A Green Building Envelope: A Crucial Contribution to Biophilic Cities - Biotechnologies and Biomimetics for Civil Engineering - page 142

Fig. 6.5 a Boston ivy (Parthenocissus) rooted in the soil and applied directly against the façade
in Delft summer 2009. b Photograph taken of the same façade with an infrared camera (FLIR)
with ambient air temperature 21 C

areas, the impact of evapotranspiration and shading of plants can significantly
reduce the amount of heat that would be reradiated by façades and other hard
surfaces. Plants buffer water on their leaf surfaces longer than building materials,
and the processes of transpiration and evaporation, can add more water into the air.
The result of this is a more pleasant (micro)climate in the urban area.
Field measurements performed by Bartfelder and Köhler ( 1987a , b ) show a
temperature reduction at the green façade in a range of 2-6 C compared with a bare
wall. Holm ( 1989 ) shows with field measurements and his DEROB computer model
the thermal improvement potential of leaf covered walls. Also Eumorfopoulou and
Kontoleon ( 2009 ) reported the temperature cooling potential of plant covered roofs
and walls in a Mediterranean climate; the effect was up to 10.8 C. Another study by
Wong et al. ( 2009 ) on free standing walls in Hortpark (Singapore) with vertical
greening types shows a maximum reduction of 11.6 C. Also Ottelé ( 2011 ) shows
that especially with living wall concepts high temperature reduction can be
achieved, resulting in better insulation values.
Perini et al. ( 2011 ) show the influence of a green layer on the reduction of the
wind velocity along the surface of a building. An extra stagnant air layer in
optimal situations can be created inside the foliage, so that when the wind speed
outside is the same as inside R exterior can be equalized to R interior . In this way, the
building's thermal resistance can be increased by 0.09 m 2 KW -1 .
These results refer to the wind speed measured at a façade covered by a well
grown direct greening system and a living wall system based on planter boxes; in
the case of living wall systems the insulation properties change according to the
materials used. The thermal resistance of a living wall system based on planter
boxes is also influenced by the wind reduction, besides the thermal resistance of
the system itself contributes to the thermal resistance and is estimated up to
R = 0.52 m 2 KW -1 .