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Device could help save water while hot tap is warming up

A new device could help cut the amount of water wasted while waiting for a hot tap to warm up.

The prototype technology developed by a student at Brunel University in London detects the temperature of water when a hot tap is turned on and diverts the stream into a pressure tank until the flow reaches a specified temperature.

Inventor Mitch Gebbie said the tank could store five litres of water at a time, the equivalent of two 30-second bursts of a tap, and cut the average household water usage by up to nine litres per day.

‘It’s five per cent of your annual water bill that you’re pouring down the drain, that’s the average estimate, although obviously it’s going to vary between different households and different people’s uses,’ he told The Engineer.

The device makes use of a simple microphone to detect when the tap has been turned on, instead of a more costly flowmeter, and temperature is measured through the thermally conductive copper pipes.

An electronically controlled valve diverts the water into a tank connected to but at a higher pressure than the cold supply so that, when the cold tap is turned on, the tank automatically empties back into the pipes.

Gebbie said the system was designed to be easily retrofitted in existing houses. ‘There are things that you put on the bottom of the boiler that restrict the flow rate until it’s hot and you use a third of the amount that you would usually waste, but this is 100 per cent.

‘Water-return systems that have a small pipe that goes back to the boiler have to be implemented when the house is built, whereas this is retrofittable.’

He is now looking to develop the system into a commercial product.

Readers' comments (27)

  • I hate to be the one to pour cold water on this superficially-good idea but there are two things our friend appears to have overlooked. 1 Most properties still have a hot water storage tank fed from a local storage tank which produces significantly lower pressure at the hot tap than the cold. So the hot water is unlikely to be able to fill the 'tank connected to the cold supply' as described. 2 It is illegal to connect the potable cold water & the hot water systems in this way, for fairly obvious health reasons. Nulle pointes for this one Mr Gebbie.

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  • If the stored water is discharged via the cold water system, you probably wouldnt want to drink it as it may be lukewarm. You would need to run the cold water tap until it is cold, so defeating the objective. Also, having been through the boiler, it may no longer meet drinking water regulations.

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  • Read the little booklet fromt the Water Research Centre, lots of interesting stuff. Your system would be impossible to get approval on several points.

    It's easier to incorporate a small instant water heater under the sink which only energises with flow; then thermostatically cuts off once the hot water arrives.

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  • There are ways around the above objections, but the more you look into this one, the more it becomes a can of worms! Since I'm not metered it is the heat that I throw away in refilling my pipework with hot water which gets me going.

    As usual I can come up with many ways around this, but none warrent the expense! Such is solar and windpower. There has to be another way?

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  • Sure the most efficient and practicle way to heat water instantly is to use an 'instant hot water heater'. They have been on the market for sometime and some now offer close to boiler water to alleviate the need for a kettle.

    I fear this solution needs a problem. And that a wider view prior to 'head in the cad' would have realised this was not a problem looking for a solution.

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  • This is nearly a good idea. I have a new boiler that has an "Eco" button that allows the boiler to "kick in" at all hours of the day to keep the water warm near the taps. I have switched this off as it is a ludicrous waste of energy (non Eco) especially as the boiler operates during the night when there is no water use! However, I do waste quite a number of litres of cold water in the bathroom in the morning while waiting for the hot water to arrive and I'm afraid this is the lesser of two evils. Re-cycling cold into hot water creates a major bacteriological risk and, while Mr. Grebbie has a great idea it may not be a safe one. He needs to read up on the L8 Legionella Avoidance regulations.

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  • it would be better to divert the "waste" water to a collection tank for feeding as "grey" water to the wc flush. This could be achieved with bimetal or wax filled valve rather than electronic.
    Although it would save water, I'm far from convinced the saving would ever give payback on the investment.

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  • As the bath and the sink are near each other I always run the cold water from bath tap into plastic milk container and then pour it into the toilet cistern, I think that would be a better target for this water and maybe try to use gravity - but that would mean longer pipe runs!

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  • Possibly not so easy for retrofitting but I think that basin hot pipes should be 10mm or even 8mm. Especially if to spare room basins a long way from the hot tank or boiler. This would halve the volume of hot water wasted and would be a smaller size to insulate for heat conservation as well.
    Retrofitting can be eased by the fact that the smaller pipe size can be pulled almost as easily as cabling and comes on a coil rather than in straight lengths.

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  • Chris Wagstaffe's suggestion is constructive.
    As the price of water is driven up by scarcity, we will all become less phlegmatic about wasting it.

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