Hot and bothered? You could be using your Air Con all wrong…

When it comes to using the Air Con efficiently, shall we blast it briefly, or just leave it on?

Aotearoa has hit some hefty temperatures this week, and despite so many people having air conditioning at home now, many of us are still unsure how to use it efficiently. And air conditioning uses a lot of energy. For example, running all the lights in an average home all day and night consumes about the same energy as one hour of air conditioning of the same space.

Some people think they can save money and energy by just blasting the air conditioning at a very low temperature, such as 17°C, for a short period of time to chill the room – before switching it off and enjoying the chilled air until another blast is needed later on. But it requires a lot of energy to get a room to a very chilly temperature.

While running it briefly and intermittently at a very cool temperature may feel thrifty, it won’t be the most energy efficient choice. Here’s what to do instead.

Reduce How Hot Your Home Gets

First, try to minimise the need for air conditioning. Look for ways to stop your house getting hot in the first place. Heat can come in from outside through surfaces such as walls, windows, and ceilings. Hot air can creep in under doors or through open windows and vents. Appliances and people inside can also generate heat. To reduce some of this heat, you can

  • close blinds and windows before it starts getting hot
  • consider external shading, particularly on north and western aspects of your house
  • improving ceiling and wall insulation, window glazing and sealing (if time and budget allow)
  • use the outdoor barbecue instead of the oven

Set and Forget Your Air Con

Turning our attention to the air conditioning unit itself, the most energy efficient action is to set the temperature to the highest value that’s still comfortable (26°C during the day and 22°C when sleeping is often recommended). Then, just let it run.

Modern units (that feature technology known as an “inverter”) will adjust their output efficiently to maintain the indoor temperature at the setting you’ve chosen. Be careful, however; setting the temperature too low can result in the unit using more power than you think it’s using (based on star rating label).

Older non-inverter units will cycle on and off to maintain the temperature, and you will generally be able to hear and feel it going on and off. (The newer inverter units, by contrast, don’t tend to cycle on and off as much; they usually just stay on and continuously modulate their output).

For non-inverter units, in general, remaining on for much longer than it is off indicates the air conditioning is working very hard. This may suggest the unit is too small for the space you’re trying to cool, or that you just have a lot of heat in the house (are you cooking a roast?). It could also suggest a fault.

Regardless of the type of air conditioning you have, for each 1°C the temperature is lowered, energy use increases by 5 to 10%. So it’s important not to over-cool. That’s why repeatedly blasting the air conditioning at a very low temperature over the course of the day isn’t wise.

This article was first appeared in The Conversation and is published with permission.

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