Canadian Consulting Engineer
“Fryscraper” in London highlights glare issues with glass buildingsBuildings Building Envelope
In the past buildings with mirror glass walls have been blamed for killing birds, but now they're being looked at twice for having the potential to concentrate sunlight and cause damage.
In the past buildings with mirror glass walls have been blamed for killing birds, but now they’re being looked at twice for having the potential to concentrate sunlight and cause damage.
The 37-storey “Walkie Talkie” building under construction on Fenchurch Street in the financial district of London, U.K. caused a sensation last week when its concave walls acted something like a magnifying glass and concentrated sunlight down on the streets below and buildings opposite. The owner of a parked Jaguar car complained that parts of his vehicle had been warped by the heat, and a video on the Guardian UK news showed people frying eggs on the sidewalk and tiles that seemed to be popping off a storefront. At one point a solar physicist from Imperial College London was interviewed standing in the hot spot and his thermometer read 90 degrees C while it sat in his bag on the sidewalk.
Designed by Rafael Vinoly, a Uruguayan architect who had similar “death ray” problems with a hotel he designed in Las Vegas, the Fenchurch street tower has been dubbed a “fryscraper.” It has an unusual shape that bows inwards from the top and sides. Halcrow Yolles are the structural engineers.
The building developers, Land Securities and Canary Wharf Group, have had to install a temporary scaffold to protect the street below, but they assure the public that the phenomenon will only happen while the sun is at a certain elevation in the sky, which will be for approximately two weeks this fall. Vinoly was quoted as saying that originally the south side of the building was supposed to have horizontal louvres, but these had not been installed.
Duncan Phillips, P.Eng. of RWDI in Guelph, Ontario says that as engineers who specialize in the environmental effects of tall buildings around the world, they analyze a variety of different solar issues, and do glare analyses fairly regularly. Most often, however, “it’s a question of, ‘Is the sunlight going to reflect off this building and cause a temporary issues for drivers or pilots?”
At the Fenchurch Street building (RWDI has had no role in the solar work), he says “it is just an unfortunate set of circumstances that they just happen to have a focal point for the reflected sunlight in an occupied point at street level.” He adds: “My sense is there are probably a lot more buildings like this that go unnoticed because the focal point is in mid-air.” In other words, while many mirror glass buildings might similarly concentrate solar glare, either the building is not in a built-up area, or the shape of the walls does not reflect the light downwards.
However, Phillips says that there have been cases where even a mundane building has reflected sunlight and caused problems: “There are reports of plastic siding melting in the sunlight reflecting off a window. There were no fancy curvatures to the architecture — it just happened to be the arrangement.”
So Phillips says that while reflective glass is useful to help make buildings energy efficient and sustainable by reducing solar gain, we may have to consider the solar
effects on the surrounding buildings in the same way as we study the wind effects. “RWDI works on tall buildings in cities like Toronto, Mississauga, Boston, Hong Kong, London and San Francisco. They all say that when you are building a tall building in their city you have to look at wind. There’s no reason why these communities can’t also say that you also have to look at glare and shade and a whole range of environmental issues.”
RWDI has done glare studies on a variety of projects around the world, says Phillips: “We have studied glare in very tall buildings, and in airports where we are looking at the impact of PV panels and reflective surfaces such as terminal buildings and how they affect pilots in the flight path. And we’ve studied miscellaneous buildings that happen to be situated next to roads.”
But the consultants found that the commercial products didn’t allow them enough “fidelity,” explains Phillips, “meaning we couldn’t input the individual mullions and very fine building geometry details.” Also, “they weren’t powerful enough to handle large sections of downtown.”
As a result RWDI has developed its own technology for predicting glare and ironically just finalized it this month.
To see the video of people reacting on the London street to the heat generated by the Fenchurch Street Building on the Guardian website, click here.