– By Chris Begert –
11 March 2010 – Rising concern over climate change continues to place increasing demands on the design and efficiency of buildings. High performance buildings that provide optimal internal comfort without adding further pressure on the environment require innovative design solutions from Architects and Engineers.
Passive Design, a methodology that addresses these issues recently came of age in Europe. Eighteen years ago, in the German city of Darmstadt Kranichstein, Dr Wolfgang Feist opened the first Passivhaus. His team designed and constructed a building in which the full potential for passive design initiatives were maximised. The House achieved ideal internal comfort without the use of major heating and/or cooling equipment.
Since then, Passive Design principles have been developed and applied across many European cities. Design teams have adapted their techniques in different building types and climate zones, from Spain to Sweden, drawing on Passivhaus principles. What is it that makes this standard so successful and what can be learned from an Australian perspective?
Extensive measurements and post-completion testing on the first Passivhaus demonstrated outstanding performance: A standard Passivhaus requires less than 15 kWh a square metre heating energy a year and its heating loads are typically below 10 W a sq m. This means that a 100 sq m apartment could be heated by a 1000W hair dryer even in the rather cool European climate.
How can such impressive outcomes be achieved? The Passivhaus Institute offers ample information on design principles and outcomes (www.passiv.de). These applied techniques are fundamentally best practice ESD1, however without compromise:
The buildings are highly insulated to achieve R-values squared of around 7 sq mK/W in roofs and walls and typically use high performing triple glazing for all windows.
Special care is taken to make the buildings air-tight in order to minimise heat loss. Combined with high level insulation, this effectively decouples the indoor climate from the weather outside.
A ventilation system, often combined with heat exchanger, provides fresh air which is heated as required.
These three principles, together with good orientation, window and shading design comprise a building that will stay warm in winter without a boiler (for example in Germany, Scotland, Sweden) and also comfortably cool during in summer (such as in Spain, Italy, Portugal).
Again, these principles are neither new nor cutting edge in themselves. What is new, however, is the uncompromised combination of the three principles. It could also be shown that it is possible that the building fabric can effectively minimise the requirement for heating and cooling systems and sometimes render it obsolete in a variety of European climates.
Passivhaus in the Australian climate?
The climate across Australia is as variable as the climate in Europe and requires different design approaches. The true value of the Passivhaus approach is the use of high performing building fabric that decouples indoor conditions from the weather outside. A ventilation system then provides the link which opens the building to the exterior whenever conditions are favourable.
SBE undertook to verify whether it is possible to build a Passivhaus in Melbourne by comparing the climate of locations in Spain, where Passive Houses have been built (Granada and Seville), with the Melbourne climate.
Winter performance was analysed by determining the number of heating degree days (HDD). This is a measure of how much heating is required (i.e. the higher the number of HDD, the colder the climate, the more heating is required).
The climates in Seville and Melbourne are fairly similar during winter. Spring and autumn are notably warmer in Seville. In Granada the winter is far more severe, exceeding 350 HDD during its peak, compared to 250 HDD in Melbourne. If it is possible to achieve Passivhaus performance during winter in Seville and Granada, there is no reason why it could not be achieved in the Melbourne winter.
A similar argument can be made for the summer performance. The following graph illustrates the number of cooling degree days (CDD) in these three cities: The higher the number the hotter the climate and the higher the cooling requirements.
It can be seen that both cities, Granada and Seville, experience much hotter summers than Melbourne. This is a strong indicator that the general Passive Design principles will provide benefits to the comfort and energy performance when applied in Melbourne.
During SBE’s investigation, the same principles were applied to a proposed new college located in Ballarat and simulated to show the energy and comfort performance. The climate in Ballarat provides good reasons for enhancing the building fabric and a school is an obvious choice for introducing a ventilation system. Ventilation systems in schools are still uncommon even though they provide plenty of benefits, especially in terms of health and productivity (such as through guaranteed access to filtered outside air). The project is in its early stages, but the results obtained so far are exciting.
In the first stage, a computer model of the building was created using the proposed standard constructions. This simulated building used about 93 MJ a sq m of heating and exceeded target temperatures squared for 485 hours each year during occupied hours.
Next a ventilation system and enhanced building fabric was introduced. Walls and roof were insulated to R7 and all windows comprised highly efficient double glazed units. The climate in Ballarat is fairly volatile; making it a perfect case for the intelligent use of thermal mass and as such was applied to internal walls.
As a result, the simulation showed that the building used only 53 MJ a sq m for heating, a 43 per cent reduction. Furthermore, the building will exceed its target temperatures for only 135 hours each year during occupancy, a dramatic 72 per cent improvement to our base case.
Worthy of further consideration: picture a week where the internal temperatures are well above 30°C for a number of consecutive days. How well could you study and learn in such a space? How well would you react to frustration after being in such a classroom for hours? Can such a space still fulfil its essential function, that is, provide a healthy and productive learning and socialising environment?
The enhanced fabric itself cannot provide similar comfort to air-conditioned spaces yet. We expect further benefits from tempering the incoming air to offset the cooling demand completely via a labyrinth. However, the building performs exceptionally better than it would do having a conventional design. Not only is the number of hours above 27°C reduced by 72 per cent, but the peak temperatures are much lower as well.
The winter performance of the building was also outstanding: Computer modelling showed that the temperature of the enhanced building never dropped lower than 12°C, even in the harshest Ballarat winter. Furthermore, temperatures from one school day to the next rarely dropped below 15°C in our ‘Best Practice ESD Facility’, thereby limiting heating requirements the next morning. Comparatively, a standard construction performs poorly, with lowest temperatures dropping to 5°C and less.
Passivhaus in Australia
The design techniques described by the Passivhaus Institute offer the opportunity to achieve significant energy savings and radically improve internal comfort in climates like Melbourne and Ballarat. More research needs to be done to analyse the behaviour in warmer climates.
While the suggested techniques can be summarised as standard ESD advice, the Passivhaus Institute needs to be credited for not compromising on any of the principles and measuring their success in numerous projects over many years. Their data made an excellent case for implementing ESD from the very start. By significantly reducing the size of the building systems, Passivehouses remain economically competitive. Consequently, European local and federal governments as well as the European Union have started to include the standard in their policies, often calling it one of the pillars of their carbon reduction strategies.
The climate in Australia is probably more volatile than the continental European climate and therefore it is important to be careful when adapting design techniques from overseas. But it is exactly the volatile nature of the climate here that could proof to be advantageous when combining Passivhaus / ESD techniques with high levels of thermal mass.
We can design well performing and superior buildings that provide more comfort and use less energy. However, it is important that this goal is embedded from the very beginning of the design and that it is being followed through all stages.
The Passive-On Project
Passive-On is a completed research and dissemination project which was funded within the Intelligent Energy for Europe SAVE programme. The project worked to promote Passive Houses and the Passivhaus Standard in warm climates.
– Chris Begert works with SBE (Sustainable Built Environments)