Wednesday, October 2, 2013

Electricity Maths and My Dishwashing Habits

Sometimes it really pays (pun not intended) to do the maths associated with your household habits.

We bought one of those electricity metering thingy-me-bobs a while ago and tested how much power our dishwasher uses.  I also had someone come out for an electricity usage audit.

Here is the surprising maths.

Method 1
Rinse dishes before stacking in dishwasher to remove most of the grease, about 10 minutes of running hot water.
Run dishwasher on shortest cycle possible with a 4-in-1 tablet at 40 deg C

Cost for hot water (assuming $250 per year for a 10 hot minute shower and dish rinsing done once a day as told to me by energy auditor) = 68.49c
Cost for dishwasher running for 42 minutes, 0.99kWh used @ 54.39c/kWh (my peak rate) = 53.85c

Total 122.34c or $1.22

Method 2
Only scrape off the solid bits into the bin or chook bucket and stack straight into dishwasher
Run dishwasher on 111 minute cycle with a 4-in-1 tablet at 65 deg C and a couple more rinse cycles

Cost for dishwasher running for 111 minutes, 1.213kWh used @ 54.39c/kWh (peak rate but hardly ever used at this time) = 65.98c

Total 65.98c or $0.66

Considering that my tap runs at almost 7 litres per minute I am also using 70 litres to rinse whereas the most my dishwasher uses according to its manual is 13 litres.  Add on water rates and my old method of rinsing is looking a less lot like a good idea.

Guess who isn't rinsing anymore and just lets the "slave" do it?  :-)

And of course I usually take advantage of the delay timer whenever possible and wash at 16.44c/kWh overnight!

Best wishes

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