Civil Engineering Reference
In-Depth Information
Fig. 2.4
A section of one building block and a particular of the external façade with the two dif-
ferent cladding systems
than in the countryside inducing higher energy consumption for cooling and dis-
comfort for people. The reasons for this are (Kleerekoper et al.
2012
):
• The night cooling of surfaces by radiation to the sky is blocked by the presence
of buildings; the heat is intercepted by the obstructing surfaces in the street can-
yons, and absorbed or radiated back to the urban tissue.
• Built areas change the thermal properties of surface materials (absorption, emis-
sivity, thermal capacity).
• The evaporation from urban areas is decreased because of 'waterproofed sur-
faces'—lack of “natural” soil and vegetation. As a consequence, more energy is
put into sensible heat and less into latent heat.
• If tall buildings are present, they provide multiple surfaces for relection and
absorption of sunlight in low albedo materials.
• Air pollution in the urban atmosphere absorbs and reemits long-wave radia-
tion to the urban environment; moreover, combustion processes, such as traffic,
space heating and industries, release anthropogenic heat.
Studies suggest that, in metropolitan urban heat islands, air temperatures in sum-
mer can be up to 4 °C warmer than the surrounding countryside (Arrau and Peña
2011
), due to the extremely large heat capacities of built surfaces that make up for
a huge reservoir of energy. The UHI may also affect the wind patterns, develop-
ment of clouds and fog, humidity, and the rate of precipitation. Other effects include
