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geothermal options

Posted by mamabirrd (My Page) on
Wed, Jul 23, 08 at 16:27

I am building a new house and its time for heat/air system. With fuel prices im looking into geothermal. Trying to get an idea of what my options would be.

If it matters, the house is new construction, 2x6 walls, 2500 sq feet with a fair amount of windows.

I had a well drilled on the property for water prior to geothermal consideration, maybe this can be used as open loop? It is only the well, no tank or pump yet. If this is doable what are the water quality considerations?
I have the acrage to install horizontal loop, but my soil is very sandy. I have building experience but no geothermal. I have a backhoe :). I am in western pa and read copper dx system not recommended here cause we are too acidic. I dont understand this because copper is used for water lines in new homes?
What is likely my best option? I will call in an expert, I just wanna have some idea of the considerations before I blindly dive in. I am just starting to look into this so any advice at all appreciated.

thanks in advance, mamabirrds husband


Follow-Up Postings:

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RE: geothermal options

Not an expert in GT here but understand up north, GT is the way to go if you can afford the initial outlay. As I understand it, you need a number of dedicated wells for the GT system to work. The GT system runs pipe loops down and back up several wells, the number of which is determined by the installer. I think the acidic issue refers to the ground conditions attacking buried copper, not the action of your potable water eating the pipes from inside.


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RE: geothermal options

You may well be right that if you can have copper water supply lines that you can install DX as well. Have your soil tested. Even if it is too acidic, sacrificial anodes can be installed that would protect the copper ground loops. Speak with installers that do DX and ask for references of people who you may contact that have DX for at least 5-years.

A DX system will be less expensive to install, maintain and operate than an open loop well system. I have not heard of problems with DX in PA; let us know what you discover.

SR


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RE: geothermal options

I am thinking about replacing my old HVAC with a new Water Furnace geothermal system. My home is 3,700 sqft with unfinished basement at 600sqft that I will finish. I live in southern Connecticut and the house is a two story colonial. I know I want a single unit system with a 2-stage compressor and variable speed blower, and a back up electric heat pump. I have 2 estimates. Estimate 1 gave a heating load of 92,641btu, saying the Geo system could fully heat the house at ambient temps down to 27 degrees before the electric heat pump was needed. He recommended two 500-550 ft wells. Estimate 2 stated a heat load of 72,000btu, and the Geo system could fully heat the house until 7degrees, then the back up heat, and 3-300ft wells. Any ideas?


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RE: geothermal options

Dont like either but caller # 2 is who Id choose.

SR


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RE: geothermal options

SR-Thanks for your response. I have read through enough of these forums to know that you prefer DX systems, but have seemed to always add honest, thoughtful and sincere info out there. I too prefer #2, and not soley for the lower heat threashold. What don't you lilke about either? It's not a DX?


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RE: geothermal options

Hi Jules:

While I often prefer DX I do not in your case as you live in CT. Im not sure I would take the risk. Any properly designed and installed GSHP system will work just fine. Leaving DX out of the mix, no one ground (or lake loop) heat exchanger properly designed & installed, is better than any other. All varieties should provide efficient heat exchange for the design temperature and size of the system. What is ultimately chosen is determined by site-specific conditions at the location.

Heres what #2 is proposing, a 6-ton system drilled to a depth of 150ft/ton, 2-tons per borehole.

Heres the plan I suggest you follow. First, a Manual J-8 heat gain/loss calculation done on your home with a copy you retain. Its worth paying for. This should be done after youve done all the other measures such as caulking windows and doors, added insulation etc. as this will result in lower heat loss/gain and require a smaller, less expensive system.

Next you need to know all the weather (bin) data for your city. This will provide you with the system design temperature for your site and what outdoor temperature your system has to be designed for. Other important things are determined from design temperature, such as, how much antifreeze is required. This in turn affects a host of other things as well, which is why you need to hire a knowledgeable professional.

I would suggest a closed loop system, a minimum of 150ft ~ 200ft per ton of borehole to be software determined (I prefer 200ft). 3/4in HDPE pipe, only 1- ton per borehole, parallel configuration with properly designed reverse return headers. If you get that done right youll be well on your way to having a properly designed GHX.

The reason why all these contractor want to drill deep is for their benefit not yours! More than 1- ton per borehole (deeper) means less trenching & excavating, 3-boreholes instead of 6 half the trenching; easier and cheaper for the contractor. While it can work, it does not result in the most efficient GHX. Geothermal is all about efficiency. Deeper boreholes also mean larger (more expensive) diameter HDPE pipe, more fluid, more antifreeze, larger (more expensive pump[s]) etc.

As a professional geothermal designer/consultant its hard to overstate the importance of finding the right professionals in your area.

Good hunting,

Steve


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RE: geothermal options

Steve, is a DX system practical in Florida for cooling? I haven't heard of any installs in my area. Water source heat pumps were common for a while but declining water tables brought on a ban on those systems. I wonder if much could be saved here where cooling is the main issue and 'normal' air to air condensers are so efficient.


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RE: geothermal options

Steve, once again I see logic to your response. I agree, in an ideal world one 200' bore hole per ton, but I don't have sufficient accessable land for more than 3 bore holes. Most of my property is very rocky, steep mountainside woodlands, and terraced old New England farm rock walls. The frontyard has the septic and leaching feilds. Without digging up the driveway, the only available spot is about 60'x60' along the back of the house. Getting 3 holes is about it.

Curious, what did you mean about not risking DX in CT? I did look into DX, but the local contractor was not very responsive.


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RE: geothermal options

Hi,

"I am just starting to look into this so any advice at all appreciated."

I suppose that the GSHP might reduce your heat bill by half?
(depending on how fuel prices are where you are).

Just wondering if you have priced a package of more insulation, better windows, better sealing, passive and/or active solar, ... That would also reduce your energy bill by half. And, how does it compare with the extra money you would have to invest in a GSHP? And, how the the long term costs/maintenance would compare?

Gary


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RE: geothermal options

Re: garymunson

"Is a DX system practical in Florida for cooling?"

Since liquid to air geothermal is practical in Florida (after all Florida Heat Pump is in Florida) I dont see why DX to air shouldnt be practical. Dont take my word for it; you must do your own research. Contact the manufacturers of DX HPs and ask for installers in your area.

Re: jules

"The only available spot is about 60'x60'."

60′ x 60′ should give you enough space.

"Curious, what did you mean about not risking DX in CT?"

There quite a bit of discussion in one of the accreditation courses I took regarding serious problems with DX in CT. It seems that all the systems failed prematurely due to acidic soil eating away at the copper ground loops; they all had to be abandoned. This was quite a while ago, perhaps 20 years ago or more. While the geology hasnt changed, the industry has matured. The copper ground loops can be protected with the installation of sacrificial anodes along with the copper pipes. I would want some pretty serious guarantees before installing DX in CT. It may be that this applies only to certain parts of CT, but again the burden falls to the purchaser to do their homework. Personally, if I lived in a questionable area, I wouldnt install DX unless I had a neighbor next door that had a DX system for 20-years without any trouble Caveat Emptor!

SR


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RE: geothermal options

To SR--It's guys like you that make this forum what it is--great source of information. Thanks.


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RE: geothermal options

Jules - Thanks!

Steve


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RE: geothermal options

Try this site:

http://www.gotohallowell.com/

I also live in Ct. and was looking into this type of heat pump...it says that its good to ZERO degs without electric coming on?? I just wonder if anyone out there has use it and if so with what results. I know its fairly new to the market, but still curious.

Bigal


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RE: geothermal options

big al 41, Hallowell is a outdoor heat pump. Maybe the technology has improved, but when my wife lived in VA her home was heated with an outdoor heat pump and during cold times it could not heat the house sufficiently.


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