Geothermal heat pumps are powered by electric motors. A moment's quiet reflection will suggest to you that they therefore need electricity.
Now if we were really committed to being off-grid, self-sufficient, and other hyphenated adjectives -- and more importantly had another five grand or so lying around -- we'd generate our own geothermal heat pump power through photovoltaic cells -- solar cells to the masses. We'd have batteries to store the juice at night and for a week of cloudy weather, and an inverter to turn the juice into alternating current (household current, or AC power).This is not going to happen.
This being the case, our engineer had to make sure there were enough spare circuit breaker positions in our service box to handle the 240V heat pump, water circulation pump and fan motor. If there were not, the cost would go up to cover a new or expanded box.
Because of the ductwork running to the attic, we also needed to move some wall outlets. This led to an electrician getting zapped into a rather funky dance step from a presumably non-zapping (ground) wire. He suspects our circuit breaker box, which at one point in its history (ten years ago) had rainwater leaking out of it. This is generally not considered a good thing. It happens more often than you might think: when rain gets into a badly sealed power line conduit. Consequently the internal metal bars that carry electricity to the circuit breakers are rusty, and the electrician, understandably, looks askance at that. He also attributes another problem we discovered after he left -- no power in two bedrooms -- to that box. My former-electrician friend Meg and I suspect the zapping problem is actually because the previous homeowner did some funky wiring of a switched outlet. She further suggests cycling the circuit breakers off and on, and that fixes the bedroom power issue. The electrician proposes a $1200 service-box transplant. I propose to wait a bit on that.
Life in the Trenches
While flocks of ducts settle into the house and electricians do the funky chicken, work on the outside continues. The first part of this is pumping a slurry of Bentonite grout down the well hole, around the pipes. This ensures that heat transfers predictably to and from the earth, and tightly packs the pipes in the well hole. Bentonite is mostly a natural mineral that expands when wet, sort of the way modern diapers do, and goes from a slippery slurry to a cement-like grout very easily. It's also known as driller's mud. Similar substances are vermiculite (meaning, I believe, worm cellulite in Latin) and kaolinite, which is what makes Kaopectate so effective. Our drilling contractor had two guys with decades of experience... who were baffled when the slurry kept hardening in their pipe on the way down the well. After much theorizing about heating from the sun and several phone calls to the grout guys, a miniscule amount of a polymer added to the mix (like a tablespoon per 80 lb. bag or something) made all the difference.
The second outdoor project entails digging a trench 4' or more deep (to avoid frost), that runs from the house to one well and then to the other. The pipes will be laid in this trench, and plumbed so that half the water goes through one well, and half through the other.[picture or video of trench with pipes] The pipes are not-very-bendy plastic and they come in segments that are joined by heating. Judging by the enthusiasm of our piping people (well wranglers), the tool that heats the plastic is utterly fabulous.
There are two main pipes, one for the water to go out, one for it to go back in, laid in the bottom of the trench. Two holes are cut at that depth into the concrete basement wall, using a neat-o carbide-tipped coring tool, and the pipes run through the holes into the basement.
To keep water and mice from flowing* through the small gap between pipe and hole, the outside must be sealed with hydraulic cement. It's important that the cement goes on the outside so that pressure from groundwater in the soil pushes the cement against the wall and not out into your basement. Inside, the pair of pipes turns 90 degrees up the wall and across the basement ceiling to the heat pump. A fancy, flange-y looking panel mounted on a plywood vertical "service" board connects the two pipes to the heat pump. The service board also serves the electrical connections.
The grouting and the trenching both took about a day. Like many excavation projects, it takes two guys to do the work at any given time, two to stand around waiting for the first two to get done, and three or four other stiffs (including homeowner) to watch.
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