Hello, I would like to do a ground loop at my home for a 5 ton GSHP.  I live in Rhode Island and have a contractor who can dig 8 feet down for me with a 3' wide bucket for a good price.  I can go about 125-150' on a single trench length and could do multiple parallel trenches if needed.

I was thinking I may usea 'slinky' design with 3/4" or 1" pipe.  The question is, how much of either?  I know I want to maintain a Reynold number above 2500 to assure turbulent flow while balancing this against pumping losses.  I will be using (3) 1.5 ton GSHPs to cool and heat the house.  I have a gas boiler with baseboard for backup.  If I can get away with several loops which I can terminate in the house with no fusion welding, that would be ideal. 

Thank you - J

without the use of software and knowledge of local conditions, the gross rule of thumb is dig as deep as you can and install as much pipe as you can afford. With a dig depth of 8 feet you may want to layer your slinkies.
Eric

OK, also, is therer a recommendation for fill over/under the piping vs. just backfilling with the dirt removed? Sand, clay, etc? What types?

Again, I'm located in New England. I expect a max. ground temp of 52 degrees at 8 feet, but maybe even a bit lower. The ground is rocky with granite all over, typical New England rock field...

The most important thing about the backfill is no sharp rocks that will kink or damage the loops immediately or later. You may also want to do some research regarding soaker hoses installed over the tops of the slinky's. They allow you to add moisture to a dry loop if the temps get to out of whack.
Eric

Reynolds number only matters if you are trying to use minimum pipe.
j