Building for a future climate

Global warming is pushing temperatures upwards, but are Australia’s buildings being designed to handle these future conditions? Probably not, according to a report produced by DeltaQ for the COAG Energy Council.

The report aims to quantify the impacts of climate change on the built environment, and recommend how building regulations should adapt.

“The key thing that struck me was that buildings designed to be in operation 50 years from today were still actively being modelled and designed based on climate data from at least 20 years ago,” says Grace Foo, M.AIRAH, who wrote the report in collaboration with the project team comprising DeltaQ, Northrop Consulting Engineers and Exemplary Energy Partners.

“This means that in 2070, we would have buildings operating based on climate data from the 1980s! That’s crazy considering what we know about climate change.”

More cooling, less heating

In the future, significantly more cooling will be required compared to heating. It is estimated that by 2050 there will be around half as many heating degree days (a base of 18°C), but more than double the number of cooling degree days (a base of 21°C).

The report found that using appropriately sized HVAC plant for a future climate (2050) would reduce heating energy by between 70–90 per cent, and increase cooling energy by between 30–80 per cent.

“When assessed in terms of capacity for HVAC plant sizing, our research found that chiller size increased by 10–20 per cent and boiler size decreased by around 20 per cent,” says Foo.

“If we retained HVAC plant sized using the baseline climate, occupant thermal comfort decreases between 20–35 per cent in a daytime application like an office, or 2–47 per cent, depending on the climate zone, in an overnight application like a hotel.”

To retain the same HVAC plant sizing to service a future climate, the window U-value, SGHC, wall U-value and roof U-value would need to be improved by about 50 per cent in an office building. This is slightly lower for an overnight building (hotel), but in the same ballpark – a 30–50 per cent improvement for all attributes and a 70 per cent improvement for U-value.

Design dilemma

Although using future climate files makes sense, it poses a dilemma for designers.

If they use a future climate file, the modelled greenhouse gas emissions of HVAC plant, particularly cooling energy, will increase. Heating plant would still be sized on the baseline climate file, to cope with the current heating load so that building occupants don’t freeze before the climate warms up.

Foo explains that the Deemed-to-Satisfy (DTS) requirements in the NCC need to be updated to reflect the change.

“Changes to the NCC are generally subject to a cost-benefit analysis,” she says. “The underlying technical modelling that led to the 2019 Section J revision typically only considered the economic (energy) and greenhouse gas emissions benefits. The methodology at the time did not include occupant thermal comfort as part of the criteria analysed for DTS stringency changes.

“Our research found that there can be scenarios where the reference building using only DTS measures will not meet the PMV thermal comfort requirements.”

The report recommends that the stringency of Section J DTS provisions should be reviewed against an updated cost-benefit analysis using future climate files, and increased where beneficial, particularly for requirements related to cooling equipment. Thermal comfort should also be included as an assessment criterion when reviewing changes to DTS provisions.

“We are definitely not asking for occupant thermal comfort to be reduced as part of this recommendation,” says Foo. “Our recommendation to consider thermal comfort in the next iteration of DTS revisions is because there is no requirement for energy or thermal comfort modelling to be undertaken when a building uses the DTS pathway to comply with the NCC. I don’t know what the final answer will be ahead of doing the work, but we don’t want to end up with buildings designed with larger HVAC plant to cope with a warming climate, leading to higher greenhouse gas emissions, which then further exacerbates the issue of climate change.”

File under future

Foo notes that the Building Code of Australia currently does not require modellers or designers to quantify resilience to climate change in a building design, and many modellers do not have easy access to credible climate files for this purpose.

“Australian modellers can get access to future climate files either by manipulating climate files themselves or by purchasing them from climate files suppliers,” she says.

“At time of writing, the only Australian ‘shovel-ready’ source in an hourly format that modellers can apply directly into energy and thermal modelling software is the Ersatz Future Metrological Year (EFMY) files developed by Exemplary Energy Partners. CSIRO has also developed some files, but at the moment it is largely for application in the residential market and for NatHERS, so not widely available to the standard modeller/design team.”

The report recommends that a nominated government or industry body should manage and host a centrally available database of “accredited” climate files.

“Australia has the opportunity to address this issue by learning from our counterparts in the UK, who provide a centralised source for a range of climate files, accounting for locale (urban/rural/suburban) and projected future climate under a variety of emissions scenarios,” says Foo.

Such files would take into account the changing climate as well microclimates such as urban heat islands.

“We hope that some of these changes could be applied to the 2022 edition of the NCC,” says Foo, “but it is looking like there is significant development work that still needs to be completed, particularly with the centralised climate file repository recommendation, before new requirements can be released.”

To read the report, click here.