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 ;)

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  1. Posted March 20, 2007 at 15:12 | Permalink

    Name and shame the sucky dishwasher.

  2. Posted March 20, 2007 at 15:51 | Permalink

    Bernie —

    an Indesit DG 6100 W (energy efficiency rating “C”, according to that page!)

  3. Posted March 20, 2007 at 15:59 | Permalink

    I agree, name and shame. I did some measurements a while ago, but never did anything with them. I must do them again and post the results. Good post, thanks.

  4. Nishad
    Posted March 20, 2007 at 19:07 | Permalink

    See, back where I come from, the amount of energy used by the dishwasher dishwasher is equal precisely to that required to make two cups of tea :-)

    Seriously, I do wish there were some analysis about having domestic servants (which is absolutely universal in Bombay and India more generally) at a relatively good rate of pay vs. having dishwashers and hoovers and such like, including energy issues, quality of life (for both employer and employee), money saved for employer, money earned by employee vs. other (most likely non-existent) potential jobs, and so on.

    I can’t even guess as to what the result would be…any of JM’s Indian readers want to take a shot?

  5. Posted March 20, 2007 at 19:19 | Permalink

    whoa, that’d take a lot of hard sums to work out.

    also I’d say the other Indian readers are probably sobbing in fear of the Irish cricket team demolishing them next, after Pakistan. you’ve been very quiet on that count Nishad! ha!

  6. Posted March 23, 2007 at 15:44 | Permalink

    Dishwashers are cold fill only these days. I know heating water by gas has got very expensive over the last 5 years but it’s still about 30% cheaper with a modern boiler IIRC.

    We use our dishwasher on a timer that goes off at 3pm and start the beast at 3am. In my book that’s greener too as it uses constant sources of power (coal hydro wind Etc) over the variable ones such as gas and fission. It’s cheaper too because it’s on economy 7.

    The worst appliance for sucking the juice is a tumble dryer. They spend ages heating and all they do is pump moist hot air out the door. Fluffy towels just aint worth it on my book, and a cheap dryer amost doubled my power bill last year. sigh

    TGIF, have a good one!

  7. Posted March 23, 2007 at 15:59 | Permalink

    Yeah, I have a feeling we may have to get a dryer, unfortunately, what with a sprog on the way — I hear they practically eat clothing. C is still very anti-dryer though…

    For some reason, our local electricity supplier no longer has an “Economy 7”-style scheme, where the leccy is cheaper at night, as far as I can tell!

  8. Posted April 5, 2007 at 09:56 | Permalink

    There is still ‘Economy 7’ or nightsaver I think they call it. The standing charge is more though.

    Dishwashers actually use very little water. I think the reason they use cold-fill is because by the time the cold water in the pipes has run off, and the hot water in the hot tank actually reaches the dishwasher, it’s nearly full. Also, 30 percent is a very small saving, considering that only the exact amount of water that actually needs to be heated is heated by the dishwasher.

    If you read the markings on the meter, they should explain how to convert revolutions to KWh (i think there are ten revolutions in a tenth of a kWh on mine, so if you multiply the number of revolutions by 100, you’ll get the KWh usage. Of course what really matters is the average ‘draw’ in kW rather than the KWh. This calculation of this is elementary and is left as an exercise for the blogger. It is haphazard though, to directly compare the draw of an appliance that is on for an average of 30 minutes /day to a device that is plugged in and running, 24/7.

  9. Posted June 20, 2007 at 20:20 | Permalink

    why use a dishwasher ? let’s convert to hand washing and save energy and our enviroment :)

  10. Posted July 10, 2007 at 20:40 | Permalink

    Very interesting breakdown of your power usage. Does a lot of heat escape from the dishwasher while in use? I wonder if with age cracks have formed letting out heat to make it less efficient. Cheers.

  11. Posted July 11, 2007 at 14:22 | Permalink

    can’t say I ever noticed a lot of escaping heat, no…

  12. Posted January 21, 2008 at 23:34 | Permalink

    Congrats to fuse 8 for consuming the less power with 4 appliances in standby! lol =)

  13. Posted September 2, 2009 at 15:44 | Permalink

    I did some measurements a while ago to see how competiative, but never did anything with them.

    We all need to do our best to stay as green in our enviroment.

  14. Posted January 4, 2013 at 09:25 | Permalink

    i have the same situation in my house, a 60 amp fuse panel (original), when a prueiovs owner needed more power in the kitchen, for newer modern small appliances, a window air conditioner, etc. they added a small 4 circuit breaker panel to cover the extra load. then another prueiovs owner had a rec room added in the basement, so another double fuse box was added for that. my wiring consists of knob and tube (original), bx (the metal covered), added somewhere along the way, and romex (plastic covered) for the latest upgrades! my guess is that none of them wanted to spend the extra to upgrade the entire house to a new 150 or 200 amp service and have all the power they could ever want. the funny thing is, in the ten years that i’ve lived here, we’ve never had to replace a fuse, it’s only the circuit breakers that trip!