Quote:
Originally Posted by Spiv
Since I will start from scrap, I was thinking to install the slinkies below the ground floor slab.
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OK...
The principle of Ground Source heating is that the heat ultimately comes from the sun, and that heat that is held in the ground, is harvested for use in our home.
There is a component of the overall ground heat that comes up from deep in the earth, and usually, the deep earth-thermal energy is small. In general, it is safe to estimate that 97% of the heat energy in the ground is directly from the sun, and 3% is from deep thermal.
Only in very rare situations, does the majority of the heat come up from the ground, due to thermal flow. If you are lucky enough to live in an area where hot water springs are very close to your build, then that source can certainly be harvested.
If you had a bore hole drilled straight down, and water circulated in pipes in the hole, this thermal well would pull in heat from the earth that is surrounding it. Heat moves very slowly in earth, but if you were able to visualize the heat movement, you would see the greatest movement closest to the bore hole, and progressively slower movement, farther away. For practical purposes, you could imagine this movement out to sixteen feet away from the bore hole. In truth it goes farther, but has tapered off so much that it would be considered to be not important. In some areas, such as very frigid areas, the useful diameter is considered to be even larger, as much as twenty-five or more feet. Where I live, a bore hole of 225 feet depth will yield a Ton (12,000 BTU/hr)
So for simplicity, you could imagine that your bore hole is a cylinder, with a radius of sixteen feet. If you place another bore hole sixteen feet away, both thermal wells will be competing for the same heat, but generally, sixteen foot bore hole placements are considered to be OK.
If you have a horizontal pipe, buried in the ground, you have the same situation, but the closer you are to the surface, the less remains of the cylinder.
Slinkys are highly redundant, but they are easy to put in, and overall, they have been proven to work. Where I live, to get a Ton of heat (12,000 BTU/hr) using a slinky configuration, will require an 80 foot long trench buried at least six feet deep. I know from my own measurement, that some of the heat come from rain.
Even with a slinky installation, the same 'cylinder of heat' model of extraction exists. And it is still true that the heat ultimately comes from the sun.
So, my questions for you are,
- If you build your thermal slab on the top of a slinky field, where will the heat ultimately come from?
- Will the slinky field suck heat from your thermal slab?
Best,
-AC_Hacker