CountryByNet.com Forums :: Frostfree Hydrants, Ditches, and Pump Questions

Stoney, There is nothing wrong with theory, in practice.

I wish I were a better touch typer cause I gotta say a lot to communicate the info at the level of detail you need/want. I'm a graduate of the Christopher Columbus school of touch typing where we learned to search for, discover, and then land on the keys we want, one at a time.

OUTSIDE FORCE? What happens is the dirt goes below freezing down to a certain typical average depth. If you bury a pipe less than that depth it will lose heat to the ground and its temp will asymptotically approach the dirt temp, freezing and bursting. The water stores some heat but doesn't manufacture it so its heat will flow into the ground and it will cool below the freezing point. Insulation will DELAY but not prevent that. IF you let the outside water run all the time there would be a constant supply of heat in the water in the pipe and if the flow rate were high enough and the initial temp were high enough it wouldn't freeze. Not an elegant or conservative fix unless you have enough water ($) to spare to fill a pond.

R-VALUE OF DIRT? Forget for a moment the R-Value and consider the thermal storage capacity of the earth. If we place a thermometer near the surface (in air) and a series of thermometers at ever increasing depths, say every few inches, we can look at the temperature "profile" and observe its changes in the short term, diurnal (daily), seasonal, climatic, etc time periods. Unless you are at a radioactive hot spot of near an active volcanic structure, or have thermal springs, your thermometers will read as follows:

The one in the air will change rapidly and be near the temp that a "standard weather station" (those little white boxes) would show. The one just below the surface will change more slowly and when the air temp is rising it will rise but more slowly. Each lower thermometer will lag the change of the one above and have a smaler temperature excursion. Down about 10 feet the temp will probably change much much less than 1 degree all year. The temp at that depth will be approximately the average annual temp of the surface. Down at 10 feet or so the change is difficult to note on a seasonal basis but as the areas climate changes so will that temp as it will reflect the average.

The frost depth is the deepest that freezing is expected based on your climate. Code goes enough below the depth of deepest freeze for a safety margin. (I didn't mention R-value did I?)

The above described effect is mostly due to thermal mass (and some small bit of R-value.)

Your analysis "So, if you burried it 2 feet deep and put R-2X of insulation on top of and around the pipes, then you'd create the equivalent of 4 feet and therefore it wouldn't get any colder under 2 feet..." is flawed. Mostly because you assume the temp below the surface is controlled by R-value. Thermos bottles have a terrific R-value. Fill one half way with tap water and put it in the freezer. Tomorrow take it out and shake it to see if it froze yet. If not return to freezer and repeat. IT WILL FREEZE because the water does lose heat and it is not replaced.

IF you let your remote faucett run into a pond and the flow rate were high enough and the water at the source were warm enough it wouldn't freeze. If the water were hot, say from your hot water tank you wouldn't need to run nearly as much. If you recirculate it you wouldn't even waste water.

The R-value of dirt is variable and if you knew it for your project location/conditions your plan would fail because your theory is flawed.

As to really long heater tapes... Not required. Use multiple shorter ones. I seem to recall that they were made in lengths up to at least 25 feet. In one application where I didn't need/want the rated output I put a couple in series. P=IE I=E/R therfore P=E2/R so the power dissipated by two strips in series is one half the power of one strip. This power is distributed between two strips so the heat per unit length is 1/4 the normal value. Alternatively you can run the strips from a light dimmer and regulate the power that way. giving them the equivalent of 1/2 voltage cuts the power to 1/4 normal.

Check some manufacturers (Thomas Register is on-line now) you might be able to buy tape in 100 ft or longer rolls. With heater tape to provide heat, R-Value is of interest and will help. The instructiions with the tape caution you about overinsulation. They fear a melt down and subsequent liability issues.

If I were doing it I would run a heater tape(s) the full length of the burried pipe. I would suround the pipe and tape with lengths of foam plastic pipe insulation and place that combo inside a larger plastic pipe and bury that. I would place a thermistor next to the pipe near where it connects to the frost free hydrant(still under insulation) and run the wires back to the house. I would monitor the temp via the thermistor and set the lamp dimmer where needed to get about 35-38 degrees.

Seal the end of the larger pipe really well where the inner pipe exits to connect to the frost free hydrant. I'd probably do a little research on sealants and not just squirt some GE Silcone II 50 year caulk at it. Seal both ends of the concentric pipes.

Sounds like a lot but it is only two runs of pipe, thermostatically controlled heater tape, cheap light dimmer, pipe insulation some a caulk tupe of sealer, some wire, a thermistor, and misc. YOU HAVE THE TIME. You can monitor the thermistor every so often with an ohm meter till you are satisfied you are making enough heat.

You calibrate the thermister by placing it in a glass of ice water (crushed ice, not cubes) with the full run of connecting wires installed. Note the reading. Compare to a thermometer. Replace ice water with tap water and note the resistance and thermometer reading. Get comparisons at a few temps between freezing (slush) and say 45-50 egrees. Now you have a claibrated electronic thermometer to install in your pipe to read the pipe temp. You should be able to find a thermistor bead for a buck or two.

Again, sounds like a lot but it isn't really, I just take a while to explain it.

THE DOWN SIDE IF you lose power to the heater tape the pipes will freeze and burst. Is the grid super reliable at your loacation? Do you stay current on your electrick bill? Do you have a reliable automatic emergency backup generator?

Maybe a deeper trench isn't all that bad of an idea.

Pat

"I'm not from your planet, monkey boy!"

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