Reverse cycle air-con can be sustainable, after all

Last week, I asked how air-conditioning could be considered a “sustainable” renovation (as promoted by Fair Trading in their somewhat premature notes on minor renovations).

Well, blow me down with a ceiling fan – reverse cycle air-con CAN be sustainable as a means of heating a home – and very much so. But there’s a catch … you have to switch it on.

Flat Chat Strataguru Sir Humphrey explains …

In this article JT asks rhetorically “… since when did the installation of air-conditioning become a positive action in sustainability?”

Well, crucially, the quoted bit of legislation refers to ‘reverse-cycle air-conditioning’. In areas where heating rather than than cooling dominate it is both cheaper and more energy efficient to use reverse-cycle air-conditioning for heating than to use plain resistance electric heaters or gas.

Gas is getting expensive and its contribution to global heating are barely less than coal once fugitive emissions are considered. Meanwhile, the electricity grid is getting cleaner all the time.

When electricity is put through a resistance heater, the energy is converted to heat with 100% efficiency. Similarly, burning gas in an unflued heater inside the room is 100%.

Ducted heating systems and heaters with the gas burned externally often have substantial losses so might be 70% efficient.

In contrast, a heat pump system, aka reverse-cycle air-conditioner, uses one unit of electrical energy to move 3 to 5 unit of heat from the outside air to inside. It is at least 300% efficient. Consider it as a renewable heat harvesting device.

Many people don’t realise just how much less electricity and lower emissions are involved in using a reverse cycle air conditioner compared to other forms of heating.

Some will even have these sitting on their walls unused in winter while they run other heaters that are more expensive to operate and produce higher emissions.

So, to answer the question: Air-conditioner became a positive action in sustainability when when used to replace less efficient, higher emitting forms of heating.

Of course draft-proofing and improved insulation that reduce the need for heating and cooling go hand-in-hand. Getting off gas heating can be the first or last step in getting off gas entirely, which has financial and environmental benefits.

BTW: In my defence, I did ask Fair Trading how air-con could be sustainable but they didn’t give me any of the information Sir Humphrey kindly provided above. I was still wrong, but at least I tried – JimmyT