HyGCHP Modeling Tool

Reduce the cost of implementing geothermal heat pump systems on your building projects by going hybrid. A hybrid geothermal heat pump system can lower your costs by reducing the peak capacity of your ground loop and allowing you to install a smaller, less expensive ground heat exchanger. HyGCHP is a software module that can help you analyze this option!

An easy-to-use, but sophisticated method of analyzing various hybrid geothermal configurations is one piece that has been missing from the world of geothermal analysis tools. With our free modeling tool, HyGCHP (Hybrid Ground-Coupled Heat Pumps) you can use the powerful TRNSYS-based ground heat exchanger module* to investigate several configurations of geothermal system, including both conventional geothermal systems and various hybrid options, from heating dominated to cooling dominated systems.

Use HyGCHP to:

  • Determine how much money a building owner can save by choosing a hybrid geothermal system.
  • Select optimal sizes for the equipment in a hybrid system.
  • Compare different hybrid geothermal approaches in terms of energy and economics for a given building project.
  • Analyze the effects of different control strategies for your geothermal or hybrid system.

* The ground heat exchanger model in TRNSYS is based on the well-accepted and validated Duct Storage (DST) model, originally created by Hellstrom.

With assistance from the University of Wisconsin Solar Energy Laboratory, we studied three working hybrid system installations to compare their economic and environmental impacts with other HVAC systems. The study was funded by the United States Department of Energy, Alliant Energy, and Madison Gas and Electric.

We collected a year of operating data on three working hybrid system installations to analyze the economic and environmental impact of the hybrid approach and to compare it to other HVAC system designs. We used this data to investigate what contributes to an effective hybrid design and to validate energy models of these systems.

As a result of this project we developed documents and tools for HVAC system designers to use, including this freeware version of our model, to assess the benefits of applying the geothermal hybrid approach on their building projects.

Other resources

Our work on this project complements other resources available on hybrid ground-source design, operation, and economics.


  • For basic design information, see: A Design Method for Hybrid Ground-Source Heat Pumps by Kavanaugh (ASHRAE Transactions 1998); other work by Kavanaugh and Rafferty. Available for purchase at the ASHRAE Bookstore.
  • Oklahoma State University has completed in-depth research on hybrid ground-source systems. Recent research focuses on an array of different hybrid control options and is summarized in a thesis by X. Xu (pdf).
  • Hackel's previous work at the University of Wisconsin looked at optimal size and control of hybrids, including a few sample control sequences.


  • Ground Loop Design 2010 or GLHEPro can be used to test out the viability of some hybrid designs (its hybrid functionality is relatively basic).
  • TRNSYS and EnergyPlus (well-tested full-building simulation software packages) have the capability to complete detailed sub-hourly models of hybrid ground-source heat pumps systems.