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You generally need significantly less loop per ton when the loops are installed below 15', as is common with horizontal directional drilling or vertical drilling.

This is primarily due to the fact that the temperature fluctuation is much less at 15' than at 4-6' depth of horizontal trenched systems and secondarily due to the water content that affects thermal conductivity is also more stable at depth.

-Adam
Hydrogeologist

Are the potential contractors using a computer based heat gain/loss program? You might want to look at this grout, a little pricey but I think its worth it. There are some inherent problems with grout in general...be sure to do your homework.

http://supergroutproducts.com/flash/

Lots of info to consider! My soil is sticky yellow clay fron 2' to 22'.(South central Minnesota) Apperentely a moist soil. They will bore about 15 feet down and 4 loops at 410 feet per loop. I was told tubes are 205 feet long and must have a out to the field and back to the house to make 410 feet per loop.
Is this a reverse return you were talking about? Never heard that term. By the way this would be a horizontal boring loop field.
The HP would be a 4 ton Bryant GT-PX split. 6 year old single story ranch style house, 1344sf with full basement. 2 by 6 walls, R-45 in ceiling. Heat with forced air propane. Does all this sound like a feasible/wise investment? Wish I could say what the final quote was, but rules are rules.
Thanks for any info,
Also any advice on Fed 30 % tax credit I should be aware of?

all piping should be reverse return. I agree.

the length numbers I got from the engineer. And in field findings I would have to agree.

A pump sized with enough head will draw more amperage, usualy 2 pumps for push pull. which raises the operation cost is another reason.
with geo we are nittygrity on operation cost are we not? why spend the money to do geo if we are not.

Never said longer loops would not work. Higher temp drop or rise will come from it.


I must add to my previous post. I stated when horizontal. I should have stated on either horizontal or vertical.... bla the rest. Hose connections were for the purge cart.

Originally Posted by softail124

Cool Breeze
I do not agree with you on limiting the loop length to 350 feet, the is no difference on a vertical loop field or horizontal, as far as length, or fusing and purging practice. The length of the header piping and manifolds need to calculated for proper pump sizing. Also the field must be piped in a reverse return, and filled and purged with a purge cart that is capable of forcing all of the air out of the system. I have done many systems like this, vertical, horizontal and slinky loops, and have never had an issue with removing air or balanacing, as long as great care is taken in making all the loops very similar as far as length in the field.

I agree. I have 3 parallel loops all 1000' long. They were plumbed slinky style in a reverse-return configuration, and it all works just fine.

Cool Breeze
I do not agree with you on limiting the loop length to 350 feet, the is no difference on a vertical loop field or horizontal, as far as length, or fusing and purging practice. The length of the header piping and manifolds need to calculated for proper pump sizing. Also the field must be piped in a reverse return, and filled and purged with a purge cart that is capable of forcing all of the air out of the system. I have done many systems like this, vertical, horizontal and slinky loops, and have never had an issue with removing air or balanacing, as long as great care is taken in making all the loops very similar as far as length in the field.

the feet per ton is determined by the soil. I am not familure with that area to give an acurate answer. But do not run loops over 350 ft max. the head loss in the piping will require a much larger and noisier pump.

and if they are doing it horizontal request flow controls per loop. ball valves on the supply and retuna long with a hose connection on atleast one of the loops for purging.

Seen it not done like this and was a nightmare!!!

I "plan" on using split closed cell foam pipe insulation. I haven't gotten around to it yet though.

Just lurking for my own education. Only way to be notified when more posts come through.

Originally Posted by djastram

I've installed both all-in-ones, and splits. Both are good systems, I think.

The picture below is the install at my house. I chose a split, to take advantage of the "dual fuel" program from my power company. That program requires fossil fuel back up, thus the 90+ furnace.

DI what are you using for loop pipe insulation?

Minn
I would find out the grouting method the horizontal boring contractor is going to use. You mentioned they are going to "grout as they go". If they are using drilling fluid as a grout, that is not acceptable, as drilling fluid is only a 10% solids at best. When we do a horizontal job, we pull a tremie along with the the ground loop, and then pull it back pumping in a thermally enhanced grout that ends up being about a .93 btu/hr ft and abou 65 % solids. With a small pecentage of solids, you have the possibility of dehydrating the hole, and having the bore hole dry up, leaving you with an empty bore annulus after a few years.

I replaced the 2.5 ton R-22 A coil with a 3 ton R-410a A coil.

I didn't do anything with my blower speeds, my temp rise is right where the book says it needs to be.

I'm very happy with mine. I really like the nice even heat, instead of the blast of hot, gradual cool off, blast of hot, etc. etc.

dj

split system

djastram, did you use the existing cooling A-coil that may have come with your furnace or did you need to replace with compatible coil to match the new heat pump? My existing A-coil is rated 2.5 ton. The gshp is rated 4 ton.
Did you need to modify the furnace blower?
I only feel rushed into this because of impending ground freezing and the ability to take advantage of 30% fed tax credit for year 2009. My local utility is also providing a nice rebate. Last but not least, it would be nice to turn up my t-stat from 55 to maybe 68!

I've installed both all-in-ones, and splits. Both are good systems, I think.

The picture below is the install at my house. I chose a split, to take advantage of the "dual fuel" program from my power company. That program requires fossil fuel back up, thus the 90+ furnace.

With an investment this big, do not rush into it or feel pressured by any of the contractors. I was researching GSHP s for over a year before I actually bough my house. Therefore when I found a house I had already decided to go that route. I also considered the ability to install GSHP hx fields at every house I looked at.

split systems

Thanks for the advice crash11. The contractor who wants to bore the horizontal loop wants to install a split system in my home. A 4 ton Bryant GT-PX. This is a two stage compressor, utilizing my existing LP furnace. I have an A-coil(2 1/2 ton) installed in the plenum but never hooked up the condensing unit. I'm assuming they would take that out and install a different coil? or maybe not. They also will be removing the blower and upgrading to proper cfm. Would they or should they use a blower that is variable speed because of the 2 stage compressor? Would that even work because they are using my furnace as the air handler.
The other contractor wants to use a stand alone system (econar 2 stage 4 ton) utilizing my existing duct work with back draft dampers on the duct work but is more expensive.
I'm going nuts here because this is a very big investment for me and I only have a couple weeks to decide.
Thanks for any help.

400 ft per ton sounds reasonable. There's no way to know for sure without seeing it for myself, but I can tell you this much..... having less pipe in the ground with excellent thermal contact to the earth is far better than more pipe with poor contact.

The other advantage of having only about 1600' of pipe is you can probably get away with a single circulation pump instead of a dual pump package. Most manufacturers recommend a dual pump package for a 4 ton unit and only a single pump for a 3 ton unit. I think you could achieve 10-12 gpm with a single pump. Then you use a little less electricity and it costs even less to install. Also, the standard pump packages always come with a spot for a 2nd pump anyway. So if 1 pump doesn't get you enough flow you can always just buy the 2nd one.

bore horizontal loop field

Thanks for the info. Crash 11, you were right. I called back the one contractor who wants to bore instead of trench and indeed they go down 15 feet with the bore machine and grout at the same time. Now what concerns me is they install 400 feet of tube per ton intead of 800 feet per ton like the other contractor wants to. Do you think this would be sufficient to handle a 4 ton HP in Minnesota? Just found out from the well company I have sticky yellow clay from 2' - 22' which apparently is good soil to have. Also this contractor uses the Bryant GT-PX model utilizing my existing propane furnace. They
would have to increase blower CFM on the existing furnace.
Again, any insight/information would be appreciated.
Thanks,
John

Advantage to horizontal boring is not digging up your yard, go a couple feet deeper and make sure it is grouted.

have you concidered vertical wells. Thats what we have done most of, 200' of well give you 400' of loop. Around here we hit some kind of water at 75', it may not be useable water for a well but it is still good for heat transfer. We can get by with 400'/ton so one well/ton, I try to encourage the HO to go with one extra well just to help maintain loop temp, the warmer you keep the loop in the winter & the cooler in the summer the more efficeint the HP.