26 Jan 2024

Climate impact of air conditioners

From Morning Report, 8:20 am on 26 January 2024
Hand holding remote control directed on the air conditioner

Photo: 123RF

New Zealand homes are not designed to keep us warm in winter.

Now, with a scorching week behind us, it is clear most do not keep us cool in summer either.

Nigel Isaacs, a senior lecturer in architecture and building technology at Victoria University, said this was because Kiwis do not build houses to regulate what comes in.

"We have a tradition of designing houses for maximum glass, because we seem to confuse windows with design.

"But we fail to recognise that limitless views come with limitless problems."

Windows, especially single-glazed ones, let heat pass through far more freely than walls.

This applies to the sun's rays in summer as much as warmth disappearing in winter.

Dr Wentao Wu, a senior lecturer of engineering at the University of Canterbury, moved to Christchurch a year ago.

Previously, he lived in Shanghai, Boston, Nashville, Zurich and Naestved in Denmark.

He said he was shocked by the state of our homes.

"I'm not sure New Zealand has made the right decision in terms of heating and cooling.

"Most buildings have very large windows and single glazing. But a wall is only as strong as its weakest point.

“No matter how much insulation you put in, if you don't have double glazing, it will fail."

Isaacs acknowledged there had been a real focus on improving the quality of our homes recently.

But this has focused primarily on warming houses in winter.

"We're essentially creating insular boxes where the indoor temperature increases as the outdoor temperature increases."

Now, as extreme summer heat occurs more frequently with a warming climate, more and more people are relying on air conditioning to manage the heat.

"Our solution has been to turn on the air conditioner," Isaacs said.

"But that comes with an environmental impact as well as cost."

However, according to Sustainable Engineering director Jason Quinn, it was hard to say whether a reliance on air conditioning was harmful.

Any unit that cools in summer also operates as a heat pump in winter, he said.

Those units tend to be more energy efficient than older electric heating options, meaning less net emissions over the course of a year.

"If you use resistance electric heating to heat an average house in New Zealand, it produces about 300 kilograms of carbon a year, roughly speaking.

“But if you use a heat pump instead it's only 100kg- so the saving is 200, and the impact of cooling with that same heat pump in a really hot house in summer would be less than 100kg.

“So it tends to be a much smaller impact."

Quinn said some countries, like Spain, were considering intentionally designing houses that overheat in summer to reduce the energy load in winter.

"Power demand spike is in winter, so in summer we have an excess of power," he said.

"By designing houses that hold heat better than they cool, we can shift some of that demand to the quieter months, which is beneficial if you look strictly at emissions."

In countries like New Zealand where we fall back on fossil fuels when energy demand exceeds renewable supply, building designs that reduce the load in winter would help to decrease emissions overall.

But emissions reduction goals do not exist in a vacuum, and Quinn acknowledged this approach depended on a reliable electricity network.

"If you design buildings that overheat, but then lose power, you can't operate your air conditioner to keep it cool inside."

Isaacs said the best approach to managing summer heat and winter chills was a holistic one that regulates the sun, heat storage and heat loss.

Design techniques like external shading, ventilation and hard materials go a long way in managing the elements.

"You can design a house so that the amount of heat coming in is moderated," he said.

"Methods like managing the amount of sun you let in with external shading, or using materials like brick and concrete which soak up heat during the day and let it out at night can go a long way."

But what about earthquakes?

"It's easy to just say 'but this is New Zealand', and write these things off.

“But we shouldn't simply say glass is bad and insulation is good, or concrete and brick are bad - they're all good.

“We just need to use them together."

Isaacs and Quinn both said the current Building Code does not promote this mixed approach.

"The Code is a minimum standard, it describes what you can't build worse than," Quinn said.

"It's not designed to promote good design, and because the cold is what has bothered us so far, it pretty much just focuses on heating."

But now, with climate change bringing more extreme weather in the summer as well as the winter, Kiwis needed to adapt.

The Ministry for Business, Innovation and Employment has a programme underway that aims to ensure building design improves to cope with the changing climate.

Whether funding for this work will continue under the new government is yet to be seen.