Wednesday, 16 May 2012

Don't do the laundry on the Eco setting...

...or, yet another case for monitoring.

We have a new, shiny, Bosch Advantixx 7 washing machine. Bought, not least, because of it being a Which? Best Buy, its excellent A rating on energy consumption, and a nice button marked "Eco Program".

We also now have one of Current Cost's Individual Appliance Monitors, which allows us to plug any device we like in through it, and (by dint of some handy software of my own devising and a free installation of Splunk) draw graphs of its power consumption over time.

Anne normally uses the 40ºC cottons programme for our general washes, with the Eco button pushed in, 'cause, well, you know, it's Eco, so it must save energy, right? So we thought it would be interesting to graph[1] the power usage of the machine. And here we go:

  avg(watts)6:00 AMWed May 920127:00 AM8:00 AM9:00 AM10:00 AMtime01,0002,0003,000avg of watts
Things to note:
  • there's about a 15 minute wide peak at 2.1kW while it heats the cold water fill.
  • there's a peak at the end for the spin cycle, and two smaller ones where water gets pumped in and out
  • the 'tail' after the water heats up, while the machine's just turning the drum and, you know, doing the laundry, averages around 100-130W
  • total power consumption for the roughly 3 1/4 hours is 0.9 kWh.
So. Let's try that with the Eco button off.

w9:00 AMSat May 1220129:30 AM10:00 AM10:30 AM11:00 AM05001,0001,5002,0002,500
Interesting. Key points to note:
  • the water takes almost exactly the same time/amount of power to heat - there's a dip which might suggest there's a thermostat there, but several test cycles on different days suggested the incoming water temperature didn't make much difference;
  • there's an extra pump cycle;
  • the tail averages about 90-100W, rather than 100-130W;
  • total power consumption for the roughly 2 1/4 hours is... wait for it... 0.73 kWh
Yup. That's right. The Eco programme at 40ºC takes longer and uses more power. (And before anyone asks, yes we ran this several more times last week on both settings).

Now, of course, what I'd like to do is run another CurrentCost monitor to track the water flow, and see which uses less water, but that'll have to wait until they make one!

Points to take away from this:

  • Don't just assume the Eco setting will do what you think it does;
  • Cold-fill washing machines use most of their energy (about 0.5kWh) heating the water. I really miss our old hot- and cold-fill one, especially since my hot water is free! Manufacturers, if you're listening....
  • Having said that, the water heating peak usage is less than the peak output of our solar PV panels.
Next time? We graphed the tumble dryer!

[1] These graphs will require a modern browser with decent HTML5 support - apologies if you can't view them. Also, apologies that they're not quite the same scale!


  1. The best "eco" button on my washing machine is the "time delay" one which means that the whole thing is done on cheap night-time electricity!

  2. Or in our case, when the sun's out :D

  3. Definitely when the sun is out. Would love to hear Bosch`s explanation on exactly what the Eco button does

    1. Yes - I think you should point Bosch at this post (perhaps suggesting that you're planning to point the media at it too...) and ask them to comment. (And if they don't, then of course you *should* point the media at it.)

  4. Would like to run the same test on our Bosch Dishwasher, Eco setting takes a lot longer.