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called canyon effect (valid only for new buildings). To the fi rst category belong
the following actions:
– Cool roofs/façades: By applying building materials with high solar refl ectance (high albedo) and high infrared emittance (cool materials) one can
reduce the cooling load of a building, and thus one can limit the heat emitted
by the use of air conditioning facilities to the building’s surroundings. Though
cool materials can be applied for both roof and façade surfaces, it is usually
easier and cheaper to apply them to existing roofs, making the method of
“cool roof” creation more prevalent in daily practice.
– Green roofs: a green roof means a roof covered by a vegetative layer of variable width. Compared to traditional high absorptive roof surfaces, green roofs
bringing about lower surface temperatures, thus leading to lower cooling
loads in the building itself. Irrigation of these roofs can reduce the air temperature next to the roof, as an outcome of the evapotranspiration effect of the
vegetative layer. When applied to a large group of buildings, green roof are
believed to have a signifi cant effect of urban air temperature.
– Green façades: vegetation can also be used as an overlaying layer for facades,
either by enabling the growth of climber plants directly on the façade surface
(thus shading parts of it) or by adding a more substantial bedding “wall”
which connects to the façade and functions also as an insulating and evapotranspiration layer similar to that of a green roof.
– Street geometry, which is defi ned by the shape of the buildings and their orientation, might also have an impact on UHI intensity levels by increasing air
fl ow rate through the street, thus replacing the warmer air “trapped” between
buildings. Although changing the geometry of existing streets is limited, large
urban projects regularly introduce the opportunity to increase the effects of
advection by a careful design of their geometry.
– Pavements play also an important role in the formation of the UHI phenomenon, since conventional paving materials (mainly concrete and asphalt) tend
to absorb large amounts of solar radiation during daytime and to release it to
the cooler surrounding air (cool pavements). Another property of these paving
materials is their limited permeability to water, which prevents the absorption
of water in the ground and thus reduces the evaporation potential of the ground
surface which may help in reducing air temperatures (pervious pavements).
• Cool pavements are built of materials which have higher albedo (higher
solar refl ectance) values than conventional paving materials, usually
because of their lighter color.
• Pervious pavements: pavements of pervious materials which enable the
draining of water through the porous pavement surface. The water is thus
absorbed in the subsoil and evaporates when the paving material is heated,
resulting in lower surface temperatures of the pavement. Pervious pavements are also helpful for the storm water management, and then for the
prevention from fl oods.
5 Decision Support Systems for Urban Planning
called canyon effect (valid only for new buildings). To the fi rst category belong
the following actions:
– Cool roofs/façades: By applying building materials with high solar refl ectance (high albedo) and high infrared emittance (cool materials) one can
reduce the cooling load of a building, and thus one can limit the heat emitted
by the use of air conditioning facilities to the building’s surroundings. Though
cool materials can be applied for both roof and façade surfaces, it is usually
easier and cheaper to apply them to existing roofs, making the method of
“cool roof” creation more prevalent in daily practice.
– Green roofs: a green roof means a roof covered by a vegetative layer of variable width. Compared to traditional high absorptive roof surfaces, green roofs
bringing about lower surface temperatures, thus leading to lower cooling
loads in the building itself. Irrigation of these roofs can reduce the air temperature next to the roof, as an outcome of the evapotranspiration effect of the
vegetative layer. When applied to a large group of buildings, green roof are
believed to have a signifi cant effect of urban air temperature.
– Green façades: vegetation can also be used as an overlaying layer for facades,
either by enabling the growth of climber plants directly on the façade surface
(thus shading parts of it) or by adding a more substantial bedding “wall”
which connects to the façade and functions also as an insulating and evapotranspiration layer similar to that of a green roof.
– Street geometry, which is defi ned by the shape of the buildings and their orientation, might also have an impact on UHI intensity levels by increasing air
fl ow rate through the street, thus replacing the warmer air “trapped” between
buildings. Although changing the geometry of existing streets is limited, large
urban projects regularly introduce the opportunity to increase the effects of
advection by a careful design of their geometry.
– Pavements play also an important role in the formation of the UHI phenomenon, since conventional paving materials (mainly concrete and asphalt) tend
to absorb large amounts of solar radiation during daytime and to release it to
the cooler surrounding air (cool pavements). Another property of these paving
materials is their limited permeability to water, which prevents the absorption
of water in the ground and thus reduces the evaporation potential of the ground
surface which may help in reducing air temperatures (pervious pavements).
• Cool pavements are built of materials which have higher albedo (higher
solar refl ectance) values than conventional paving materials, usually
because of their lighter color.
• Pervious pavements: pavements of pervious materials which enable the
draining of water through the porous pavement surface. The water is thus
absorbed in the subsoil and evaporates when the paving material is heated,
resulting in lower surface temperatures of the pavement. Pervious pavements are also helpful for the storm water management, and then for the
prevention from fl oods.
5 Decision Support Systems for Urban Planning