Detecting ice in water pipes....by using a motor?

Hello,

We design domestic water temperature controlled showers.

Stepper motors adjust hot and cold flow rates.

If the water in the pipes is ice, and we try and rotate the stepper valves, these valves break.

So do you know how we can detect if the water is ice or liquid.?

...its not terribly useful to use a thermistor....anyway, we already have a thermistor in the "mixed" pipe outlet....since water can be at zero degrees and liquid if it is agitated ....(made to flow a bit)

...the problem is that if our thermistor reads zero degrees or therabouts, we don't know if its ice or water....and we have to disallow the shower form turning on.....and customers are unhappy when there shower does not work.


I was thinking that we could put like a small rotary "fan" in the water pipe, and energise it.........we could then measure the current flow to it to see if the water was ice or not....because if it was ice, then the "fan" would not be able to rotate and it would be in "locked rotor" state.....as such ...would more current flow to its coils?

...i would have thought so , since the back EMF would be lower.(?)

....because if less electric current did flow, then we could measure this current to assess whether we had ice or liquid water in the pipes.?

I will assume that the shower has a detector which confirms that the mains water pressure is above a certain threshold (that threshold will be above the environmental air pressure).

When the mains supply is frozen, then the pressure will be maintained (and proably increased as a consequence of expansion).
When the valve controlling flow into the heating chamber opens, and the supply has NOT frozen, then the presure will be maintained.
When the valve opens, but the supply IS frozen, then the pressure will be released.

You'll have to work the rest out yourself . . . . I am not going to give you the basis of a patentable invention on here!

Hi

No the shower doesnt have a detector for mains water pressure

If both hot and cold were frozen, then i can't see how pressure would be released by opening (or trying to open) the stepper valves.


In any case, if cold is frozen, and hot is opened even for a short time, then the customer would be scalded.

Can't you just monitor current when you are stepping to determine whether or not the motor is stalled?

hi,

the stepper motor currents are limited by current sense resistors->comparators...i am afraid we would not see more current in the event of stall.

Hi,
Not sure I understand. You are breaking valves because you are applying to much force to them when they are frozen.
Is there not a clear driver current difference when operating the motor normally and when the valve is frozen?

my sincere apologies...its not so much the valves that are breaking when the cold pipe is iced...but its the fact that if the cold pipe is ice..then hot may come througfh alone, and the customer could get scalded.

i apologise for my confusion...there is something in some showers which breaks if the water is ice..........its something called a bar valve.., and i was confusing it with the stepper valves..sorry

Where is the pipe generally freezing? Options outside, on an outside wall, at the mixing valve.
This problem can be easily solved, but I need to know what mechanism you are trying to ivercome.

Red

its not really the pipes freezing that is our problem.

-pipes freezing is the customers problem.

Our problem is when the cold water is at zero degrees centigrade, but still liquid, and yet our shower thinks its frozen and so won't start the shower up.

You can get flow switches that are basically a non magnetic tube, with a magnetic float inside them. They are mounted vertical with the flow coming in at the bottom. So when the water flows, the float rises and a reed switch actuates when it has risen by a certain amount. If you had a solenoid mounted higher then the float, if you put a current through the solenoid you could lift the float if it was in water, not if it was in ice. So if the reed switch operated its water. if you turn the current off, the float should fall (depending on the water flow) - the switch opens, you then turn the power on again. The floats do take a couple of seconds to fall, so a current every 5 secs or so should work OK.
Frank
Frank

eem2am,

You have described having a problem that just doesn't make any practical sense.

Is your product specified to work with 0C water?
Was this a single customer, that had an issue one time, because magically he knew that he had 0C water available but that the valve would not operate?

How about turning on the cold water first and measuring the temperature of the water coming out before you add the hot water? Since you have control of the flow (with the stepper motor driven valves), you could just "drip" the water at first to make your temp measurement. Shouldn't the temp in the "mixed" pipe change from it's prior ambient temperature reading (assuming of course that the temperature in the shower stall was also not 0C).

-the product can work with 0C water...but currently, the software tells the shower not to come on at all if the thermistor reads 0C when a shower is "requested"

So , do you mean that we should open the cold valve and measue the temperature?

...if it was opened and read 0C we still wouldnt know if the cold pipe was iced or not.

..then if we dribbled some hot in, it would scald the customer even of it was only a dribble.....and we have strict regulations about this.

Do you mean that we should open the valves and then just turn them off again if it was too hot?...............the problem with that is that its too late then....hot scalding water has dripped on the customer, and they have their litigational heads on these days so as to claim a good bit of compo out of us.

i wish the problem didnt make practical sense....and that it would just go away....but unfortunately it is very real...and unfortunately so much so that i can't explain why publicly

eem2am,
Assuming that your thermistor is in the "mixed" pipe, I have a hard time believing that it would be 0C from the ambient temperature without any water flow (who takes a shower in a 0C environment). So let's say that the thermistor is reading 23C, once you attempt to "dribble" the cold water, if the temperature stays at 23C, you have no water flow, if the temperature starts changing, you have water flow.

Do you mean that we should open the valves and then just turn them off again if it was too hot?...............the problem with that is that its too late then....hot scalding water has dripped on the customer I don't understand, just how fast is your system able to respond to a large temperature change?

.the system isn't quick enough to stop scalding if , say, the cold pipe is frozen, and so only hot gets through into the mixing chamber.

It can be 0C because the mixing chamber and stepper valves often are placed in the attic, which is often insulated , so it can be well below zero C up there...even if it is warmer inside the house proper.

eem2am,

This "problem" is not making any sense at all, so I will not continue beyond this message.

If your system cannot detect the water temperature fast enough to prevent scalding, then your system is deficient.

If the mixing valve is in an environment that is "well below zero C" then the water is frozen, and you already said that the valves would not turn on below 0C (I would worry more about burst pipes in this environment). And if it were well below zero, than turning on the "cold" water (even at 0C) would change the temperature being read from the thermistor.

Why on earth would this sort of product be specified for use with a temperature range that included "frozen", 0C, water?

-Though i can assure you that this problem exists...............recently we had our switchboard absolutely jam packed, with screaming angry customers complaining that there shower would not come on in the cold weather......

-these customers did not have burst pipes
-however, in all cases , there unit was up in the attic


...the fact that they did not have burst pipes tells me that their water was not actually frozen.

...the fact that there shower did not come on tells me that the thermistor , in the mixing chamber was reporting zero degrees C or lower.


yes our system is deficient in the way in which you decsribe.

However, without increasing the cost ten-fold, its very difficult to have a solution to it cheaply.


...so now we are looking in to ways of detecting ice in pipes.

the best ides so far seems to be a coil and plunger in the water pipe (like a solenoid) , which would not actuate if it was ice, and would give more high peak current in a switched driver circuit....which we could detect to say it was ice.

You assumption that when the sensor reeds 0 degree the water is ice is not correct,
first of all you have a tolerance in the temperature measurement which is probably small but
also there is a difference between the ice point and freeze point,
0 degree is the ice point of pure water in a normal pressure of 1 atmosphere,
this is a temperature at normal atmospheric pressure at which it is possible for solid and liquid water to coexist,
the freeze point is below that and both will be different with impure water and different pressure.

That doesn't solve your problem of course but it gives you a different perspective.

Alex

yes thats correct,

We are so scared of scalding the customer that we assume the cold pipe is iced for any temperature that may possibly feasibly result in an iced cold pipe.

An (ultra)sonic transducer applied on the cold water pipe?
After applying an impulse to the sensor, I think the echo returned is completely different if the water is in liquid or solid state...

The only way i can think to solve this problem it to have a mix chamber after the hot and cold valves,
you can open the cold valve and use a sensor (temperature or level) to detect if the chamber starts filling which means that water is not frozen,
then you open the hot too (followed by the cold valve) and when the mixed water temperature in the chamber if the same as the requested one you open the valve of the chamber.

A second option would be to open the hot water (a little and close it again) so that the mix chamber measures a temperature rise,
then open the cold water to see if the temperature in the mix chamber lowers which means what cold water in flowing,
then open hot and cold to get the temperature you need in the mix chamber and open the mix chamber valve.

The mix chamber valve should close after the hot and cold valves so that the chamber remains empty after each use (water flow).

Alex