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Mon Dec 3, 2012, 09:47 PM

In case you've never seen the hole for a horizontal geothermal field

This went in on our project today.

6--loops each 600 total feet long, in a trench 8 ft deep, 14 feet wide and 300 feet long.

Digging started around 7:30, trench was covered over by dusk (4:30ish). Ready for tomorrow's topsoil replacement, so the ag field it went under will be ready to farm in spring




On edit, this can't really be called frugal, but it'll be energy efficient.

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Response to HereSince1628 (Original post)

Tue Dec 4, 2012, 09:42 AM

1. I suppose if you dug that thing yourself, it might show some evidence of frugality!!!

It looks interesting, in any event...

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Response to MADem (Reply #1)

Tue Dec 4, 2012, 10:23 AM

2. Hopefully, the efficiency of the system in operation will yield savings

in the heating expenses.

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Response to HereSince1628 (Original post)

Tue Dec 4, 2012, 11:41 AM

3. I thought they were vertical and have never seen this.

How does it work?

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Response to cbayer (Reply #3)

Tue Dec 4, 2012, 12:38 PM

4. Vertical is usually just used when space is limited.

It's cheaper to dig trenches then to bore deep holes.

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Response to cbayer (Reply #3)

Tue Dec 4, 2012, 12:39 PM

5. It works pretty much as does a geothermal well...

...water with an anti-freeze in it is pumped from the field to the heat exchanger in the house--where its heat transfers to a refrigerant that when compressed releases heat...and cools the water--to a temperature at or just below freezing (iow the antifreeze isn't about being in the ground...but about the capacity of the compressor that is literally the heat pump. The space needed in the basement for the mechanicals is the same.

This field was about half the price of a vertical system of the same thermal capacity. Wells obviously fit better onto a smaller property.

People sometimes talk about geothermal without appreciating the potential size of 'the footprint'. When I first started looking into horizontal fields I was thinking about something like a large swimming pool not a fast food parking lot. The installers loved this site because it went under an ag field located on a drumlin (basically a low glacial hill of sand and gravel) that made the digging and backfilling easy...free of woody roots or boulders and freedom to pile the overburden. The entire footprint used during the install was the length of a football field and about half as wide.

This field will serve a three bedroom home with a full, heated basement...the house has ~2500 sq ft of heated/air-conditioned living space. Although it's built in southern Wisconsin, it's the building's 475 sq ft of south-facing solar absorbing glass and the potential for heat gain=cooling demand that actually pushed up the size of the system.



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Response to HereSince1628 (Reply #5)

Tue Dec 4, 2012, 01:00 PM

6. Sounds like a great system.

So, the system is entirely self-contained and has no emissions?

The only other system I have seen was horizontal and tapped into underground thermal vents. This sounds decidedly different.

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Response to cbayer (Reply #6)

Tue Dec 4, 2012, 01:05 PM

7. There are no local emissions. WE-Utilities requires a 300 amp electrical service

I think there is 1 nuclear plant operating in WI.

The nearest generation plant is a natural gas plant, but much of WI runs on coal.

on edit...the engineering specs for this application said 200 amp service was adequate as 80 amps is the typical 'hard start' demand, BUT, long runs of constant heating in very cold weather (-15 and lower...) tend to refrigerate the ground around the field making it unable to keep the home warm...the back-up built into the system by the manufacturer is classic electrical heating coils which have tremendous electric demand.

The house as constructed has wood (the house comes with a woodlot) set up to be a supplement in such periods. Hopefully we would never have to see a heating bill based on old-fashioned electrical heat.

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Response to HereSince1628 (Reply #7)

Tue Dec 4, 2012, 01:33 PM

8. I hope you will continue to post about the results as winter really sets in.

We are currently off the grid, but on a boat in a warmer climate. We have recently begun talking about a land based system that would replicate some of what we have now. Geothermal, which we currently can not employ of course, is an option we don't much about but should begin exploring.

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Response to cbayer (Reply #8)

Tue Dec 4, 2012, 01:46 PM

9. In the interest of frugality...the system may not go into service before mid-Mar...

The building is still under construction...so i won't heat until it's insulated, and that can't happen until the HVAC ducts are in place and the electrical is run.

That puts me on a timeline that would lead to a "hard start" in late Jan to mid Feb...typically our coldest weather ... I think I"ll try to avoid a knock-our-socks off electric bill as the place where record-keeping on it's performance starts.

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Response to HereSince1628 (Original post)

Tue Dec 4, 2012, 07:27 PM

10. Looks interesting.

I hope that it works the way you expect it will.

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Response to Curmudgeoness (Reply #10)

Tue Dec 4, 2012, 08:28 PM

11. The pic is the trench that holds a heat transfer system for a geothermal assisted heat pump

At the bottom of the trench are 6, 600 ft long loops of pvc tubing that will cycle water near ground temperature (here that means about 35 F at its lowest) to a heat exchanger in the house and then back to the underground system of loops.

The system works according to Boyle's Law...the short version of that is when a fixed volume of gas expands it cools, and when a gas is compressed it heats. If you have a compressor that runs air-powered tools you may have noticed that it gets HOT when it's compressing air but when you release the air the air that expands out the exit valve is cold. That's the phenomenon of gas physics called Boyle's law.

In a geothermal assisted heat pump, the water from the underground system of tubing exchanges its thermal content with a heat exchanger in the basement of the building being heated or cooled. In the winter water entering the heat exchanger from the ground warms the refrigerant (relative to outside air) and the refrigeratn expands. When that refrigerant is then compressed the heat given off can be used to warm the building, and the cooled water returns to the ground to be rewarmed.

In the summer, the heat produced by compression can be absorbed by the heat exchanger and 'dumped' into the ground via cooler water moving through the heat exchanger. The compressed refrigerant when allowed to expand cools and is used to air condition the house in summer.

In the summer it's works much like a refrigerator...you may have noticed the radiator coils on the back or bottom of a refrigerator you've moved. Although a refrigerator is used only to cool, it dumps heat into the room where it sits--you can feel that at the back of your refrigerator if it's easily accessible.

Unlike a refrigerator or an air-conditioner, a geothermal assisted heat pump can run in both directions heating in winter, cooling in summer. It also generates hot water year round.

The 'field' is used to exchange relative warmth (or coolness) with the ground. In the bottom of the field in the picture, aka the trench in the picture, now lay 3600 linear feet of water containing tubing that exchanges its heat content with the ground. This 3600 feet of tubing is the 'heat source/sink' for the system.

The economics of this type of heating depends a temperature difference between the air in the house and the temperature of the ground. It works out favorably because currently available energy used for heating (fuel oil, propane, electricity--but in Wisconsin not natural gas--not available at this rural building location) is more expensive than the electricity required to compress the refrigerant that "pumps" the heat out at the heat exchanger.

If global warming continues (and it should across my remaining life) this system will become more and more cost effective for this building in southern WI. Although the effectiveness of the system is challenged by prolonged cold periods below zero which can result in cold (heat stripped) returning water actually freezing the ground, climate change will make such now infrequent periods, uncommon or absent.

Estimates of cost of heating this building with propane on 2012 prices is $1500 and another $200 for cooling annually and another ~$200 for hot water (~$1900 total), with the geothermal assisted heat pump that yearly cost, depending on 'avg' weather, these costs could be $700-$1000 per year.

Hard to say if the economics actually works out until we get there.








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Response to HereSince1628 (Reply #11)

Tue Dec 4, 2012, 09:54 PM

12. Thanks, I love the details.

It leaves me with a few questions. Is it really possible to heat a house when the ground temp is well below the temp you need in the house? Can it really pull that much heat from ground that is (at the lowest) 35? Or will that require supplemental heat at that point? I have always been baffled by heat pumps, since I lived in Houston and had a heat pump----and cooled the house when temps outside were in the 90's. I only half understood it, but I did see it work.

Also, would the heat removed from the house in the summer have any affect on crops planted? Will it warm or dry the soil more than normal?

Fascinating system. You will have to give it a year of use and let us know what you think of it.

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Response to HereSince1628 (Original post)

Mon Jan 21, 2013, 12:06 AM

13. What did you dig it with?

I'll be installing this myself next month, still haven't gotten the cost of the digging nailed down. I want to rent a tractor with backhoe and loader, maybe a trackhoe, not sure yet.

I'm in a house I recycled, 1900ft farm house I bought and had moved here for 25k total, but the furnace is horribly inefficient, and there is no AC which just won't do in 105 degree summer heat so I settled on the geothermal for efficiency as well as a lot of upgrade on the houses insulation and such.

I already have my cost of living down to about $1200 per month, and half of that is mortgage and property taxes.

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