Environmental Engineering Reference
In-Depth Information
for Hedera helix of 2.6 up to 7.7 m
2
leaf/m
2
wall (Bartfelder and Kohler
1987a
,
b
),
a leaf surface area of 2,600 up to 7,700 can be calculated.
Measurements carried out by Rath and Kießl (
1989
) on the effect of green
façades on the SO
2
concentration show that the concentration of SO
2
was clearly
lower between the foliage than in front of a non-greened façade.
Field measurements conducted by a national research program in the Nether-
lands (IPL
2006
) to investigate the effect of a vegetation corridor on the reduction
of PM
10
levels near a highway (A50), show a minor contribution of the vegetation
corridor on the concentration levels measured in the ambient air. They estimated
the effect of vegetation smaller than 10-31 % on the traffic contribution of par-
ticulate matter, due to the high uncertainty of the used measuring equipment.
6.4 Temperature Regulation and Insulating Properties
Due to a Vegetation Layer
Buildings consume roughly 36 % of total energy use and 65 % of the total elec-
tricity consumption. Kula (
2005
) suggests that a wide scale green roof imple-
mentation could significantly impact energy savings. According to Dunnet and
Kingsbury (
2004
) every decrease of the internal building temperature with 0.5 C
may reduce the electricity use with 8 % for air conditioning in summer periods.
Akabari et al. (
2001
) concluded that since 1940 the temperatures in urban areas
have been increased by 0.5-3 C. Akabari et al. (
2001
) also estimated that 5-10 %
of the current electricity demand of cities is used to cool buildings just to com-
pensate the 0.5-3 C increased temperature.
Green roofs, living walls (LWS), and green façades create their own specific
microclimate, quite different from surrounding conditions. Due to this specific
microclimate, both around the building and at grade are affected. Depending on
height, orientation, and the location of surrounding buildings, the façade is sub-
jected to extreme temperature fluctuations (hot during the day and cool at night),
with constant exposure to sunlight and wind. The climate on a roof or at a façade is
comparable with an arid or alpine climate, and only suitable to specific types of
plants. Most of the Sun's radiation that is adsorbed by concrete, bituminous
materials, or masonry is reradiated as sensible heat. Asphalt, concrete, and masonry
will reflect 15-50 % of the received radiation (Laurie
1977
), greening paved sur-
faces with vegetation to intercept the radiation before it can hit hard surfaces can
reduce the warming up of hard surfaces, especially in dense urban areas.
A study in Toronto carried out by Liu and Baskaran (
2003
) shows clearly the
temperature difference between a bare and green roof. Temperatures up to 70 C
were measured for the bare roof, whereas the temperature on the green roof remains
around 25 C. The consequence of this is that the roof membrane (bituminous
material) of the bare roof ages must faster due to UV light compared to a green roof,
which is protected by the substrate and plant layer. Since UV light deteriorates
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