By the time you read this article the entries in the $1 million
“Zerofootprint Building Re-Skinning Competition” will be in the capable
hands of eight judges. I won’t be surprised in the least if the general
public hears a lot more about glass and glazing than it ever has.
That’s partly because the competition is specifically designed to
generate publicity and “jumpstart” interest in the concept.
There is also a very good reason that professionals in the glass
industry should be aware of this competition: competitors intend to
retrofit five occupied buildings and monitor the energy performance for
three years. Take my word for it – you’re going to hear a lot about it.
Unfortunately for the sponsors and 28 experts appointed to advise the
competition organizers – I suspect it won’t all be good news.
A glazed double facade (GDF) can be defined as two layers of insulated
glass separated by a significant amount of air space, that is to say, a
second glass facade is placed in front of the first. These two
envelopes act as insulation in theory by enabling the air to circulate
in the cavity. In some cases the ventilation of the cavity is
controlled by fans or openings. The envelopes are not necessarily
airtight and automated equipment, such as shading devices, are often
installed. We are also starting to see “hybrid” systems with materials
other than glass and as a result the term GDF may not be applicable for
very long.
I recently surveyed the existing literature that has been written about
these incredibly complex building systems and discovered what amounts
to a tremendous amount of speculation about their performance in both
new and retrofit construction. By the way, the idea is not new. It has
been around for more than 100 years and the concept actually predates
insulating glass. Only recently have I heard people refer to the
concept as “re-skinning.”
The key performance issues are safety, stability, occupant comfort,
acoustics, energy efficiency, control strategies, air
quality/ventilation, daylighting, maintenance/cleaning and cost.
Until recently there were very few articles written that provided an
independent review of these systems. Dr. Karl Gertis, director of the
Fraunhofer Institute of Building Physics in Germany, wrote the most
comprehensive and is considered the leading expert on the subject.
He concedes that they have become very fashionable; however, his
article really knocks the wind out of the sails of the people who have
been actively promoting these systems, to the surprise of many.
To start with, in North America they can be four times as expensive as
a conventional building envelope. He also states that in spite of all
the claims made about improved energy efficiency in the buildings they
should in fact be rated as energy guzzlers.
He also states that computer simulations cannot be relied on, practical
measurement results are lacking and apart from a few special cases,
they are unsuitable from a building physics point of view. Moreover,
they are much too expensive and most of the performance claims that
have been published have proven to be wrong or untrue.
He notes that the arguments against these systems are much more important than the arguments for them.
He was referring to new construction. When you get into the field of
retrofitting double facades, life will get even more complicated as I
suspect the organizers of the competition will soon discover. First of
all, 30-year-old buildings will demonstrate defects as a result of
their service life and will require a complete audit as well as
repairs.
Secondly, as I was taught early in my career, it’s not considered good
practice to carry out untested experiments on occupied buildings.
And lastly, I have read that the average tenant has a tolerance of
about one day when it comes to maintenance and construction retrofit
activity. In other words, if you can’t accomplish the task in one
12-hour shift, you are going to hear about it.
Brian Burton is the business development
manager for Can-Best (www.Can-Best.com) and is a frequent contributor
to industry trade publications in the field of building science. He can
be reached at
This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
|
