Double Skin Facade

DOUBLE SKIN FAÇADES MORE IS LESS?

Lead Author: Brett Pollard, BLArch, BArch Contributing Author: Mary Beatty, BS, BDes Arch

HASSELL Level 2, 88 Cumberland Street Sydney, NSW, 2000, Australia [email protected]

ABSTRACT The term double skin façade covers a wide range of façade systems and types from narrow fully sealed assemblies to systems with fully operable external louvers or shading devices. All of them have one thing in common, the outer and usually the inner skin is highly glazed. The use of double skin façades has increased significantly over the last 10 to 15 years, primarily due to the benefits attributed to them in regard to increased energy efficiency and improved day lighting. There remains debate, however, about whether these benefits would be more effectively provided by a well designed, traditional, single skin façade system. Indeed a German study from 1999 1 concluded that “It becomes apparent that DSFs (Double Skin Facades) - apart from special cases - are unsuitable for our local climate (German) from the building physic's point of view. Moreover, they are much too expensive. If they are nevertheless designed in order to keep up with architectural fashion, building physics support is indispensable.” This paper will survey the various types of double skin facades systems, exploring their features and functioning followed by a review of examples, both constructed and proposed, from North America and Australia. The paper will then assess and analyse recent research and examples to attempt to reach a conclusion as to whether with a double skin façade, more really is less.

from a paper written by Dr Karl Gertis, director of the Fraunhofer Institute of Building Physics in Stuttgart, Germany. The paper is called "Sind neuere Fassadenentwicklungen bauphysikalisch sinnvoll? Teil 2: Glas-Doppelfassaden (GDF)" published by ©Ernst & Sohn Bauphysik 21 (1999), Heft. A summary of the paper in English was obtained from http://gaia.lbl.gov/hpbf/perfor_c.htm

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B.Pollard, M.Beatty ATTRIBUTED BENEFITS The primary benefits attributed to DSF are their ability to save energy and permit day lighting of the internal spaces of the building. In regard to the reduction in energy use, DSF are credited with the ability to mitigate the impact of the prevailing climatic and environmental conditions on the interior of a building, allowing a reduction in the size, extent and operation of a building’s Heating, Ventilation and Air Conditioning (HVAC) systems. In some cases DSF have been credited with eliminating the need for air conditioning altogether. Battle McCarthy, a United Kingdom based engineering and landscape architectural practice, state on their website that “…. double skin buildings are able to reduce energy consumption by 65%, running costs by 65% and cut CO2 emissions by 50%, in the cold temperate climatic prevalent in the United Kingdom when compared to advanced single skin building.” Specifically, DSF are reported as achieving reductions in energy use by;
Reducing heating demand. DSF achieve this in a number of ways. Firstly, the cavity

between the inner and outer skin forms an additional layer of insulation to the building, preventing heat loss. Secondly, warm air in the cavity can be used to preheat fresh air being introduced into the building for ventilation. Thirdly, extensive glazing allows sunlight to be used for passive heating of the interior of the building.
Controlling solar gain. In warmer months and climates, the cooling demand can be very high due to solar gain through windows and the fabric of buildings. DSF can reduce the impact of this solar gain by allowing shading devices to be installed in the cavity between the two skins, preventing sunlight from reaching the inner skin. The shading devices are normally adjustable to ensure that views through the highly glazed façade are retained as much as possible. Warm air trapped within the cavity can be expelled by natural and/or mechanical ventilation to prevent it from heating up the interior of the building. The cavity protects the shading devices from rain and wind, especially on tall buildings, as well as providing access for maintenance of these devices. Allowing natural ventilation. Natural ventilation provided by operable windows in the

inner skin is believed to significantly reduce the load on the HVAC system by providing fresh air and cooling comfort for the occupants of a building. DSF can allow for natural ventilation even in high rise buildings by providing protection for windows in the inner skin from wind and weather. DSFs can also be used for passive night time cooling of a building’s structure, and a stack effect can be created within the cavity to improve cross ventilation and purge hot air from the building. Increased access to daylight due to DSF is a direct result of the high levels of glazing in the skins. The specific benefits of daylight are;
Reduced artificial lighting requirement. Daylight can significantly reduce the requirement for artificial lighting within a building. Daylight can potentially become the major source of lighting for the perimeter of the building with artificial lighting only being required when the sun is not shining. This results in reduced electricity demand and therefore saves energy.

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B.Pollard, M.Beatty

Improved occupant comfort. Access to daylight is seen as an important component of occupant comfort and is believed to contribute to improved productivity, reduced eye strain and reduced stress levels.

In addition to these two primary benefits, there are a number of other benefits ascribed to DSF including:
Acoustic protection. DSF have been used to provide acoustic protection for buildings

located near roads and railway lines. In theory, the outer skin provides a barrier to noise while allowing windows in the inner skin to be opened for natural ventilation.
Views. As buildings with DSFs generally have highly glazed facades, the occupants to

have increased access to views which is believed to improve wellbeing through greater connection with the outside world and reduced eyestrain.
Enhanced security. DSF are said to improve security due to the presence of an

additional layer of building fabric that can impede illegal entry through the façade of the building. The outer skin can also allow internal windows to be opened for natural ventilation in high security buildings or at night when the building is unoccupied while maintaining perimeter security. The outer skin can also be reinforced or armoured to provide additional protection.
Futureproofing and increased building lifespan. This results from having a fully glazed

façade with a high degree of environmental control for the perimeter zone. In theory, this allows enhanced flexibility in the arrangement of furniture and spaces within the building as there are no blank walls or other impediments. Therefore the building can accommodate future needs without extensive renovations or demolition.
Pollution barrier. In much the same way as the acoustic and security protection, DSF are

claimed to allow natural ventilation in polluted locations with the outer skin screening pollutants permitting windows in the inner skin to be opened.
Emergency egress. If maintenance walkways are present in the cavity between the two

skins they can be, according to some authors, integrated into the emergency egress paths. Until recently double skin facades have been used as an energy saving strategy predominantly in colder climates of Europe and North America. In recent years they have begun to be used on buildings in warmer climates such as Australia however research for this paper indicates that they are being used for differently in warmer climates. In the Australian buildings researched, the external façade is primarily used to reduce energy consumption and improve occupant comfort by reducing solar gain to the building though the use of louvers or blinds located in the cavity and operable windows on the internal skin to allow for natural ventilation. Another difference is that, unlike in colder climates where air in the sealed cavity is intended to be warmed by the sun or artificially to reduce load on the artificial heating systems, the cavities in Australian double skin facades are more commonly designed to be well ventilated to allow warm air to escape by creating a stack effect, thus reducing the cooling load on the buildings.
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B.Pollard, M.Beatty DOUBLE SKIN FAÇADE TYPES There is no accepted standard for grouping or defining the different types of DSF. The literature reviewed for this report found a multitude of ways to classify them. For example, Harris Poirazis in his comprehensive review of DSF found more than six different ways of classifying them. Bestfacade, a European Union project set up to review and put in place best practice guidelines for DSF, has developed a classification system for DSF based on their own extensive review of the literature and built examples. Their system is based on three sets of criteria: the type of ventilation, the ventilation mode of the cavity and the partitioning of the cavity. While extremely comprehensive this system does allow for a large number of potential system variations and too many to describe and provide examples of in this report.

Fig. 1: Bestfacade DSF Classification Diagram (VDF = DSF) WP1 Report

Source: Bestfacade

In 2000, Lang and Herzog defined three basic types of DSF. This classification has been adapted and developed by Terri Boake of the University of Waterloo’s School of Architecture. While relatively basic, it does allow for easy understanding of the different DSF types and was considered the most suitable classification system for this report. The different types of DSF are: ƒ ƒ ƒ ƒ the Buffer; the Extract Air; the Twin Face; and the Hybrid System

In addition to these 4 basic types there is one additional distinction between DSF, whether the cavity is continuous or divided into compartments, usually on a floor by floor basis.

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B.Pollard, M.Beatty Buffer Double Skin Facade As the name suggests this type of DSF provides a buffer between the external conditions and the interior of the building. The cavity essentially functions as an insulating layer with the added benefit that any heat that builds up in the cavity can be expelled in the warmer months, usually by natural ventilation created by the stack effect. It is suggested by Lang and Herzog that both skins of buffer facades are typically single glazed but it has become more common for the outer skin to be single glazed and the inner skin to have double glazed insulating panes installed. Automatic blinds are usually installed within the cavity to reduce solar gain in summer. It is typical for this type of DSF to run continuously for the full height to the façade with the only interruptions being perforated or grid mesh access ways for maintaining the glass. If narrow cavities are used, maintenance access is usually provided by making the internal glazing operable. The disadvantage of this is the disruption that can occur when access is required. There are no openings in the internal skin and none in the external skin apart from ventilation inlets at the base of the DSF and outlets at the top. Typically the ventilation inlets are controlled by automatic dampers and exhaust fans can be installed to assist with removal of the heated air from the cavity. There is no natural ventilation of the interior of the building through the DSF and the building’s HVAC system is completely separate from the DSF. However, some buildings have reclaimed the heat that is expelled at the top of the DSF and reused it in the HVAC system.

Fig. 2: Buffer DSF Source: Boake UW

Figs. 3 & 4: Business Promotion Centre Germany Source: www.fosterandpartners.com

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B.Pollard, M.Beatty Extract Air Double Skin Facade Extract Air DSF use the cavity between the two skins as an exhaust path for the return air from the HVAC system. This allows the heat of the return air to warm the cavity space and enhance its insulating effect. The exhaust air is expelled at the top of the DSF, usually after the heat has been extracted for reuse in the HVAC system. In the warmer months heat gain is moderated by the continuous extraction of the return air and the heated air from the cavity. Additional outside air can be introduced at the base of the DSF, if required. Solar gain to the interior of the building can be further reduced by using shading devices mounted in the cavity. This system uses a single layer of glass in the outer skin and double glazing for the inner skin. As the cavity is effectively acting as duct, it tends to run continuously up the façade of the building. The width of the cavity can be narrow or wide with similar access provision as for the Buffer Façade type. This type of DSF is reliant upon a building’s HVAC system and so can use more energy than DSF that use natural ventilation during benign climatic times of the year. Although not stated in the literature reviewed, it may be possible to use the stack effect created in DSF to extract air from the building’s interior without use of the HVAC System

Fig. 5: Extract Air DSF Source: T Boake UW

Figs. 6 & 7: Bürogebäude Felbermayr, Salzburg, Austria. Source: www.architecten.at

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B.Pollard, M.Beatty Twin Face Double Skin Facade These types of DSF are categorized by having two skins that are able to be opened to permit natural ventilation of both the cavity and the building’s interior. Typically the outer skin is single glazed and the inner skin is double glazed and contains the water, air and vapor barriers for the building. The extent of openings in the skins can vary significantly depending on the ventilation strategy to be employed. The outer skin can act as a wind shield to allow the windows in the internal skin to be opened to permit ventilation and/or night cooling of the building’s interior regardless of the wind conditions or height of the building. If the DSF is required to assist with insulation against the cold, the openings can be closed to make it act like a Buffer DSF. As the range of potential options with this DSF is large, the cavities can be narrow or wide, continuous or compartmentalized. Shading devices can also be installed within the cavity. The advantage of this DSF over the other two is that it is able to more easily discharge the heat that can build up at the top of the cavity. However, if effective sealing of the outer skin can’t be achieved it may not function as well as, say a Buffer DSF, in the colder months. Therefore this DSF tends to be built in locations without an extensive and prolonged heating requirement unless the insulating performance of the inner skin increased.

Fig. 8: Twin Face DSF Source: T Boake UW

Figs. 9 & 10: Daimler Benz (Debis) Building, Berlin Source: www.coltinfo.net Source: www.rpbw.com

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B.Pollard, M.Beatty Hybrid Double Skin Facade Hybrid DSFs can be a combination of, or variation on, any of the previous three DSF types. The façade of the New York Times building, while not strictly a DSF, can be seen as a variation of the DSF. This is on the basis that an additional layer (skin) has been added to what is essentially a fully glazed building. Here, a layer of carefully spaced ceramic rods have been positioned off the glazed facade to reduce solar heat gain and glare while still admitting daylight to the interior of the building. The design goal was to reduce the energy consumption of both the HVAC and lighting systems of the building. Extensive studies were undertaken by the consultant team in partnership with the Environmental Energy Technologies Division (EETD) of the Lawrence Berkeley National Laboratory to develop both the external skin and the automated internal blinds that make up the other half of the daylight control system. The project has only been recently completed and will be studied by EETD to determine whether the predicted $20,000/floor/year energy savings are achieved.

Fig. 10: New York Times Building Source:www.brianrose.com

Fig 11: Detail of ceramic shading elements Source: architecture.com/MID

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B.Pollard, M.Beatty DESIGN CONSIDERATIONS As with all building systems and technologies there are a number of additional considerations that need to be addressed other than just benefits and system functioning. The design of DSF requires that the following issues are taken into account;
Floor area. If a building needs to use all of the available site area, for example if the site

is in an inner city location, the cavity required for the DSF can reduce the available floor area for occupation or leasing by the owner. Alternatively, if a site is not as constrained, the DSF cavity can lead to increased floor area and therefore increased impact on the site.
Floor plan shape. The prevailing climatic and solar conditions primarily impact upon

the interior spaces that are located directly adjacent to the windowed facades of a building. These spaces are commonly known as the perimeter zone and typically extend 3.5 to 4.5 meters into the building. The heating and/or cooling loads present in the perimeter zone tend to be high but vary depending on the time of day and year. If a building directly abuts another building or has a windowless façade, the outside conditions have far less or no influence on the adjacent spaces. These spaces as well as the spaces that are located away from the edge of the building are known as the centre zone. The heating and/or cooling loads in the centre zone are relatively stable and tend to be much lower than the perimeter zone. However, this is dependant on the type of plant, equipment, computers, lighting and occupants located in the centre zone. The ratio of perimeter zone floor area to centre zone floor area can affect the degree to which external conditions influence the design and size of a building’s HVAC system and therefore the contribution that a DSF can make to reducing HVAC energy requirements. If a floor plan is long and narrow, the ratio of perimeter zone to centre zone will be high and therefore the HVAC system will need to focus on the external conditions. If the DSF can mitigate the external heating and cooling loads the capacity or length of time the HVAC is required to run can be reduced. However, if a floor plan is squarer, the ratio will be lower and so will be the potential contribution of DSF to reducing overall HVAC energy use. Similarly if a building abuts others, has only one glazed façade or limited amounts of glazing the potential benefits of a DSF will be lower than on a building with a large amount of glazing.
Heat build up in cavity. The upper sections of a continuous DSF cavity can become quite

hot and cause overheating in the adjacent internal spaces even in the cooler months. The DSF needs to be designed to address this potential heat build up by either providing additional air extraction or another means to allow the heat to escape.
Glare control. As DSF are usually highly glazed, the issue of glare within and around

the building needs to be addressed. Daylight controls such as internal blinds and screens will be required as well as consideration given to the placement and orientation of work spaces to ensure that glare from the daylight doesn’t adversely impact on the building occupants. Similarly, potential outward reflections need to be addressed by either the use of special coatings or films and/or careful orientation and positioning of glazing relative to sun angles.
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B.Pollard, M.Beatty
Additional façade cost. There is usually additional capital cost associated with DSF as an additional façade(s) is required. A 2003 report by Stribling and Stigge put the additional cost of a DSF in the United States at approximately 50% more than a comparable single skin façade. Maintenance requirements. DSF, especially wide cavity types, can have much higher

maintenance requirements than single skin façade. This is because there are four glass surfaces that may require cleaning. Ventilation of the cavity also needs to be adequate to prevent condensation and the need for additional cleaning. While maintenance walkways can be provided within the cavity to clean the glass and maintain blinds, access to the outer face of the glass is required, with this normally being provided by another separate access system.
Smoke management impact. DSF can impact on the smoke management system of a

building in a number of ways. DSF make it difficult to use the façade of building to expel smoke as the cavity will fill with smoke and may spread to other floors if their windows are open. This can certainly occur with single facade buildings but the situation is exacerbated in DSF buildings because the smoke is unable to be dispersed by wind. Using the cavity of a Extract Air DSF as a smoke exhaust duct or path would require significant fire engineering input.
Fire protection. The potential for fire spread also needs to be addressed as sprinklers

may be required within the cavity where building codes require spandrels constructed from fire resistant materials. CLIMACTIC STABILITY The vast majority of DSF have been constructed in Europe, especially northern Europe, primarily because of their high heating requirements, the high cost of energy and the desire for increased natural light. Increasingly, examples are appearing in benign climates were the heating requirements are not as great. So what about hot climates? It is apparent from a review of literature on building energy use that the biggest potential reduction in energy use can occur in buildings located in more extreme climates (ie very cold or very hot)? Buildings in hot climates can have very high external heat loads to deal with for all or part of year. Traditional building techniques usually addressed this by using passive or low energy techniques such as shading and fans to provide comfort cooling. However, the nature of modern buildings and changed user expectations can make it difficult to implement these strategies in office and other large buildings. The high external loads coupled with high internal loads from computers and lighting necessitates the use of HVAC systems to provide cooling for all or a significant portion of the year. The use of DSF in hot climates is not nearly as extensive, with far fewer having been constructed and reported on than in the colder areas. Of the literature found for this report few studies and reports related to DSFs in hot climates. Hesse and Amato (2006) have reported on the DSF that they have analysed in Hong Kong and have concluded that ventilated Buffer DSF offer the best ability to reduce external heat loads for buildings with HVAC system. They did not report on whether DSF have been used for natural ventilation of interior spaces of buildings.
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B.Pollard, M.Beatty A Masters thesis written in 2004 by Vijaya Yellamraju investigated the suitability of using of DSF on office buildings in India. The report was based upon building energy simulation of theoretical buildings located in Hyderabad and New Delhi. Various arrangements of the DSF were modelled to find the optimal solution. Unsurprisingly, the report found that on some faces there was extensive heat build up in the cavity and that this led to increased heat loads within the building. It did find that loads could be slightly reduced with shading and increased ventilation of the cavity. The report recommended that the best performing system decreased the amount of glazing to about 50% of the façade and introducing masonry for the remainder. Interestingly the cavity of the masonry was modelled to match the cavity of the DSF which effectively made the glazed sections of the DSF triple glazed widows

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B.Pollard, M.Beatty NORTH AMERICAN EXAMPLES OF DOUBLE SKIN FACADES Museum of Contemporary Art Denver Location: Denver, Colorado, United States Date: Area: DSF Type: Architect: Energy Analysis:
Description:

2007 2,500 m2 (27,000 sq.ft) Extract Air/ Continuous (TBC) Adjaye Associates & Davis Partnership Architects Enermodal Engineering

Hygrothermal Zone: Cold

Approximately 50% of the façade of this newly completed building is a DSF. It comprises an outer double glazed insulated curtain wall and an inner skin of translucent MonoPan, which is a sandwich panel comprising a core of honeycomb polypropylene faced with fiberglass reinforced polypropylene. The cavity between the two skins is used as an exhaust path for internal air. Enermodal Engineering reported that the majority of the predicted 36% energy savings were due to the design of the mechanical systems and that the DSF functioned as well as a good double glazed insulated façade. They also reported that the introduction of ventilation through the DSF only reduced the heating and cooling loads by an additional 1-2%. No information could be found about the construction of the DSF or its detailed functioning.

Fig. 12: View of 15Th and Delgany Street Facades source: www.wallpaper.com & Ed Reeve
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B.Pollard, M.Beatty Seattle Justice Centre Location: Seattle, Washington, United States Date: Area: DSF Type: Architect: M & E Engineer: Energy Analysis:
Description:

2002 26,750 m2 (288,000 sq.ft) Buffer/Continuous NBBJ, Seattle CDI Engineers Arup

Hygrothermal Zone: Marine

This DSF forms the main South-Western (5th Avenue) façade of the Seattle Justice Centre. The DSF is 9 levels high and the width of the cavity between the inner and outer skins is 750mm (30inch). The outer skin is a single glazed curtain wall, the inner skin has double glazed insulated low-e panes and both skins use clear glass. Automatic semi transparent blinds are located within the cavity and fixed aluminium walkways are provided for maintenance. Operable louvers are located at the top and bottom of the cavity to adjust the air flow through the cavity. It is apparent from a review of the available literature that the energy efficiency benefits of the DSF are limited due to it being located on only one façade, the closed nature of the court rooms beyond and the relatively benign nature of the climate. There have also been reports of glare issues from the increased day lighting.

Fig. 13: Seattle Justice Centre - 5th Ave Source: author

Fig. 14 Detail view of DSF cavity Source:http://leedcasestudies.usgbc.org

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B.Pollard, M.Beatty Telus Building Location: Date: Area (gross): DSF Type: Architect: Mech Engineer:
Description:

Vancouver, British Columbia, Canada 2000 12,000 m2 (129,800 sq.ft) Twin Face/Continuous Busby & Associates (now Busby Perkins + Will) KEEN Engineering

Hygrothermal Zone: Marine

This DSF is a retrofit over the face of an existing building. The outer skin is double glazed with bands of clear and fritted glass while the inner skin is the existing concrete and masonry structure with single glazed windows placed in the existing window openings. The cavity is 900mm wide. The windows of the inner skin are opened manually and the external windows are remote controlled. Ventilation to the cavity is controlled by dampers as well by the external windows. Solar powered fans at the top of the cavity assist with ventilation when required. It is reported that the whole building was designed to use 30% less energy than one designed to ASRHAE 90.1 -1989. However, no detailed information could be found that assessed the actual energy benefits of this façade. It should be noted that the local authority agreed to allow the DSF to be built over the footpath on the proviso that it would be removed if required.

Fig. 15 Telus Building façade Source: www.architecture.uwaterloo.ca

Fig. 16: Telus Building diagram Source: www.architecture.uwaterloo.ca

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B.Pollard, M.Beatty Biomedical Science Research Building, University of Michigan Location: Ann Arbor, Michigan, United States Date: Area (gross): Architect: DSF Type: M & E Engineer: Sustainability: DSF Modeling:
Description:

2006 40,400 m2 (435,000 sq.ft) Polshek Partnership Buffer/Continuous Baro Roa + Athanas Buro Happold Mojyaba Navvab – University of Michigan

Hygrothermal Zone: Cold

The extensive DSF covered almost the entire southern façade of this research laboratory and office building. The outer skin is a single glazed unitized curtain walls while the inner skin has double glazed insulated panes. The cavity is approximately 900mm (36 inches) wide and 4 floors in height. Ventilation is provided at the top and bottom of the DSF. Blinds are provided within the cavity as is a track mounted window cleaning frame. The façade was subjected to extensive modelling and testing by a team from the University of Michigan. This included construction of a full scale mock up of one floor of the façade. The DSF is reported by the team to have made a significant contribution in reducing the heating and cooling loads on the building. It appears from the literature that at one stage a floor by floor DSF ventilation strategy was being considered but a continuous DSF was constructed.

Fig. 17 Southern Elevation showing DSF Source:http://uuis.umich.edu/cic/buildingproject/images/bsrb.jpg
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B.Pollard, M.Beatty AUSTRALIAN EXAMPLES OF DOUBLE SKIN FACADES Aurora Place/Macquarie Apartments Location: Sydney, Australia Date: Area: DSF Type: Architect:
Description:

2005 4,262 m2 Twin Face Renzo Piano Building Workshop

BCA Climate Zone: 5

A version of the Twin Face DSF has been used in Sydney, Australia by the Renzo Piano Building Workshop (RPBW) for the eastern façade of the Aurora Place/ Macquarie Apartments building. Here, the cavity of the DSF is very wide and compartmentalized both horizontally and vertically with the cavity acting as the balcony for each apartment. The outer face is a fully louvered glass wall and is capable of being almost completely open to allow heat to escape and breezes to enter. Blinds are also provided to allow for shading and glare control. The inner skin is made up of glazed sliding windows to the apartment. The success of the DSF in reducing heat gain and energy use is not known at the time of writing, but use of a highly glazed facades was dictated because of the extensive harbour views to the east of the building. This façade is a development of RBPW’s Daimler Benz (Debis) building in Berlin.

Fig. 18: Aurora Place/Macquarie Sydney Source: www.rpbw.com

Fig 19: Detail view of louvres Source: www.pushpullbar.com.au

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B.Pollard, M.Beatty University of Sydney Law School Building Location: Sydney, Australia Date: Area: DSF Type: Architect:
Description:

Due for completion early 2009 18,250m2 Twin Face/Buffer FJMT

BCA Climate Zone: 5

The external skin consists of panels of glass, approximately 3.3m x 2.8m which extend approximately 1 metre from the internal façade, are supported on stainless steel arms fixed to the floor slab. The glass panels protect the timber louvres from UV radiation and serve as a weather barrier to the internal "skins". The intermediate skin of automated, vertically pivoting louvres sit approximately 600mm from the internal façade and are designed to project the internal façade from solar heat gain. The internal skin is not fully glazed, but consists of horizontally pivoting windows, which allow for natural ventilation and hot air escape, positioned above perforated panels with acoustic insulation in the lower part of the façade designed to absorb noise rising through the cavity from below . The cavity between the facades is designed to function as a thermal chimney with hot air from internal spaces being drawn up into the cavity and released. The bottom of the cavity is open and the top of the cavity has automated louvres with rain sensors to allow ventilation of the cavity in fine weather. In addition to the induced natural ventilation, each office is fitted with an individual air conditioning unit. The cost of this façade is in the order of 3-4 times the cost of a normal single skin façade.

Fig. 21: Eastern façade Source: www.usyd.edu.au

Fig. 22: Detail view of facade Source: www.usyd.edu.au

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B.Pollard, M.Beatty Design Hub, RMIT University (proposed) Location: Melbourne, Australia Date: Area: DSF Type: Architect: ESD Consultants:
Description:

Construction to commence in early 2009 11,000 m2 Hybrid Sean Godsell & Peddle Thorp Architects in association Cundall

BCA Climate Zone: 6

The choice of a double skin façade for this building is a site and function specific response and appears not to refer to the function of other double skin facade buildings either overseas or in Australia. Rather than using the external skin to reduce solar gain, this building uses it to actively capture the solar energy. The external façade is a translucent “smart skin” made up of more than 16,000 sandblasted glass cells, some of which have photovoltaic collectors to harness solar power. The cells track the sun via the building computer automation system to help shade and power the building. The skin has been designed to be upgraded over time to accommodate new solar technologies as they emerge. When it rains, the sandblasted surface becomes transparent, adding a further dimension to the dynamic nature of the façade. The inner skin is a high-performance, double-glazed layer, which presumed to be fixed as the information available states that users have the option of introducing filtered fresh air through the floor to their work area. No information was provided about the ventilation of the cavity.

Fig. 25: View of Proposed Façade Source: www.rmit.edu.au

Fig. 26: Detail View Source: www.rmit.edu.au

ISES-AP - 3rd International Solar Energy Society Conference – Asia Pacific Region (ISES-AP-08) Incorporating the 46th ANZSES Conference 25-28 November 2008 Sydney Convention & Exhibition Centre

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B.Pollard, M.Beatty VS1 - South Australian Water Headquarters Location: Adelaide, South Australia Date: Area: DSF Type: Architect: ESD Consultants:
Description:

Due late 2008 35,000 m2 Hybrid HASSELL Cundall

BCA Climate Zone: 5

This 10 story building in South Australia was designed to be the headquarters of South Australia Water. Staff surveys provided the foundation for many aspects of the design brief and included requirements for natural light for all, openness and transparency and a minimum 5 Green Star rating (the building has achieved a 6 Star Green Star rating). The building is located on a relatively narrow, deep site with an exposed western façade. The building has high performance double glazing to the north, east and south facades and a double skin façade comprised of clear double glazing and a fritted veil on the western side to reduce solar loads while retaining access to daylight and views. Spandrel panels on the east and west façade reduce the area of glazing and solar loads, horizontal shading on the northern façade reduces solar load on the glazing in the summer and vertical fins on the southern façade (with manual blinds) control glare in the late afternoon. Automated blinds on the north, east and south façades help to reduce any potential glare.

Fig. 27: View of Northern & Western Facades Source: HASSELL

Fig. 28 Section

ISES-AP - 3rd International Solar Energy Society Conference – Asia Pacific Region (ISES-AP-08) Incorporating the 46th ANZSES Conference 25-28 November 2008 Sydney Convention & Exhibition Centre

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B.Pollard, M.Beatty BUILDING SCIENCE LITERATURE REVIEW It is important when trying to determine the worth of a building system to go beyond architectural magazines, web sites and product brochures to see what is being reported by building specialists and scientists. As previously mentioned, back in 1999 Dr Karl Gertis was very unsupportive of DFS in contrast to Lang and Herzog who in 2000 were much less dismissive, suggesting that the potential return in energy savings and improved worker productivity could make the higher cost of DSF a worthwhile investment. To try and determine what the current engineering and building science opinion is of DSF more recent reports and conference papers were examined and the findings are summarized below;
John Straube & Randy van Straaten - The Technical Merit of Double Facades for Office Buildings in Cool Humid Climates, 2001 - These authors undertook a general technical review of DSF to determine whether they reduced heating and cooling loads, allowed for better natural ventilations and daylighting and helped to provide improve external noise control. After examining each of the ascribed benefits and comparing the technical performance of alternative industry standard solutions they concluded that DSF “…are merely one approach to overcoming the large energy consumption and comfort problems that are created by excessive glazing areas of inferior performance…..The most environmentally sound…… solution avoids the problems that DFs (DFS) are intended to solve by reducing glazing area and increasing the quality of the glazing product.” Dirk Saelens, Jan Carmeliet & Hugo Hens - Energy Performance Assessment of Multiple Skin Facades, 2003 – This study was based upon computer simulations of different DSF

strategies for a hypothetical single story building in Belgium. They concluded that in order for a DSF to reduce heating and cooling loads that the shading systems and functioning of the cavity air flow needed to be capable of adjustment via a “sophisticated control mechanism”.
Nassim Safer, Monika Woloszyn & Jean Jacques Roux - Three-Dimensional Simulation with A CFD Tool of the Phenomena in Single Floor Double Skin Façade Equipped With a Venetian Blind, 2004 - This study was a detailed examination of the effects of placing

blinds at different points within the cavity of a double skin façade. While the study concluded that the blind is most useful if located near the inner skin as the air velocities in this position are less than in the outer and middle position. The writers then indicated that more research was required for a more conclusive position to be arrived at.
Ian Doebber & Maurya McClintock - Analysis Process for Designing Double Skin Facades and Associated Case Study, 2006 – Both of these authors are employed by the respected

engineering firm Arup which has carried out the engineering for many DSF around the world. Indeed at least one of the study authors is understood to have worked on the design of the DSF for the Seattle Justice Centre. In this paper, the authors described the analytical process and computer modelling that is used to design DSF. They concluded the paper by saying that provided DSF were carefully designed and matched to the correct climate that a DSF can allow full height glazing to be used and still achieve occupant expectations.

ISES-AP - 3rd International Solar Energy Society Conference – Asia Pacific Region (ISES-AP-08) Incorporating the 46th ANZSES Conference 25-28 November 2008 Sydney Convention & Exhibition Centre

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B.Pollard, M.Beatty
Elisabeth Gratia & Andrea De Herde - Guidelines For Improving Natural Daytime Ventilation In An Office Building with a Double Skin Façade, 2006 – This Belgian study

originally written in 2004 was aimed at determining how best to cool a building with natural ventilation with a DSF. The study was undertaken in the context that, as Belgium’s climate is relatively benign and modern office buildings in such climates are more likely to require cooling rather than heating, that natural ventilation should be able to play a role in reducing energy use. Through computer simulation the hypothetical building was modelled with a DSF orientated in different direction relative to the sun and prevailing winds. The study concluded that by using the stack effect, enhanced by correct positioning to the prevailing winds to allow night cooling of the building by natural ventilation, DSF could be a successful strategy. However they also stated that much more modelling and research was required before this approach could be applied to a real building.
Kurt Roth, Tyson Lawrence & James Brodrick- Emerging Technologies - Double Skin Facades - 2007 – In the October 2007 edition of the ASHREA Journal these authors

reported on their review of DSF from an North American context. They were very scathing on the ability of DSF to deliver on their stated advantages without complex control systems and decried the lack of actual building performance assessments. They concluded that all the benefits of a DSF can be achieved more cost effectively by using other building systems. CONCLUSION So what has this review and examination of DSF found? Well firstly there is a limited amount of literature on this subject as many of the articles and reports reviewed for this report all had similar reference lists. This gives weight to the various authors’ calls for more research into DSF including the study and reporting on their actual performance in a range of climates. It is only through new, detailed research and study that our knowledge and understanding of DSF will develop. In regard to some of the ascribed benefits such as pollution barriers, emergency egress, acoustic protection and future proofing, the effectiveness of DSF are hard to prove. Certainly with the acoustics benefits, the author has worked on several large infrastructure projects which required acoustic barriers to be provided to reduce the impact from traffic noise. In all cases careful attention had to be paid to provide a complete, uninterrupted barrier to the noise otherwise the noise attenuation properties of the barrier would be greatly reduced. In addition the reflection of noise had to be avoided wherever possible as it could lead to significant noise impacts for surrounding properties. Typically the noise barriers had to be positioned by canting the panels slightly upwards or downwards or by installing perforated panels with a backing of sound insulation to absorb the noise. None of the examples in the literature about DSF used to provide acoustic protection appeared to successfully address all these issues. As to whether the energy saving benefits attributed to DSFs are correct or not, it is certainly the case that DSF can play a role to reducing heat loss where a façade is fully glazed. However, well designed, high performance glazing such as double and triple glazing can achieve similar results. Fully glazed façades can definitely provide an abundance of daylight for some of the interior spaces of a building but can also bring
ISES-AP - 3rd International Solar Energy Society Conference – Asia Pacific Region (ISES-AP-08) Incorporating the 46th ANZSES Conference 25-28 November 2008 Sydney Convention & Exhibition Centre

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B.Pollard, M.Beatty glare unless the daylight is carefully controlled and moderated. It is important that we question the desire for all glass facades and select the most appropriate design strategy for each situation. In regard to hotter climates, the use of DSF can be more problematic due to the need to reduce solar heat gain as well as providing cooling for the interior of buildings. Fully glazed facades are probably the wrong design choice in such climates if the goal is to save energy. The recently completed Council House 2, in Melbourne Australia took the approach that each facade needs to be separately addressed and designed to deal with the prevailing conditions rather than adopting a uniform approach and then applying it to all four facades. One façade uses a hybrid DSF to shield the building from unwanted solar gain, allowing views to be gained when shading is no longer required. As the cavity is easily able to be naturally ventilated there is little or no heat build up. It is these types of creative responses that take building technology, examine it, understand it, adapt it and develop it, rather than blindly replicating it. This is how we will probably see the greatest gains made in our quest for low or zero energy buildings. REFERENCES DOUBLE SKIN FACADES Aarons D M M & Glicksman L R, Double Skin, Airflow Facades: Will the Popular European Model Work in the USA?, Building Technology Program, MIT, from www.tjju.com/ebook/doubleskin.pdf, 2000 Draft Battle McCarthy, Double Skin Analysis –www.battlemccarthy.com, June 2000. Blomsterberg A (Ed.), Bestfacade: Best Practice for Double Skin Facades – WP5 Best Practice Guidelines, EIE/04/135/s07.38652, from www.bestfacade.com, Boake, T M, The Tectonics Of The Double Skin: Green Building or Just More Hi-Tech Hi Jinx? – What are Double Skin Facades and How Do They Work?, ARCC/EAAE International Conference on Architectural Research, Montreal, May 2002 from www.architecture.uwaterloo.ca/faculty_projects/terri/pdf/tectonic.pdf 2002 Brock L, Designing the Exterior Wall – An Architectural Guide to the Building Envelope, John Wiley & Sons, Hoboken, New Jersey, 2005 Chen A, Back to the Times: Revisiting The New York Times Headquarters Building Upon Its Completion, web article www.lbl.gov/Science-Articles/Archive/sabl /2007/Oct/nytimes.html, 2007. Doebber I & McClintock M, Analysis Process for Designing Double Skin Facades and Associated Case Study, from http://gundog.lbl.gov/dirpubs/SB06/doebber.pdf, 2006 Gonchar J & Reina P, Glass Facades Go Beyond Skin Deep – Designers Stress The Importance of Integrating With Building Systems, Engineering News Record, 2 October 2003. Gratia E & De Herde A, Guidelines For Improving Natural Daytime Ventilation In An Office Building with a Double Skin Façade, Solar Energy 81 (2007) p435-448, Elsevier, 2007
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B.Pollard, M.Beatty Harrison K, Tectonics Of The Environmental Skin, University of Waterloo School of Architecture, from www.architecture.uwaterloo.ca/faculty_projects/terri/ds/ double.pdf, 200? Hesse M & Amato A, Ventilated Façade Design In Hot And Humid Climate, presentation to the Green Room, 2006 Lang W & Herzog T, Using Multiple Glass Skins To Clad Buildings: They’re Sophisticated, Energy-Efficient, And Often Sparking Beautiful, But Widely Used Only In Europe – At Least For Now, Architectural Record . http://archrecord.constrcution.com/features/green/archives/0007edit-.asp, 2000. McClintock, M, (Arup), Façade Solar Control Strategies, unpublished, 2006 Poirazis H, Double Skin Facades for Office Buildings – Literature Review, Division of Energy & Building, Department of Construction & Architecture, Lund Institute of Technology, Lund University, Lund, Sweden, 2004 Potvin, A, Neutralizing the Canadian Climate – The Double Facade System at the New CDP Building in Montreal (Presentation), ASES - Solar 2007, Cleveland, July 2007. O’Reilly, D, Dual Skins – Designs Not Popular in Canada’s Harsh Climate, Daily Commercial News and Construction Record www.dcnonl.com, 2007 Roth K, Lawrence T & Brodrick J, Emerging Technologies - Double Skin Facades, ASHREA Journal October 2007 Saelens D, Carmeliet J & Hens H, Energy Performance Assessment of Multiple Skin Facades, International Journal of HVAC&R Research Volume 9 NR2 pages 167 – 186, 2003 Safer N, Woloszyn M & Roux, J J, Three-Dimensional Simulation with A CFD Tool of the Phenomena in Single Floor Double Skin Façade Equipped With a Venetian Blind, Solar Energy 79 (2005) 193-203, 2004 Santamouris M, Farou I & Zerefos S, Bestfacade: Best Practice for Double Skin Facades – WP2 Report “Cut Back of Non-Technological Barriers”, EIE/04/135/s07.38652, from www.bestfacade.com, 2005 Straube J & van Straaten R, The Technical Merit of Double Facades for Office Buildings in Cool Humid Climates, www.buildingsolutions.ca , Draft White Page for Discussion, 2001. Streicher W (Ed.), Bestfacade: Best Practice for Double Skin Facades – WP1 Report” State of the Art” EIE/04/135/s07.38652, from www.bestfacade.com, 2005 Stribling D & Stigge B, A Critical Review of the Energy Savings and Cost Payback Issues of Double Facades, CIBSE/ASHREA Conference 2003 www.cibse.org/pdfs/8cstribling.pdf Yellamraju V, Evaluation & Design of Double Skin Facades for Office Buildings in Hot Climates, A Thesis - Texas A&M University, 2004.

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B.Pollard, M.Beatty Seattle Justice Center Cascadia US GBC, In Depth Case Studies Seattle Justice Center, from http://casestudies.cascadiagbc.org/lessons.cfm?ProjectID=225, & http://casestudies.cascadiagbc.org/energy.cfm?ProjectID=225 City of Seattle, Sustainable Building: Case Study City of Seattle Justice Center, from dpdlNEWS, February 2003. US Green Building Council, LEED Case Studies – Seattle Justice Center, From http://leedcasestudies.usgbc.org/overview.cfm?ProjectID=225, 2006. Washer G, The Seattle Justice Center, Student Case Study, University of Waterloo, from www.architecture.uwaterloo.ca/faculty_projects/terri/, 200?. Telus Building Boyes, Henderson, Krejcik, Sibbald, William Farrell Building – Telus, Student Powerpoint Study, University of Waterloo, from www.architecture.uwaterloo.ca/faculty_projects/terri/, 200?. Boake T, M Harrison K & Chatham A, The Tectonics Of The Double Skin: Green Building or Just More Hi-Tech Hi Jinx? – North American Case Studies, University of Waterloo School of Architecture, from www.architecture.uwaterloo.ca/faculty_projects/terri/ds/tectcase.pdf, 200? Kujawski Canadian best practices in sustainable retrofit design, www.greenbuilding.ca/down/bc/retrofit_3case_studies_canada.doc, 200? from

Museum of Contemporary Art, Denver Pappas A, Energy Performance of a Double Skin Façade – Analysis for the Museum of Contemporary Art, Denver, Solar2006, from www.solar2006.org/presentations/tech_sessions/t45-p201.pdf, 2006. Navvad M, Full Scale Testing & Computer Simulation of a Double Skin Façade Building (Paper) , Building Simulation 2005 - Ninth International IBSPA Conference, Montreal 2005. Navvad M & Varodompun J, Thermal Performance of a Double Skin Façade Using Full Scale Testing & Computer Simulation and Actual Building (Presentation), ISES - Solar 2006 Australian Building References University of Sydney Law School building.shtml

Building:

www.usyd.edu.au/about/new-

VS1: David Clark, Director, Cundal, ARIAH Conference Melbourne - Nov 2007 ,www.cundall.com.au RMIT, Design Hub Vision, from www.rmit.edu.au/propertyservices/designhub

ISES-AP - 3rd International Solar Energy Society Conference – Asia Pacific Region (ISES-AP-08) Incorporating the 46th ANZSES Conference 25-28 November 2008 Sydney Convention & Exhibition Centre

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B.Pollard, M.Beatty BRIEF BIOGRAPHY OF PRESENTER Brett is an Architect and Landscape Architect with extensive experience in Australia nd Europe and has played a key role in some significant, long running projects such as the infrastructure projects at Homebush Bay fro the Sydney 2000 Olympics, the Cross City Tunnel and the award winning North Sydney Olympic Pool. As well as working a Senior Associate in the Sustainable Futures Unit at HASSELL, Brett will soon take his Masters in Design Science (Sustainable Design) from the University of Sydney. He has recently returned from five months at Vancouver's University of British Columbia where he was researching various aspects of sustainability including building energy performance and sustainable housing initiatives. HASSELL has supported Brett through his studies, which aim to build upon the firm's already considerable strength in sustainable design. Brett is also a Green Star Accredited Professional of the Green Building Council of Australia.

ISES-AP - 3rd International Solar Energy Society Conference – Asia Pacific Region (ISES-AP-08) Incorporating the 46th ANZSES Conference 25-28 November 2008 Sydney Convention & Exhibition Centre

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