Ground-coupled heat exchanger

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  #1  
Old 12-20-2019, 07:21 PM
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Default Ground-coupled heat exchanger

There is a lot of discussion on TOTV about putting solar panels on the roof, but does anyone have experience of using a ground-coupled heat exchanger?

To explain: "A ground-coupled heat exchanger is an underground heat exchanger that can capture heat from and/or dissipate heat to the ground using the Earth's near constant subterranean temperature to warm or cool air or other fluids for residential or industrial uses."

I should have thought that the relatively high water table in TV would make the use of one quite efficient, saving a lot of electricity when heating/cooling one's home.

Thoughts?
  #2  
Old 12-20-2019, 09:54 PM
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IMHO, I agree with you, and I was quite surprised that these are not the standard here, we had these back up north. I am hoping someone with HVAC experience can provide reasons for not using a ground sourced HVAC system. While the installation cost is higher (burying the heating/cooling loop), there should be a significant savings on the electric bill.
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Old 12-20-2019, 11:22 PM
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When building a previous home, not in The Villages, we got a quote on a ground source heat pump (Water Furnace). The system would have required 4 bore holes 250 feet deep for the closed loop heat exchange. We also considered an open loop system using well water. The payback was pretty far out. Another concern was the lack of multiple vendors - there was only one in our area and I prefer to have multiple sources. We went with a high SEER air source heat pump.

For The Villages, the high upfront costs, long payback period, lack of installers, and possible installation issues with the small lots are all impediments. If any builder around here was going to install ground source heat pumps it would be Green Key Village and they aren't doing it.

Quote:
Originally Posted by Arctic Fox View Post
There is a lot of discussion on TOTV about putting solar panels on the roof, but does anyone have experience of using a ground-coupled heat exchanger?

To explain: "A ground-coupled heat exchanger is an underground heat exchanger that can capture heat from and/or dissipate heat to the ground using the Earth's near constant subterranean temperature to warm or cool air or other fluids for residential or industrial uses."

I should have thought that the relatively high water table in TV would make the use of one quite efficient, saving a lot of electricity when heating/cooling one's home.

Thoughts?

Last edited by biker1; 12-22-2019 at 09:05 AM.
  #4  
Old 12-21-2019, 07:20 AM
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Quote:
Originally Posted by biker1 View Post
When building a previous home, not in The Villages, I got a quote on a ground source heat pump (Water Furnace). The system would have required 4 bore holes 250 feet deep for the closed loop heat exchange.
Thank you, Biker.

The system I am envisaging is one with pipework (shaped like that on the back of a refrigerator) buried just a few feet underground, where the soil temperature still remains almost constant throughout the year.

It may be that the lots aren't big enough to lay sufficient pipe, or maybe one would have to go deeper in Florida, but I am hoping someone has already done some research on this.
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Old 12-21-2019, 07:55 AM
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Yes, a horizontal closed loop is another option. The company that gave me a quote only had experience with vertical loops. If you are serious about this then I would start looking for vendors and find out if it is feasible, what the cost would be, and how far out is the payback. One advantage of the ground source heat pumps is that they typically have a longer lifespan than air source heat pumps, particularly if you live in coastal areas.

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Originally Posted by Arctic Fox View Post
Thank you, Biker.

The system I am envisaging is one with pipework (shaped like that on the back of a refrigerator) buried just a few feet underground, where the soil temperature still remains almost constant throughout the year.

It may be that the lots aren't big enough to lay sufficient pipe, or maybe one would have to go deeper in Florida, but I am hoping someone has already done some research on this.
  #6  
Old 12-21-2019, 09:24 AM
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The systems I saw were actually a series of looped loose coils that were buried in sand and covered in sand, a few feet underground. Depending on the 'tonnage' of the system the number of loops would be adjusted. As I recall the loops were a flexible PVC, like the type used in the irrigation systems here. All were connected in parallel to common input and output headers that went to the compressor unit. I think there were valves on each loop in case of a leak so that loop could be isolated.
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  #7  
Old 12-21-2019, 09:40 AM
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Quote:
Originally Posted by Arctic Fox View Post
There is a lot of discussion on TOTV about putting solar panels on the roof, but does anyone have experience of using a ground-coupled heat exchanger?

To explain: "A ground-coupled heat exchanger is an underground heat exchanger that can capture heat from and/or dissipate heat to the ground using the Earth's near constant subterranean temperature to warm or cool air or other fluids for residential or industrial uses."

I should have thought that the relatively high water table in TV would make the use of one quite efficient, saving a lot of electricity when heating/cooling one's home.

Thoughts?
I did a Google search on "geothermal heat pump florida", and there was a lot of info, several dealers in the area, and some discussion about cost, these then to be much more expensive, but much longer life, and much more efficient.
Also, while thinking a little more about this, tree roots are an item that probably needs serious consideration with these systems.
The other option I saw back up north was a well system BUT the wells were closed loop. In this case each 'well' was a sealed vertical pipe that was installed in a standard well shaft, with a thermally conductive fill one the outside. Enough were installed for the required tonnage of the system.
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  #8  
Old 12-22-2019, 07:51 AM
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several feet below grade, isn't the earth's ambient temp's always the same ? absent frost, of course, but even 2' below frost line, temp should be 65f +/-,,, this link may be helpful
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Old 12-22-2019, 08:51 AM
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There are a number of ways to implement the pipes in the ground:

- deep bore holes (a few hundred feet) with pipe up and down. This is a good approach when you don't have a lot of land.
- horizontal pipes a few feet down over a fairly large area.
- circular coils of pipe about 6 feet in diameter in holes about 10 feet deep. I only saw one install of this type so I am recalling the dimensions from memory.
- pipes can also be installed in a nearby lake.
- if you have well water then you can run well water through the heat exchanger and then dump the water back into the ground or a lake.

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several feet below grade, isn't the earth's ambient temp's always the same ? absent frost, of course, but even 2' below frost line, temp should be 65f +/-,,, this link may be helpful
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Old 12-22-2019, 09:45 AM
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Geothermal systems are becoming much more common but they generally do require a "significant" amount of real estate and you often cannot build anything over the top of them (similar to septic fields). You'd probably have to talk with an installer to see if you have enough property to effectively use one of these systems but per the attached reference Florida is one of the locations where these systems are most common. My experience is these are very good solutions.

5 Things You Should Know about Geothermal Heat Pumps | Department of Energy
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Old 12-22-2019, 01:14 PM
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We installed a geothermal system in Pa with vertical closed loops. Depth was 220 feet. The horizontal system would have covered a large area plus, as stated, would need to be careful not to put anything on top of it. With the federal tax credits and the 1% financing by the State and the savings by not having to replace our oil burner total cost was around 7K. Without those three things I would not have been able to cost justify the changeover. The folks who bought our house told us the geothermal system was what convinced them to buy and they did pay more for our house then others that were available. Of course that comes under the find the right buyer project.
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Old 12-22-2019, 04:06 PM
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The last house we built in Maryland was custom and I demanded Geothermal which was rare at the time. Had vertical loops.
But. the ground there was heavy clay not sand and we had longer period of cold weather. It cost $12K extra, but it was comfortable warm heat not the cold air from an air source heatpump like we have here. It was worth it.
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  #13  
Old 12-23-2019, 09:55 AM
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You don't have to bury the pipe very deep as the soil above is a good insulator - I have seen 1.5 to 3 metres quoted, 40 metres long, and PVC is as effective as metal

Just be sure to check for other buried pipes/cables before digging
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Old 12-23-2019, 11:31 AM
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Quote:
Originally Posted by Arctic Fox View Post
You don't have to bury the pipe very deep as the soil above is a good insulator - I have seen 1.5 to 3 metres quoted, 40 metres long, and PVC is as effective as metal

Just be sure to check for other buried pipes/cables before digging
I would question that as it's not insulation that's important, it's heat dissipation and that requires distance and consistent temperatures while the slurry circulates. When I got the (3) competitive bids on our system all recommended closed loop at least 200' deep. While the shallow loop system is effective it significantly limited what could be done with landscaping and trees and patios etc.
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  #15  
Old 12-23-2019, 12:15 PM
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For those of us who have pools, why can’t I use it for a cooling source? I would like to put that house heat into my pool water - MUCH more efficient that trying to dissipate it to the hot air in the summer!

The only explanation I have found is that the pool companies are different than the A/C companies.

A GOOD A/C company should give you options.
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