By Scott Willey
22 November 2010 – Favourites: The Building Code of Australia has controlled the energy efficiency of glazing in office buildings since 2006. It is the tightening of the control in the 2010 provisions of Section J that could toll the end for the ubiquitous “glass box”.
The Facade Design and Engineering conference in Melbourne 16-18 November discussed the latest in facades with a strong focus on sustainability, and a roundtable on how Section J will impact on facades.
It was a timely prompt to discuss the progress of facade technology and its role in green buildings. With 40 per cent of the energy use of commercial buildings being for heating and cooling, facade efficiency offers the primary potential to reduce energy consumption. Some public sector clients are now calling for an additional 30 per cent increase in energy efficiency above that of minimum regulations, raising the bar even further. Despite the heavy bias that orientation plays on solar loads, existing towers tend to be similar or identical on all facades, and the market continues to push for more glazing.
The BCA’s 2010 requirements for glazing may change this. University of Melbourne Associate Professor and facade expert, Dr Eckhart Hertzsch, welcomes the new requirements, given the impact that facades have on operational energy, though he points out the code is still quite behind European standards. He says glazing can contribute about 20 per cent to cooling loads in commercial buildings, and if the glazing is floor to ceiling, the load can increase by as much as 80 per cent.
One impact of Green Star has been for building occupants to be placed closer to glazing in an attempt to improve outlook and natural light. Increased natural light and outlook are acknowledged to enhance healing in hospital patients, increase learning in school students and increase productivity in office environments. The challenge remains to gain this amenity while decreasing energy consumption.
Currently double glazed insulating glass units or IGUs within aluminium-framed curtain walls dominate the Australian market. Triple glazing, while gaining momentum in Europe for its resistance to heat loss, is not as relevant here due to our warmer climates. For some Australian climates losing heat through lower performing glazing can actually be beneficial in reducing cooling loads.
Solar gain is instead the major issue for Australia, yet sun shading on commercial towers is still noticeably rare. Without shading, the only defence against solar heat gain is that which can be gleaned from a combination of glass tinting, applied soft or pyrolytic surface coatings, or applied ceramic frits – as seen on the University of Melbourne’s distinctively “spotty” Business and Economics Building.
Advances in technology have moved from low-e glazing that would allow 80 per cent of the natural light admitted in heat gain, to high performance coatings where the heat gain is reduced to 50 per cent. There are solutions that provide both shade as well as reflecting some natural light up to ceilings in order to gain greater penetration of natural light. These systems include external light shelves and internal concave blind systems which, although simple, are not widespread.
Strategies for change
facade warranties of 10 to 15 years are deceptive when the facades themselves may have a service life of 50 years or more. What is an appropriate design life for a facade when predicting beyond, say, 20 years, when there is potential climate change as well as changes in building use and architectural fashion?
Night purging of stale air is starting to reduce the problems associated with buildings which, for more than 30 years, have been little more than hermetically sealed glass boxes. Using heating ventilation and airconditioning or HVAC economy cycles to take advantage of unconditioned external air is now common practice, and the future could see more of this daytime ventilation happening through facades rather than via ductwork. Seemingly in contradiction to the current push for glass facades to segregate occupants from the elements, the new facades appear to be more about diffusion.
This will mean greater ventilation through facades, and thus the need to potentially retrofit more permeable assemblies over time. Arup’s Melbourne facade specialist, Chris Hube, sees the value of “designing for disassembly” as one way to ensure the flexibility needed to incorporate future changes and spread the material impacts over a longer life and the reuse of materials.
When the culture of corporate Australia awakens to the need for change in corporate attire, buildings will no longer need to be designed for keeping occupants in woolen suits refrigerated on 30°C days. By discouraging such attire the Japanese Coolbiz program has allowed thermostat set points to climb from 21°C up to 28°C. Though this jump has been criticized as too extreme to keep workers productive, it is clear that changing cultural attitudes to comfort will expand the possibilities greatly for natural ventilation and permeable facades.
Double Skin facades
Permasteelisa’s Technical Manager Marc Zobec said his company is one of several involved in a European Union-sponsored project with the Fraunhofer Institute, to look at ways to put more building services within a building’s external skin. Solar cooling collectors, shading devices, lighting diffusers and spandrels with phase change material are potential inclusions in facades and all have the potential to shake up the contemporary understandings of building services.
Many double skin facades that produce great efficiency in cooler climates, aren not suitable for Australian climates. Dr Hertzsch cautions their use, saying it is crucial that the inlet and outlet paths for glazed DSF are sized correctly to avoid overheating from hot air build-up in the cavity. Hassell overcame this in their Adelaide SA Water building, by providing a DSF only on the building’s western face, and leaving it fully open to air movement on all sides. The second facade uses ceramic frits on the glazing to limit sun penetration.
Frankfurt’s Commerzbank Tower uses a DSF with external shading systems to allow operable windows, which results in the tower being able to utilise natural ventilation for up to nine months of the year. Australia’s first fully glazed double skinned tower is currently under construction in Sydney’s six star Green Star rated 1 Bligh Street. It will use an outer glazed facade to protect computer-controlled sunshading, and thus mitigate heat loads.
Hertzsch notes DSF are often talked of as being one system, when actually they are multiple systems in layers and cavities. “With layers, there is a lot of scope for fashion,” he says, and the ETFE (Ethylene tetrafluoroethylene) membrane used to clad Beijing’s Water Cube with inflated pillows is an example of this. It expands the potential for DSF with its low weight and light transmission properties that come at comparatively lower cost than conventional glazing systems. Hamburg’s Unilever Haus also uses an external layer of ETFE, though in this case as a single skin used to protect operable aluminium sunshading from Hamburg’s up to 100 kilometre per hour winds.
The mandatory disclosure of energy efficiency requirements now in place under federal regulation will expose the performance of existing buildings to market scrutiny. This will increase pressure for the upgrading of facades on existing stock.
Chris Hube sees adding sun shading to existing ‘glass boxes’ as an obvious way to increase energy efficiency whilst maintaining existing facades. US figures suggest air leakage alone can contribute up to 40 per cent of the heating and cooling loads on buildings, and thus periodic remedial works such as the replacement of gaskets becomes an obvious way to make savings. Hube says Arup has estimated for a Brisbane scenario that addressing infiltration would have approximately a three year payback period.
Perhaps re-skinning buildings periodically with new facades may be the strategy for the uncertainties of climate change, technological advances and architectural fashion, whilst allowing for performance to be re-optimised every 20 years.
Balancing performance against embedded energy and other environmental impacts is becoming more crucial. Increasing the life of components through designing for disassembly is one way to justify an initial high embodied energy. Chris Hube aims to “dematerialise” the systems he employees once a design-life and system has been chosen. The bulk of contemporary framing is manufactured from virgin aluminium, known to be very high in embodied energy, though readily recyclable. To avoid aluminium, highly recyclable polymers are now being used with fibre-reinforced composites in ‘pull-trusion’ profiles. Even timber is being evaluated for facade framing for towers, in an effort to reduce material impacts.
Glazing advances including gasochrome (gas filled cavities that change colour), thermachrome (colour change with temperature), photochrome (change colour with light) and electrochrome (colour change when electrically charged) are on the way, though the holy grail for facades is smart materials that can intelligently self-regulate in a similar way to that of human skin. Earlier this year Dr Hertzsch ran a facade Design and Performance intensive workshop in which industry professionals participated. Participating in the two-week program was an international expert on biomicry and architecture, Professor Dirk Henning Braun from the Stuttgart practice, Braun Associates.
In the field known as biomimetics, Braun’s work looks to animals, insects and other parts of nature to learn how we might create highly efficient materials and structures. He says, “It would be arrogant and highly uneconomical not to use and to analyse the potential of these natural structures and systems.”
“Due to the increasing costs of energy we need for heating and cooling our buildings, architects and engineers seek for smart solutions in nature which deal with similar or equivalent problems in a different way. Usually we answer these requirements by using an enormous amount of technical systems for air ventilation, energy recovery or filtering, etc. Nature solves these requirements with smart, low-tech solutions which have been proved over a million years.”
Braun points out that the role architecture should play as a link between society and the environment is not a static one. ”In order to play the role of a collaborative link, architecture, buildings and infrastructure need to be able to adapt to these changing conditions … the possibility of natural materials, structures and processes to adapt to changing circumstance is self-evident”. It is especially exciting to recognise that all if these ideas are, per se, adaptive and multifunctional, which makes them a particular challenge for the architects and engineering of tomorrow.“
Rather than mimicking nature in materials, Brisbane academic Dr Janis Birkeland has proposed integrating living organisms within building facades themselves so as to generate eco-services. Arup’s Brisbane office has been assisting with the engineering of structures that can be used to combine terraria, aquaria and passive solar systems into a single facade system. Going beyond internal living walls or the sky gardens promoted by Singaporean architect Ken Yeang, Dr Birkeland believes adding these frames to new or even existing buildings will turn what is otherwise a sterile zone into a bio-productive interface, and thereby begin to reverse a building’s negative environmental footprint.
There is a growing need for whole-systems thinking in building which will require new forms of design collaboration. Dr Hertzsch sees the researchers’ role as that of informing architects and building planners, saying that “having them on board during the early design phase will help immensely”. Integrated design, where all parties are involved in the design process, is going to become critical as new facade choices affect or replace conventional building services.
Until a new wave of materials is ready, designers will need to be increasingly strategic in the way they use materials. Given a 50-plus year lifespan, the facades being built now will leave a legacy which outlives their designers.
Scott Willey is a Melbourne based sustainability writer & architect