2 September 2013 — Conference: We could well need more high performance glazing and shading systems, and upsized thermal plant, pipes and cables, Christine Demanuele, a mechanical engineer with WSP Built Ecology, has found in her research.
Speaking with The Fifth Estate after presenting at last month’s Australian Institute of Refrigeration, Airconditioning and Heating’s The Future of HVAC 2013 conference, Ms Demanuele also said the trend of designing buildings for only 50 years did not seem “very sustainable”.
In her home country of Malta, her mother’s house was 200 years old, she said.
Ms Demanuele said as an industry, “we are becoming increasingly aware of the risks that climate change may pose to the performance of our buildings”, and that little was understood about the impact.
“We don’t ask about how a building will function in 2080. Perhaps it is too far away, and people think, ‘Who knows what will happen then. I might not be around,’ but it is discussion we should be having.
“Cost is also a problem because you can’t quantify the benefit and some people might think the climate predictions are wrong.
“But if you go back 100 years in Australia, it is getting warmer and there are more droughts; we have to start adapting.”
To test her theories, Ms Demanuele created models of two buildings in Melbourne, one a modern, new “BCA2013” building, the other “a typical 1970s” building.
Results found that a new office building in Melbourne designed to the current code was likely to experience around six times more warm hours in 2080s compared with current conditions.
A thermal simulation model was constructed for the buildings, which had a square plan with nine levels, with a central core and 30 per cent glazing on all façades. The overall net lettable area for the building was about 900 square metres.
A present day weather file for Melbourne was then morphed according to the 2020s, 2050s and 2080s scenarios to generate future weather files.
The buildings were then simulated for one year using each hourly weather file for Melbourne present-day, 2020s, 2050s and 2080s.
As an extra test, the new and existing building models – under the 2080s weather scenario, were used to investigate the influence of passive design measures, including shading, high performance glazing, additional wall and roof insulation and exposed thermal mass combined with a night purge strategy, on thermal comfort.
The hours the building was occupied with a temperature in excess of 26°C were then analysed, with the temperature chosen as one above which occupants would be uncomfortable.
The results showed that for a new building, that by 2050 the number of hours above 26°C doubles compared with present conditions and increases to around four times by 2080.
The 1970s building showed a similar trend.
This was despite the cooling system having unlimited capacity, with the increase due to increased radiant temperature.
Ms Demanuele told the AIRAH conference that “the modelling results demonstrate that occupants are likely to experience an increasing number of warm hours in office buildings in the future”.
“While work practices may change and people may adapt to increasing temperatures, it is prudent for designers to include a degree of flexibility into their designs to prepare buildings for a changing climate.
“The results emphasise that while airconditioning systems may be capable of maintaining air temperatures below required set points, this will not necessarily translate to preserving thermal comfort in a space.
“There is a level of uncertainty in climate change forecasts, with the IPCC releasing various risk scenarios for future climate.
“Determining which data to focus on for design decisions ultimately depends on the expected lifetime of the building and its systems, as well as the owner’s appetite for thermal comfort risk.
Building fabric needs to be upsized
“While HVAC systems may be replaced within 20 or 30 years, therefore could theoretically be upsized if required, building fabric is likely to last much longer, therefore passive measures such as high performance glazing and shading systems need to be incorporated at the design stage.
it is not just the thermal plant which may need to be
upsized; pipes and cables
may also need to have increased capacity
“Further, it is not just the thermal plant which may need to be upsized; pipes and cables may also need to have increased capacity.
“These changes may not be as easy to implement during a building refurbishment, emphasising the need for adaptation strategies to be considered at the design stage.”
Ms Demanuele said there was also a discussion about whether to include passive measures that add what may seem to be unnecessary cost to the building, or to upsize the HVAC system or increase capacity at each replacement.
“The use of active initiatives is likely to increase the energy consumption, hence carbon emissions, associated with operating the building, therefore contributing to the problem which a designer is trying to mitigate.”
Ms Demanuele also pointed out that passive measures would relieve the pressure on mechanical systems to perform, especially on peak days.
Current practice tended to oversize thermal plant or add spare capacity but is was risky to rely on spare systems for a building to perform in warmer weather, as this could leave a building vulnerable to unplanned events or break downs, which may become more common in extreme weather, she said.
Another factor to consider is the effect of radiant temperatures on thermal comfort, which are not addressed by air-based systems, even though air temperatures may be kept within targets.
Again passive initiatives could help with both thermal comfort and carbon efficiency.
As climate change took hold, it was possible that a new office building in Melbourne designed to the current code was likely to experience around six times more warm hours in 2080s compared to current conditions, Ms Demanuele said. And peak cooling load could increase by more than 20 per cent under the 2080s weather scenario.
“Based on the modelling results, the most effective strategies at improving thermal comfort conditions and decreasing peak cooling load in the future are high performance glazing and shading.”
What might not work so well would be thermal mass and night purge since night time night time temperatures could be higher.
Ms Demanuele said the study highlighted the need for designers to design more flexible buildings that could adapt to warmer and more extreme conditions”.
One idea was to include a “future proofing assessment” as part of building regulations compliance.