Within the IGSHPA closed loop design standards manual for pipe placement, section 2a.4, calls for buried GHP piping containing antifreeze and passing within 5' of any wall, structure or water pipe shall be insulated with minimum R2 closed cell. I am assuming this is because of possibility of surrounding ground formation freezing having an effect on these "structures" as result of the GHP temps going below 32? Which then may destabilize the structure, like a foundation footing? Within the IGSHPA closed loop install guide, for sizing and design, is stated that trench length is reduced as multiple pipes are installed in single trench. Within example #3 on page 76 I notice a ratio of 4 pipe/ft per foot of pipe or 225 trench/ft per 900 pipe/ft. As there is no 12" pipe separation inside trench for slinky install I wonder where I may find the applicable rule for trench reduction per coil? If there is one?
Yes, you freeze the water in the ground which expands and damages adjacent structures such as a wall or footing if placed too close. IGSHPA has a specific manual for slinky style closed loops - Slinky™ Installation Guide(#21050). Your question might be better answered in that document.
I signed onto the Looplink program and have appt with a tech on Monday. As I already have heat/cooling loads figured tech tells me I can go right to the loop configure. And really great news in my extreme case I'm told there is provision for "STACKING" of slinky, taking into account reasonable distances! This is great news! I'm hopeful I can satisfy the heating load of 3.5 ton with slinky, with the available area around foundation, without going to expensive borehole! We'll see.
You won't be able to model your application very well. Heat travels through the ground in predictable fashion. One of the things adding complexity in your case is the house wall shielding heat being transported to the pipe from the direction of the house wall. All you can do is simply putting as much pipe in as it fits. pipe is cheap, and you have a relatively small load.
Yes I agree. And then to run test for capacity after startup to see how much borehole I'll need to reach 100%. A question for you....will the lowering of ground temp immediately surrounding slinky coil cause the relative higher area temp (55*) to advance faster toward coil as coil temp is lowered? I think the term for fluid temp differential transfer is osmosis? Also, the greater the differential the faster the transfer? That could help! I wonder if there is a chart for this, for variety of soils? Charting temp differential over time? And rates of transfer? So to stack two coils (with distance between) drawing down temps in winter may escalate the migration of warmer surrounding ground temps faster, as opposed to one coil? I think you're saying that there is little downside to packing the pipe in. Definitely prepared to do that. Yes the foundation wall will be the impediment for transfer for one side. I'll depend on transfer from below and two other sides. I got that.
Osmosis: a process by which molecules of a solvent tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one, thus equalizing the concentrations on each side of the membrane. It has nothing to do when is going on in the ground in geo. The pipe is not a membrane, and molecules do not penetrate trough it. How do you run a test for capacity after startup? You don't know what your seasonal load is, and how you ground behaves, until after a full season. Do you do A/C with the system too? The energy taken out of the coil is a constant, and therefore out of the ground, is determined by the heat pump as a function of your house load. Yes, on start up, you immediately drive you loop temp down, and the soil immediately next to the pipe. Then it depends on how much heat the ground can transfer to your pipe to make up for it. NO! A higher delta T is not good, since it indicates that the load of the house drives down the temperature in the pipe and in the surrounding soil. This simply means that the ground cannot transfer heat fast enough to the pipe, so the delta T (temp differential) increases automatically to compensate, until it is high enough to suck enough heat out of the ground. Forget charts, you need to understand where a higher temp differential is coming from. It happens automatically when the ground cannot keep up with transporting heat towards the pipe.
The second sentence tells me that the "rate" of heat transfer from ground to pipe can be variable, depending on Delta T. And if higher Delta T continues over time, the surrounding ground formation temp would be lower. Delta T being a "lower" temp in this case? Until it is "low" enough to suck more heat out of ground? Where I'm going with this....if I have TWO slinky coils stacked, putting greater load on surrounding ground formation, would this ramp the "rate" of heat transfer through ground to pipe, that would otherwise not happen with only one coil? Giving me more capacity at faster rate than I would otherwise not have with one coil? I don't know how to say this any better. I'm trying to justify a "two-coil stacked" install for greater increased benefit. I also used wrong term regarding measuring capacity. I do understand a full seasonal load has to be obtained, for both heating and cooling, to do this. NOT upon startup!
No, the amount of heat transferred from the ground to the pipe is pretty constant. It depends on the house load and the efficiency of the heat pump, among a few other things. If the ground cannot transfer enough heat to the pipe, the ground close to the pipe gets colder faster, which drives up delta T. Delta T being the temp between the fluid in the pipe and then ground. Yes, temps get low enough to suck more heat out of the ground. Yes, two coils would result in more surface area for the heat transfer to occur, plus you would connect to more volume of ground, thus reducing the delta T and increase the amount of ground the pipe is connected to. This will not double the heat capacity, since soon or later they will steal heat from each other, but you get much more heat transfer than from just one pipe.
Your statement about loading the ground with pipe has got me thinking. Thoughts go to looking at the treed slope from street below to top flat area (100' run). Now considering directional boring in addition to slinky at top. This could place pipe at 20' below grade (trees) average. Slope is approx. 55 degrees. Any familiarity with this? What kind of separation would I need between each bore? With this depth do you think the trees would be affected? On a per foot basis, is slinky coil more efficient than a two pipe with u-bend in borehole?
With a 18" pitch slinky, you get about 600ft of slinky in a 65ft trench and run the tail back to the header pipe. In our area, you need 7 trenches of 65 ft to get the same capacity out of it like a 500ft borehole with highly conductive grout. No trees will unlikely be affected by the boring 25ft below. But I don't get it. Why don't you drill a single 6" hole somewhere (at the street below?) and run 2 pipes into your house somehow? And move on with your life!
I guess I needed to run all the options and numbers to arrive at costs, which I think I'm there now. Would the 500' borehole serve the 3.5 ton heating load? What size pipe would I need? Larger diameter better? Would two 250' bores be better or not? I would have access from neighbor adjoining driveway for a drill rig at rear (top) of property. If your answer above in the affirmative then next step is shopping for price from drillers.
OK...this is advise over the internet. I do not know your grout conductivity. Usually, in my area, 400-500 ft with 1.0 to 1.6 conductive grout, and 1.25 -1.5" pipe, supports a 4 ton load. I prefer a single borehole, which give your space constriction, should help.
