I can't offer a masterclass,
but I can tell you what works for us, a family of four,
with a creaking ~10-year-old slimline simple domestic dishwasher
as of November 2009.
(Shortly after writing this our old DW24 dishwasher packed up (2009/12/12),
and given that it had already been repaired at least once,
and had shown signs of going dangerously insane,
we ordered a replacement ZDS2010 which we have reviewed.)
The basics are very simple:
- Run your dishwasher only when it's full if possible
because you get more for the detergent and energy that goes in.
- Run the coolest/quickest programme that will do the job
because heating water uses almost all of the energy consumed.
- Choose a programme that lets your dishes dry in the air
since a 'thermal dry' uses a fair bit of energy and is usually
not needed if you have time and/or a dish rack for recalcitrant items.
These last two steps for us save us about 1/3rd (0.86kWh instead of 1.27kWh)
of our total energy consumption per load,
using 'Quickwash' at 65°C in our old machine which was too ancient to have cooler washes
(in our new machine the "ECO" 50°C cycle generally works very well).
Note that you probably can't use water above 45°C for hand-washing,
so anything hotter than that in the dishwasher is likely to give a better wash
and kill more bugs...
Before putting the plates, pans, etc, in:
- Scrape off any excess food before loading the dishwasher
(maybe for your compost bin)
so that the detergent is washing the dishes not your discarded food!
Rinsing dishes under a tap is probably unnecessary and wasteful of water.
The wash programme on our ancient (Zanussi DW-24 slimline) dishwasher
that I normally used ('heavy soil')
is a prewash (essentially a cold rinse with some detergent)
followed by a full hot wash, hot rinse and thermal dry.
Instead maybe:
- Run the cold rinse programme with a little detergent
(or soda crystals or non-foaming washing-up liquid to be effective cold)
to prevent food caking on, especially dairy products,
and/or if the full wash is not going to be run for a while.
- Clean the filters (if bunged up) before the main wash
so that the water pumping, etc, is as effective as possible,
and again not merely spreading old food around the machine!
Your dishes will be cleaner for it.
A cold rinse can get a lot of dirt off the dishes and uses virtually no energy:
I can't even measure the consumption on my plug-in meter,
so it's way less than making a cup of tea,
and no more than (say) a few percent of the full wash.
If you are in an area short of water then you may skip this step;
in rainy London I sometimes go wild and do a rinse in the morning
to get the milk/porridge/etc off the breakfast dishes,
and again in the evening and empty the filter before the main wash!
For extra greeny points (and possibly extra savings depending on your tariff):
- Run the main wash on a delay/timer at 2am
or as near as you can get,
for example just before you go to bed,
not right after the evening meal!
- Turn off the dishwasher at the wall when done
to avoid any standby losses from the dishwasher or timer.
Why 2am?
When electricity demand is highest the transmission system is under strain
and there may well be
dirtier or higher-carbon fuels
generating the electricity to run your dishwasher;
in the UK one peak is typically early evening.
Conversely, if you can run the dishwasher in the wee hours, maybe 1am to 4am,
much less CO2 is likely to belched out to run your wash,
in future maybe even zero when wind (etc) is meeting demand.
(Cold rinses take so little energy that you should do them when you need them.)
Maybe once per week,
or if the machine seems to be clogging up or ineffective,
or for/after a particularly greasy or dirty load:
- Clean the filters
which in our case is brushing them and/or rinsing under a tap.
- Run a 'maintenance' wash
with the machine empty or at least not jammed full,
and/or using a hotter wash than usual,
to shift any grease and gunge that has been accumulating,
and that might even bung up your drains or damage the machine.
If you are in the market for a new dishwasher,
eg because yours is beyond repair:
- Buy the most energy-efficient model that you can
which will probably pay itself back in saved energy.
- Don't buy a bigger model than you need.
There's a lot of speculation on the IntarWebs either way,
but it seems that if you follow the steps above
then you may have a lower environmental impact than washing by hand,
while saving money and a dull chore...