Architecture has always been interested in transparency but this characteristic hasstrong implications for energy performance. For many years architecture hasneglected this factor but today, in a time when society has developed an awarenessof the carbon footprint, architecture must restructure its approach and process.Transparency is still possible but its implications must be taken into considerationfrom the very beginning of the process: when façades are designed with respectsolar exposure and the advantages of internal natural ventilation, transparencybecomes sustainable in terms of energy balance in addition to contributing toarchitectural expression

Baldassini, N.

English

TU Delft Open Access Journals

Challenging Glass 2 – Conference on Architectural and Structural Applications of Glass, 
Bos, Louter, Veer (Eds.), TU Delft, May 2010. 
Copyright © with the authors. All rights reserved.  
North, South, East and West: The 
Environmental Approach to Transparent 
Design 
Niccolò Baldassini 
RFR, Niccolo.baldassini@rfr.fr 
Architecture has always been interested in transparency but this characteristic has 
strong implications for energy performance. For many years architecture has 
neglected this factor but today, in a time when society has developed an awareness 
of the carbon footprint, architecture must restructure its approach and process. 
Transparency is still possible but its implications must be taken into consideration 
from the very beginning of the process: when façades are designed with respect 
solar exposure and the advantages of internal natural ventilation, transparency 
becomes sustainable in terms of energy balance in addition to contributing to 
architectural expression. 
Keywords: Glass, Environment, Natural Ventilation, Integrated Design 
1. Introductions 
The German expressionist avant-garde focused their attention on transparency as a 
political issue believing that a transparent architecture permeated by light could also 
have social implications. On the other hand, the expressionist architects showed how 
transparency is related to technology, and, in particular, the Glass Pavillion of Bruno 
Taut highlights the limits of the technology of the time. 
 
In the Eighties and in the early Nineties the High-Tech movement, thanks to its strong 
interest and advances in technology, was able to dematerialise the façade and remove 
the usual frames by substituting them with glass fins or wind cable trusses. The 
envelopes of iconic buildings of that period, the Willis Faber and Dumas of Norman 
Foster, the Project 117 of Future Systems, are sealed enclosures, rather than permeable 
skins, thus requiring the use of mechanical plants to control the internal conditions. 
 
In the Eighties, the innovative development of double facades was a first attempt to 
reduce air-conditioning and has opened a new discourse. In parallel, transparent 
envelopes are not limited to prestigious buildings but have begun to characterise many 
typologies of common building. 
 
In this continuous development toward the immaterial building, we are now facing a 
new generation of buildings where transparency is sustainable thanks to a thorough 
approach which relates the facade to the external environment and, in particular, to sun 
exposure. 
 
Challenging Glass 2 
2. New strategies in the design of transparent facade 
RFR has designed transparent buildings from the very beginning of its activity starting 
with the Bioclimatic Green Houses of La Villette. Continuing from that experience, 
each successive project is a step in a new direction which contributes to an ongoing 
evolution. The projects developed in the last ten years also show some new trends.  
They go beyond the usual structural use of glass and the dematerialisation of the surface.  
They go beyond the maximalisation of transparency in pursuit of the realisation of 
facades which are not an event in themselves, but contribute to the global functioning of 
the building. The project here presented traces this recent evolution, particularly with 
reference to environmental and energy considerations which are today becoming a 
primary design parameter in our society which has a growing consciousness of the 
importance of reducing the carbon footprint. 
2.1. Avignon TGV Station 
The Avignon TGV Station (arch. AREP/Duthilleul, 1998-2001) has been designed with 
reference to a particular Avignon site and its environment which is characterised by a 
strong sun in the summer and the Mistral that blows from the Rhone Valley. One result 
of this is that the building is 450 meters long, as is the train itself, in order to protect the 
passengers from the wind while waiting the train. The south facade is opaque, in order 
to prevent direct sunlight from penetrating the space, and a transparent north facade 
allows direct views of the sky over the trains while the passengers are waiting. 
 
A CFD study proved that the shape of the building was effective in sheltering the train 
platform. A simulation of the slow air movement proved that the air flow was consistent 
with the need to ventilate the inner space for extracting heat. Since the building is 
slightly curved and the North facade is sloping, an illumination study was developed to 
be sure that the inner space was efficiently protected and that the glass frit was effective 
in shading the critical areas. 
 
    
Figure 1: Interior space of the Avignon TGV Station. - Figure 2: Wind analysis. 
 
With respect to the glazing technology, for reasons of geometry it was not possible to 
decompose the surface using only flat glass. Instead of using curved glass, the skin is 
composed of cold bent (elastically bent) double glazing units. The sealant joint of the 
double glazing unit was proven to be sensitive to the combination of the bending stress 
and stress due to the variation in temperature and volume of the chamber. To avoid 
North, South, East and West: The Environmental Approach to Transparent Design 
over-stress the units were specifically developed as “pressure equalised double glazing 
units,” one of the first application of this new technology.  
2.2. Nile House and Danube House 
A further step ahead is represented by the design of the atriums of Nile House, Danube 
House (2000-2005) and Amazon Court in Prague (arch. Kohn Pedersen Fox, 2005-
2009). The first two buildings are characterised by South-facing facades and a 
transparent roof. The atrium acts as buffer zone: it is neither heated nor air-conditioned 
and its function is to reduce the heat exchanges between the office (facing the atriums) 
and the exterior spaces with a volume of an intermediate temperature. The atrium is 
naturally ventilated, and, during the summer months, openings at the perimeter of the 
roof extract hot air. Additional fans augment the natural ventilation at peak time. 
 
Starting from this principle, other parameters came into play such as functional 
organisation, structure and shading strategy. The atrium assures the circulation through 
the building. The stairs and lift are on the south façade, and the walkway along the 
facade gives access to the wings of the building, while providing a view over the 
historical city centre. From the technical point of view, these walkways act as horizontal 
wind trusses and they also have the additional function of brise-soleil thanks to their 
horizontal depth. 
 
The same concept applies to the roof structure. Efficient, slender, but high beams shade 
the internal façade, reducing the glare in the offices but allowing an unobstructed view 
of the sky from the bottom of the atrium. 
 
        
Figure 3: Nile House. - Figure 3 and 4: Danube House. 
 
This project shows how an integrated design which deals simultaneously with the 
several design parameters can lead to new solutions coherent with the energy-saving 
considerations while creating a pleasant public space. 
2.3. Elm park Development 
More sophisticated is the design of the double facades of the Elm Park Development in 
Dublin (arch. Bucholz Mc Evoy, 2001-2008). Contrary to many standard cases of the 
projects of the Nineties, the double facade here is not an added element to the building, 
it is conceived in conjunction with the opposite façade, and its role goes beyond the 
Challenging Glass 2 
function of extracting hot air since it also activates cross-ventilation. Moreover, the 
cross-ventilation has a daytime and a night-time regime: during the day the double 
facade sucks away hot air, while, during the night, the fresh air flush cools the ceiling 
before being extracted by the facade. 
 
In order to take maximum advantage of the thermal mass, the concrete slabs are 
exposed without any false ceiling. Such a solution maximises the heat exchange 
between the air and the slab, reducing the slab temperature so that during the day its 
lowered temperature compensates the increase in temperature due to the working 
activity. 
 
Completely new is the fact that the efficacy of the double facade is reinforced by the 
extraction effect created by the wind acting on the façade’s openings at the roof level. 
This strategy has been developed on the basis of Dublin weather analysis and is made 
possible by the coincidence of hot days with windy days. CFD was used in order to 
prove that the roof openings are in negative pressure areas. 
 
Moreover, given that the building is composed of five parallel blocks, there was a risk 
of a masking effect of one building on the adjacent one. CFD analysis was used to 
analyse the interaction between the buildings and has demonstrated that the air flow was 
not compromised by the sequence of blocks. 
 
The architectural logic merges with the technical considerations, and both the outer 
aspect and the inner spaces are the expression of this thorough design process. Last but 
not least is the integration with the surrounding landscape, thanks to the use of wood 
structures that smooth the transition between the natural and the artificial [1]. 
 
       
Figure 5,6 and 7: Double façade of the Elm Park Development.. 
2.4. Strasbourg 
The Strasbourg TGV Station extension (arch. AREP/Duthilleul, 2003-2008) is the 
consequent evolution of the Avignon TGV station, but, in this case, the facade is facing 
South, instead of North, and the inner space is still naturally ventilated. This radical 
change is the result of many factors coming together, such as the new glasses now 
North, South, East and West: The Environmental Approach to Transparent Design 
available, improved calculation possibilities, and, most importantly, a new technical and 
architectural consciousness that reflect the know-how accumulated in these last years. 
 
The zone of overlap between the new shell and the roof of the existing building is used 
for extracting hot air, while the main entrance and the two side doors are used as air 
intake. Moreover, as with a “puit canadien”, the enclosed hall is directly connected to 
underground tramway station so that the incoming air is at lower temperature, thus 
reinforcing the cooling effect due to the natural ventilation. 
 
The glass is printed with a variable frit pattern up to 75% coverage on the upper parts of 
the shell in order to reduce the solar gain within the space. A Southwall XIR film 
reflects part of the non visible energy spectrum and a low-e coating on the interior side 
in order to minimise thermal radiations in the inner space  
 
    
Figure 8 and 9: Strasbourg TGV Station. 
 
Water nebulisation, at ground level, helps to control the temperature by taking 
advantage of the evaporation effect, which retrieves energy from the air. In addition, a 
series fans move the air, increasing the feeling of comfort which depends not only on 
the absolute temperature but on the psychological aspects of perception and on the 
exchange of heat between the air and the skin of occupants of the space. 
 
Further, the curved glass panels are not hot bent but cold bent using the innovative 
technique of cold bending the glass on a jig before its lamination in the autoclave [2 and 
3]. 
 
This building shows that the dream of total transparency is now possible thanks to a 
wise design that merge together all the technical, environmental and architectural 
variables. 
2.5. Banca Intesa-San Paolo Tower 
The visual aspect of the Renzo Piano San Paolo-Intesa Tower (Turin, 2007-2012) is 
marked by two double facades facing West and East. The external skin is a transparent 
screen composed by an interrupted series of louvers which extends well above the roof 
of the tower. In spite of its appearance, this double facade has a specific function and 
Challenging Glass 2 
interacts with the building in a new way, addressing the particular requirements of the 
bank’s activities, which prohibit having both transversal ventilation and night cooling, 
as is the case with Elm Park. 
 
The double facades, during the winter, act as a buffer zone mitigating the energy loss. 
During the summer, openings located every four floors, evacuate the heat accumulated 
in the chamber. The most relevant function is at night time, and, in this case, the 
strategy is to circulate the air inside the perforated slab instead flashing it. Consequently, 
the louvers, corresponding to every floor, are opened to let the air enter into the slab and 
go through the entire width of the building to be extracted on the opposite facade. The 
air cools the concrete slab and activates their thermal mass by reducing the temperature 
of the internal space during the day, as in the case of Elm Park. The air is drawn by the 
difference of pressure between the West and East façade, generated by the wind acting 
on the building. 
 
    
Figure 10: Wind pressure chart. - Figure 11: Study Model 
 
The pressure differentials have been validated thanks, firstly, to CFD simulation as well 
as to a vast regime of wind tunnel tests using various physical models (a 1:200 model 
for the pressure acting on the façade and a 1:50 model used for determining the pressure 
inside the double facade cavity). With respect to the design of the slab, the loss of 
pressure within the duct was determined using a 1:1 mock-up test. 
 
These data have been post-processed on the basis of the meteorological chart in order to 
evaluate the behaviour on the overall year. The openings of the facade and those of the 
slabs are controlled by computer system connected to several sensors used for collecting 
the primary environmental data, such as internal and external temperatures, wind speed 
and direction, etc. 
 
The South facade corresponds to a different logic. The external stairs are enveloped by a 
glass screen composed of louvers, in order to transform the vertical space into a winter 
garden. Every landing becomes a pleasant space to rest in the winter, when it is 
protected by the wind, and in the summer, when the breeze blows through the open 
louvers.  
 
The exterior aspect of the tower is founded on an architectural concept, but the exposure 
of the facades drives the expression of the building and illustrates its relationship with 
the environment. 
North, South, East and West: The Environmental Approach to Transparent Design 
3. Conclusion 
The crystal skyscrapers of the economic boom of the 80’s, with their four identical 
elevations, have mutated into organic buildings. The lessons learned in these years 
dictate that each elevation is now specifically designed as a transparent skin perfectly 
adapted to the sun’s orientation and well integrated into the environmental design of the 
entire building. The scientific approach, the developemment of new “ad hoc” technical 
solutions, such the cooling slab of the Intesa San Paolo Tower, and the new design 
strategies, are the tools for pursuing more and more efficient and sustainable buildings.  
 
These technical advances, the new know-how, and a burgeoning design culture which is 
sensitive to the environment and energy use, have nowadays reversed the perception of 
glass facades. In the eighteenth century, a glass envelope was nothing more than a 
greenhouse to cultivate tropical plants in the hostile English climate. Today, a south-
oriented, transparent, and naturally ventilated envelope creates a comfortable 
environment for human activities even during the hottest summer days. 
4. Acknowledgements 
The climate and environmental engineering studies for the TGV Avignon station and 
Banca Intesa-San paolo Tower were carried out by RFR-éléments. For the Nile House 
and Danube House projects, RFR cooperated with Battle McCarthy, and on the Elm 
Park Developemment and Strasbourg TGV Station with Transsolar.  
5. References 
[1] Baldassini, N., Geometry, mechanics and the environment: integrated transparent thinking, in: 
Proceedings GPD, 2009, 713-717. 
[2] Baldassini, N., Cold bending: from structural glass to glass technology, in: Proceedings ISSAG, 2008, 
7-12. 
[3] Baldassini N., Pottmann H., Raynaud J., Schiftner A., New strategies and developments in transparent 
free-form design: from facetted to nearly smooth envelopes, to appear in International Journal of Space 
Structure. 
Challenging Glass 2 
 


North, South, East and West: The Environmental Approach to Transparent Design

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