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Author Topic: leaving taps running to prevent freezing - any rules of thumb  (Read 7497 times)
westwalesj
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« on: December 30, 2011, 05:45:01 PM »

Has anyone got any rules of thumb for what flow rates need to be to stop pipes freezing? I'm guessing you could work it out from the physics, but I was hoping for a handy calculator... These are outdoor cold water pipes (private water supply). 25mm MDPE.
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HalcyonRichard
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« Reply #1 on: December 30, 2011, 07:20:21 PM »

Hi
    It depends on a number of things. Are the pipes buried ? I think the standard now is 750 mm deep. Anything less might freeze. Usually a slow trickle is all that is needed. But if you have long pipe runs it will take more flow. It takes 4.2 J/g to heat water by 1 C but 334 J/g to freeze water so as long as the flow is reasonable it will be O.K. I have seen frost proof taps designed to be used with underground pipe. When the tap is turned off the water in the vertical part above and below ground drains out - so there is nothing to freeze in the danger zone.

Regards Richard
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Heinz
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« Reply #2 on: December 30, 2011, 08:24:09 PM »



My supply is spring fed to an underground tank, then inch MDPE to the house about a foot deep. Even in summer the water is cold. The pipe freezes where the connection to the house is as it comes above ground and through the wall. It is mega insulated but if it's -12 ? or less the pipe freezes overnight and it's insulation off and blowtorch time  facepalm
If I leave the kitchen cold tap dripping just enough so the drip is a long drip but the drips aren't joined up, this is enough to avoid any freezing even in the crazy arctic temps we've had in the last few winters... This also makes the pump in the wee pump hut cut in and out every so often and hopefully not freeze.

Heinz
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westwalesj
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« Reply #3 on: January 05, 2012, 10:15:50 PM »

I'm trying to avoid burying. Its about 200 metres of pipe, on a very steep hillside; couldn't get an excavator up it, so a 750mm deep trench definitely not realistic. Was wondering if people had advice based on frost stats or thermostats attached to solenoid drain valves etc?

334 J/g to freeze water; so if i work out the volume of water in the pipe, then the heat loss through the pipe wall. And then the heat gain from a flow of water coming in to the pipe from the spring? And then work out the flow rate of the water coming in that is needed to keep up with the heat loss from the pipe? Or is it more difficult than that.
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Heinz
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« Reply #4 on: January 05, 2012, 10:30:56 PM »

If you can't dig a trench for it, could you just cover it with something? Mad thought, many horse owners have a problem getting rid of the manure. Get a load from a stable and wheelbarrow it to the pipe and dump it on?? Frost cover and some heat in the one go.... ?? If you did this now it would be frost safe for this winter, do it again in the next couple of autumns and the cover will probably be deep enough to not need any further poo

Heinz
« Last Edit: January 05, 2012, 10:33:39 PM by Heinz » Logged


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ecogeorge
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« Reply #5 on: January 05, 2012, 10:59:36 PM »

I'm trying to avoid burying. Its about 200 metres of pipe, on a very steep hillside; couldn't get an excavator up it, so a 750mm deep trench definitely not realistic.
You haven't a hope in hell of stopping that length from freezing! sorry !!
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rhys
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« Reply #6 on: January 05, 2012, 11:43:57 PM »

Trace heating tape not very renewable though need a nuke to power it opps!
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Philip R
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« Reply #7 on: January 06, 2012, 01:08:28 AM »

rhys,

Do not try to be controvertial and a twit bashing nukes on this thread. Jibes are unwelcome.

Your bit of trace heating is powerred by incremental addition of fossil fired capacity. Learn about merit order and you might understand.

Enough of Rant.

More inportant, running any water to waste, ultimately increases load on the potable water and ultimately sewerage systems. Drinking water is carbon intensive. They reckon 1 cubic metre of water requires about 4kWh to pump, purify, disinfect and then aerate, pump, etc once peeed and pooed into.

Bit of trace heating and lagging might reduce this demand, but could increase it. Need to do your sums.
PhilipR
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Heinz
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« Reply #8 on: January 06, 2012, 01:21:56 AM »


More inportant, running any water to waste, ultimately increases load on the potable water and ultimately sewerage systems. Drinking water is carbon intensive. They reckon 1 cubic metre of water requires about 4kWh to pump, purify, disinfect and then aerate, pump, etc once peeed and pooed into.

Bit of trace heating and lagging might reduce this demand, but could increase it. Need to do your sums.
PhilipR

I think the original poster was talking about a private supply, a spring or a loch, so not much (any?) carbon involved.
Trace heating and lagging by horse poo is the answer ....

H
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dhaslam
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« Reply #9 on: January 06, 2012, 01:23:39 AM »

Mad thought, many horse owners have a problem getting rid of the manure. Get a load from a stable and wheelbarrow it to the pipe and dump it on?? Frost cover and some heat in the one go.... ??

I was going to cover the meter  with clay.  After charging over 3000 for the water  connection the council installed the meter on the surface, they are now proposing to charge water rates as well.    So that is a third reason  for using the stuff, great idea.    
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bxman
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« Reply #10 on: January 06, 2012, 08:33:55 AM »

What is the soil like? Maybe a contractor could winch a mole drainage plough  down the slope,pulling in the pipe at the same time however knowing Wales the rock is probably only 3" down, so back to poo!
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HalcyonRichard
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« Reply #11 on: January 06, 2012, 09:25:42 AM »

Hi Westwalesj,
                    You said :-

"334 J/g to freeze water; so if i work out the volume of water in the pipe, then the heat loss through the pipe wall. And then the heat gain from a flow of water coming in to the pipe from the spring? And then work out the flow rate of the water coming in that is needed to keep up with the heat loss from the pipe? Or is it more difficult than that. "

Thats basically it. But from experience the water does not freeze easily. It goes through a slush stage and ice is a good insulator. The problem times are when you get a lot of days/time near or below zero. Reading between the lines - if you are gravity fed from a stream then having a trickle or more running should stop the freezing. With my practical hat on you could try an "experiment". When you have a cold snap measure the spring temperature - run the tap at a reasonable rate. Then after a goodly time measure the temperature from the tap. This would give a reality check to any assumptions/calculations. By the way has the spring/stream ever frozen ?

Regards Richard
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Moxi
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« Reply #12 on: January 06, 2012, 09:58:59 AM »

Westwalesj

Can you have a priming tank thats heavily insulated at the head of your supply that allows you to drain down the pipe over night ? then in the morning fire a solenoid valve to reprime ? it should take less than five minutes to drain and prime the line and would be a lot better than trudging out to defrost the line ? 

Moxi 
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ecogeorge
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« Reply #13 on: January 06, 2012, 10:03:16 AM »

Went to Brecon Beacons last Dec.
This is what you're up against!  Grin Grin


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djh
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« Reply #14 on: January 06, 2012, 10:27:20 AM »

200 m down a steep slope sounds like a hydro power opportunity rather than a problem?
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Cheers, Dave
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