Environmental Engineering Reference
In-Depth Information
19.2.3 Shadings
Shading of urban surfaces can be provided by shading devices and structures, such
as tents, pergolas, canopies, etc., or by trees. Shaded urban surfaces receive smaller
amounts of solar radiation, thus having lower temperatures. This results in lower
ambient temperatures in open spaces and in reduced rate of heat convection to the
building interior, when shading is applied on a building façade. Papadakis et al. (2001)
reported that the radiation incident on building façades reduces by 70-85% when trees
are planted close to the building. At the same time, temperatures in the area around
the trees were significantly lower than those in non-shaded areas.
19.2.4 Thermal sinks
Ground is characterized by its ability to store incident solar radiation as heat, con-
serving a constant temperature throughout the year. In this way, the underground
temperature is lower than the aboveground air temperature during summer and higher
than the air temperature during winter. The fact that the ground has a much lower
temperature than that of the environment aboveground is enabling it to be used as
a natural heat sink, during summer, by dissipating heat from aboveground construc-
tions to the ground. Taking advantage of the ground temperature is achieved through
ground-to-air heat exchangers, meaning tubes that are buried in the earth. The air
enters the tubes, circulates underground and exits the tube having a lower tempera-
ture. The designation of this system varies, being referred to as both “earth tubes'' or
“ground-coupled air heat exchangers'' (CRES, 2011).
Fintikakis et al. (2011), through simulations and field measurements, evaluated the
microclimatic modifications that were applied in the historic centre of Tirana (Albania).
The mitigation techniques that were applied were cool materials, green spaces, water,
solar control and earth-to-air heat exchangers. The researchers found that the maxi-
mum temperature drop due to all the applied techniques was 3
◦
C, while the maximum
contribution of the earth-to-air heat exchangers was found to be close to 0.7
◦
C.
19.2.5 Combination and interplay of mitigation strategies
Each of the above-mentioned mitigation techniques have positive results in reducing the
heat island effect when applied in the urban environment. However, the combination
of some or all of the strategies, depending on the specific site and weather patterns,
will have multiple benefits.
One of the few studies in which different mitigation techniques were tested inde-
pendently and in combination was carried out by Rosenzweig et al. (2006). The main
aim of the study, which concerns the city of New York, was to test various mitiga-
tion techniques, like urban forestry, green roofs and light surfaces, and to understand
how they could affect New York City's surface and near-surface air temperatures. The
researchers studied the implications of the interventions both on the city scale and on
six smaller case study areas, including on appropriate open spaces where the techniques
could be applied.
Results of this study show that the mitigation strategies tested can reduce surface
and near-surface air temperatures, but there is substantial variability in the magnitude
Search WWH ::
Custom Search