Horizontal system trench length

Discussion in 'Vertical and Horizontal Loops' started by cynical2, Sep 11, 2010.

  1. cynical2

    cynical2 New Member

    Hi all, I found this site researching geothermal systems. I have a 20 year old A/C and nat gas furnace that needs replacing, so I'm working to educate myself on the options.

    My location is near Cincinnati. House is 2500 sqft in the top 2 floors, and another 1000 sq ft of finished space in a partially finished basement.

    I was quoted a complete Bryant/Carrier 4-ton geothermal system with horizontal layout for $15,000. Installer said he would make 450' of trench, and use a 6-pipe configuration. The trench would be 4' wide and 6' deep.

    He claims 100' of 6-pipe configuration yields 1-ton of capacity...and that he adds 50ft to that "just to be safe". The 6 pipes would be 3/4" pipe, the main pipe would be 1-1/4".

    Does this make sense? Based on what I've read, it seems woefully short on capacity...though I haven't seen a lot of 6-pipe installations discussed. That being said, the guy is experienced with several good references.

    Thanks in advance for any help!
  2. SoundGT

    SoundGT New Member

    Usually it is not a good idea to second-guess a local installer that has a good reputation. So, not questioning his local rule-of-thumb estimate for trench capacity, the first thing that should be done is calculate a heating/cooling load on the home and then go from there.

    Ask if the installer is a current certified or accredited IGSHPA installer. The load can be done by the certified installer, a qualified residential energy technician, or a mechanicall engineer. See how that matches the trench length scenerio.

    Finally, I suggest that you ask him for two references of clients that have a similar system and home envelope quality/quantity and give them a call.
    Good luck. Going GEO is a good solution.
  3. Tom Noden

    Tom Noden New Member

    software for horizontal ground loops

    I am using the sample software for Geocomfort. with 14 tons of equipment the calcs only show about 1100 ft of trench. seems small. it also says the flow is too low. what is the normal flow rate for a 6 ton unit? I thought 15-18 GPM.
    Also where can I find a trencher for 8 ft deep in the Philly area? otherwise a 4ft wide backhoe bucket is all I can find.
    looking for advice on horizontal ground loop design. :)
  4. SoundGT

    SoundGT New Member

    You said 14 tons of equipment - I assume you mean GXHP. The "normal flow is 2.7 to 3 gpt - or 37.8 to 42 gpm. Would need to have a copy of your inputs for the trenching program but unless the thermal conductivity is very high or the ground is very wet - I would also suspect a input error. Give us more detail or give me a call and we can walk through it with you. We are in the business directory for Utah and other Rocky Mt. states.
  5. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Tom I don't understand the question. Are we designing for 14 or 6 tons? How big is the house? even 6 tons is a lot.
    Cynical, 6 pipe guys in mid MI use 150' of trench/ton. Being considerably further south you could probably get away with less. If installer has a good rep and track record I would look at that more than pipe design.

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