3 Ground Source Heat Pump (GSHP) System Design Questions

Expert Instructor Ryan Carda discusses vertical boring systems, horizontal ground loops and Energy Recovery Ventilator ducting on the IGSHPA Certified GeoExchange Designer (CGD Plus) Training discussion board…

Student 1: Would you say that the addition costs associated with vertical boring are greater than the cost of extra piping necessary for a horizontal system?

Ryan Carda: To a point – HDPE pipe itself is very cheap. The cost savings comes when you compare the cost to excavate to local drilling rates.

In most cases, you’ll find that the economics start to tilt in favor of vertical systems (vs. horizontally-trenched) for systems 15-20 tons and larger. For systems of that size (20 tons and larger), the cost for excavation, backfilling and compaction pile up in a hurry (pun intended).

For for smaller systems, horizontally-trenched installation is usually cheaper. Again, the difference depends on labor rates, drilling costs, excavation costs, etc. in your part of the world.

In SD, I’d say the going rate for residential vertical bore installation is around $1800-$2000/ton. Horizontally-trenched residential systems probably go in for around $1400-1500/ton.

Student 1: Have you ever seen horizontal ground loops at deep earth depths? Are they common or are we much more likely to see trenches up to 8′?

Ryan Carda: Most horizontally-trenched applications are installed at 8′ or less. It will likely be cost prohibitive beyond that point. Especially once you consider the fact that if installation depths are greater than 15 ft below grade, you’ll have to account for unbalanced ground loads. Cost will begin to favor vertical or directional bore installations.

Student 1: When incorporating an ERV (Energy Recovery Ventilators) into system design, is the ducting separate from the GSHP system ducting or is it integrated?

Ryan Carda: There are many ways to integrate fresh air in a commercial system.

In most cases, peak loads from fresh air requirements (based on peak occupancy) are really high but the actual usage when in place is low… (i.e. – the building is designed based on a peak load/occupancy rate the building rarely, if ever, sees.) High peak loads (and high installed capacity requirements) on top of low run/usage time = poor payback for a geo investment.

In a system like this, the best way to go is to install a fresh air system that is completely decoupled from the geo portion with it’s own dedicated energy recovery, heating/cooling system, and ductwork so that the fresh air loads don’t effect the geo sizing/performance.

In the case where fresh air requirements are relatively low and used constantly, it would make sense to integrate that portion of the system in with the geo equipment. In fact, there are a few manufacturers that build heat pumps with a ERV system built in the cabinet.

Enroll in Ryan’s IGSHPA Certified Geothermal GeoExchange Designer (CGD Plus) Training 8-week course today and earn 25 P.E. professional development hours and2 IGSHPA CEU Points while working with IGSHPA Manual authors/industry professionals, Ryan Carda and Dr. Charles Remund. You’ll also get an unlimited 6-month subscription to LoopLink PRO.

Enroll in Dr. Charles Remund’s FREE Commercial Geothermal Heat Pump System Design lecture for an introductory look at ground heat exchanger design for a commercial geothermal system. 

About instructor Ryan Carda, P.E. – President, Geo-Connections, Inc.

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.

Continue learning about the International Ground Source Heat Pump Association (IGSHPA), Geothermal, Hydronic Heating and HVAC Design:

• Free Course: High Performance Building and HVAC 101
• Hydronic-Based Biomass Heating Systems
• Geothermal Designer Boot Camp + LoopLink RLC Certification
• IGSHPA Geothermal Installer Accreditation Training
• Entry Level Geothermal Professional Certificate Training
• Mastering Hydronic System Design