5.5.1 Design Guidelines: Percentage of Open and Built Space
The designing of open spaces is very important for the urban environment and thermal comfort both in indoor and outdoor spaces. It is found that, the open spaces include roads, paves, setbacks, empty plots, urban green etc., and all the hard surfaces are responsible for higher value of MRT. So it is essential to reduce the hard surfaces in the urban area.
Roads and Streets:
As the highest MRT values found on roads and streets, it is recommended to minimize the roads and streets, or to maximize the use of heat reflective materials. Solar shading with urban green can be a good solution for reducing MRT.
Footpaths:
Footpaths of the study area are made with brick and concrete pave, which show higher MRT value in simulation study. Use of soft pave, permeable pavements and solar shading with urban green can be a good solution towards reducing MRT close to footpaths.
Parking area:
Though the study area do not have dedicated outdoor parking lot (all
buildings have their own parking in the ground floor or basement), the parking area is
one of the important elements of the urban site. The parking area should not be directly
97 exposed to sun. Parking area should be designed with soft pave, permeable pavements, solar shading devices and urban green.
Setback:
The setback of the buildings of the study area is mostly made of hard pave, which contributes to MRT increase. Heat radiated from building surface can also be trapped in the setback area. Again, there found stagnant air in narrow setback area due to compact urban setting. For ensuring better environment, proper setback area should be provided of minimum hard surfaces. Soil, water permeable covering, plants and soft surface should be provided to absorb the radiated heat in the setback area.
Empty Plots:
Urban empty plots also found bare and covered with hard pave in the study area. Urban empty plots should be designed as urban green.
Urban Green/ Urban roadside green:
The amount of canopy shading determines the cooling effect of the green areas and trees (Shashua-Bar & Hoffman, 2000). According to Shashua-Bar & Hoffman, about 80% of the cooling effect contributes by the tree shading in summer time in their studied area (Tel-Aviv urban complex, Israel) (Shashua-Bar & Hoffman, 2000). Urban green is very important for reducing MRT.
Again dense plants hinder the wind flow and elevate the relative humidity, which is not even desired. So, the design of a green area, the implementation of road side green and the selection of plant species should consider the orientation, climate and microclimate of the site.
5.5.2 Design Guidelines: Urban Street
Urban streets have intense impact or urban microclimate. For street shading, the east- west elongated roads provide the best result.
Due to the sun path and sun angle, the north-south elongated roads remain more exposed to the sun throughout the year, which is not desirable for energy consumption.
But shading, urban green, green wall etc. can be solutions to reduce the MRT in the north-south elongated roads.
5.5.3 Design Guidelines: Canyon Ratio
Canyon orientation is very important for street shading. In terms of street shading, the
north-south oriented canyons provide the best results. So the north-south canyon is
preferable than the east-west oriented canyon. Again, the increment of the canyon ratio
98 increases the shading area. Higher canyon ratio means narrow and deep apertures which are good for providing shading. According to Ahmed, “the area under shade in the canyon increases with increment of canyon height for a constant width, up to 2:1 H/W ratio and above this level building height does not contribute to a significant increase in shaded area” (Ahmed, 1995).
Table 5.5.a: Design Guidelines
Urban Morphology
Elements Environmental
Effects Example Guidelines
Percentage of Built area and Open space
Roads or Streets
Contributes to high MRT value Radiate heat
Rises local temperature
Minimizing urban streets and constructed with soft pave.
Create solar shading with urban green.
Footpaths
Contributes to high MRT value Radiate heat
Rises local temperature
Minimizing footpaths and constructed with soft pave.
Create solar shading with urban green.
Setback
Hard pave of setback contributes to high MRT
There found stagnant air in narrow setback area.
Radiated heat from building surface can trapped in setback area
Setback area should not be covered with hard surface.
More green area should be provide to absorb the radiated heat
99
Empty Plots
Bare empty plot is responsible for high MRT value.
Empty plots should not be bare.
There should be plants or urban green in empty plots.
Urban Green
Urban green helps to reduce MRT value.
Dense urban green create surface roughness which hinder the wind flow.
--- Urban green should be designed and provided properly.
Urban roadside green
Create shade on roads and footpath which protect the surfaces from direct solar radiation
There should be roadside plants to create shades on the roads.
Urban Street (north-south and east west elongated road) north- south elongated road
North-south elongated roads are more expose to sun throughout the year, which is not desirable for energy consumption.
Minimize north-south elongated road.
Solar shading, urban green, green wall etc. can be solutions to reduce the MRT
East-west elongated road
The buildings create shades on east-west elongated roads
East-west elongated roads are more desirable for energy consumption and spatialization.
Solar shading, urban green, green wall etc. can be solutions to reduce the MRT
100
Canyon Ratio
north- south oriented
North-south canyons performed better than east-west canyons in terms of energy consumption..
S N
North-south canyons are preferable.
Solar shading, urban green, green wall etc. can be solutions to reduce the MRT
east west oriented
East- west canyons are more expose to sun
throughout the year. E W
East- west canyons are not preferable.
Solar shading, urban green, green wall etc. can be solutions to reduce the MRT