Solar Water Heating And Washing Machines

Q: We had solar water-heating panels installed on our roof last year and as a result the hot water in our tank frequently reached as high as 60C in the summer. (We have always kept the boiler thermostat set lower than this, originally to prevent children from scalding themselves and then in order to save energy.) In consquence we actually ended up with an embarrassment of hot water; we fondly supposed that the washing machine drew its supply from the hot water pipes it was plumbed into, but discovered by trial and error that it was instead filling with cold water and sitting there using electricity to heat it. The mechanic told us that it would only use the hot feed if we set a very hot wash, presumably on the assumption that the domestic hot water supply was set to a far hotter temperature than is in fact true in our case! Now that machine has given up the ghost and we need a new one - but things seem to have got even worse in the last few years. All the new waashing machines I've seen boast that they don't have a hot water feed at all, on the grounds that it is "more efficient" to heat the water /in situ/, or else assume temperatures in excess of 60C as before. Is there any way we can use our summers of endless free hot water to perform a more eco-friendly wash - short of washing clothes by hand in the bath, that is?

A: The only way you can use the hot water up in your washing machine is to buy one of the few remaining hot and cold fill machines still available, then sort the washing so that as much as possible is washed at 60 degrees, and as little as possible is washed at 40 degrees. However, this is likely to result in smaller loads/more frequent washes, so the extra electricity used, and extra wear and tear on your washing machine, will more than cancel out any savings. You may just have to accept that cold fill only washing machines are wasteful in relation to solar heated water (which isn't 'free' until the energy savings exceed the cost of installation and maintenance). Well your summer "free" hot water is actually your most expensive as your solar heater saves you about GBP30-50 per year in water heating costs but probably cost you several thousand pounds to install. That aside you could always put a changeover valve to allow you to manually select a hot feed for a single input machine, but you would then have no control over the wash temperature and if the incoming water was too warm and this could damage certain items. A more complex solution would be to install a thermostatic mixer valve on hot and cold feeds with a single output to the washing machine set such that the water to the machine never exceeded 40deg. None of the above makes a great deal of sense though as the energy required for washes using low temperature powders in low water content machines is quite small so there would be no monetary saving after taking into account installation costs.

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