DOUBLE SKIN FACADES:

FEASIBILITY FOR SOUTHAMERICA

 Leandro G. Heine

Research Center Habitat & Energy - CIHE

Faculty of Architecture, Design and Urban Planning

University of Buenos Aires

Pabellón 3, Piso 4, Ciudad Universitaria, C.P. 1428, Buenos Aires, Argentina

E-Mail: lheine@argentina.com

Guillermo D. Marshall

Estudio Marshall & Asociados – Curtain wall Consultants

Marconi 690  7°B , B1636GHB , Olivos , Provincia de Buenos Aires, Argentina

E-Mail: consultores@estudiomarshall.com

www.estudiomarshall.com

ABSTRACT

The ever increasing importance, and apparent success, of multiple skin glazing systems in Europe poses the question of their feasibility in other contexts. This paper seeks to identify and establish the applicability of these systems in the southamerican scenario, defined by the following cities south of 30°S: Montevideo 35.0°S, Buenos Aires 34.5°S, Santiago de Chile 33.2°S, Rosario 33.0°S, Córdoba 31.1°S, Porto Alegre 30.1°S. These are the most important cities of the Mercosur “common market corridor”, and as such will probably be the first to have an advanced/innovative building from the technology point of view, if or when the chance occurs. Obviously, they are very different from Geneva, Vancouver, Frankfurt, London or Berlin, cities which already boast some of these “environmentally friendly” buildings.

A considerable amount of material from different media (congress proceedings, magazines, books, various other publications on paper and downloaded from the internet) was analyzed, some double skin buildings were visited and interviews were conducted with responsible parties and other specialists abroad, to clarify which DF types would be potentially useful, which parameters must be considered and which are the likely problems and challenges designers will face in this context.

The paper therefore addresses the following comparative issues: Climate, Integrated Design processes, Loads analysis, Culture and Economy, Construction.

Some preliminary conclusions are:

There are no real “market reasons” for DF buildings here at the moment: there is not enough “energy efficiency” awareness nor mandatory regulations, capital investment in buildings does not contemplate long-term benefits associated with DF implementation, the construction industry is fragmented and it is not used to innovative, integrated design processes.

However, there is great potential for DF systems if they can greatly reduce the cooling loads (due to the high radiation and higher temperatures typical of the area) with proper shading, because energy costs are rising and imported HVAC equipment is very expensive. Also, in a local economic crisis context, architects, planners, contractors and owners have shown to be very creative and collaborative in achieving innovative solutions if the benefits are proven.

Keywords:  double skin façade, feasibility study, energy efficiency, South America

INTRODUCTION

The DF (double-skin facade / Doppelschalige Fassaden / doble fachada) consists basically of two glazed façade layers which are separated by an air space in between. This type of façade has been sufficiently explained and has many different types according to the functions it must perform (Nolte and Pasquay, 1997; Oesterle, 2001).

These functions include one or more of the following:

·        Increase or improve the use of natural ventilation (in buildings where this is not usually possible because of wind speed and/or pollution, noise, etc.) to reduce the use of air conditioning thus reducing energy consumption, size of equipments,  risk of SBS, etc.. Sometimes, this includes occupant control of the immediate environment.

·        Reduce solar gain in summer (thus reducing cooling loads) by incorporating solar protection devices in the cavity (where they are protected from the outside environment).

·        Improve sound insulation (specially for buildings in noisy environments, eg: near highways or airports).

·        Improve thermal insulation (eg: acting as buffer-spaces, reducing global U-values).

·        Contribute to passive heating or cooling strategies.

·        Improve day lighting management/penetration, thus reducing artificial lighting and subsequent heat gains.

·        Increase occupant comfort in areas next to the façade by avoiding hot or cold radiation effects.

CURRENT KNOWLEDGE

In order to illustrate the advantages of DFs, current knowledge usually relies on a comparative analysis of a DF system vs. an equivalent conventional single skin facade. These advantages include, for a cold temperate climate:

·        Increased worker productivity and satisfaction (in the case of office buildings) due  to the individual control of their environment.

·        Reduced energy consumption (up to 65%).

·        Reduced associated CO2 emissions (up to 50%).

·        Reduced sound transmission (up to 20 dB).

More conservative calculations establish the reduction in energy consumption at 30%. The differences in performance are due to the different bottom-line scenarios that are chosen to make the comparison and the variations within the mid-european climate.

New and improved DF’s are possible thanks to the improvement in computer simulation processes which allow for complex integration scenarios between HVAC systems, automated or user controlled comfort parameters, and reaction to outside seasonal and daily variations of climate. To do this, highly skilled and specialized interdisciplinary teams are assembled to design, test and monitor  performance results of the DF. Usually associated to university research centers, these teams also receive financing from the construction industry interested in offering more and better products.

However, an important drawback, , is price (Initial investment): DF systems can cost twice (or more) than conventional facades due to increased engineering, material and installation costs. To offset this, whole-life costing must be evaluated (reduced building operating costs, smaller and cheaper HVAC equipment, reduced lighting equipment, etc).

Another important factor affecting DF successful implementation is environmental awareness. These new generation of buildings are marketed as more and more energy efficient and environmentally conscious. In Europe, specially in Germany, owners and promoters compete for the latest and most architecturally “green” building, to support a “greening” of corporate identity. Building codes rise the threshold of their requirements to catch up with global warming awareness and rising energy costs, pushing conventional high-rise building solutions to improve their performance. Thus, buildings compete for “green labeling” that constitutes another argument for promotion and sales. Given the circumstances, consultants and research centers offer DF solutions as a high level, promising solution, promoting superior comparative results widely in specialized congress meetings and scientific and architectural publications. DF’s are extremely popular within prestigious architectural offices: “transparent” all glass high-rise buildings can be made, as Mies van Der Rohe once dreamed of for Berlin, and the consequences of this choice are not always evaluated (Lang and Herzog, 2000).

Contrasting with this “high-tech” positivist scenario, detractors appear who alert that not all that glitters is gold, that comparisons and simulations always make DF’s the winner because they are compared with old technology, poor-performing single skins. They suggest revising the sophisticated DF solutions and replace them with common-sense, proven solutions. Example: reduce glazed areas and/or use exterior shading to reduce solar gains instead of using complex evacuation gadgets of the inter-skin space (Straube, 2001). Also, some DF’s have had overheating problems. This must be clearly avoided.

It must be noticed, however, that some of the  problems a façade has to solve, whatever façade type it is, are man-made and can be avoided: speculative or pre-conceived typologies not adequate for their site/environment/climate, high levels of noise that must be shut out by the building skin, air pollution that must be filtered by the HVAC system, lack of sun-access rights which may cause future buildings to change the original performance hypothesis. These, among others, have led to revise or change planning, energy and transport policies which are outside the scope of this paper but that notoriously affect the performance of a façade.

FEASIBILITY STUDY

To define the southamerican scenario (between latitudes 30°S and 35°S), the cities chosen are: Montevideo 35.0°S, Buenos Aires 34.5°S, Santiago de Chile 33.2°S, Rosario 33.0°S, Córdoba 31.1°S, Porto Alegre 30.1°S. The following comparative issues are addressed:

Climate

In figs. 1 and 2 are presented the comparative results of 3 critical variables that determine the  cooling and heating loads calculations, that are very different for cities where DF’s have been applied than thops for the cities presented in this paper. For the first group, we have an annual mean temperature between 8,9 and 10,6°C, very much below than what we have in Buenos Aires (16,8°C), in Rosario (17,2°C) or in Córdoba (17,7°C). Comparing with the former, these higher temperatures are accompanied by a higher availability of global annual horizontal radiation (H_Gh) which means higher day lighting levels, and diffuse and reflected radiation. However, global vertical radiation facing the equator (the sunniest facade) is not so different.

There are greater differences between winter mean temperatures and a bit less for summer mean temperatures. This means very different exterior temperatures which must be determined accordingly. Also, “peak” scenarios with simultaneous high temperatures and high radiation levels must be evaluated (eg: West façade, afternoon). This is very important because typical DF designs tend to favor overheating of the interstitial space.

Graphs data has been obtained with Meteonorm 4.1 software, and double checked with available data in Argentina (Grossi, 1998).

Ambient humidity is another critical factor that impacts on comfort levels.  High absolute values for south America (not quantified in this paper) mean large latent heat loads, need for dehumidification in summer and condensation problems in winter. A direct natural ventilation strategy (such as many german DF’s have) may not be valid for south America and must be studied carefully. Problems of this type have occurred even in some european DF’s (Pasquay, 2001).

Integrated Design

“Active” (mechanically ventilated) DF’s are different from conventional systems because the façade is physically integrated to the HVAC equipment. “Passive” (naturally ventilated) DF’s must also be considered as an integral part of the energy strategy and climate control concept of the building. This is a starting point very different from the current and usual design process in most of southamerican architectural offices. Without a collaborative and interdisciplinary design approach, a DF may even be harmful for the performance and functionality of a building.