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Week Twenty-One - Different Cooling Systems

Save 55+ kilograms CO2e per person per year

· Weekly experiments

My preschooler

- Squawk! Mummy, pretend I'm a pirate parrot and pretend I copy everything you say.


- ... said the politician to the union.

Squawky the coal parrot toes the party line

But is it Art?

This is my last post about how to cool a house in summer. I'm behind schedule because I've been preparing a piece for Canberra's Art, Not Apart festival in March. If you go see it you'll know it's art, because it's made of Lego, not spreadsheets. Until then, back to the spreadsheets.

Fans, air conditioning or evaporative cooling?

Anything that uses a lot of energy emits a lot of carbon dioxide and equivalent emissions (CO2e). How much CO2e do different cooling systems emit?

The traditional wisdom is that air conditioning is energy-intense and fans are eco-friendly. I'm not rich or committed enough to dismantle our evaporative cooler and install a series of temporary replacements to test this out, so I did the next best thing. I compared specifications for portable appliances from OfficeWorks. I've looked at scenarios to keep a family of three cool over summer, being three fans, two evaporative coolers or one air conditioner.

Scenario 1 - two portable evaporative coolers - lowest power use

At only 72 watts combined, the portable evaporative coolers use very little power. This is consistent with my experience of a central unit. I compared our power bills for the three years before and after we installed evaporative cooling, and we only emitted an extra 100 kilograms of CO2e after installing a central evaporative cooler. This is probably why it was so hard for my family to cut back by using the system more efficiently. It's already an extremely efficient system.

Scenario 2 - three portable fans - medium power use

At 340 watts combined, three fans take a big chunk from your total electricity usage, almost five times more than the evaporative coolers above. I also find them far less comfortable. Use fans wisely. Turn them off when you're not in front of them. Pick energy-efficient models.

Scenario 3 - one portable air conditioner - high power use

At 1100 to 1650 watts, the air con units used over fifteen times more power than the evaporative coolers and three times more than the fans. They're even worse if you want to air condition a whole house, rather than a single room. Air conditioning deserves its reputation for being power-hungry.

A fan might keep you cool in summer

A fan of fans? Choose fans over air con, but use them wisely.
Evaporative cooling emits less CO2e than fans, but it doesn't work in humid climates.

Passive cooling 

Passive cooling means keeping cool without using electric cooling appliances. It's generally regarded as the most ecological method. Ideally, it involves original design-and-build decisions, like orientating your house to minimise summer sun on windows and using building materials that provide good insulation. Retrofits might include planting deciduous trees that give summer shade and winter sun, installing awnings, blinds and extra insulation and closing blinds during the day.

There is embedded energy and emissions in building materials. If you're building from scratch, build for passive cooling and passive heating. But if you have to dismantle existing infrastructure and install virgin material in its place, the embedded CO2e may outweight the energy savings. It's a complex calculation to make.

I tested out some passive cooling retrofits. I installed an awning over my study window, a draught-proof dog door to replace our hole in the wall and some cheap window insulation (which promptly peeled off in the 40-degree heatwave). I then monitored our power use over the following three weeks. My household electricity dropped from 108-kilowatt hours per week to 79-kilowatt hours per week. If sustained over summer, this would reduce my per-person emissions by 110 kilograms CO2e. But the heatwave had also ended for that period, so the reduced power use could have been due to the weather. It's impossible to tell.

How much CO2e can you save?

I conclude that anyone could cut 55 kilograms CO2e per person per year with some basic measures, like simple passive cooling retrofits and using their cooling system more efficiently. This is a small cut. As a society, we'd be better off switching the grid to renewables, which would save over 900 kilograms CO2e during summer alone.

If you have central air conditioning, you can save more than 55 kilograms CO2e by turning your air con to a higher temperature / lower power setting, using it more efficiently and adding passive cooling. Do that, but also help us switch the grid at the next election.

Greens politicians support #stopadani protest

Politicians at a recent #StopAdani coal mine protest in Canberra. Some are for real, others mere puppets.

Spreadsheet calculations, notes and data sources in the 'Notes' section, Week Twenty-One.

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