Hi guys. In 2002, I got a quote to change my home heating system to a Geothermal system. I'm in one of the coldest parts of the Continent. Tonite we'll be at -32C (-26F). The only other thing besides the breakdown of the quote that I remember from the estimator, was that below the frostline, the earth is at 55 F degrees.

The quote broke down like this:
Drill 14 50-foot holes down 10 to 12 feet apart: $6,000.
Drop down the U-shaped 2" PVC tubes and fill them with Anti-freeze: $4,000
Supply and install the Heat Exchanger: $5,000
Supply and Install the new ductwork: $8,000

The one that bugged me the most was the heat-exchanger. It had a 10 year warranty. Today, 6 years later, the same unit is at $8,000. What will it cost in 4 more years?

Well, I came up with my own idea:

Dig down (12 feet down) the full width and depth of a double garage: $3,000

Setup insulated and water sealed concrete forms with 18" columns spaced 4 feet apart and capped off with a concrete 'roof' 12" thick and also insulated, 6 feet from the bottom concrete floor (Sealed concrete bunker type), so that the top is 6 feet below ground. At -50C (-58F), the frost line would be at most at 4' 6" down. Fill the bunker with round field stones for heat/cool storage.

Next run solar heat from roof mounted dual pane heaters and push that into the bunker during the winter (80 F during winter, on a cloudy day), 400 F during summer). During the summer we just wouldn't push the solar heated air into the bunker. Instead push the cool air from the bunker into the house.

My heat exchanger? 2 24" industrial fans (2 HP variable speed 240 VAC) - one for exterior air into the bunker, one for pushing the bunker air into the house ducts.

Two 8" ducts into the garage to heat it up during the winter from the bunker - closed in summer.

Total installed cost:
Excavation: $3,000
Concrete work: $10,000
Fans (my heat eschanger): $400

Total cost: $14,000

Future replacement costs: New fans every 5 years? $500?

Operating cost over 7 cool and cold months?: $10.00 per month Hydro. But the car won't need to be plugged in for the block heater.

The other system would have cost me $1,000 every two years to replace the antifreeze, plus higher hydro costs to run the compressor in the Heat exchanger.

Anything wrong with this picture?

 

I should have added that I want it that big to handle the air turn-over of 6 times per hour for the basement, and two upper floors. That's the recommended frequency, since our homes are closed up for so long during our cold season(s).

 

Without giving it too much thought, I see a couple of problems here. You say that at -58F the frost line would be at most 4' 6" down. That may be true but that doesn't mean that just below the frost line the ground is warm. It just isn't below freezing.

You've only got a six foot thick layer of stone to store heat in and only heating it with 80 degree air. Stone is not a very good thermal storage medium, there isn't much of it and you're not heating it very much. The heat losses will be pretty high.

In the summer time how is the stone going to get cool? All that insulated concrete surrounding it will prevent much heat from conducting out of the "bunker" and into the surrounding earth.

Even if you could keep the stone cool, what about the humidity? Warm humid air being drawn through the stone bed will give up it's moisture. You'll need a way to keep the bunker pumped out. And again, at that depth the ground won't be THAT cool.

I think a lot more engineering is needed here. $14,000 is a lot of money to spend on an unproven idea. At least the geothermal guys are working from a past proven concept.

 

All good points to ponder. Thanks. I'll see if I can comeback with answers and repost.

 

I didn't see the cost for the roof mounted dual pane solar heaters in your estimate.

I'm in agreement the bunker won't hold enough heat. I'm pretty sure the Geothermal industry has ruled out such a concept, otherwise they would be selling more systems due to the lower cost.

How would your solar energy help at night? If your just worried about the daytime and are willing to invest that kind of money why not look into a solar panel set up to run heaters? With an inverter you could also use it to produce electricity during the warm months.

 

I've built the Dual-Pane panels before for a green-house operated year-round in Central BC. Used windows, some paint, hardware, a couple fans, PVC ducting. Maybe $600 to $800.

I can't agree or disagree with your comments because I haven't had a chance to go through my math. I do know that using Stones to collect heat mass has worked in Green-houses, above ground. Below frost, the earth does stay warmer and if the garage is on top of the area, properly insulated and air-sealed, that has to add a bit more insulation value to reduce the exposure for the earth mass below, including the bunker. I haven't given up on the idea.

I can why the Geothermal Industry hasn't pursued it more, because they are usually called in to build AROUND the house, not under it. How much warmer is the earth under a basement floor?

I'm going to talk to a couple of folks at the U.of M., that I met at a home show a couple years ago, and see if they can help out with the calculations, too. Thanks for the comments.

 

I don't know much about the Geothermal systems other than what I've read, but I do work in the construciton industry (commercial not residential) The Geothermal systems I have seen going in on new buildings were always installed by drilling all the holes.

I also don't know if the radiat heat off the stones would be enough to to provide sufficient ducted heat. Of course this is all speculation on my part from a part of the country that never sees temperatures anywhere near that.

Good luck with your project.

 

Thanks. Is it not in use in Texas to replace AC, or does it not prove cost-effective?

 

We received a quote on geo thermal 2 years ago and we were looking at 12-14,000. the company here in Indiana uses a horizontal boring machine to install the lines, they bore multiple lines at a given depth and dig down on the ends to connect the lines forming loops. We opted for heat pump with electric back up and use our outdoor boiler for the primary heating of the house and water and rely on the heat pump while out of town.
We installed the boiler 5 years ago and still have not ran a set for the garage, I currently heat the garage with a salamander.

 

Yes it's used down here for cooling, and heating the 2 months we need it. It's been cost prohibitive because energy used to be cheap. With higher gas & electric rates the payback period is becoming shorter

 

Geothermal systems still use a heat pump. Heat pumps don't work at low temperatures, so the geothermal liquid, which is theoretically 55 degrees, provides enough heat for the heat pump to work. It basically extracts and concentrates the heat. If you just circulate 55 degree water through a fan, you'll have 55 degree air. That's why the heat exchanger costs so much- it includes a heat pump. I love the idea of geothermal systems- they also cut way down on A/C. The efficiency can be as high as 36 SEER. But right now, they cost so much that it would take 20 years in energy savings to break even (at least with the system I looked at). Maybe as they come into wider usage, prices will drop. I've always wondered if you could build a system, based on a regular heat pump, and use geothermal wells to improve the efficiency. What would happen if you dug a hole 20' down and built a room for your heat pump? (I know, it would fill up with water!) Interesting stuff!

 

Love your signature Jay, we watch the Red Green Show re-runs up here, all the time!

My plan isn't really Geothermal, other than keeping the warm stones way below the Frost line. I would just have to augment their winter temperature from 55F to 73F using solar air heaters (We have more intense sunlight even with the cold.) My house is perfectly angled to get maximum solar value for about 8 hours during a winter day. And the new roof (French Mansard style, using Steel panels is also angled (15*) to tap the best solar refraction angle.) Mansard roofs look like a trapezoid from the side. We have a small city lot (35 X 75), and with an insulated (R52) greenroof, we can keep the warmth in far better, and grow herbs (my wife is Mexican and grows her own chilli peppers and spices) on the roof. Our walls are already R33, and the basement is R26 insulation.

 

If you drill 12 holes, 6" diameter, 50' deep, you'll have three times the surface area of a 20'x30' floor.

 

Thanks for that. Just downloaded your calculators. I'll give them a spin.

 

Actually, I stand corrected, it's only a touch over 1.5 times more surface area... plugged in diameter instead of radius. DOH!