Impact of changing pipe size for a horizontal loop

Discussion in 'Vertical and Horizontal Loops' started by Rob, Sep 9, 2013.

  1. Rob

    Rob New Member

    I am a horizontal directional driller and do a fair amount of work installing horizontal loop fields for local HVAC contractors. Typically we use a 300' shot (600' total pipe) per 1.5 tons at an average depth of 15-18' using 3/4" pipe that are 10' apart and then depending on the size of the job use either 1.25" or 2" from the manifold to the building. I am doing a large job on a medium sized site and am considering increasing the size of the pipe in the loops to 1" or even 1.25". Can anyone tell me how that would impact the total amount of pipe needed? The total job requires 35 tons.
  2. waterpirate

    waterpirate Well-Known Member Industry Professional Forum Leader

    Hi and welcome.

    By increasing the pipe diameter you are really only reduceing friction loss. The tonnage requires what it requires in regard to total pipe length, not diameter.
    Hope this helps
  3. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    However....since the diameter of the pipe increases, the contact area to the ground increases as well. But also the thickness of the increases, hindering heat transfer. But overall you gain about 10% to go from 3/4" to 1.25". We measure that with our monitoring, but also every loop software will confirm that.

    More importantly, you need about 3x the volume for 1.25" versus 3/4", which will create a thermal inertia, similar to a buffer or thermal storage tank, meaning that the loop when heat gets rejected in cooling mode will heat up slower, and stay cooler. The opposite will occur in heating mode. The thermal inertia is something the loop software does not account for, but the performance gain is significant.

    I would always go with larger pipe if practical, but wrestling 1.25" pipe is another issue. You also need 3x the amount of antifreeze, so sometimes you don't save much upfront expenses. Make sure you calculate pressure drop, flow and make sure the reynolds numbers are not too much off. But overall I would account safely for a 10% performance gain

Share This Page