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Week Thirty - Heat Pumps

A heat pump heater/air conditioner saves 122 kilograms CO2e per person per year

· Weekly experiments

My kindergartner

- Mummy, I don't need a jumper. I just run around like this and I don't feel the cold.


- Is it some new kind of heat pump technology?

A little girl runs around in the snow in a t-shirt

Best of the rest without a test

I started this project for two reasons. I wanted to see if I could cut my carbon footprint by 75% instead of the federal government's stingy one-tonne cut. And I wanted to test out the greenwash.

There's a constant stream of green lifestyle tips and products claiming they'll fix the world. We clever apes are great at coming up with these ideas but bad at judging which ones work. Some of my favourites are the fly in / fly out ecoresort, the jumbo 5-star energy-efficient fridge and monthly subscription services that send you junk you don't need wrapped in eco-friendly cardboard. Feel free to buy any of this stuff, but don't imagine it's saving the planet.

One of my rules in The Carbon Diet is that I'll run the numbers and test the thing myself to make sure it works in real life. I'm breaking that rule for heat pumps. I haven't tested any, but I can't walk away from household energy without covering them.

Why heat pumps?

The last three energy experts I spoke to said heat pumps are where it's at. The technology has come of age and they are incredibly efficient. Instead of using lots of energy to produce heat, they use a little energy to move heat around. They circulate heat in a refrigerant and use evaporation and condensation to transfer heat from one location to another. Fridges work like this. They pump the hot air from inside the fridge into refrigerant coils on the outside, which is why those coils feel hot. The same principle can be applied to a clothes dryer, a hot water system, a reverse cycle central heater/air conditioner, a heated spa or a pool.

broken image

A heat pump works by pumping heat. Diagram courtesy of Envtec Services Limited.

How much CO2e will heat pumps save?

- A heat pump clothes dryer might use 63% less energy.

- A heat pump hot water system might use 50-65% less energy.

- A reverse-cycle heat pump heater/air conditioner might use 30-60% less energy for heating.

Read this list with caution. The sources are old, so while savings may have maintained or improved with newer tech, I didn't test any to see how they performed in real life. In any case, something can be efficient but still use lots of unnecessary energy. It is energy-intense to use a clothes dryer rather than the sun, to build and heat a private pool or to set your thermostat to 25 degrees in winter. No matter what tech you use, you're wasting energy and carbon with these choices.

How much CO2e will the average person save by switching to a heat-pump heater?

When I looked at winter heating in weeks 7-9, I found the average Canberran with no slab heating generates 333 kilograms CO2e per person per year to heat their house in winter. I cut that to 148 kilograms CO2e by turning the temperature down three degrees and adding insulation and draught-proofing. In weeks 19 - 21, I found the average Canberran generates 159 kilograms CO2e from summer cooling. I cut that to 96 kilograms CO2e by setting the temperature higher, using the cooler smarter and using passive cooling too.

A reverse-cycle heat pump heater/air conditioner might save 50% of the energy used for winter heating and summer cooling. If so, that would save around 122 kilograms CO2e. This is definitely worth doing for an end-of-life replacement. It may be worth a system upgrade too, but that's an expensive choice to make. There's embedded carbon in the equipment, but for savings of this size, they'll be offset fast.

Some people have large, poorly-insulated houses with slab heating, air conditioning and a thermostat set high in winter and low in summer. They generate far more than average for winter heating and summer cooling, so a reverse-cycle heat-pump will save far more than 122 kilograms CO2e per person per year. In this case, upgrade.

Other smart ideas to reduce household energy

I audited my power use with outdoor meters, an appliance meter and thermometers. But some people might prefer a clever device, like a smart meter or an app that tracks usage. Whatever tech you pick, you need direct measurement to find out how your household uses energy and where you can cut back. Don't rely on generic advice that doesn't apply to you.

There are state and federal government rebates on appliances, water heaters, space heaters, solar panels and more. When looking at any major upgrade or renovation, check to see if rebates apply.

If you're building or doing major renovations, consider the carbon footprint of your materials, recycle wherever possible and build in passive design and energy efficiency.

I didn't test many other energy-saving tips, like covering your pots while you cook and matching the pot size to the element size. I suspect the savings are small but real. Follow any advice that sounds reasonable BUT be careful with advice from an industry trying to sell you stuff. If the savings are minor, they may not offset the embedded carbon in the new goods.

Some choices are inherently high-carbon, like a big house or a private pool. Think hard about why you want these before choosing.

A swimming pool with green slime shows what happens when you neglect pool maintenance

Think backyard pools are sexy? They're energy-intense, underused & many end up looking like this.