, transporting “cool air” and servingprevailingly to alleviate extreme temperatures (such as linear waterbodies and railways; which both, in contrast to highways causeno or only little pollution loads. Roads, too, may fulfill the cool airtransporting function; however, due to the high load of pollutantsare not categorized as desired ventilation channels.).In this Thesis, the concept of cold and fresh ventilation channels istaken as equal.According to Kuttler, the general features of the ventilation channelsshould be as following (Kuttler in Marzluff 2008, p. 235):• roughness length z < 0.5 mo• zero plane displacement d : negligibleo• length ≥ 1,000 mMa• width ≥ 50 m (depends on lateral obstacles); according to variousinvestigations, a width of 100 – 200 m is, due to its effectiveness,more desirable 26• width of obstacles within the ventilation channel is 2 – 4 times theheight of the lateral obstacles (min. 50 m)a.Mbb.Fig. 33 Ventilation effect of a green space ishindered when surrounded by closed houses’front (a), and better when the building blocksare opened and there are streets leading towardsthe open space (a).• height of obstacles within the ventilation channel ≤ 10mIn compact urban areas however, even a small-scale vertical circulationbetween residential block and adjacent green space proves effective(Andritzky and Spitzer 1981). The depth of the cold air penetratingfrom these local circulations into the built environment is however determinedby both the design of a green area and by the form of thesurrounding buildings. If for example a green area is in a depression orsurrounded by a wall, the air exchange is hindered and thus the penetrationdepth reduced; or, if a green area is surrounded by closed, highhouses' front, the climate meliorating effect is confined to the immediatevicinity (fig. 33a), as proven in the Tempelhof Study (Appendix4). Conversely, in a loose building structure, with open building blocks26 SenStadt Berlin and BSM 2009, p. 46; Mayer and Matzarakis 199228Climate Sensitive Urban Design in Moderate Climate Zone: Responding to Future Heat Waves. Case Study Berlin Heidestrasse/Europacity
Page 1 and 2: Master’s Thesis in Urban Design:C
Page 3 and 4: ContentsAcknowledgements 5Abstract
Page 5 and 6: 4Climate Sensitive Urban Design in
Page 7 and 8: Abstract Deutsch/GermanAusgehend vo
Page 9 and 10: 8Climate Sensitive Urban Design in
Page 11 and 12: ing population 5 ) - more than a ha
Page 13 and 14: as the immense climatic effects of
Page 15 and 16: • Urban geometry: Tall buildings
Page 17 and 18: -°CFig. 11 Photographs of thin veg
Page 19 and 20: Fig. 14 Photograph of the square an
Page 21 and 22: the values of water balance of vari
Page 23 and 24: size, lower than in cities of North
Page 25 and 26: wave radiation towards the sky. In
Page 27: Impact of the street orientation on
Page 31 and 32: a. b.On the other hand, a concave w
Page 33 and 34: a.b.-°C-°C50-300 m-°CNot only te
Page 35 and 36: 2.5 Literature review: Lessons lear
Page 37 and 38: 3 Climate-Sensitive Urban Design(CS
Page 39 and 40: ought in the section 3.4, are mainl
Page 41 and 42: 3.2 Proposed CSUD GuidelinesThe set
Page 43 and 44: effect of a water body reaches into
Page 45 and 46: the street);c. Option b) + some of
Page 47 and 48: • Reduce quantity of lanes, where
Page 49 and 50: 3.3 Examples of CSUD in built urban
Page 51 and 52: 3.4 Climate-Sensitive Urban Design
Page 53 and 54: a.The proposal features a number of
Page 55 and 56: Action category ‘Ventilation’Ve
Page 57 and 58: Fig. 91/P18 West-East (W-E) Section
Page 59 and 60: 4 ConclusionsBased on the need to a
Page 61 and 62: Complementing recommendations regar
Page 63 and 64: GlossaryAdiabatic coolingAlbedoAmbi
Page 65 and 66: Mitigation “Measures taken to red
Page 67 and 68: SourcesBibliographyAgenda 21, onlin
Page 69 and 70: Matzarakis, A. (2001): “Die therm
Page 71 and 72: The Physical Environment, online:
Page 73 and 74: Fig. 25 The ‘sky view factor’ .
Page 75 and 76: Fig. 93Fig. 94Proposed street and c
Page 77 and 78: Appendices76Climate Sensitive Urban
Page 79 and 80:
Type of landuseDirect impact and ef
Page 81 and 82:
Appendix 2 City of Toronto’s Stud
Page 83 and 84:
(BAF - Biotope Area Factor continue
Page 85 and 86:
The building of the Institute of Ph
Page 87 and 88:
Castello development, seen from Lan
Page 89 and 90:
Bo01 seen from the 56th floor of th
Page 91 and 92:
(Bo01, Malmöcontinued)Water is the
Page 93 and 94:
Appendix 9 Posters Climate-Sensitiv
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Thesis document - Jana Milosovicova - Urban Design English

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