Ryan Carda, P.E. is the author of the International Ground Source Heat Pump’s official design and installation guide. Carda’s Antifreeze Volume Calculator for Geothermal Loopfields free tool is used in his Entry Level Geothermal Professional Certificate Training.
Here’s what the tool looks like:
Uses: This calculator is used to quickly determine how much antifreeze will be needed to reach the target […]
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.
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When designing geothermal ground loops, this is an issue that a lot of people get hung up on. Because of the advantages of, we use parallel circuits in ground loops almost exclusively in our industry. Read more to hear why.
When loops are tied in series with one another, they will all see the full system flow rate (because there is only one flow path) and the pressure drop through the loops add together. Because there is only one flow path, the pump must overcome the pressure drop through each consecutive loop as the fluid travels through the system from the supply to the return line. The pump will be required to produce the combined pressure drop from the series loops at a shared flow rate.
In a parallel system, the flow through each loop will be the same. We add individual loop flows together to get the combined total system flow rate on the supply-return line back to the heat pump. The amount of pressure required to overcome friction losses through each loop (because they equally share the total system flow) will all be the same. The pump will be required to produce the combined flow rate from the parallel loops at a shared pressure.
To Summarize:
In a series system, the total length of the well pipes would have to be figured in calculating head loss while in a parallel system only one loop needs to be calculated.
Parallel flow: Individual loop flow rate adds at a common pressure drop
Series flow: Individual loop pressure drop adds at a common flow rate
Series system
Advantages include: Single flow path and pipe size, higher thermal performance per foot of pipe, since a larger diameter pipe is required.
Disadvantages include: Larger water or antifreeze volume of larger pipe, higher price per foot of piping material, increased installed labor cost, limited length due to fluid pressure drop and pumping costs.
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