Geeking out on the ‘leccy bill
A good post from Lars Wirzenius on measuring the electricity consumption of his computer hardware. Here’s a previous post of mine on the subject.
With the rising cost of energy, a keenness to reduce consumption for green purposes, and an overweening nerdity in general, I did some more investigation around my house recently.
I have a pretty typical Irish electricity meter; it contains a visible disc with a red dot, which spins at a speed proportional to power usage. (There’s a good pic of something similar at the Wikipedia page).
The fuse-board works out as follows (discarding the boring ones like the house alarm etc.):
Fuse 7 - gas-fired central heating (on), fridge (on), kitchen power sockets
Fuse 8 - TV in standby, idle PVR, Wii in standby, digital cable set-top box, washing machine
Fuse 9 - telephone, DSL router, Linksys WRT54G AP/router
Fuse 10 - bedroom sockets, home office with laptop, printer, speakers, laptop-server etc.
The approach was simply to turn off the house fuses at the fuse board, one by one, and measure how long it took the disc to make a full revolution; then invert that (1/n) to convert from units of time over a static power value, to some notional unit of power consumption over a static time interval (I haven’t figured out how to convert to kW/h or anything like that, they’re just makey-uppy units).
| Fuses | Time/power | Power/time |
|---|---|---|
| Baseline (all fuses on) | 22.71 seconds | 0.0440 |
| Fuse 7 off | 43.03 | 0.0232 |
| Fuses 7 and 8 off | 57.92 | 0.0172 |
| Fuse 7, 8 and 9 off | 84.88 | 0.0117 |
| Fuse 7, 8, 9, and 10 off | ~20 minutes (I’d guess) | 0.0008? |
(I stopped measuring on the last one and just estimated; it was crawling around.)
Breaking out the individual fuses, that works out as:
| Fuse | Power/time |
|---|---|
| Fuse 7 (central heating, fridge, kitchen bits) | 0.0208 |
| Fuse 8 (TV, Wii, set-top box, washing machine) | 0.0060 |
| Fuse 9 (phones, routers) | 0.0055 |
| Fuse 10 (home office, bedrooms) | 0.0109 |
Good results already: (a) it was pretty clear that fuse 7 was doing all the quotidian legwork, eating the majority of the power, and (b) the TV equipment and internet/wifi infrastructure was pretty good at low-power operation (yay). However (c) the computer bits aren’t so great, but still only half the power consumption of the kitchen bits.
Breaking down the kitchen consumption further:
| Appliances | Time/power | Power/time |
|---|---|---|
| Gas central heating on (rechecking the baseline) | 20.46 | 0.0488 |
| Gas central heating off | 34.15 | 0.0292 |
| Washing machine on (40 degree wash) | 13.65 | 0.0732 |
| Dishwasher on | 2.53 | 0.3952 |
| Dishwasher and dehumidifier on | 2.53 | 0.3952 |
Subtracting the baseline:
| Appliance | Power/time |
|---|---|
| Gas central heating | 0.0196 |
| Washing machine | 0.0244 |
| Dishwasher | 0.3464 |
| Dishwasher and dehumidifier | 0.3464 |
So the central heating, despite being supposedly gas-fired, eats lots of power! I guess this is the electric pump, used to drive the heated water around the house to the radiators. Ah well, I’m not skimping on that ;)
More practically: the dishwasher result is incredible. That’s 30 times the power usage of the house’s computer hardware. This is a ~7-year-old standard dishwasher; obviously green power consumption wasn’t an issue back then! We’re running it less frequently now, obviously; the odd hand-wash of bulky and nearly-clean items helps. With any luck when we move in a few months, we can replace it with a greener model.
The washing machine is about what I would expect, so I’m OK with that.
Also interesting to note that our dehumidifier is unnoticeable in the volume of the dishwasher; I could have tried to work it out properly in isolation, but couldn’t be bothered by that stage ;)
