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ground water by underground lines

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by rancherburn, Oct 8, 2013.

  1. rancherburn

    rancherburn Member

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    when I installed my boiler lines 4 years ago there was water in the trench. after 4 years of back aches from cutting and splitting 14 full cord of fire wood I decided to dig up my underground lines. Guess what the water is still there. I did some surveying to see if I could drain the water away from my lines and the only way I can is to raise my lines. The tile will have to run about 300' with about a 12" drop and if I put a foot of rock on my tile the lines will only be down about 2' and I live in northern Wisconsin. I've read a lot on this site about foaming in the trench but will this work in high ground water situations. I'm looking for any ideas I really need to make this system work. thanks for any input

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  2. woodsmaster

    woodsmaster Minister of Fire

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    With high ground water I think I would use thermopex or similar to make sure no water can reach the pipes. I'm sure when the water tables are up my thermopex probably lays in some water but I don't notice any effect.
  3. Tennman

    Tennman Minister of Fire

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    You've probably read my story in the sticky about my first year heating ~180' of dirt between my boiler and the house. Lots of springs around and thru our old house. After redoing my underground with closed cell foam (theoretically water impervious) my energy loss measured by water temp out and back became 1-1.5 degF for almost a 440' total round trip (I've often seen less than 1 degF for the round trip). That's measured when the furnace blower is not on, house not taking energy out of the water. You didn't mention how your lines were insulated. I'm certain there's some water around my lines, but with that much foam as I now have it's clear I'm not losing any significant energy between the pex to the dirt. Most of my loss now is un-insulated lines in the root cellar and boiler barn. I agree with what JT says above. With at least 4-5" of foam between pex and dirt everywhere water's no issue. It appears Thermopex is a good product. I chose to foam in trench to get thicker insulation and for me I was able to do it for less money. In trench foaming prices vary dramatically contractor to contractor. If you're heating dirt for a long distance it will kill your efficiency.
  4. hartkem

    hartkem Member

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    If it were me I would want thermopex or similar with standing water. I would hate for you to have to do it a third time if the water ever did penetrate the foam.
    rowerwet likes this.
  5. Holley

    Holley Member

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  6. avc8130

    avc8130 Minister of Fire

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    I've been trying to weed through the advertising and the nonsense also.

    I just can't wrap my head around where all of this water is coming from. I think about my property.

    I plan to go ~2-4 feet down when I run my lines out to my shop. My wells are 600 and 700 + feet deep. I live on a hill top on a shale ridge. I just don't see how my lines would ever wind up "floating".

    Everywhere I look on the web is another vendor advertising "wrap" pipe. Some use the foil-faced garbage. Some use closed cell foam sheeting.

    I like the products that have solid closed cell foam filling the protective layer, but I want a 3rd line in there to run some domestic water also.

    Is water "fouling" the insulation only a concern with high water tables?

    ac
  7. Holley

    Holley Member

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    1 to 1.5 degree round trip drop is not too bad but we really need to know gpm flow to quantify the loss. If you were pumping 15 gpm with a 1.5 degree loss that would be roughly 11,250 BTU/Hour. If your pump runs 24/7 that's 270,000 btu/day or in a 200 day season 54 million btu. Depending on the efficiency of your boiler that's an extra 3 to 5 cords of wood a year that is being cut, split and loaded. If you are pumping 7.5 gpm the loss (and extra wood consumed) is half that..still a lot.

    That said, if you were pumping 15 gpm with that 1.5 degree drop that works out to about 25 btu/hr per running foot and that's in line with Thermopex and other good district pipe systems. If you're pumping at half that rate with that same 1.5 dg drop you're doing really well..particularly in your wet ground condition.
  8. Tennman

    Tennman Minister of Fire

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    Holley, Interesting math. I probably should create a model of our energy waste, but I've been so pleased with the improved operations and warmer house vs the first year I thot I was doing well. But your point is well taken, I should take a look a how much wasted energy I'm consuming. My heating season is pretty much 120 days. To heat our inefficient 5,000 sqft home we burn ~6-7 chords, so the estimated wasted wood/season is certainly not 3-5 chords. I should have a better handle on consumption, but hopefully this year I will. At the moment adding storage for the upcoming season and will be focusing on minimizing that lost energy and tightening the efficiency. I do run the pump 24/7 which is an energy waste that I hope to address this year. But I'm certain I'm not wasting energy in the dirt. My Taco 0013 was sized based on the estimated heat and gpm needed to get the energy the boiler produced to the house. I do know when I dug up my failed first underground everything was saturated and muddy. So my line is absolutely surrounded by wet dirt. FYI, our home is near the Alabama/Tennessee line, with ~37 degF mean winter temp. That explains relatively low wood consumption on a 160+ year old leaky home to keep the downstairs at 68F. Thanks for the numbers. I'm going to try to collect better consumption data this year with the upgrades.
  9. Holley

    Holley Member

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  10. Holley

    Holley Member

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    The math's pretty simple. BTU/hour is "approximately" 500 x gpm x DT where DT is the temperature drop. The best way to get a handle on it for testing is to throttle the pump back to decrease the flow which will increase the temperature drop. It's pretty darn hard to accurately read the difference between 1 and 1.5 degrees but if in the example above, you reduced the flow to 3 gpm the same heat loss would then read as 7.5 degrees. The next problem is how to read the flow. You either need a flow gauge or you need to measure the pressure drop across the pump in PSI, convert that number to feet of head ( PSI x 2.31), and then look at the manufacturers pump curve.

    You can buy a flow gauge for about $75. If you have a flat plate heat exchanger in the circuit the flow qauge might not be a bad idea anyway as it will help to determine if the hx is fouling and needs cleaning.
    PassionForFire&Water likes this.
  11. Bob Rohr

    Bob Rohr Minister of Fire

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    Maybe it would be best to try and deal with the water. Any way to pump it from a low spot in the trench? Water is an excellent conductor and even tube in a water tight sleeve with only a few inches of insulation will lose more than you would expect.
    Fred61 likes this.
  12. Fred61

    Fred61 Minister of Fire

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    I wholeheartedly agree with Bob. You're still going to split more wood than if the water wasn't there. I would work a little harder to try to eliminate it. Of course, that's easy for me to say, speaking from the hills of Vermont where the cows have two legs on one side that are shorter than the other and all the pitchforks are ground with each successive tine is shorter, it's easy to run a drainage tile to lower ground.

    Water runs on top of ledge. Anyone building on land that is shallow to ledge will see dampness or water even if the soil is sandy or well draining. I would probe around with a back hoe or excavator looking for a crack and try to make some sort of drainage channel.
  13. avc8130

    avc8130 Minister of Fire

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    That's my question? Where is this water coming from?

    If there is no ground water to speak of, realistically how much water are you going to find in your lines?

    ac
  14. rowerwet

    rowerwet Minister of Fire

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    wrap pipe is garbage, plenty of horror stories where it floated out of the ground. Thermopex is rated to loose 1 degree per 100 feet.
    I had 85' in southern maine going to my outdoor pellet boiler, the snow over the septic melted first, I never could see where the thermopex ran.
    thermopex only needs 12-24" of dirt over it.
    Do you need domstic water out at the boiler? You can get three and four line thermopex, it just costs more.
    I added a domestic water fill valve at my HX in the basement, one of my kids looking out the window would let me know when water bubbled out the top for filling.
    this also let me use domestic water pressure to purge air from the lines during filling with the help of ball valves in the boiler loop.
  15. avc8130

    avc8130 Minister of Fire

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    Where is that water coming from? I could believe the horror stories if I lived somewhere with a sump pump in my basement...but I have to go 1/8 mile into the Earth to get enough water to drink.

    I'm actually not running the lines to my boiler. I'm running the lines to heat an out-building. I was hoping to run the 3rd line to bring year-round potable water to the building.

    ac
  16. rowerwet

    rowerwet Minister of Fire

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    clay pan or rock just a few feet down will cause it, a spring can as well. water in the earth is still a mostly unknown thing, just be glad it isn't running in the basement!

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