Zanussi Jetsystem Washer/Dryer - 50 degrees

Thursday 27th March, 2008
So another week goes by since I washed the towels at 40 degrees Celsius. As you may remember, washing and drying the set of cotton towels in a 40 degree wash used 2.67kWh of electricity.

How will it compare if we raise the temperature to 50 degrees? Clearly we'll need to raise the water temperature by another 10 degrees so it's going to use more power, but how much?



As with last week's test, I fully cleaned out the washer filter before the test. In doing so, I noticed a bit of white sludgy powder residue in the filter. This happens from time to time and, as we use detergent liquid, it can't be washing powder. It's actually undisolved water softener tablets. This happens a lot with cheap own brand tablets like the ones from Tesco. They often leave some residue in the soap drawer too. We only bought the Tesco brand once, but we're still using them up. I recommend you only use good branded softener tablets, e.g. Calgon, or just use very cheap, very pure, soda crystals as Keith Milner suggested in the comments last week. Another tip is to ensure that the softener tablet is always placed right to the back of the soap drawer. This ensures a good water flow over the tablet ensuring it gets dissolved as well as possible.

As clearly there were softener deposits in the bottom of the washing machine drum, I decided it was time to perform a maintenance wash. This involves performing a "boil wash" on an empty load. The traditional boil wash is actually 90 degrees these days, people used to actually use boiling water back in hand wash times. So, having unloaded the towels, I set the washer to do a 'quick' 90 degree Celsius cotton wash with maximum 1600rpm spin and pushed start.

The same processes kicked in as last week, but this time there was a little more water intake. Clearly there is no laundry in the drum and the cycle fills to a pre-determined level. With no volume from the laundry, the only way to fill the washer is with water...cold water...that needs to heat to 90 Celsius. This was going to eat some juice.

Cycle complete, the meter told me the power consumed...1.71kWh. That's pretty much two thirds of what it cost to wash and dry the towels at 40 degrees. Ouch. Whilst the odd boil wash is essential to keep everything all nice and fresh, you can certainly see why they should be avoided where possible.

But what about the cost of the 50 degree wash? Well, the three towels 'store dry' exactly as they were last week, but washed at 50 degrees instead of 40, had a total power consumption of...2.76kWh. An almost negligible difference of some 0.09kWh, that's about 1 pence extra at today's electricity rates. In fact, as we can't guarantee that the water intake temperatures were exactly equal in both tests then the difference may be even closer...or potentially further away...but I'd say 1 penny is about right.

How can they be so close? Well, the scientists amongst us will remember something from school about the rate of a reaction related to temperature. Those with a good memory may even remember something about Q10 and it being related to enzymes. Of course, enzymes are used in modern detergents to allow us to wash at lower temperatures and still kill bacteria and remove stains. This makes the Q10 reaction theory highly appropriate. I'm going to quote from the National Centre for Biological Education at Reading University in the UK.

"Consider high temperature/rapid processing. The Q1O rule states that for every 10 °C rise in temperature, the enzyme will react twice as fast. Of course, this is only true up to a point i.e., until the enzyme is denatured, but substantial catalysis can still be achieved in a short time if lesson timing demands it e.g., washing powder proteases can clear particular types of photographic film in just five minutes at 65 °C."


So raising the temperature just 10 degrees can double the rate of reaction. So we have to use more electricity to heat the water but, once it's there, the clothes will become clean quicker and a shorter cycle time can be used. A shorter cycle means less power, less drum rotation, less wear on the washing machine and less time to keep the water warm.

So, washing at 50 degrees Celsius doesn't appear to use a significant amount more electricity. It also get your clothes cleaner.

Next week we'll be washing at 30 degrees to compare but stay tuned until then whilst I measure some smaller appliances around the house like the kettle, toaster etc.

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