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Posted by Reinhard on February 19, 2008, 7:44 pm
> Here's what I'd like to do:
>
> Run well water through a geothermal heat exchanger and then discharge
> the same water into the yard and eventually into a pond.
>
> I prefer not to go underground and below frost depth with discharge
> pipe.
>
> I would like to simply have water discharge above ground. How can
> this be done without discharge pipe freezing?
>
> My first thought is a antisyphon device similar to what's on outdoor
> spigots.
>
> Discharge pipe is 1".
>
I assume you intend to run a pipe all the way to the pond above ground.
If the pipe does freeze it likely can't be thawed until spring so you
would need a backup system or you would have no geothermal heat or a huge
mess wherever the discharge ended up. Potential for very expensive damage
both within the house and outside of the house is very high without a
backup system. Note backup must be totally independent of the first
system or it would just fail same as the first system. Designing for cold
system water flow is a huge engineering challenge. A foolproof system
would cost a lot more than just burying the pipe in the first place.
You would have to insulate the pipe no matter what or it would freeze if
you get cold like we get.
Could you run the flow into a pipe that was large enough to flow under
gravity alone? 3 or 4 inch should do it if you have a reasonable slope.
Design this so that it would drain empty between cycles and the heat
trace could be routed into the pipe from the top - maybe from the top of
a tee that was a few feet long to prevent overflow. Then the heat trace
would only have to heat the inside of the pipe and not the outside air.
The geothermal system lowers the temp of the discharge water as it sucks
the heat out of it and so you have very little heat left in the
discharge. The installer set my geothermal system flows so that the
discharge water was at 38 F which gives a bit of safety factor against
freezing within the heat exchanger. It leaves a very poor safety factor
against freezing in a surface discharge pipe.
If the water cools to freezing temp before it reaches the end of the pipe
it becomes frazil ice - small super-cooled ice crystals - that
consolidate into solid ice almost instantly and in difficult to predict
locations. the system could seem to run fine for a while and then on a
cold night it could instantly solidify.
Use PE pipe because it won't split if it does freeze.
Your perfect solution, but very expensive is insulated PE pipe that has
heat trace inside the insulation already and could run a a pressure
discharge. Last time I looked, many years ago, the cost was $5 to $15 per
foot. There are many water systems up north using this pipe and most are
barely buried or are buried within permafrost.
How would you keep the pond from overflowing or the ice buildup from
getting out of hand?
It gets very cold up here in central Canada and I have seen some water
pipes that were left running all winter to keep them from freezing. Only
works if the huge ice pile that results can be located where it does no
harm. very expensive to waste that much water. In your case running the
well pump all winter would only cost a couple of hundred dollars extra
over letting it just cycle when the house thermostat calls for heat.
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