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# Geothermal Loop Design: Series vs Parallel Flow Path Analysis

Ryan Carda

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.

Parallel system

Fabricated from smaller diameter pipe, which is generally less costly, special care must be taken in flushing to get all the air out of the piping loop.

Advantages include: Lower cost pipe, less antifreeze required

Disadvantages include: Special attention to assure air removal, attention to balanced flow, within plus or minus 10%, in each parallel path is required

See the below illustration.  It may help.

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#### Ryan Carda

Ryan Carda, P.E. is a Mechanical Engineer at Geo Pro, Inc. and is a co-founder of Geo-Connections, Inc. (creators of LoopLink Geothermal design software). He is a co-author of “Design and Installation of Residential and Light Commercial GSHP Systems", developed in cooperation with the International Ground Source Heat Pump Association (IGSHPA). He has been involved in the ground source heat pump industry since 2006. His involvement in the industry has included training hundreds of students, as well as hands on experience designing, installing, commissioning and troubleshooting of all types of geothermal systems. Ryan graduated with his Master of Science degree in Engineering from South Dakota State University in 2006. Ryan enjoys instructing newcomers to the industry in hopes that they leave sharing his enthusiasm for geothermal technology. His main goal is to help promote and build confidence in ground source heat pumps through education in order to help it become a main-stream technology.

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