Detecting ice in water pipes....by using a motor? 16

[schnell]

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.?

 

[schnell]

Thankyou jraef,

I am going to look for one of those flowmeters and check out the price etc.

...i just need to know "flow or no-flow" so i'm hoping i can get a cheap one...and preferably one with small paddles.

Of course, as you rightly say, "Electric Showers" with 10KW heaters are used in uk to get instant hot from a cold tank.

Of course, the temperature regulated showers concerning this post use pre-heated water from a large tank (and mix it with cold to get selected temperature), as you also describe.

 

[danw2]

I can just imagine that incredibly astute customer who knows that ice and water can be a slurry and the expectation that the shower water should flow even under those conditions.

"My pipes didn't break yet, your shower should have worked. I know because when the water really freezes, then the pipes break and my shower water comes through the ceiling not through the shower nozzle."

 

[msquared48]

It's harder for flowing water to freeze.

So, why not create a loop in the attic area subjectto freezing for the water to flow, having a small impeller to move the water and a small section of heat tape on the loop portion of the circuit to put additional energy into the water to keep it from freezing. This hydraulic circuit could be automatically disabled electrically when the cold water valve was opened with a small sensor, and re-engage when it was turned off. You could also work in an attic temperature gage to turn the system on or off at a certain temperature.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[sibeen]

and so the hot can come through alone and scald the person becasue theres no cold water mix.

Sorry, I'm a bit confused here. Admittedly I live in a place where freezing water pipes aren't actually a problem.

Why would you heat water up to such a temperature that it can scald people and then add cold water to cool it down?

Wouldn't a better system to be a single feed in, heat it to a controllable temperature, and leave it at that? If the upstream pipe is frozen, then there is no flow and simple detection will pick that up.

 

[Skogsgurra]

Scalding occurs at quite low water temperatures while the hot water is kept at a higher temperature (schnell says: "the temperature regulated showers concerning this post use pre-heated water from a large tank") for several reasons (dish-washing, killing bacteria like legionella etcetera).

So, in a complete system, it is necessary to do just what schnell and his colleagues do.

schnell: It could be worth-while to study that valve/sensor combination. Plunger and valve can sit in water while solenoid is outside with a stainless steel tube separating the two. Eddy currents in the stainless tube could be a problem, but I don't think it would be a major one.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[waross]

You are trying to detect and protect on very fine line and a very narrow window of opportunity . If it is cold enough to freeze a valve, it won't be long before something else freezes and breaks.
If you can't or won't protect the pipes from freezing then consider a installing electrically operated stop and waste valves in a warmer area. Slope your piping and automatically drain it when the temperature of your valve is close to freezing.
Failing that the best option may be a large warning to the effect.
WARNING!!!
SCALDING HAZARD!!
IT IS THE OWNERS RESPONSIBILITY TO INSTALL THIS SYSTEM IN SUCH A WAY THAT ALL COMPONENTS ARE PROTECTED FROM FREEZING!!!
FAILURE TO HEED THIS WARNING MAY RESULT IN PERSONAL INJURY AND/OR PROPERTY DAMAGE!!!
Trying to detect freezing after it happens but before it does damage is like swinging a big stick from the small end while balancing on a knife edge.
You can probably do it but is it a good idea.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[automatic2]

I can't imagine your concept being consumed by a customer who can't keep thier pipes from freezing. Luxury over basic needs.

What happens if you loose power when a correction to cold is required, besides scalding.

Here's what I'd be thinking. Consider hydraulics, and specifically an anti fall situation (in your case, anti extreme)

your flow is developed by a piloted flow control valve, each obtaining it's pilot pressure from the other source. Lack of pressure from one source prevents actuation of the other.

 

[Skogsgurra]

We are mostly technicians in here. And we may think that it is silly to detect freezing instead of preventing it.

But I am afraid that the need is real and that marketing has demanded a solution. There are so many circumstances we don't know about or can imagine.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[MikeHalloran]

I'm thinking, ditch the steppers.
Instead, use spring-closed PILOTED valves, driving the pilots with force motors controlled by PWM.
The cold water pilot also needs a position transducer of some sort; if the pilot won't move, the valve is frozen.



Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

Attempting to "detect ice" in shower water is not good industrial practice. If you don't want product liability issues you need to avoid treachery like, "Is there ice or isn't there?".

You're talking about an entire product development cycle just for the ice detecting aspect. Never go into a product development cycle and add a second one half way through, especially for an anti-lawsuit device!

Think about how a successful company would do this. Put a thermistor on the pipe just like the others you are already using. If it gets within 5.0F of freezing inhibit your system. It's that simple. No guessing required. If the customer doesn't like seeing the system inhibited he can heat trace his cold water lines - he should anyway as that's already too close to freeze damage.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Right on Keith. lps

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[btrueblood]

Even a thermistor with a 5F limit might not work if the cold spot and frozen pipe is somewhere upstream of the thermistor, or solenoid ice detector, or whatever. If it must be done, as Gunnar suggests, then a recycle loop should be considered. That still only works if the recycle loop completely covers the length of cold pipe exposed to freezing conditions.

I still think some fairly simple logic would limit risk - open the cold water valve first, and verify flow (or pressure between valve and showerhead), before commanding hot water valve open. Tell the consumer to turn the faucet on before standing under the shower head, but at worst they get a momentary squirt of ice cold water, which should serve as a wake up call to RTFM. But a good micro should be able to sense and respond to a pressure rise (or lack thereof) in less than a tenth of a second, and either have the flows well balanced (i.e. at bathing temperature) in that time, or shutoff and illuminate the ice cube symbol.

 

[zekeman]

"We are mostly technicians in here. And we may think that it is silly to detect freezing instead of preventing it.

But I am afraid that the need is real and that marketing has demanded a solution. There are so many circumstances we don't know about or can imagine. "

I strongly disagree. If the thermistor reads 0, then the system should shut down as it does now since one can conservatively reach the conclusion that 0 means ice , period.
It is ridiculous to make a system that actually detects solid ice, since 0 says if it isn't ice, it will be ice soon,

I don't see any reason to pursue any further changes in the design which I suspect has worked and would continue to work. Looks like an unnecessary makework project for someone.

 

[Skogsgurra]

Zekeman

The reality is that temperature very often 'hovers' around 0 C. The reason is that water in lakes and in snow on ground acts as a buffer that keeps temperature fixed at the 'plateau' where water freezes and ice melts. That makes the time when the shower doesn't work quite long and that is, as I understand the OP, what someone in (probably) marketing wants to avoid.

Using a thermistor with temperature tolerances that may well be a few centigrades means that you have to set the limit a few degrees above zero, which increases the span, where the shower is unnecessarily shut off, even more.

There are many reasons why this may look like a bad idea. But, can we really judge? Shall we? The original question is not about how silly or not it is to detect if water has frozen. It is about how to detect if it has frozen.



Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[zekeman]

ok, now sounds reasonable.

Then I propose using a jacketed heat exchanger type entry where the hot water is in an outer jacket and the cold water flows thru the inner pipe.
Then, you can't have a freeze, without both lines frozen.

 

[ScottyUK]

In the UK most modern domestic showers are designed to stop all flow on loss of the cold supply. This is accomplished by even the basic showers without any electronics at all, which suggests it is accomplished through a hydraulic arrangement operating on a valve. Buy one, take it to bits and see how they do it.


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If we learn from our mistakes I'm getting a great education!

 

[danw2]

Check out "pressure independent valves" used in HVAC.

I would guess that a derivative of such would stay closed on no flow.