For a while I’ve been interested in figuring out why I send so much money to NStar every month. That interest has spawned some product ideas, a business plan or two, and a few purchases.
The simplest method to identifying the energy use in your home is to measure it appliance-by-appliance. While one could go around with a multimeter and perform some calculations there’s an easier method: the P3 International Kill A Watt. This is a small module which plugs into an outlet and has a front-facing receptacle into which you plug the appliance or devices you want to measure.
The display will show real-time consumption in watts as well as real-time current. Consumption over time is shown in kilowatt-hours (kWh), the unit by which electric utilities measure for billing. Kilowatt-hours are calculated by multiplying the power in watts by time. For example, a 100-watt lightbulb left on for an hour would consume .1kWh of electricity.
Additionally the unit will show other characteristics of AC power such as voltage, frequency and power factor.
The Kill A Watt is straightforward in use, with one downside: you have to unplug what you want to measure. Not a big deal for a fridge but it’s annoying when you want to measure a computer system.
That said, I was able to determine with the Kill A Watt that my old home server was consuming around 180 W 24×7. That worked out to 1577 kWh/year, and at my electric rate of $0.1605/kWh the server was costing me about $253 per year to operate. Whoa.
I replaced the tower server with a Mac mini server which consumes about 15 W. That results in an annual charge of about $21.
Big difference!
I also was able to determine that my home entertainment system – LCD TV, amplifier, Xbox 360, Blu-ray player – when turned off still consume about $70 of electricity per year. This is because those devices have a ‘standby’ mode which allegedly reduces the power-on time but essentially just a waste of money. Typically these loads are referred to as ‘vampire’ loads. I didn’t include the DVR in the calculation since that is legitimately left active – though there is certainly opportunity for decreasing the energy use of those devices as well.
Other computers in the home also added up to another approximately $30 per month by not being correctly configured to go to sleep when idle, or in the case of an XP machine, ignoring that configuration and remaining on in spite of my best efforts.
The challenge with the Kill A Watt is that you can only measure what you plug in; it is not useful for monitoring things like central air conditioning, lighting, etc. For that, there are some other options which will be covered later.