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Originally Posted by AC_Hacker
The best source of info I have found is the IGSHPA book, "Closed-Loop Ground-Source Heat Pump Systems: Installation Guide". It's not cheap, and I wasn't able to find a copy that was used that was much more reasonable.
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I just had the opportunity to be in a Ground Source Installers class (the engineer who oversaw our project was the teacher), and I was able to borrow the "Installation Guide" since it was the main textbook for the class. I haven't given it back yet, so if you want me to look up anything let me know. I voice recorded the class as well, so if there's anything from that you're interested in I can try to find it. I'd post a transcript, but it's more than 2 full days of teaching (3 days total, minus installer test, and fusion hands on and tests), and I don't type all that fast.
Quote:
Originally Posted by AC_Hacker
What I've been able to determine is that there are different ways to get the Ground Source heat. Some are cheaper than others. ranking from cheapest to most expensive goes something like this:
1) Closed Loop Pond
2) 'Open Loop' pump & dump systems where you take water out of an aquifer and dump it back to the aquifer or to a river or use it for irrigation.
3) Trench type systems using a 'slinky' arrangement or a linear pipe arrangement.
4) Closed-Loop boreholes.
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I'd never really liked the pump & dump idea before, seemed like it had the potential to be a waste of good drinking water. In the class he mentioned (I don't recall if it was per ton, or for a regular house (3-5 tons)) per year a pump and dump will use well over a million gallons of water!!!!
One generalization was for X feet of borehole, a horizontal trench system will use 3X feet of pipe. (need to take another look at that: did they mean feet of borehole or feet of pipe in borehole (ie 2X: down & up)). In the IGSHPA book there are examples of multiple pipes in horizontal trenches: you need more pipe overall (vs 1 pipe per trench), but less trench total. (though it's not double the pipe half the trench length--since the 2 pipes close together interact)
Quote:
Originally Posted by AC_Hacker
Sizing the loop field is a matter of knowing what your building heat load is and knowing what the thermal transfer characteristic of your particular soil is. On the other blog, I set out how to test your own soil to determine what your heat transfer rate is.
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Per the class, determining the building heat load is the first and most important step, because everything else hinges off of that: the inside units and the size/configuration of the outside pipe. Too little outside pipe and the water temperature won't stay stable, too much and you've overspent on boreholes and pipe.
Interestingly, while heat transfer plays a big role, since a "proper" test costs around $5000 (though that can be rolled into the install since there'd already be that borehole dug), it's not normally done for installs under 25 tons or so. Instead, they assume ".9" (mid to lower end, I think) for the calculations.
The other main issue, is grouting the boreholes after the pipe is placed: this helps couple the pipe with the ground to get the best heat transfer, as well as prevents aquifers from being contaminated by ground or close to the surface water.
Quote:
Originally Posted by AC_Hacker
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Links are dead for me: they go to error pages.
Oh, and I have some pictures of the install I was working on, if anyone is interested.