This isn't technically Wofati, but since it's using a lot of the same physics, I thought you people might be able to help shed some light.
I'm wanting/wishing to run geothermal lines under my courtyard (1500 sq ft) as it is built. I'm not looking to heat or cool the courtyard itself, but since it will be a high traffic area even in the dead of winter, I'd like to offset the temperature of the stone floor
enough that you can comfortably walk barefoot on it in the summer, and have it be mostly free of snow and ice in the winter. We're talking a very simple setup with one coiled loop of plastic pipe buried 10-12 feet under the courtyard, and another buried maybe 6 inches beneath the surface, hooked together by a simple pump.
What I'm trying to figure out is, is the math even there? In reading other geothermal forums, the general consensus seems to be that geothermal is insufficient for ice melt, due primarily to much higher
energy level required to change from ice to
water. However, intuitively, it would seem like, if I took all the energy that was baked into a square foot of stone during a day in the middle of July, and relased it in a day in the middle of January, that seems like it would be enough to keep the stone free of ice and snow, at least most of the year. However, I don't truly understand the maths involved. Can I store all or even most of that energy for that long? How much earth battery would I need to store all that? Most geothermal people start their calculations with how fast you lose your heat in your house. Obviously, for an open air courtyard, that's going to be pretty high. But their assumptions are also that A) you want to maintain a stable, comfortable temperature, which I don't, and B) that you're using a heat pump to compress the heat out of the water and distribute it to the air, which I'm not, and C) that ice melt needs to happen fairly immediately, whereas I'm perfectly happy if it needs to take 12 hours or so.
My scenario is this. I'm in upstate, NY, so, for example, this last winter we got probably 6-8 decent snowfalls around 6 inches each, and one that was 30 inches of snow. This is fairly typical. Winter temperatures usually bottom out around the 0-10F range with a 15-20 below zero event happening once every few years. In the summer, it's typical to see 90-100F in July and August. I have a beautiful, 27 acre property that is all gentle southern slope. I think I have a pretty high water table, and there is a natural spring maybe 200 feet uphill from our build site. Soil is pretty decent. The entire property was young forest when we got it, and
cattle pasture 40-50 years before that. So we've got a middling clay/sand mix and a lot of organic material in the soil. The courtyard will be surrounded by half-buried buildings, mostly heated, most in the hundred sq ft range. I can and will probably want to extend the umbrella out beyond them as well, possibly offering additional protection to the courtyard. Where there aren't buildings, there will be a 5-6 foot wall surrounding the courtyard, so hopefully wind scrubbing will be reduced.
It seems to me that my challenges are two-fold: 1) Can I hold the heat from summer into the winter? Especially if the water table wants to creep up into my battery? (For what it's worth, the ground is always most saturated in the Spring, and in the Fall the water table drops considerably, even sometimes drying out the natural spring for a month or two.) 2) is there any sense in trying to insulate the bottom coil to help retain the heat I'm depositing? I'm not sure I could ever afford to do that anyway, but if I could, would it be worth the effort and expense? 3) Can I effectively transfer the heat if the stones are just going to radiate it right to the atmosphere? Is this a
project that requires careful, thoughtful design? Or is it a lost cause that the math just doesn't support?
Or is there another approach entirely that would be more appropriate?
