We’ve found it useful to focus on both articles that will help companies with their sales and marketing AND design and installation. A few weeks ago, I shared a piece – thanks to Ryan Carda – on geothermal flow path analysis for ground loop design that came from a discussion forum from our advanced geothermal design course.  My plan is to share more technical discussions that are happening within the course. If you are installing or designing geothermal projects, these articles will be useful to you if you never take the training. This is my goal.

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Here are a few tips on on vertical and slinky bore design.

Vertical Bore Design

1)      The target (optimum) flow rate versus pipe size is:

• 2.8 – 3.2 gpm per loop for ¾” loops
• 4 – 6 gpm per loop for 1” loops
• 5 – 9 gpm per loop for 1.25” loops

Staying within those flow ranges per loop will keep you well below the maximum recommended flow rate for head loss (4 ft per 100’ of pipe length, Figure 5.4) and above the minimum flow rate required for turbulent flow.  For the vertically-bored design, I recommend using two loops for 6 gpm per loop with 1.25” pipe.

2)      There were a few questions regarding the maximum recommended flow rates shown in Figure 5.4 and the optimum flow rate ranges I provided during the PowerPoint lesson.  For example, I recommend sticking to the suggested flow rate range of 5-9 gpm per 1.25” loop.  Keep in mind that we shoot for an optimum head loss of 1’-3’ of head loss per 100 ft of pipe length when selecting pipe size for a given flow rate.  The upper bound shown on the graph (at approximately 12.5 gpm per 1.25” loop) shows the absolute maximum recommended head loss through pipe of 4’ of head loss per 100 ft of pipe length.

Keep in mind that with 1” and 1.25” pipe, our run lengths are usually longer (deeper bores to represent more GSHP capacity).  If your head loss is in the neighborhood of 4 ft per 100 ft of pipe length, the pressure drop through a 400 ft bore (800 ft run length) can be significant (4 ft of head per 100 ft of pipe x 800 ft run length = 32 ft of head in the loop itself!).