While the subject of air infiltration or ‘whole building air tightness’ design and construction is common across Europe and North America where it is legislated and must be proven via pressure testing the finished building, Australian building’s air tightness has not had the privilege of this energy efficiency and comfort focus until now.
With proven operational improvements of up to 25 per cent energy reduction for heating, air infiltration is now seeing a rapid focus in both domestic and commercial Australian sectors.
Thankfully, in the absence of any current legislative sticks to start the conversation, the Australian domestic sector is now seeing the beginning of a great movement that will aim to improve the design and construction of building air tightness, amongst other objectives.
With the Australian Passive House Association Official National Launch Party Launch party in May of this year, it is exciting times for those looking to adopt the merits of high quality construction techniques to building performance.
But how about the commercial sector - our offices, schools and hospitals? Are we seeing traction in the air tightness design realm and what are the benefits?
On the frontier of such discussion, I am happy to report that façades in commercial buildings are now indeed seeing a greater focus befitting of their innate role in performance and comfort.
Without revealing project sensitive specifics, I can say that we are now seeing evidence of Victorian hospitals and offices integrating the first steps of air tightness design to test the quality of construction techniques via a super useful Green Star Innovation Challenge on the subject.
For the Green Building Council of Australia (GBCA), this Building Air Tightness Innovation Challenge is a win as they get to see how far away we are from International construction quality to set a realistic benchmark to grow toward - and eventually integrate into - Green Star. From a builder/developer perspective, we get to gauge the value of air tightness design and construction, submit the performance to the GBCA while gaining one or two relatively economic points for their project.
But what can we hope to gain across Australia if we design and test for air tightness? Are benefits restricted to the colder, southern climate zones?
If we look at a current project (15-storey office, 70 per cent high performance vision glass, BCA fabric minimums, Melbourne climate) we can parametrically assess the potential for dollar savings in multiple climate zones. The results look really positive, illustrating that air tightness design is very much central to building envelope optimisation.
Using compliance (Section J - Alternative Pathway to compliance [JV3]) as a baseline - while putting aside the fact that this approach is somewhat meaningless as it offers no requirement to test build quality and is very much testament to the ‘rubbish in, rubbish out’ adage of energy modelling - we can begin to see clear opportunities and the sensitivity to designing for air tightness design.
Looking at space heating reduction opportunities alone, it is clear that on our medium sized building example in colder climate zones, improving to Typical (five m³/hr/m²@50 Pa) and Best Practise (two m³/hr/m²@50 Pa) for an office generates annual savings of $20,000 to $25,000 per annum based on 12 cents per kWh.
Within warmer climates, the saving are not as high as the period of heating is clearly much shorter. However, this still generates annual savings between $6,000 and $15,000 per annum.
So the results speak for themselves. Valuable from Hobart to Sydney and increasingly so as the surface area of the building envelope increases beyond that of the brief study here, is the National Construction Code now considering this significant value to design as a minimum compliance goal? Are we missing the greatest benefit of high performance design by ignoring the elephant in the room? Should Best Practise targets emanating from UK standards be converted into targets for Australian buildings or are they less advantageous across our highly varied climate zones?