Open Loop design aspects

[geowannabe]

Looking for more detailed info on open loop design concerns, especially plumbing issues. I have been studying geothermal for 5-6 years casually as I designed, engineered and finally built my own house over the last few years - 1500 sq ft ( plus basement) log home in rural central NY. I am at the point now where I seem to know as much as the local HVAC contractors I've spoken with - residential geothermal has not taken off here at all, which really frustrates me. Other heating options are basically limited to oil, propane or electric - winter temperature range is not good for an air source heat pump, and lots of rocks and roughly total rock at the 4 ft mark makes closed loop install problematic/expensive. I have 2 existing drilled wells on the property, good separation from each other. Great and clean water flow from one (20+GPM), will check the other for handling discharge rate this spring when the water table is high. I will also do a thorough water chemical analysis this spring, but wanted to start tentative plans for a system install, and cannot locate any sites which give more than cursory details about open source, would appreciate any helpful advice on where to look. I know that unit longevity can be a big issue, but with good unit pricing ( relatives in the business) and no additional expenses beyond the second water line install, the cost benefit of putting in an open loop seems quite good if I design well and implement correctly. I'd be looking at a 3 ton unit, most likely a Trane.
Thanks in advance for any help!

[tecman]

Consider open loop with caution. There is a high service rate on open loop systems. Water quality as far as acidity, scale, dirt, sediment, etc can all have a serious effect on the system life and performance. You will need about 10 GPM for 3 tons. This can cost a bit to pump, depending on the head you need to lift. Your water quality may look good now, but during a dry stretch, when the water table drops and you are pumping hours a day, you may start picking up sediment. I have seen a number of systems that needed regular service or expensive repair due to water quality.

This can all be minimized with water treatment and filtering, but that is another expense and maintainance issue. If you have a few acres, I would suggest looking into putting in a closed loop instead. Sure it will cost some, but it is virtually maintainance free once installed.

Look at ClimateMaster. Very good dependable unit at a reasonable cost. They are considered by some to be the leader in Geo systems.

paul

[karsthuntr]

Tecman has good advise. You could also do closed loop wells instead of horizontal loops. If your ground is rocky this would be a ood option. Contact a local well driller to find out cost and wether they have done geo before. Most drilling companies will drill geo wells at half the cost of a normal well.

[Black Adder]

ClimateMaster recommends 1.5 gallons per ton that works out to 4.5 gallons not 10. Open source is the most efficient of the Geo systems. We install them all the time and have not had any problems providing your water supply is good. Suggest if you do go this route go with ClimateMaster. Have used plenty of their equipment and have had no issues. Once again as in all installs it mostly comes down to the installer.

[dan sw fl]

Originally posted by tecman
Look at ClimateMaster. Very good dependable unit at a reasonable cost. They are considered by some to be the leader in Geo systems.

paul

http://www.climatemaster.com/download/Unit%20Manuals/97B0045N01.pdf

[tecman]

Originally posted by Black Adder
ClimateMaster recommends 1.5 gallons per ton

Just a note: 1.5 GPM/ton is the minimum recommended. It will work, but a higher flow rate improves performance. I agree that 3 is on the high side, but I would try to keep it at 2/ton if possible.

paul

[geowannabe]

Thanks for the link to the install bulletin, that is far more comprehensive than the Trane info I reviewed as far as the installation requirements. I had 5-6 GPM consumption in my mind after a review of 3 or 4 vendors.
I was aware of the water quality issues raised and would not consider it if the maintenance issues appear to be looming for me. I will do the detailed chemical analysis but have no evidence of likely issues (no sulfur smell, good cleanliness,no iron staining, soft water etc.).
I really want to go geothermal for the heating season, the local climate and house sited in the shade limits the cooling needs to a very few days if we have a hot muggy August. Since the area is rural, a couple local well drillers have the market cornered and it is about $14-18 per foot four years ago. I am certain based on discussions with HVAC suppliers in the region that I am once again a pioneer locally. I would definitely go closed loop if I had a pond, but that's another story....
As far as pumping costs, I am working with about 30-40 feet of head and 70 feet of water in the well, so it isn't a major expense consideration. I run filtration for the whole house at 10 micron, with very little sediment picked up. Due to the increased volume I would plan to install coarse and fine filtration for the house, with an additional in-line filter for the unit. I also envisioned the cupro-nickel exchanger option would be a wise investment. Thanks again for the pros and cons and the link.

[jerrygr]

Water temp dictates water flow per ton needed. Cupro coils are a must have item. I have installed water towers in houses(in Florida). NY might need to much sump heat to function properly. Are you going to use a discharge well?

[tecman]

If you look at the numbers, 6 GPM at 36,000 BTUs results in a 12 deg F delta. In upstate NY the GWT is about 50 degrees, so a 12 deg delta gets you dangerously close to the freezing point. A few more GPM would be a good safeguard.

As far as closed loop, you do not need a pond. For 3 tons a 500 foot trench with 4 pipes is ideal. The last one I had installed was 500' long x 7' deep. The digging and backfill time was 16 hours. Multiply by the local rate and you can estimate your excavating costs. Add the cost of pipe and the installer to put it in properly and I think you will find it is less expensive than drilling a couple of wells.

paul

[geowannabe]

Paul, good input on getting close to freezing point- thanks. I want to make sure I am happy downtream without surprises. Both wells are already on site - dug and paid for,that fact put more weight on a hard look at the issues around open loop. I had one drilled for my water supply 4 years ago, the other was on adjacent property that I just acquired next door. On a closed loop option I really can't foresee trying to get 7' deep excavation, the basement was about 5-1/2' and is basically on semi-solid rock with the last foot being really tough digging with a beig shovel. Vertical well with pipe loop, vertical drilled hole piped and grouted or open loop using both existing wells is what my research keeps coming back to as my options, that is why I continue researching and asking questions and finally found more geothermal resources on this site than all others. I know open loop is definetly comparatively cheap in the short run, but I do take a longer term view and want to understand all the variables so I can make an educated decision. As for the pond reference I made, I got my friend to do geothermal using a closed loop pond setup (for his Kentucky retirement home) and he loves it.

[tecman]

Originally posted by geowannabe
On a closed loop option I really can't foresee trying to get 7' deep excavation, the basement was about 5-1/2' and is basically on semi-solid rock with the last foot being really tough digging with a beig shovel.

Actually rock like that is the best thermal coupling you can have. Dig till you hit rock and put the pipe down in screenings. Not to keep pushing you to closed loop, but the ground conditions you mention seem ideal.

paul

[mnhunter]

Sorry to jump on your thread geowannabe but I have a couple of questions for some of the geopros.

I had a water analysis done and my well water has 15 grains of hardness and NO iron. The well will not run dry. If any possible sediment is filtered, what other issues should I be concerned with in having an open loop installed?

Thanks

[dan sw fl]

Originally posted by mnhunter
Sorry to jump on your thread geowannabe but I have a couple of questions for some of the geopros.

I had a water analysis done and my well water has 15 grains of hardness and NO iron. The well will not run dry. If any possible sediment is filtered, what other issues should I be concerned with in having an open loop installed?

So don't jump on ! Do You know how to start a post?
Hopefully, NO ONE will respond to this intruder! !!

[mnhunter]

wow, sorry.

[geowannabe]

Tecman wrote:
Dig till you hit rock and put the pipe down in screenings. Not to keep pushing you to closed loop, but the ground conditions you mention seem ideal.

Happy to perhaps have this back on the table as one potential option. The real issue I envisoned (beyond bringing in decent fill for the intial backfill) is that 48" is the area's rated below frost line. When I put in the well water line I had big equipment and it was working to get me that deep. They were able to push the basement 1-1/2'deeper by opening up a large space and finding some softer areas and then spreading out. I think I could still get away with this if I use the slinky approach in a single wider trench. Nothing is impossible, just time and money. It seems that I am at a point where I need to get a water analysis and also see if I can expand my local contractor search a bit and get a range on estimates for closed loop option, since I can't do that one myself! I know there is no such thing as one correct answer, this discussion is very helpful to me!

[flange]

if you are going open loop, you may be concerned about stratification in the well, supply and return piping should extend to differing lengths into the well.