Will we keep cranking up the aircon as we watch the planet burn? 

We have conjured up a dark future with our addiction to air-conditioning, but as we enjoy our dream lifestyle, this luxury is cooking the planet and sentencing the poorest and most disadvantaged to a nightmare of cooling poverty.

As the planet warms, the technology that we use to stay cool is making the climate hotter. Sixty percent of the world’s population faced extreme heat last summer (Climate Central, 2023), and more than 2.5 billion of these people did not have access to cooling (IEA, 2018). In India alone 630,000 people die each year from high temperatures (Davis et al, 2021). Cooling accounts for a fifth of the electricity used in buildings. 10% of all global electricity consumption is by and large used by the richest and coolest countries (IEA, 2018). Additionally, the refrigerants used are themselves a deadly greenhouse gas. 

In the face of climate chaos, ecological collapse and species extinction, will we keep cranking up the aircon as we watch the planet burn? The simple answer is “yes”, the basic premise of the new energy efficiency provisions of the National Construction Code (NCC) in 2022, is that all new homes will be air-conditioned. The NCC requires a new minimum thermal performance rating of 7 stars under the Nationwide House Energy Rating Scheme (NatHERS). And, all new homes must not exceed a legislated annual energy use budget. Annual energy use is calculated assuming that the home is air-conditioned 24/7, and based on mandated allowable minimum and maximum temperatures that sit in a very narrow range, to determine when the air-conditioning kicks-in. 

This article will highlight some of the problems with the NCC including the following: 

  • outdated climate files, and the lack of consideration to future-proofing of homes for a warming climate; and, 
  • the dangers of the assumed reliance on air-conditioning in determining compliance, and the need for an assessment pathway for passive low energy homes.

Why are we adding expensive construction and mechanical equipment to try to make damp, dark, poorly ventilated, multi-skinned homes that mould loves, liveable? 

Future-proofing for a hotter climate

The NatHERS climate files used to estimate the air-conditioning needs of a home are based on historical averages, consequently placing an undue emphasis on heating. The NCC 2022 ignores the fact that our climates are warming and that over the life of a building (20, 30, 50 plus years) the climatic conditions will change hugely. This is how bizarre the situation is: based on CSIRO climate predictions and the new energy provisions of the NCC, if we were to design a home to suit 2050, we would not legally be allowed to build it now — even though that house would use significantly less energy for cooling in the climate of 2020 (Upadhyay, 2022).

We are not allowed to build homes that are future-ready, that can keep people safe and reduce energy bills. It is not a straightforward matter of retrofitting homes in the future. The incorporation of mechanical heating, ventilation, and air-conditioning, leads to radically different building forms, layout, construction, and landscaping than if priority were given to a passive design approach. 

Cool it!  

The NCC assesses the performance of homes assuming that the home is air-conditioned and that the air-conditioner is on. Modelling of homes in Western Sydney shows that code-compliant homes become unsafe when the air-conditioning is turned off, for example, in a heatwave-induced blackout or when air-conditioning is unaffordable (Upadhyay, 2022). Why use ducted mechanical ventilation when opening a window is free and unpowered? Natural ventilation uses less energy than mechanical ventilation so it is inconsistent for the NCC to use ducted mechanical ventilation as the baseline.  In the context of the COVID-19 pandemic, the CDC advises us to “open doors and windows as much as you can to bring in fresh, outdoor air” (CDC, 2022). Residential ducted air-conditioning, which is not mainstream practice in Australia, is very expensive to install, uses a lot of energy to run, is leaky, and is difficult, if not impossible to clean or drain. There is a 20-40% conductive loss of heating and cooling energy through ductwork, before delivering it to rooms (Harvey, 2012).

Reliance on aircon puts unnecessary pressure on our power grid, leaving cities vulnerable to energy failure. Furthermore, not everyone can afford to use aircon, so what are we saying about equity both nationally or globally? Air conditioning our homes stretches the capacity of the national electricity system, particularly during heat waves.  When the electricity demand peaks, the supplier either increases the price to discourage use – variable pricing regime, or cuts off power to some areas – load shedding. Moving into emergency mode, how will the privatised energy company decide who will lose power? Will the choice be the neighbourhoods that generate the least profit? Will there be access to publicly cooled spaces in these neighbourhoods?  We are seeing a huge wealth disparity between those who can and cannot afford air conditioning – aircon has become a new marker of class. The safest, fairest and lowest energy option is to build a climate-responsive home that uses little or no energy for heating and cooling. The NCC makes this very difficult.

Addicted to aircon

Most of us on this continent live in one of the most benign climates in the world, yet we have developed an insatiable demand for conditioned space. We go from our air-conditioned home to our air-conditioned car to our air-conditioned workplace and so on. We are so obsessed with a luxury 22°C that we have lost sight of how often a building provides adaptive comfort. 

The narrow band of thermostat settings required by NatHERS creates more energy demand, than would be determined by other thermal comfort models. An adaptive comfort model takes into account how people interact with buildings, so considers things like what clothing is worn, what windows are open, are the shades down. Interestingly, research shows that buildings designed for adaptive comfort are considered more comfortable by occupants than buildings relying on air-conditioning, even in the same conditions (Luther, 2019).

All models are wrong…

NatHERS is the software modelling tool used to demonstrate energy efficiency compliance with the NCC administered by the Department of Climate Change, Energy, the Environment and Water. AccuRate, BERS Pro, FirstRate5, and HERO are the predictive energy thermal modelling tools based on the CSIRO calculation engine, Chenath, that are accredited by NatHERS to determine a star rating. A home is rated based on the amount of air-conditioning, heating or cooling, that is predicted to be needed to keep the home within a set comfortable range. This range is legislated using thermal comfort set points that favour highly insulated and sealed-up buildings. The NatHERS energy rating discriminates against the application of climate responsive design such as heavyweight rammed earth homes and lightweight tropical homes. 

NatHERS used in ‘Regulation Mode’, which is required for building approval, does not suit passive low energy homes, or for that matter existing vernacular homes. NatHERs can’t handle the behaviour of the occupants, natural, stack-assisted and mass-linked ventilation, radiant heating or cooling, or the way different materials store and release heat. NatHERS ‘Free Running Mode’ attempts to model how a home responds naturally to its climate, but currently cannot be used for certification, and is fairly limited in terms of what can be modelled.

The NCC focus is on R-value (resistance to heat flow) which is relevant to lightweight construction and insulation; but thermal capacity (the ability of a material to store heat) which is an advantage of heavyweight construction (bricks, earth, etc), is ignored. Materials with a higher R-value will provide better insulation, resisting heat loss (or heat gain). On the other hand, the high thermal capacity of heavyweight construction can reduce heat flow from the outside to inside by storing the heat within the walls, floors or roof, slowing the heat flow from one side of the wall to the other (thermal lag) which helps keep the room temperature stable.

In winter, internal mass absorbs the heat generated during the day from the sun slowly releasing it during the night and the next morning. In summer, the internal mass absorbs heat in the daytime which lowers the room temperature and good ventilation at night will clear the heat and cool down the mass for the following day. High thermal mass can significantly reduce costs, improve comfort and eliminate or reduce the necessity for air conditioning.  Passive solar design balances the amount and placement of mass with other key considerations, such as windows, shading, insulation, orientation, ventilation and occupant behaviour to optimise building comfort. Unfortunately, the NCC is based on the assumption of air conditioning and favours highly insulated lightweight construction which cannot store heat. Due to the relatively low thermal resistance of heavyweight building materials, it’s very difficult to achieve NCC compliance. 

Cooking the planet

As the demand for air-conditioning goes up, the energy required to power all that cooling will, paradoxically, burn more fossil fuels, generating more carbon, supercharging global warming. Furthermore, air-conditioners must discharge the heat that they extract from the environment. Heat rejection from air-conditioners increases the outside air temperature exasperating the urban heat island effect and adding to the cooling load of buildings. This means that even more energy is needed to cool down buildings. As air conditioners use a lot of power, the more they are needed, such as in an intense heat wave, the more likely there will be widespread blackouts. 

Refrigeration and air-conditioning equipment is estimated to generate more than 11% of Australia’s annual greenhouse gas emissions in 2019 (Expert Group, 2021). A typical residential unit might lose 10% of its refrigerant (hydrofluorocarbons) each year through leakage, or release all its refrigerant entirely if it is thrown away without being properly drained. All refrigerants used in cooling have a global warming potential and affect the ozone layer.  

Shiny new things

Perhaps a greater issue is that the NCC only addresses new homes. New dwellings built each year are only about 1.4% of the total number of existing dwellings. The Government’s Your Home guide states that heating and cooling use the largest amount of energy in the home, accounting for around 40% of household energy use (Australian Government, 2024a). Therefore, in terms of impact, there needs to be a focus on practical retrofitting options. There are many hurdles to retrofitting — the absence of appropriate information, the lack of a retrofit industry, a perception of risk and the economic reality that much of the value created is in the public benefit and not monetizable by the homeowner.  Overwhelmingly, the housing industry is driven by developers who see that the easiest way to make the most money is greenfield residential estates, which is also a revenue spinner for state and local governments.

We need to change how planning accounts for climate change. High rise apartment blocks, it turns out, are the biggest energy guzzlers in the residential market – by some 30%, use more water and occupants are no more likely to use public transport – and with basement car parking stretching boundary to boundary there is nowhere for a creek to flow or a tree to grow. 

We need climate-responsive planning, neighbourhood settings and refuge areas.  We know that nature-based solutions can be a city’s most powerful way to make the urban environment more comfortable and to reduce cooling demand (UNEP, 2021).

Modifying the urban microclimate using vegetation, water and channelling breezes can significantly reduce temperatures by up to 12°C (Bartesaghi-Koc et al, 2020). Two western Sydney streets are only a short walk apart, but when it comes to temperature there’s a lot that separates them. Due to tree cover, the difference in air temperature between these two streets is up to 8°C (Pfautsch & Rouillard, 2019).

The past is sunk

The committed or ‘sunk’ emissions of all the stuff that we have already made — from fashion and cars to homes and power plants — will push us over 2°C temperature rise (Davis & Socolow, 2014). Human-made materials now outweigh the entire mass of living matter on the planet. We must move away from reliance on high-energy materials like concrete and steel and energy-hungry processes like air-conditioning. Ideas like passive low energy design, retrofitting and reuse, eliminating plastic, switching to natural materials don’t fit with the current market framework; large-scale, long-term systemic change is not part of the standard model of capitalism which relies on us buying more and more stuff.

The total life cycle energy use in a building is a combination of embodied energy — the energy used in building material production, transport, construction, maintenance, renovation and final demolition, and operational energy, and the direct energy used to run the building. The proportion of embodied energy compared to the operational energy use of a home is growing substantially with the increasing specification of energy intensive materials required by the NCC. The Government’s Your Home Technical Manual calculates the embodied energy of a home as 53% of total energy use over the 50-year life of a building (Australian Government, 2024b). Reduction in embodied energy resulting from building design, materials selection and manufacturing processes has an immediate impact on emissions, locking in embodied carbon as soon as the home is built. It is a relatively known reduction not dependant on factors such as occupant behaviour and grid decarbonisation over time.

Take a deep breath in

Ducted air-conditioning and ventilation systems are crawling with significant biological hazards which are often made worse by a low relative humidity inherent in-home air-conditioning (Boermans, 2019). In the Netherlands, ducted systems are now banned for the use of thermal energy distribution in homes (Grove, 2019).

The air quality of ductwork is problematic, particularly when toxic materials such as PVC are used. Health Care Without Harm Europe has identified significant health issues at all stages in the lifecycle of PVC, that PVC is the most environmentally damaging plastic being used, and that safer alternatives exist. Some countries in Europe have already banned PVC from landfill (e.g. Germany, Sweden, and Finland) and many cities have restricted or banned the use of PVC, including in construction (Spain, Netherlands, Austria, Vienna) (Health Care Without Harm Europe, 2021). Europe is moving towards phasing out PVC entirely. 

The sealing of the building envelope against air leakage combined with air-conditioning means increased condensation and persistent damp which leads to problems with mould and reduced air quality. Some 40% of Australian homes have mould causing asthma, respiratory ailments and allergies (Dewsbury & Law, 2016).

The COVID 19 pandemic highlighted the value of natural ventilation over mechanical ventilation with WHO recommending the use of 100% fresh air in response (WHO, 2020). All airborne diseases (common cold, flus, viruses and bacteria) are spread through mechanical ventilation, yet the NCC does not require a house to be naturally ventilated or to have cross ventilation. Although the NCC mandates that a home must have ventilation with outdoor air to maintain air quality, there is no requirement to verify that adequate ventilation and air quality is achieved.

Alternative assessment pathway for passive low energy buildings

Avoiding air-conditioning should be considered best practice by the NCC.  The safest and lowest energy option is to build a home that uses little or no energy for heating and cooling and that will be resilient to more extreme climate conditions and blackouts. “A passively designed home can deliver a lifetime of thermal comfort, low energy bills, and low greenhouse gas emissions” (Australian Government, 2022).

NatHERS modelling of ducted mechanical air-conditioning is based on the assumption that the windows would be closed when the outdoor air is not within the narrowly defined comfort zone, but is this a true reflection of how people behave? Obviously, the infiltration of unconditioned outdoor air will significantly reduce the efficiency of ducted systems, yet the NCC assumes model behaviour by the occupants. On the other hand, alternative conditioning methods such as radiant systems, tolerate the windows being open for longer periods of time allowing for fresh air ventilation. Importantly, radiant cooling-assisted natural ventilation can provide an acceptable level of comfort without the use of air-conditioning throughout most of Australia (Daniel, 2017).

Concluding remarks

Complicating all this, is the massive lack of monitoring of how homes actually perform and the validity of the current thermostat set points– “the software is still taking a stab in the dark about a house’s actual performance” (Law, 2023). Models, after all, are imperfect representations of the real-world and the results are only relevant within the closed world of the model itself. It is ridiculous that modelling is being used as the regulatory tool without being suitably tested in the real-world. 

Energy efficiency provisions have been introduced to the NCC progressively from 2003. Despite the intention to increase energy efficiency of housing by improving the thermal performance of the building envelope, we have not achieved any reduction in energy use in dwellings. What we see is the exact opposite, and further significant increases in energy use are predicted (Wingrove et al, 2024). We need a climate appropriate, low embodied energy design regulation focused on the reduction of greenhouse gas emissions and response to climate change. 

We can’t air-condition everyone everywhere all the time; our planet’s atmosphere cannot sustain even our current use of air-conditioning (Jay, 2021). The NCC paints a scenario of reliance on ‘guilt-free’ air-conditioning powered by renewable energy. This doesn’t address the impacts of air-conditioning: peak load demand, the Global Warming Potential of refrigerants, or safety of occupants in heat waves when power is lost.  It doesn’t resolve the negative relationship between indoor air quality and efficiency. It doesn’t consider embodied energy, or climate change resilience, or whether designs assist, rather than hinder, the transition to renewable economies. It doesn’t respect the most vulnerable of us.

This article was written on unceded Yugarabul, Yuggera, Jagera, Turrbal land where the First Peoples of this country have lived sustainably since time immemorial. I acknowledge their frontier wars, their fallen warriors, and I pay my respect to Elders past, present, and emerging.


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Marci Webster-Mannison (PhD, BArch, BDes Studies) is an architect and activist known for deep green architecture and urban design. With over 40 years of professional practice specialising in the tertiary, health and science typologies, Marci has worked in the private, government and academic sectors, in cities, rural, regional and coastal environments. Amongst over twenty state, national and international awards for their architecture, Marci received a Special Jury Award (AIA), for contribution to the advancement of architecture and environmentally sensitive design. Marci’s work is informed by a commitment to effective interdisciplinary collaboration and the project-specific aesthetic, social, and ecological context of design.

Image credit. Aircons by Sherwin (2006) CC BY-NC-ND 2.0 DEED.