IEEE Spectrum September, 2010 - 12

Frankfurt Tower's
Power Trick

A sensor-tuned facade lets
fresh air in without throwing
energy out

Y

ou don't need to seal yourself
in to live green. That's the
message from the engineers of
the Westarkade, a colorful high-rise that
officially opened in Frankfurt in July.
The 15-story glass tower glows
with natural light and offers windows
that open-a comfort that can wreak
havoc with energy efficiency. But the
Westarkade's first-of-a-kind "pressure
ring" facade and sophisticated, sensorrich control scheme promise to consume
no more than 100 kilowatt-hours of
energy per square meter per year. That
would make it a world-class energy
miser, using half as much energy as a
conventional office building in Europe
and as little as a third of the U.S. average.
"It's an aggressive goal, especially
with this building that's all glass,"
says Mark Perepelitza, a facade
expert with Zimmer Gunsul Frasca
Architects, based in Portland, Ore.
The Westarkade's dynamic facade is
a descendant of a 1990s German design

SEnSiblE SyStEm: the Westarkade tower integrates data from dozens of
sensors to keep the tower from consuming power. photo: kfW Bankengruppe

that was developed to manage excess
sunlight in glass towers. Horizontal
venetian blinds installed outside of the
tower's glass envelope reject unwanted
summer heat, while a pane of glass
installed over the blinds and ventilated

When ChiCkens AttACk
Continued from previous page

chickens: Each image is
slightly different from
the last, with humans or
chickens moving relative
to one another within the
video's frame, and each
kind of crowd has its own
signature flow pattern.
To show that the
method could apply to
hens, Dawkins, Roberts,
12

and their colleagues did
experiments in which some
statistics from the opticalflow pattern correlated
well with an established
but much more arduous
method: watching how
individual chickens walk.
Farmers can hire trained
experts to evaluate the
health of flocks by scoring

NA * Ieee spectrum * september 2010

at the top and bottom protects the
blinds from high winds. The "double
skin" design comes up short, however,
when architects add windows that open,
which is typically mandated under
European labor codes. Winds create

each chicken's gait, but those
experts can't constantly
monitor a flock, says
animal behaviorist Harry
Blokhuis of the Swedish
University of Agricultural
Sciences, in Uppsala.
"It was an engineering
challenge," Roberts
recalls. "Could we mimic
the laborious labeling
with a computer?"
Roberts turned to hidden
Markov chains, a kind of
mathematical model that

uses noise in a data set to
estimate the underlying
"normal" signal and then
identify when the signal is
going awry. Then the team
applied it to footage of more
than 300 000 commercial
free-range chickens. They
found telltale behavioral
disturbances in the flocks
that had the most feather
damage. Zoologists who saw
the results "were certainly
really surprised that we
could forecast so well
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Table of Contents for the Digital Edition of IEEE Spectrum September, 2010
