advanced building skins 14 | 15 June 2012 - lamp.tugraz.at - Graz ...

Advanced Building Skins
1.5 Closed-Cavity-Engineering, Further Advantages
In addition to the named advantages of a Closed-Cavity-Façade there are further essential advantages
compared to conventional single or double layer façades. But there are also technical challenges that
need to be solved design wise jointly with the manufacturer and the façade planning team.
The second part of this lecture will deal with another project example, the Marina Tower, and will
discuss how a ventilated cavity double layer façade can be optimised in terms of sustainability.
1.6 Delicate, Slender Facade Profiles
By omitting operable windows which require double profiles, the façade profiles themselves can be
designed much more slender (by approx. 50 %!!), because they only need to hold fixed glazing
elements. Visually they are connected almost flush to the glazing surface, which leads to an
aesthetically much more pleasing design.
1.7 Facade Cleaning Costs Cut in Half
The decisive disadvantage of a regular double layer façade compared to a single layer façade is the
fact, that a double layer façade also features double the surfaces of glass that need to be cleaned.
Depending on the site of the building this needs to take place two or three times a year.
But not so in the case of a Closed-Cavity-Façade. Because the interstitial space of the façade cannot
and doesn’t need to be opened, the internal surfaces do not need cleaning … just as is the case in a
regular single layer façade … but even better, the sun shading system, e.g. in the form of slender
aluminium louvers in light colours, does not need any cleaning ever.
If one calculates these savings in cleaning costs over a 25-year life span of a large building, this
accumulates, depending on the size of the project, to significant numbers in the area of 7 digit Euro
sums.
A Closed-Cavity-Façade is of course predestined for countries or cities with strong air borne pollution,
such as major cities in Asia and the booming regions of China, where façade cleaning twice or three
times a year is not sufficient.
Tasks to be solved in the Closed-Cavity-Approach
The lack of condensation needs to be ensured
When designing a Closed-Cavity-Façade special care needs to be taken during the planning and
production phase, to achieve a much tighter interstitial space or cavity than is usually necessary in a
normal façade. Even with the utmost care this might not be possible ... a façade is not a Swiss watch.
To ensure the lack of any condensation a system of tiny stainless steel pressurized air ducts is installed,
supplying the cavity by means of a capillary system with constantly cleaned and dried air at a small
surplus pressure. This way a permanently conditioned cavity zone is ensured with a very low and safe
dew point during all seasons. Pressurizing elements is a viable and well proven approach, which
ideally supplies the pressurized air from a central plant. Weather data and necessary dried air supply is
controlled electronically, ensuring a low energy input. Vertical air distribution in shafts and horizontal
supply routes in stainless steel are maintenance free.
Each façade element can be adjusted individually in its air supply, even retrospectively, by means of
its corresponding capillary system.
1.8 Technical Mock-up’s and Long Term Trials
To double check all technical solutions of the façade element in a scientific way and to eliminate any
risks, the client of the F. Hoffmann-La Roche project commissioned two separate 1 to 1 scale mockup’s
to two different façade contractors prior to awarding the contract, and the elements have been
tested thoroughly. These tests have been carried out by the most renowned independent German
testing centres. Amongst others, the lack of condensation in the façade has been tested in correlation
with the supplied air volumes and in correlation with the air tightness of the façade
In addition long-term tests have been carried out successfully, e.g. a 20.000 fold lowering and raising
of the sun shading system under cavity conditions. The optimised louver system is stable despite of
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