The Hidden Cost of Airconditioning

I have been living in my house now for about 10 years. When I purchased it there were two 3Kw split system air conditioners installed. I have used them over the years but their reach wasn’t sufficient so I recently installed a Daikin system upstairs so I could get some sleep on those hot Queensland nights.

The Power Meter

Now like all good energy savers, I got a wireless power meter from Queensland government back when they were free, but since I had just installed solar panels, I used it to monitor how much electricity my solar system was supplying.  So over the years I haven’t taken much notice of how much power we were consuming.  Then recently, when Masters Hardware was closing down, I purchased another power meter that connects to my computer so my original one was left over. So In decided to shift it to my house mains.

I quickly noticed I was using around 720 watts of power. I wasn’t concerned about that in the day time because the computer is on, and various other things were using power. But then I noticed, day and night, I was still using at least 700 watts of electricity. I thought I must have it connected wrongly so I did some investigation to see if it was right and where the power was going. One complication is my house has three phase power and I had some questions about how to connect it properly – but using 700 watts day and night still didn’t seem to be correct.

Power Leakage Detection.

So I turned off each circuit breaker one by one and watched the power meter until I found the culprit. It turned out the electricity leakage was all down to my split system air conditioning systems. Each was drawing about 350 watts on my meter when they were on standby! So when they weren’t even running I was using the 700 watts of power!

Standby Power Costs.

My son is an electrician who specialises in air conditioning. So when I asked him, he said it’s usually the heater which keeps the oil temperature in the compressors warm, and therefore thin enough, to allow the compressor to start easily. He said it was important in some climates as the oil got very thick when it was cold and the compressor wouldn’t start.  But since I live in Queensland and a cold day here is 15 degrees celsius (that was on Tuesday this year) he added that we may not need to warm the oil here, nor on most of the east coast of Australia.  So for 10 years, it seemed I was using 16.8 Kw Hrs per day to keep my air conditioning oil warm.  At 25c per KwHr that is $4.20 per day or about $370 every 3 months.

The truth was not quite that simple. So I asked him to come and disconnect the heaters. When he came he discovered I was using around 150w for each unit – not 350w like my power meter said. So much for the accuracy of my free power meter! Still 150w per unit is 300w total and therefore every three hours on standby that passes, is another 1KwHr or about 25c. So the cost for each day was about half of what I calculated.  Only $2 – not $4. But it is still significant at around $600 per year. Unfortunately disconnecting the heater was impossible because of the way it is wired in my system.

How Common is this Leakage?

I wondered if my air conditioners were unique or whether this was common.  A quick search on the net confirmed that many systems had these heaters inside but only a few use as much as 150w of power in standby mode.  My Daikin system uses only 5w of power when I measured it but it is a 2016 model and so 10 years younger then the other two systems. The general consensus on the web is you either disconnect the heaters or put in a thermostat to switch them on only when it’s cold outside. You could switch them off at the breaker in the power board or on the switch beside the outdoor unit as long as your willing to go out and switch them back on before you need them. You should also read the user manual that sometimes says they must be on for at least 4 hours before you use them!

So my recommendations are

  1. Get a wireless power meter and use it to find out if your air conditioner/s is using power even when it’s in standby, by turning all your circuit breakers off except for the air conditioners and then looking at how much power you are still using. If you have a led light that flashes on your electricity meter, you can buy a power monitor for about $62 on eBay and easily fit it yourself. You don’t have to open up the power board or take risks with electricity because you put the remote unit over the flashing led and its connected! If you don’t have a flashing led, you may need to get help from an electrician to install the unit as it will have a plastic piece that has to be installed around the main power wires coming in. However, if you can read your meter, you may not need any additional power meter. All you need to do is turn off everything in the house (including the fridge) except the air conditioner/s. If your meter had a spinning disc – time the period between the black dot passing the centre mark.  Lets say its 50 seconds. Then multiply that time by 400 (400 disc spins equals 1 Kwhr).  In our example that would be 20,000 seconds or 333 minutes or about 5.5 hours.  That’s how long it will take to use 23c of electricity and in our example represents around $1 per day. If you have a digital meter, look at the power usage and measure what your house uses over say 2 minutes, then work out the daily cost from there.
  2. Next determine if you want to continue to pay for the power, or get an electrician to remove the heater, fit a thermostat or timer to your system or put in a new system that uses minimal standby power.
  3. The easiest and cheapest method is switch your air conditioners off at the power board or main switch beside the outdoor unit when you’re not using them!
  4. Finally, if you are going to pay for power, then move to Tasmania where you really need the heaters to work!
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