Friday, November 18, 2005

Saving Power - 200 Watts at a time

I was a bit shocked to learn how expensive our electricity bills are - around $130 per month! I'll have to ask my roommate how many kiloWatt-hours that is.

So today I took a quick survey around the apartment and measured how much power is consumed by our 24/7 devices (Andrew has a Watt-meter handy. Doesn't everyone?).

The refrigerator was off the scale or nearly so - 725W. It tripped the meter's shut off circuit/fuse. However that reading is misleading because the fridge isnt always actively cooling itself. When it's idle it should drop to nearly zero.

The three computers that are always running (Webserver, DB server, and HDTV machine) range from 50W to 125W, rising with computing ability (and therefore number of cooling fans). The networking components (DSL modem, router, and gigabit Ethernet switch) add another 75W.

The stereo system burns a big 150W when in "Standby". Switching it on and firing up the amp doesn't add much above that, maybe 200W max.

The stereo and the HD machine are the most tempting power conservation targets.

There's really no need to have the stereo on "Standby" mode 24/7. I slid the power bar up towards the front so it can easily be toggled on/off. The TV, satellite receiver, etc are plugged into a different power bar so they still function without the stereo. Keeping the stereo completely switched off when not in use saves us a lot: 109.5kWh per month.

Next up was the HD machine. It's used to record HDTV programs that are broadcast over the air. So it can put itself to sleep if it wants to, but it has to be able to wake itself up for its scheduled events.

Using Windows' built-in power management I set the machine to "Sleep" itself after a specified number of minutes. Power consumption dropped from 100W to 50W. To the outside world the computer seems off - the fans and hard drives are completely powered down.

I thought I'd tried this before and failed, but this time the machine woke itself up for a scheduled recording and everything worked flawlessly (perhaps the test was back when it had the old Dell motherboard). And it's smart enough to remain active when an application like the HD recorder or Winamp are running.

Waking up (whether it's for a scheduled event or if you tap the keyboard) only takes about five seconds and it comes back up to where you were before. Pretty nice! Having the computer put itself in sleep mode will save us another 36.5kWh of energy each month.

Now this spin up/spin down isn't ideal for the hard drives. They're designed to spin 24/7. Bringing them up and down will wear them out faster, but I don't know if it dramatically reduces their lifespan (four years instead of five years?).

"Sleep" won't work for my Webserver or DB server - those machines field Website requests at all hours of the day and would kill themselves trying to sleep and wake after each request.

Anyway, conserving 200W - 146kWh each month - isn't too shabby. I would guess that's 10-15% of our total power consumption each month!


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