vertically hanging blinds with a sloping, warped façade.
Overlaying the structural and façade parametric models
enabled the visualisation of all these considerations and
helped the architects to make quick decisions early on.
Arup’s engineers also recognised early on that the
concave, warped façades might cause reflected solar rays
to be concentrated in the open spaces surrounding the
tower. This problem has become well known in a number
of building projects around the world, most notably when
parts of a motor vehicle were melted by solar rays which
reflected off the 20 Fenchurch building façade in London.
Once again, parametric modelling was used innovatively
to estimate the magnitude of these concentrated solar
reflections and investigate solutions to the problem.
Parametric software was used in a first-principles based
calculation to reflect solar rays off the façade components
and add up the reflected intensities on a ground plane.
The peak concentrated solar irradiance came to 6kW/m2.
This is about six times the intensity received from the sun.
Figure 4 shows a snap shot of the analysis during the
morning hours where the solar rays reflected off the
eastern façade is concentrated in a red band close to the
building. The contours from green through to red indicate
the intensity of the reflected solar irradiance.
Various potential solutions were considered. The final
chosen solution was to make the spandrel panels on the
façade non-reflective. This reduced the peak concentrated
solar irradiance to 2kW/m2 overall with a few small patches
of up to 4kW/m2 in places
With the acceptable level of irradiance chosen as
2kW/m2, the project team decided to deal with the
higher levels of irradiance through landscaping where
strategically placed trees would shade people from the
solar reflections.
Parametric modelling, and a close working relationship
between multidisciplinary teams, enabled Arup to realise
the architect’s iconic design and PwC’s vision of a worldclass head office.
Figure 4:
Concentrated solar
reflection analysis
18
Parametric Modelling