New Dishwasher - energy consumption measured

[Ivan]

My ancient Ariston dishwasher finally failed. I forget how old it is, but I think over 15years. The timer failed, so we had to advance it manually every few minutes (I could no longer claim no reason for replacing it). The old, dead dishwasher is available - if anyone wants it, by the way!

We decided to go for an A-rated Bush WQP12-9270 dishwasher from Argos at £169.

The dishwasher is rated at 1.05kWh per cycle (as were about a hundred others, which seemed to be quite a coincidence). I had every intention of connecting it to the hot water supply (didn't do the last one any harm, it seems), but was interested and encouraged to read that this was recommended, in the instruction manual, as long as the supply was below 60C (presumably plastic parts melt above this temperature.

I've done some basic energy-consumption measurements using a plug-in power meter and the results are below (the power meter I used, will accurately measure down to 0.5W - available in the Navitron online shop, should anyone want one):

Power consumption when turned off on the front panel -   0.0W
Power when turned on, display lit up, but machine idle - 2.4W
Energy consumption on 'normal' cycle with incoming water at:
          46C - 0.70kWh  (temperature measured at top of cylinder rather than at the end of the long pipe run)
          52C - 0.58kWh
          66C - 0.50kWh


Let's assume energy consumption is likely to be around 0.55kWh at 60C, that means a 52% electrical saving by utilising solar-heated water.

Incidentally, I think it's also made a slight improvement on our daily energy consumption - over the last week, we've imported only 2kWh/day (plus another 3.1kWh/day provided by solar PV). I have two old fridges running at the moment in the garage, consuming 1kWh/day between them exclusively storing business-related stock - which puts our domestic consumption at 4.1kWh/day - not bad when the kids are on school holiday watching 32" TV all day, and dishwasher used at least once and often twice a day.

[craigski]

We decided to go for an A-rated Bush WQP12-9270 dishwasher from Argos at £169.

The dishwasher is rated at 1.05kWh per cycle (as were about a hundred others, which seemed to be quite a coincidence).

Its interesting to compare to 'the worlds most environmentally friendly dishwasher' A++ which is rated is rated at 0.92kWh:

http://www.bosch-home.co.uk/worlds-most-environmentally-friendly-dishwasher.html

Not a significant difference to a standard 'A' rated model.

[brackwell]

Ivan,
Your domestic consumption at only 4.1 kwh/day i just find amazing!  If i stayed in bed and did nothing my consumption would be greater than that!  I currently use about 17kwh/day !
Ken

[Nigel O]

We moved to a Hotpoint Ultima FDD912 dishwasher when our previous one died.

There is specific mention of being able to connect to a suitable hot water connection point, provided that it does not exceed a temperature of 60C. Great to see at least one manufacturer taking this into consideration.

We also managed to find a LG Washing Machine that still accepts hot and cold feeds. Most appliances now like to just have the cold feed and heat the water as it is more efficient(?) than drawing from a hot water cylinder and helps them to achieve the A+ rating. Some manufacturers still don't get the idea that hot water can be free to those of us with solar thermal systems.

[Ivan]

Nigel, In which case that's BUSH, HOTPOINT and MIELE that recommend hot-feeding their dishwashers. That's a good start, I guess.
Check whether your LG washing machine actually uses any hot water. I found quite by accident that our Indesit doesn't use the hot feed on 40C or 60C washes - I discussed it with the repair man (who fixed a pin-holed pressure sensor). He said it's quite normal for modern washing machines only to use the hot feed when the was is over 60C - so as my washes are rarely over 40C, my hotfill is cosmetic!

Ken, you need to do some serious energy auditing - you must have some heaters running all day long. Likely culprits are: plasma TVs, halogen lighting, incandescent lighting, hifi/TV separates which aren't turned off at plug when not in use, knackered fridge or freezer (when I did an energy audit for my sister, I found she was using way more than I expected - turned out to be a faulty fridge using 3.5kWh/day), electric shower, security lighting, desktop or servers left on 24/7, or desktop that draws a lot of power when apparently switched off (70W isn't unusual!), electric cooking, immersion heater.....

My consumption was 10kWh/day several years ago, then 6kWh, and now down to 4kWh. I put it down to turning things off, buying efficient fridges/freezers, CFLs everywhere and switching virtually everything off at the plug when not in use. We still watch a fair bit of TV, I work until 2am most evenings, so there's lighting on until quite late. At this time of year, I'm generating between 12 and 20kWh per day from the solar panels, so my actual imported electricity is around 2kWh daily.

[MarkB]

Check whether your LG washing machine actually uses any hot water. I found quite by accident that our Indesit doesn't use the hot feed on 40C or 60C washes - I discussed it with the repair man (who fixed a pin-holed pressure sensor). He said it's quite normal for modern washing machines only to use the hot feed when the was is over 60C - so as my washes are rarely over 40C, my hotfill is cosmetic!

Our older (10 yrs?) Bosch has hot and cold fill and definitely draws on the hot water for a 40C wash. Haven't checked for a 30C wash. Shame the pipe is so long that it is only just getting warm by the time it fills the washing machine, so I guess we'd be better off with cold fill only.

In the new house, the washing machine should only be a couple of feet from the thermal store, so the problem will disappear.

[Nigel O]

I can confirm that my washing machine does draw on the hot water as evident from the amount taken from the cylinder and also the temperature of the hot water on the kitchen sink when the washing machine is on (instantly hot without running the tap). What I do now is to run the hot tap to get rid of the cold water in the pipes first; my water isn't metered so this does cost me anything. The other thing that I did was to balance the hot and cold flows into the washing machine so that they are even by partially closing the cold valve.

I also run my thermal system at a higher temperature; 80C instead of 65C. All my basin taps have cross over valves keeping the temperature at point of use below 45C. So I am maximising the amount of hot water I can get out of the system. I need to. I will have at least one laundry wash a day, sometimes upto four. It comes with the territory of having a disabled child. So does the two runs of the dishwasher and showers and baths in the morning and evening.

My system has been in for four years now. Between March and October I have ample hot water without needing to use the immersion heater or boiler. The saving for me has been £450 to £600 per year meaning that I have pretty much recovered the investment already.