Electronic detection of water flow in copper pipe?

Hello,
We are making automatic shower mixer units which mix hot & cold water to get the required temperature for a shower. We use stepper valves to adjust hot and cold flows.
These units are fitted up in people’s attics, so it gets freezing cold in winter. There is a possibility that the cold pipe water could freeze, and then only hot water would come out, and scald the customer severely. In order to mitigate this with as few as possible components, we wish to simply put a thermistor in the unit. If it is at zero degrees or less, then we will open only the cold valve at first. If there is no flow of water, then obviously we wouldn’t then allow the shower to continue.
The thing is we need to detect the flow of cold water, without putting a flow sensor in the pipe as it is too expensive….Is their a kind of hall type sensor which one can fit to the outside of the copper pipe and it will give an electrical output if there is water flow in the copper pipe?

Water flowing in a pipe causes noise and vibration along the pipe. Fasten a piezo transducer to the pipe and amplify then rectify its output. A piezo is used like this to pickup vibrations of a piano, a guitar or a drum. Then the customer gets scalded in winter only when a noisy motorcycle drives past but I do not think motorcycles are used when it is freezing (maybe scalded when a noisy truck drives past?).

It's possible with ultrasonic clamp-on flow meters. I guess, you would need to design your own instrument to achieve an acceptable price.

Why not just place a thermistor in the OUTPUT of the mixer and shut everything down if the output temperature becomes too high (Actually I would make this an independent mechanical thermostatic valve so it was independent of the electronics and power).

Regards, Dan.

It seems more sensible to put this in a heated bathroom wall, such as behind the shower control fixture, rather than the attic.

Water pipes dont belong near any freezing zones.
Mind you in Winnipeg one winter, water pipes 6 feet under was not deep enough to prevent water pipes from freezing.

Will this Thermistor detect/alert of bursting pipes? before protecting user of hot water.

Make sure to include hot AND cold water pipe foam insulation with the installation.

thanks

Why not just place a thermistor in the OUTPUT of the mixer and shut everything down if the output temperature becomes too high (Actually I would make this an independent mechanical thermostatic valve so it was independent of the electronics and power).

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thanks, but by the time its detected temperature is too high and shut the valve off, the customer (who may/may-not be disabled) will have been lashed with scalding water.

It seems more sensible to put this in a heated bathroom wall, such as behind the shower control fixture, rather than the attic.

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Too true, but this just isn't possible in some customer houses, and it has to go in the attic directly above the shower. But you are correct, where we can, we put the mixer unit either under the shower tray or behind the wall. In very many cases, this simply isn't possible/desirable, and it has to go in the attic.....and of course, these days, everyone has lagging up there so the attic is even colder.

Audioguru said:

Water flowing in a pipe causes noise and vibration along the pipe. Fasten a piezo transducer to the pipe and amplify then rectify its output.

Click to expand...

In addition to that approach, assuming that the water pressure is such that in reducing the gauge of the pipe section where is fixed in the probe do not significantly reduce flow rate, it tends to increase the effect of turbulence, thus improving this acoustic effect.

Isolate the pipes in the attic, and add a pipe heater with a thermostat if the temperature will be that low. I don't think the customer will be happy with a burst pipe in the attic.

BTW, the hot water pipe is the most exposed to frost, due to the fact that the cooled hot water has less air bubles in it. Not when the water is hot of course :smile: