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Time to close the natural ventilation loophole

How to improve indoor air quality in Australia’s public spaces? Experts from diverse disciplines have put forward various answers to this question. One solution, flagged by mechanical engineers long before the pandemic, remains frustratingly obvious for those in the HVAC&R industry: revisiting the provisions for natural ventilation in the National Construction Code (NCC).

According to the NCC, a natural ventilation solution is “deemed to satisfy” the minimum performance requirements if it has openings (generally windows and doors) measuring not less than 5 per cent of the floor area of the room required to be ventilated. But as many practitioners have pointed out, the resulting buildings rarely provide acceptable indoor air quality for occupants if they are also air conditioned with systems that do not comply with AS 1668.2.

Schools don’t make the grade

Registered architect and ARINA Managing Director Professor Geoff Hanmer took up this theme at AIRAH’s recent IAQ Conference, with a presentation on natural ventilation in schools. According to Hanmer, only about 1 per cent of Australian schools use mechanical ventilation systems that comply with AS 1668.2, meaning natural ventilation is the norm across the country. This approach, Hanmer pointed out, has two major failings.

“Deemed-to-satisfy natural ventilation under the code is unresponsive to load,” he said. “This is the biggest problem.

“The second big problem is that most of these schools have been retrofitted with domestic-grade split system air conditioners, which are relied on for both heating and cooling. But usually we have to shut the windows to make them effective.”

Based on the NCC provisions, Hanmer said a typical school office might provide 0.5m2 of openable area per occupant, but a classroom might only provide 0.11m2 per occupant, and a school hall, a tiny 0.07m2 per occupant.

“We need to get away from natural ventilation for schools,” he said.

“In future, we have to accept that schools must have mechanical systems to allow us to provide adequate levels of ventilation and effective filtration to deliver good IAQ. There is no reason why people working in an office should have safe, filtered, comfortable air delivered to AS 1668.2 while kids and educators struggle to balance ventilation and thermal comfort.

“Climate change is real and in future we will have to cope with extremes of temperature and more bushfire smoke. Early childhood education and primary schooling are the foundation stones of learning. The research on this is clear, so it’s time to put our money where the research shows us it should go.”

Unfortunately, as Sequal Mechanical’s Sonia Holzheimer, M.AIRAH, notes, some governments have actually mandated an approach that sacrifices indoor air quality.

“The Queensland Department of Education produced a ‘cool schools’ specification around 2006–07 that outlined a specific interpretation of the NCC comprising natural ventilation in the first instance and air conditioning with a fresh air supply reduced from AS 1668.2,” she says

According to Hanmer, the Cooler Schools initiative in NSW has a similar watered-down approach to AS 1668.2.

But even outside special allowances developed by government, Holzheimer says the natural ventilation provisions in the NCC are a thorn in designers’ sides. Guidance materials provided by the ABCB have even encouraged the use of natural ventilation with split systems as a DTS solution.

“As mechanical engineers, it compromises us so much,” says Holzheimer. “The NCC loophole that cites air conditioning via DX split systems and natural ventilation as an acceptable alternative to ventilation in accordance with AS 1668.2 is the equivalent of having your cake and eating it too, and needs to be closed. Natural ventilation is fantastic for domestic, Class 1 buildings. But for schools, universities, pubs etc., you shouldn’t be able to take up the DTS natural ventilation solution in conjunction with air conditioning that does not comply with AS 1668.2.

“And I don’t think it’s the mechanical engineers who are driving this. The first question you get asked by budget-conscious clients is, ‘What do we have to do?’ Well, you have to comply with the building code, that’s all.

“We have to go back to the NCC and say, ‘Can you please close this loophole’.”

A fresh air fallacy

Ross Macmillan, M.AIRAH, is a mechanical services consultant with more than 50 years’ experience in the industry, including participation in the working group that drafted Section J of the NCC. He has seen the problems emerging since the introduction of small wall, ceiling and floor-mounted split air conditioning units.

“Before these came on the scene, virtually every air conditioning system, even window units, had provision for drawing outside air through the unit,” says Macmillan “The original authors of the ventilation provisions knew this, and wrote the words assuming any air conditioning system would automatically provide outside air ventilation in compliance with AS 1668.2.

“When small split units were first introduced, mainly in domestic installation, the lack of outside air provisions was ‘overlooked’ and field experience showed there was generally sufficient infiltration to avert any problems. Since the introduction of Section J, however, new buildings are now very well sealed, eliminating infiltration of outside air, leaving the occupants of buildings with small split AC units with no fresh air at all.”

Macmillan says building developers, particularly of transportable buildings, are applying small split-type air conditioning units to increasingly larger buildings, where in the past they would have been served by ducted systems with outside air provisions.

“The problem has grown to the extent that there are literally thousands of buildings across Australia, particularly in mining and construction camps from Karratha to Gladstone, where the occupants have absolutely no fresh air supply,” says Macmillan. “I have personally inspected these camps to try to solve the problems caused by a lack of controlled, conditioned fresh air in facilities ranging from 3m x 3m bedrooms to 30m x 30m office and messing buildings.”

Macmillan agrees that the wording of the NCC should be changed to eliminate any ambiguity – and he submitted a proposal for change to the ABCB in 2013 to this effect. But he says the onus is also on HVAC designers to remain faithful to the intent of the code and not resort to the natural ventilation loophole.

“The mandatory NCC Performance Requirement F6P3 says, ‘A space in a building used by occupants must be provided with means of ventilation with outdoor air which will maintain adequate air quality’. Openable windows that are closed whenever the air conditioning system is running clearly do not meet this requirement.

“Considering also the mandatory Section J Performance Requirement J1P1 (e) and the whole of Part J5 Building Sealing requiring air conditioned buildings to be sealed airtight, then that alone nullifies any perceived allowance for natural ventilation in Part F6.

“Our ethical responsibilities are to the users of the buildings,” he says, “not whomever happens to be paying our design fees.”

Towards a solution

Brett Fairweather, M,AIRAH, from It’s Engineered, says that part of the problem is a lack of communication with occupants.

“If, as designers, we are going to rely on the minimum acceptable provision of ‘devices which can be opened’ (these being the words from the NCC), then we are relying on the occupants of those spaces to properly understand their role in actively participating in the control of the indoor air quality of those spaces,” he says. “Our design expectations need to be adequately conveyed.

“In my experience, many occupants in modern apartment developments are completely unaware of the ventilation provisions that have been selected by designers on their behalf. Many believe the wall-mounted or bulkhead AC units in their apartments are ventilating their spaces, and don’t like opening windows due to noise. Some occupants complain about mosquitoes and spiders. If the windows weren’t fitted with flyscreens, it might just reflect an underlying situation that no one really expected anyone to open those windows. But the construction was cheaper!”

Fairweather believes AS 1668.4 could provide part of the solution. The standard deals with natural ventilation and has been developed by the industry, for the industry.

“Section 2 of the standard is not referenced in the NCC, but is useful when pursuing natural ventilation designs that are better tuned to a building’s occupants, by considering both occupant density and activity levels,” says Fairweather. “For example, when applying AS 1668.4’s ‘detailed procedure’, a densely populated classroom for young students will require a minimum of 18.75 per cent of the floor area as ventilating openings. Alternatively, a sparsely occupied warehouse, with low levels of activity, will only require 2.5 per cent.”

Fairweather submitted a Proposal for Change to the ABCB for consideration in NCC 2025 recommending that consideration is given to the benefits that AS 1668.4 can bring to this situation, as a replacement of NCC Clause F6D7’s existing provisions. He says HVAC designers have a vital role to play in suggesting such changes.

“This process of contributing to improvement in our NCC,” he says, “is something we can all participate in.”

Indeed, HVAC&R News has received advice that the ABCB is currently working with Professor Hanmer to draft a scope of work for a future Proposal for Change. This work follows the recent Clean Air Forum at Parliament House – attended by both AIRAH and the ABCB. While this is not a formal commitment to alter the NCC, it shows that the ABCB is joining AIRAH and other experts in a detailed discussion about the issue.

4 Replies to “Time to close the natural ventilation loophole

  1. About time this discussion happened.
    A manually operated window is an uncontrolled (& variable) load and ventilation rate plus it’s unfiltered.
    Surely this must change.

  2. The 5% rule is over 50 years old, having originated in the old NSW Ordinance 70. It was a big improvement on previous ‘ventilation’ requirements (air bricks) but never had any scientific basis so, of course, ignored occupancy, the size and shape of the room and the location of the ventilation openings. Even worse is the way the natural ventilation provisions appear in the NCC. First, windows and doors only need to be openable when they building is built. After that there is no prohibition in screwing windows shut for security reasons for example. Second, NCC allows mechanical ventilation systems that don’t meet AS 1668.2 to default to the 5% natural ventilation rule.

    There is no doubt that the weakness of the NCC provisions helped the spread of COVID early in the pandemic and quite possibly led to deaths.

    Given there is general agreement the current NCC provisions are not fit for purpose I hope we will see AIRAH advocating for change.

  3. Its very disappointing to read that the NCC is not fit for purpose. It is even more concerning that early childhood centres, primary schools, secondary schools are starving our children from oxygen.

    An AS1668.2 provides for fresh air but recirculates the bad air. This also allows the spread of disease. I can see if the supply was set at 100% fresh air this could be a very expensive to install and run.

    I am surprised that with the technology available to us today, we cannot come up with a relatively inexpensive system that provides cool/warm fresh air to our developing children.

    Council House 2 in Melbourne finally started heading in the right direction. Purging the building in the middle of the night, providing fresh air throughout the day. Chillers like a refrigerator installed in the ceiling. The provision of indoor plants. What happened to the development of that technology? The council reported a significant decrease in absenteeism.

    Many schools have been around for over a hundred years. Most likely will be around for another hundred years. Why do we not look at the life cycle of the building and consider providing a system that will provide fresh air for the next 100 years and not provided recirculating bad air that will need to be replaced in and every 5 years. I wonder how much that will cost us over 100 years. Not just economically but socially for our developing children.

  4. Studies have been carried out in New Zealand, https://www.sciencedirect.com/science/article/abs/pii/S2352710223009816 measuring the impacts on school children using space heating and Ventilation. The figures show that it is essential to have quality air, for children to enhance focus and increase learning for these long periods of time. Other than windows, it is not a difficult proposition to install measured, closable filtered passive vents. For that matter wall mounted energy recovery systems have come a long way, which expel stale and draw fresh air at a controlled and measured rate, whilst moderating temperature control. Resorting to closed air conditioning, over long work periods of time is holistically, a disparity of resources. Long term – tiredness, lack of employee focus, possible viral transfer and reduced productivity are consistent to these environs.
    Consistent air change is also a key to keeping humidity levels down in building structures, and through consistent use the ability to lower condensation and Voc’s, from either off gasping of new materials, excess fragrance use or residual toxins from laundry soaps on clothes.

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