‘Archi-greenies’ like to proselytize that our dwellings don't need air-conditioning. While much of Australia swelters through a heatwave, it is timely to ask whether the push for no air-con is a con-job? Whilst it's true that buildings don't need air-conditioning, people do, particularly in extreme heat, and that is today’s story.

Heatwaves (three days in a row of excessive heat, say 35⁰C,) are Australia’s deadliest natural hazard, particularly for cities. Since 1890 more people have died (2887) in major heatwaves than in all the bushfires, cyclones, earthquakes, floods and severe storms combined (2368). And climate change will only increase the frequency of heatwaves, and deaths.

Thermal Comfort

A key requirement for a building is to provide thermal comfort: it’s a key commodity, part of firmness, and necessarily delightful. But thermal comfort is not a fixed value as we discussed here. There’s a spectrum of temperatures and humidities that people find comfortable (around 18⁰C in winter, 22⁰C in summer), and some people are outliers above or below those values, but we know that temperatures above 30⁰C are uncomfortable for all, verging on dangerous for some.

Those more vulnerable to heat stress include the very young, the elderly, the infirm, those who are pregnant or obese or with low mobility. Not always top of an architect’s client list, let alone as users on their radar. But for them extreme heat can be a matter of life or death.

Can dwellings, houses or apartments, maintain thermal comfort in a heatwave without AC? Can we use passive design, or Passivhaus, both of which rely on ‘building conditioning’ discussed here, to keep the internal air well below 30⁰C when the external temperature reaches up to 35 to 40⁰C for day after day. Absolutely NOT, contrary to popular mythmaking.

Which is not to deny the value of high levels of insulation, low-e double glazing and deep shade, all of which we extolled in a discussion on passive design, and last week’s discussion of ‘outdoor rooms’. But the key issue is fresh air, the base level of ventilation, which is needed in every house, but our houses ‘leak’ far more air than necessary, more as they are older.

Good ‘passive’ houses, with tightly sealed windows and doors, may restrict the hourly air change rate to two, but that means it only takes a few hours for the indoor air temperature to reach the same as the outdoor, unless the thermal mass can restrict the rise.

A ‘Passivhaus’ design can further reduce the air changes and the amount of incoming heat by use of a heat exchanger (between incoming and outgoing air), but without huge levels of pre-chilled thermal mass it can only delay the inevitable temperature rise on the inside, as it reaches the external temperature.

Both ‘Passive’ and ‘Passiv’ rely on night-time or ‘diurnal’ cooling for summer comfort, but in a heatwave the night-time temperature doesn't fall and there are no cooling breezes. And this lack of possible cross ventilation is exacerbated in built-up areas, where temperatures rise with the ‘urban heat Island effect’ and the close proximity of neighbours presents difficulties of a loss of privacy.

Providing sufficient thermal mass to offset the high temperatures of several days on end is usually completely unfeasible, except in some underground buildings.

‘Green’ architects may convince their clients to do without air conditioning, perhaps not warning them that ‘enjoying a close connection to nature’ may mean having external air temperature come indoors within 12 hours. But what happens when the clients who signed up for the ‘natural life’ sell their house and unknown, more heat susceptible, owners move in?

One irony discussed in our articles on NatHERS (here and here) is the repudiation of one of its key assumptions of AC by the architectural critics, who advocate for no AC in the most glamourous of homes, yet increasingly every house in temperate Australia is getting AC.

Whilst in winter occupants can put on extra layers of clothing, when it’s hot the reverse is not an option: you can only shed so many clothing layers. In a heatwave people's thermal comfort cannot be satisfied by ‘building conditioning’ alone. The interior will reach unhealthy, or even deadly, conditions.

The bottom line is: no matter how good the passive design may be, in a heatwave, with temperatures above 30-35 degrees for two or three days, it is impossible to maintain a comfortable internal temperature without some form of mechanical cooling (AC in the seaboard cities, evaporative cooling inland).

In a heat wave, a dwelling cannot lower its internal temperature by itself. To reach thermal comfort it will need mechanical assistance. Denying air conditioning for every dwelling is reckless, increasingly so as summers get hotter. Denying life-giving cooling for the unknown future occupant, who cannot achieve cooling in any other way, is an abrogation of an architect’s social licence.

The upside of AC

The good news is that there are three offsets to the AC’s energy use.

Firstly, AC is based on a heat pump, and they have a coefficient of performance (or COP) of 3 or 4, meaning they deliver more cooling (or heating) than the energy inputted by a factor of three or four.

Secondly the beauty of air conditioning for cooling is that it can be powered by solar photovoltaic (PV) panels. The more sun shines, the hotter it gets, the more PV panels will work to power the air conditioning without the grid.

And thirdly the design of AC is remarkably better, not just the machinery but moreover the sophistication with which it is deployed by good mechanical engineers.

Two salutary lessons

In Darwin some famous architect-designed houses were designed without any air conditioning, following the lead Beni Burnett’s Myilly Point houses of the late 1930s. But subsequent purchasers, who found the ‘build-up’ and humidity intolerable, or didn't subscribe to the original architect's idea of cross flow ventilation, have fitted AC, which doesn’t work well in the highly glazed, lightly framed and insulated designs.

And in Sydney, a medium-sized developer proudly promotes his apartments as not having any AC. Not that they don't need it; just that it's not supplied. But it’s quite often retrofitted by the owners who find that the breezes don’t follow the architect’s arrows, or that they have no desire to hear the next-door neighbour’s home theatre or impending divorce, and therefore close the windows/doors, creating stuffy internal air temperatures, and a post-occupancy AC purchase.

In summary

For architects to argue that clients should be sufficiently tolerant to accommodate houses without air conditioning ignores the house having a life beyond their client’s. For architects to say they believe in the science of climate change, but ignore basic architectural science is shameful. For architects to advocate the need to address climate change, all the while ignoring the impact that the increased heat will have on the occupants of their designs, is hypocritical.

So much of our attitude to AC is ignorance. The idea that we can do without air con is a con job.

Tone Wheeler is principal architect at Environa Studio, Adjunct Professor at UNSW and is President of the Australian Architecture Association. The views expressed here are solely those of the author and are not held or endorsed by A+D, the AAA or UNSW. Tone does not read Instagram, Facebook, Twitter or Linked In. Sanity is preserved by reading and replying only to comments addressed to toneontuesday@gmail.com

Tone Wheeler

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