How to be green – Ceiling Fan versus Airconditioning

20130301-122054.jpgI got asked recently whether running ceiling fans all night consumed more energy than running an airconditioning unit at night. So here are the calculations.

Lets take a three bedroom house, assume that all three bedrooms will either have the ceiling fans or airconditioning on all night.

First up ceiling fans. If your going to use celing fans I would recommend Big Ass Fans, not just because the name is hilarious but because they have a very broad range of fans from the sleek bamboo bladed fan to massive big industrial ones. We have used them in quite a few projects with great success.

The Big Ass Fans Haiku ceiling fan uses 30W of energy on full speed for every hour that it runs.

Ceiling Fan – runtime 20:00 hours to 06:00 = 10 hours, consuming 30W/hour gives a total energy consumption of 3000Wh or 0.3 kWh per bedroom. Roughly 6 cents and 0.3 kgCO2.

Now lets look at the airconditioning.

Assuming that you have a reasonably efficient aircondioner sized to deal with a peak cooling load of 2,000W for an average bedroom, this would need 580W of electricity at peak. However, night time loads are a lot less, lets say 500W which will draw 250W of electricity. Now it is doubtful it would run the whole time, it would cycle between on and off to keep the room cool so lets assume that it will only be drawing 250W for 30 mins every hour its on.

Air Conditioning unit – runtime 20:00 hours to 06:00 = 10 hours multiplied by the on-off cycle factor of 50% gives 5 hours, consuming 250W/hour gives a total energy consumption of 1250Wh or 1.25 kWh per bedroom. Roughly 25 cents and 1.25 kgCO2.

So an energy efficient airconditioning unit will consume about 4 times more energy. An older airconditioning unit or a window rattler will consume more than that likely to consume 6 times more energy than ceiling fans.

There it is – ceiling fans are 4 times better in energy efficiency than air conditioning for bedrooms at night time.

2 Comments on “How to be green – Ceiling Fan versus Airconditioning”

  1. Air conditioners will also inherently dehumidify the air, which may not be a bad thing on the odd muggy summer night but used often and during dryer weather it can really dry out your skin and eyes/nose/throat and affect your health. In sydney, for all but a few nights of the year, a quiet ceiling fan and a moderately open window are blissful 🙂

  2. Know what you mean, spend more than 2 nights in a hotel where you cant turn the aircon off and open a window and you feel it for days.

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