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HOW EFFECTIVE IS
DOUBLE-SKIN FAÇADE
IN PREVENTING BUILDING HEAT LOSS
Developing high performance
building facades requires
implementing efficient design,
engineering techniques and material
technologies to be effective.
Certainly, one of the most talked
about concept lately is the use of
double-skin facades.
There are several types of skins:
Insulated Glass Unit or IGU Wall
This is technically a double-skin
because there are two layers of
glass. However this is the basic
window component in all projects that
strive for any sustainability. It
is the base case for all exterior walls
built today.
The Cavity Wall
The Cavity Wall is where there is
more than 1.0m between the two
skins. The inner skin is an IGU and
the outer skin is single or laminated
glass.
The Vented Wall
The Vented Wall is where there is
less than 300mm between the two
skins. Either inner skin is an IGU and
the other skin is single or laminated
glass.
The Double-skin facade (Cavity type)
is a system of building consisting of
two skins placed in such a way that
air flows in the intermediate cavity.
The ventilation of the cavity can be
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DARWIN JAYSON MARIANO
natural, fan assisted or mechanical.
Apart from the type of the ventilation
inside the cavity, the origin and
destination of the air can differ
depending mostly on climatic
conditions, the use, the location, the
occupational hours of the building
and the HVAC strategy.
THE GOOD
The last few years have seen an
uptick in the use of double-skin
facades, or what others call a “skin
within a skin”, throughout the world.
This can be attributed to the fact that
it provides key advantages such as
durability, ecology, easy circulation of
fresh-air and use of natural
resources. One important factor to
note is that the type of double-skin
façade determines the type of air
circulation. In fact, the most
remarkable systems are those
designed in such a way that it permits
natural air circulation while also using
solar energy, converting it into
electrical energy. These are some of
the most popular benefits of double-
skin facades:
• Natural ventilation
• Better acoustic insulation -
improve noise protection
• Reducing heating energy
requirements
• Reducing cooling energy
requirements
THE BAD
However, many critics of this system
also point out that the advantages of
double-skin facades are not so clear-
cut. Many argue that similar
insulative objectives can be met by
using conventional high-performance,
low e-windows. In addition, the
construction of a second skin could
induce significant increase in
materials and design costs. From a
technical point of view, it can also be
said that building energy modelling of
double skin facades is inherently
more difficult due to varying heat
transfer properties within the cavity.
Some of the disadvantages are:
• Twice the area to build, repair,
and clean
• High first investment cost -
payback period is 5+ years
• More material in the building
• Requires fire separation in some
cases
• Not every climate is fit for a
double skin cavity wall. The
climate requires a 40 deg.
C change from winter to summer
to achieve the benefits
Putting advantages and criticisms
aside, many architects and engineers
consider this option for some of the
most iconic buildings today –
seemingly proving that the benefits
far outweigh the possible drawbacks.
One such project is the Shanghai
Tower, a supertall skyscraper in
China which, once completed in
2014, will be the tallest building in
China and the second tallest in the
world.
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THE BEST
To get some perspective about the
effectiveness of double-skin facades,
especially in the context of preventing
building heat loss, we spoke with
Marshall Strabala, Shanghai
Tower’s chief architect:
“Once finished, the Shanghai Tower
will be the world’s tallest double-skin
building. And so from the beginning,
we try to minimize the amount of
façade on the building in order to
decrease the cost and increase the
value of the façade.
“With regard to one of its key
benefits, it’s not only just about
preventing heat loss; it’s also
about limiting heat gain. We all know
that temperature usually goes from a
higher state to a lower state. This is
called entropy. In the summer, you
cool the inside of the building through
these steps:
1. Bring the air into the building,
and then Dehumidify the air
2. Cool the air to the desired
temperature
3. Push the air to the desired
location.
4. Then expel the air to the
outside and start again
5. Repeat this process about 2-5
times an hour depending on the
location.
“The latent heat of the this cool air
wants to migrate to the outside in the
summer. This is controlling heat
gain. In the winter, it’s the opposite.
It’s the hot air on the inside that
wants to migrate out of the building
where it is cold. The air temperature
wants to equalize state of energy with
the larger mass of nearby air.
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“What you’re trying to do is keep the
temperate from passing through the
façade. In the case of Shanghai
Tower, what we do is normally done,
as described above: we dehumidify it,
then we cool it, then we push it
through the fans to the office. Then
instead of throwing that air out, and
starting the process all over again,
we use it a second time by “spilling”
or diverting the cool air into the
interstitial atrium space. We use it a
second time, and why not? It already
has embodied energy that we
can use. And we then use it a third
time in a hydronic heat exchanger
that pre-dehumidifies the incoming
air.
“For example, we take air that is say,
35 degrees outside, we bring it in, we
dehumidify it to about 30deg C. Then
cool it down from 30 to maybe 18.
We pump that through the fans, we
deliver it to the office and by the time
it gets to the office it is back up to 20.
Then as it sits in the office for 30 or
40 minutes, it’s back up to about
22/24deg C. Then instead of
throwing that out, because we have a
lot of embodied energy, we use it a
second time in the atrium. And we
spill it at the top and the bottom so
we actually allow the atrium to mix
the air by natural convection.
“So you can have a situation where
the outside temperature is 35, the
atrium might be 30/28 and the inside
temperature of the office is 24. So
there’s a temperature gradient across
the facade. This temperature
gradient is what gives us a
very high insulative value in the
façade.”
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Marshall Strabala AIA AFAAR LEED ap. is the co -Founder and Design Partner of 2DEFINE Architecture.
He is an American architect, living in Shanghai, who has lead the design team of three of the ten
tallest “constructed” buildings in the world. For the last three years, Strabala has been the principal of his own
architectural firm, with over 30 years of combined experience. He was an Associate Partner in Chicago at
SOM, and the only Director of Design M. Arthur Gensler Jr. & Associates, Inc.
Hear more from Marshall Strabala and other distinguished speakers at the 3rd Annual Facades Design and
Engineering China 2013, happening on 18-21 June at Shanghai, China.
www.facadechina.com
Disclaimer:
Please note that we do all we can to ensure accuracy and timeliness of the information presented herein but errors may still understandably occur in some cases. If you believe that
a serious inaccuracy has been made, please email [email protected]. This article is provided for information purposes only. IQPC accepts no responsibility whatsoever
for any direct or indirect losses arising from the use of this report or its contents.
About the Author:
Darwin Jayson Mariano is the Online Content Manager and Regional Editor - Asia for International Quality & Productivity Center
(IQPC), a leading producer of events and conferences for business leaders around the world. Connect via LinkedIn
sg.linkedin.com/in/whoisdarwin or email [email protected]
