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Household power consumption
2014-01-13

I was listening to an episode of the wonderful podcast, Pragmatic, the other day. The discussion was about electricity, renewable energy, and related topics. I became curious about how much electricity my household appliances are using, so I decided to invest in a couple of energy meters. These can be purchased cheaply, online or otherwise, and they’re typically plugged in to a household powerpoint (wall socket / outlet). You then plug your appliance in to the energy meter.

meter-kwh.jpg
An energy meter showing the energy (in kW·h) consumed over a period of time by my refrigerator.

Most energy meters sold for this purpose have a digital display and a few buttons that allow the operator to switch between modes and reset the counters. The most useful modes I found were the power being consumed in real time (measured in watts) and the energy consumed over a period of time (measured in kilowatt hours - kW·h).

Many home appliances draw power when in standby mode. Such appliances include televisions, set-top boxes, microwave ovens, alarm clocks, computers, and phone chargers. Here is a table outlining the power consumption of the plugged appliances in my house.

Appliance Power (standby) Power (in use)
Computer (Mac mini - Late 2012) 1.5 watts 12 watts
Computer (Dell T3500 tower) 5 watts 135 - 185 watts
Computer monitor (Dell U2410 24") 1 watt 64 watts
Printer and scanner 0 watts variable
Television - 42" LCD 1.5 watts 55 watts
Microwave oven < 0.1 watts up to 1700 watts
Remote control garage door 6 watts variable
ADSL modem / wifi router 6 watts
Refrigerator 75 watts (averaged)
Washing machine 0 watts variable

Some interesting results. Despite being microprocessor controlled and having digital displays my printer, scanner, and washing machine have physical power switches so they don’t have standby modes. When I turn them off they’re properly off and draw no power.

I was also interested to see the difference in power consumption between my Mac mini computer and the Dell tower computer during use. With a power consumption of 185 watts at full noise I’m thankful I only need to use the tower computer for occasional work that requires six Xeon processors and the ability to render complex graphics in 3D. The less powerful Mac mini, at 12 watts, is far more economical for less demanding tasks such as web browsing and text editing. Additionally, I can save more than $10 a year by turning off the tower computer at the wall instead of leaving it on standby.

Some appliances don’t draw power at a constant rate, such as a refrigerator. Because of this it’s best to measure the energy consumption of a refrigerator over time, rather than the power being drawn at a given instant. The kW·h mode on the energy meter does this. Reset the counter and leave the fridge plugged in to the energy meter for a few days.

It turns out my fridge uses 1.81 kW·h per day. My electricity provider charges $0.235502 per kW·h. Hence the running cost of my fridge is $155 per year. It might pay for me to consider upgrading to a more energy efficient fridge.

The best way to work out the energy consumption of your appliances is to acquire an energy meter and run around the house testing them. It’s super fun and makes a great opportunity to clean behind the microwave oven and dust behind the television.