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Question DetailsAsked on 1/13/2014

Anyone have any experience with geothermal systems?

We are interested in replacing our expensive and dirty oil forced-air system and replacing it with geothermal for heat, A/C, and hot water. I've been doing a lot of research about it, and have concluded that the success of it depends a great deal on proper design - not just good installation. Has anyone had a recent experience in retrofitting a house with geothermal? Did the installer design it, or did you have a separate consultant/engineer? How did you choose someone?

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Ylekiyot makes good points - others to note:

1) provide for high-volume water pipe flushing capacity and connections for servicing.

2) be realistic on the heating expectations - manufacturers get way too optimistic on how low a temperature your system will handle, commonly because they base it on still air calcs so when a wind blows your house heat loss goes way up, but your heating capacity stays as sized for still air.

3) do some good research on maintenance costs - the things I have read (and run into on several commercial power scale systems I have worked on) indicate 2-3 times normal system maintenance costs.

4) regardless of what the calcs say, have a substantial alternative heating source if your area ever gets below freezing - because a system failure not only freezes up your house, but also the geothermal system pipes - NOT good.

5) be sure to get ground corrosivity tests early on if planning metal heat transfer pipes - a number of areas have such corrosive (natural or sewage contaminated) ground/water that you have to install either special piping or stainless (if running a high-pressure system as several are), bumping your cost way up.

6) be sure what your contact conditions at depth are - I have seen home geothermal systems assuming the heat transfer pipes in the well were submerged in groundwater, only to find the water table periodically dropped (usually in winter) below the pipe level - so transfer efficiency went to air versus water conductivity - a tiny fraction of design capacity.

7) don't do what I have seen in print several times - putting ground thermal energy system (as opposed to groundwater) heat transfer pipes under the house slab - not only almost impossible to repair, but in heating season you are cooling your floor slabs, and in summer you are heating it - just what you don't want to do.

8) don't forget frost burial depth for pipes to/from heat tranfer zone - I can tell you, frozen pipes do not work well, and hard to thaw out, especially if plastic so steam cannot be used aggressively.

9) make sure designers figure ground thermal balance - I have seen even commercial systems designed assuming the ground temperature will stay constant over the years, when in reality you may significantly change it with the system. Generally you do not cool it much or hurt things much that way, but in hot climate you may be dumping a lot of heat into it, increasing the ground temperature a lot over the years, which of course reduces efficiency.

10) make sure to check permitting requirements - some states and areas are starting to require permits for geothermal installations, and almost all localities require well permits.

11) be sure you have a local long-term company capable of servicing it - I have heard of high-end heat pump systems installed in way out of the way places, including on remote islands or in the woods, and then having to wait many dauys and then pay a repairman many hundreds of dollars just to get there.

12) I have been involved in various capacities on 6 commercial geothermal power or heating and probably about 30 individual building heat pump geothermal projects, and have yet to see one tht even came close to having economies equal to alternative power sources without severely biasing the input - and that includes systems where cost of electric generation fuel exceeds $10/gal, so don't go into this expecting to save money, even if you live there 30 years.

Read other comments, including some on economics, in the Home > HVAC questions and answers in Browse Projects at lower left.

Answered 6 years ago by LCD

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You can use the same company if they have a certified designer and installers on staff. In most cases you do not need to hire an engineer. Sometimes the engineer has less experience designing geothermal systems than a certified designer. Same as any other heating system you want to make sure a proper heat loss/heat gain has been. Not sure where you are but you could look at IGSHPA or CGC for qualified individuals.


Just do not undersize the loop or heat pump. Two most common problems.

Source: www.mercurygeothermal.ca

Answered 6 years ago by ylekiyot




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