Run Washing Machines with Solar Hot Water
Run Washing Machines With Solar Hot Water
Find out about the problems of running a modern washing machine with solar hot water
energy efficiency | water | solar | generalTen or more years ago, the majority of
washing machines were fitted with two inlet pipes - one
hot feed and one
cold feed. The hot water needed to wash clothes was therefore typically drawn from the domestic
boiler, and the cold water (for rinsing) taken from the mains water supply. Now it is virtually impossible to find a washing machine which is not fitted with
just a
cold feed.
Cold Feed Washing Machines
A standard
cold feed only washing machine is connected directly to the mains water supply. When hot water is required during the washing cycle, it is heated inside the machine using electricity - in fact
85-90% of the electricity used by a washing machine goes in
heating water. Even if you
wash at 30 degrees, the washing machine still has to heat the mains water (typically arriving at the house below 10 degrees) by 20+ degrees.
Washing machine manufacturers claim that
cold feed only washing machines are
40% more efficient than the older style machines with both a hot feed and a cold feed. They say this is because modern
washing machines use relatively little water (still 50 - 100 litres on average!), the litres of cold water in the runs of copper pipe between the boiler and the washing machine would get into the machine via the hot feed still needing to be heated, and domestic
boilers take time to heat up water (during which cool water will be fed into the washing machine).
We are often asked whether or not it is possible to use
solar heated water in a modern
cold feed washing machine (or
dishwasher) to
save electricity. Unfortunately, the answer to that question is
maybe.
Pre-Heated Water and Washing Machines
Sending renewably heated water into a
washing machine in order to
save electricity seems like a no-brainer, unfortunately things are never that simple. Washing machines are packed with complex
electronics (see image of washing machine controller circuit above) and
sensors which throw a wobbly when confronted with something out of the ordinary.
A washing machine expects
cold water to be fed into its
cold feed, so how it will react if you send in 55 degree water (from a
solar water heating panel) when it is set to do a 40 degree wash is anyone's guess. It may run perfectly happily with the (overly) hot water, or it may throw up an error code and stop in mid-cycle. One thing is for certain - different washing machines from different manufacturers respond differently, and the only way to find out if you can
pre-heat water before sending it into the cold feed is to try it yourself (or to find someone that already has).
Note that do so may invalidate the warranty of the washing machine.
Unless you want to
boil all of your clothes and linen, you will manually have to ensure that the water being fed into the washing machine is colder than the temperature at which you want them to be washed.
Thermostatic mixer taps are available which will do this for you (but they can be expensive). If you want to do a 40 degree wash, then you would set the mixing valve thermostat to 40 degrees, and it will automatically mix the necessary amount of cold mains water with your hot water to ensure that the water it sends into your washing machine is below 40 degrees.
A second thing to consider is that a) it is better to
rinse washing with
cold water rather than hot, and b) it is a
waste of hot water to use it to rinse washing anyway. Therefore, you either need to turn down the
thermostat on the mixing valve or (better) completely block the hot water supply before it gets to the mixing valve when the washing cycle is finished. An electronic
solenoid valve used in conjunction with a timer can automate this process cost effectively. You just need to use a
power meter to measure the electricity consumption of your washing machine during different stages of its programmes to estimate the time when water heating is complete, and then programme that into a
timer.
It is a great pity that manufacturers have pretty much phased out production of
washing machines with both cold and hot feeds since people with access to supplies of
renewably heated water have to choose between purchasing a second hand (and therefore old and
inefficient) washing machine with hot and cold feeds, or going to a lot of trouble and expense putting systems in place to enable them to use a cold feed only washing machine.
More Information
Across the internet there is a lot of information on this topic, but unfortunately it is spread out across a range of web forums. Here are some links to the more useful of those forum postings and websites:
*
Should I buy a cold fill washing machine or a hot and cold fill? - this article is packed with information about cold fill washing machines, and their advantages and disadvantages compared to hot and cold fill washing machines.
*
Solar heated water for washing machines with cold feed only
*
Using boiler to directly heat washing machine / dishwasher
*
What happened to the hot water valve in washing machines?
Article Last Modified: 13:35, 22nd Aug 2008Comment on this Article
If you have any comments on this article, please email them to
neil@reuk.co.uk.
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