Power optimization

  • By nygren
  • Sat 08 December 2007

One of my household projects the past few weeks has been to profile my home power usage with the goal of seeing where I can reduce it with small investments of time and money. The $20 Kill-a-Watt tool has been invaluable in this exercise. So far, I've managed to reduce my estimated power usage by around 10% ($190/year) with another 3% of quick-wins yet to do as well as some future projects that could yield another 20-30% savings. For the full details, here's the spreadsheet that I've been using.

Here are some interesting facts that I've learned along the way:

  • Massachusetts has some of the most expensive electricity in the contintental US.
  • In my house, just the three computers (office desktop, router, mediacenter pc) and three TiVos that were turned on 24/7 account for 425W 24x7 (and that's not counting laptops, and even with the monitors and 170W Windows box turned off). This is around half my electric bill! I suspect that many of you are in similar situations... Over time, I think that I'll start to replace some of these with low-powered Via Eden or AMD LX800 boxes with solid-state-drives. Even when buying new desktops, low-power CPUs will likely pay for themselves in MA.
  • Computer processors use up lots of power, but so do hard drives. Across my desktop computers and TiVos, I have 12 hard drives in the house. That's around 100W just by themselves! Configuring drives to spin-down when not in use can save 4-10W per drive. Taking the second CPU out of my router was also a quick-win.
  • For TiVos and other similar devices, the power costs can be a significant portion of the cost-of-ownership. For example, my Series3 TiVo draws 40W which costs about $5.50/month or $200 over three years. This is about half the cost of the service subscription!
  • Those power bricks do add up (at 500mW-2W each), but a few individual turned-off-but-plugged-in devices may dwarf those at 10-15W each. Finding those and putting together mitigation strategies for those few devices are faster wins than dealing with power bricks. For example, my subwoofers use 10-20W even when in "power-saving mode". Two Yamaha stereos that I have from \~1993 use 16W even when turned off. By contrast, my newer Yamaha receiver in my home theater only uses 1W when turned off.
  • There are some dimmable compact florescents that play nicely with X10/SmartHome dimmer switches. In particular, the Philips Marathon Alto bulbs seem to work ok so far, although it takes them a little time to warm up.
  • Plasma TVs use *lots* of power when they're turned on. My 42" 480p display uses around 220W when turned on, but 1080p plasmas are rated to use 2-3x as much. I guess this means that I should get an LCD when I eventually upgrade to 1080p.

These are the highlights of the audit along with example actions taken (or planned) to save power:

**Approx Pct** **Monthly Kwh** **Average (W)** **Example Savings (W)** **Actions to achieve savings**
**Home office computers** 21% 176 240 14 Remove unused power bricks, configure drives to spin-down when not in-use, set Windows machine to go into standby when idle, eventually migrate apps off of desktop server to lower-powered machine
**Lights (total)** 15% 128 175 54 Replace selected lights with compact florescents
**Home theater (total, with tivo+computer)** 14% 116 159 19 Used trigger cable from receiver to power supply to shutoff subwoofer and DVD player when not in-use
**Electric clothes dryer** 11% 89 122 Planned: replace with energy-efficient gas dryer
**Home router/server** 10% 82 112 18 Removed a CPU, configured drives to spin themselves down when not in-use
**Refrigerator** 7% 64 87 33 Could save \~33W by replacing with more efficient fridge
**Bedroom A/C (amortized)** 6% 49 67
**Air purifier** 6% 47 64 50 Don't keep always-on
**Kitchen lights** 4% 36 49 18 Replaced two 90W R40 bulbs with dimmable 20W Philips Marathon CF bulbs
**Halogen torchiere in office** 3% 29 40 28 Planning to replace with compact florescent
**TiVo Series3** 3% 29 40
**TiVo Series1 w/ 2 drives** 2% 20 28 28 Retired since I don't really need three TiVos
**TiVo Series2** 2% 15 20

On a related note, is anyone interested in my old Hacked Series1 TiVo (with ethernet and extra storage) before I try to sell it? I also have a bunch of incandescent R30 bulbs for ceiling canisters that are left-over from my old house. I also have an old CRT TV stand from Ikea that I'd like to get rid of to make room for a breakfast nook table.