What I Learned Today

I like to conduct experiments and measure things. My monthly electricity bill tells me how many kilowatts I’m consuming, but not at a very interesting or useful granularity. Which devices consume the most? Where could I make the most impact, in terms of turning things off or putting them on timers? What I really want is the equivalent of top, but reporting electricity consumption instead of CPU usage, for all currently active processes (devices).

Since no such thing exists, I instead went out and bought a Kill A Watt, which monitors all consumption of anything that is plugged (through it) into the wall. This is a nifty device; not only does it give you instantaneous consumption, but it will also record the total usage over time. The packaging contained a bit of over-selling, though:

Perfect for detecting voltage drops and brownout conditions before they damage delicate equipment.

Perfect, that is, if you’re sitting there ready to yank it out of the wall if the line quality drops below 120 V. It doesn’t have any automatic shutoff or power surge protection.

Once I got the Kill A Watt, I went around the house plugging everything I could find into it. Here are some of the highlights of what I learned:

• The largest instantaneous consumption comes from my microwave, at 1600 W.
• I confirmed that CFLs really do consume less energy than incandescent bulbs. :)
• My stereo uses about 40 W, whether playing the radio or playing a CD—and this amount increases with volume, as more power goes to the speakers. Same with the TV (a 19″ Samsung, 40 W, increases with volume).
• My laptop consumes 2 W when sleeping, 27 W awake with low load, 36 W charging (asleep), and 60 W charging (awake). My wireless router consumes 14 W.
• My front-loading high-efficiency washer uses 20 W when filling with water, 100 W when tumbling, and 460 W when spinning. The total consumption for one load is 0.14 kWh, which costs me all of 1.7 cents (not including the cost of the water).
• My gas dryer uses 750 W when first heating (and tumbling), then settles into 260 W once it’s hot. One load consumes 0.17 kWh, or 2.1 cents (not including the cost of the gas).
• Bottom line: I was surprised to realize that, based on this data, my biggest ongoing consumption might well be my dining room light fixture (2 75-W bulbs = 150 W), which has a dimmer switch and therefore isn’t amenable to regular CFLs. It might be worth the (more expensive) dimmer CFLs to address this, once the current bulbs burn out. However, my study was not comprehensive; I was unable to measure my fridge’s consumption, for example, nor do I have numbers for the oven, water heater, or air conditioner (which I know is a heavy consumer simply based on the seasonal change in my total bill). More study is merited!

Philip Torrone has posted instructions for how to convert your Kill A Watt into a Tweet-a-watt. That’s right, you can now tweet your consumption, for the edification of all. From the project description: “We feel there is a social imperative and joy in publishing one’s own daily KWH.” I’m content just sharing the preceding analysis, thanks!