horizontal loop field. Boring vs. excavation
I only have a few weeks to decide if I should install a geo system or not.(had our first major frost this am) live in south central minnesota, clay soil.
I am getting three quotes, 2 are in. First contractor wants to do horizontal BORING for the loop fields about 8 feet deep, the other wants to do horizontal EXCAVATION at 10 feet deep. Both will be 800 feet of loop per ton , Contractor one wants to use a two stage copeland , number two wants to use thee same 2 stage compressor, 4ton econar system. I am concrened about old foundations, rocks, debris etc. with the boring method. I am also concerned about effecieincy of the loop tubes being in contact with the ground which apparantely helps with energy efficiency.
Could anyone help with information.
The excavation method is more money than the boring method.
Thanks for any information.
Sept. 30, 2009
It's weird that the directional boring guy will not go deeper than the excavator. I had a guy tell me he would directional bore to 15 feet deep. For your climate the Econar is probably the better choice. They are setup to be better with heating than competitors. LAstly, make sure whoever does your loop surrounds the pipes with some kinda material that will make good contact like screened sand or grout.
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.
Advantage to horizontal boring is not digging up your yard, go a couple feet deeper and make sure it is grouted.
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.
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.
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.
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.
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.
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 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.
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.
DI what are you using for loop pipe insulation?
Originally Posted by djastram