Geothermal System Header Design and Repair

Geothermal System Type: Horizontal Closed Loop Ground Exchanger
Location: Prince George, BC

Proper header design for the geothermal ground exchanger is a crucial part of the design process for a geothermal heating and cooling system.  Without a proper step down header design, it can require a very large pump, several pumps in series, or be completely impossible to purge air from the in-ground piping system.

Earth Fire Energy received a project to fill an existing geothermal heating system with water, purge the air, and add the appropriate amount of antifreeze to the geothermal ground exchanger. The entire geothermal system had been installed by the home owner a few years prior and had never been commissioned.

As the geo system was filled with water, we started discussing the design and configuration of the existing ground exchanger. After a few quick calculations, it was clear that it would be impossible to purge all of the air from the piping system because a step down header had not been installed. A step down header design is used to reduce the flow rate and pressure required to purge air from the piping system.

The ground exchanger was composed of a 3” pipe for the header and five - ¾” branch lines. In order to purge the air from the 3” branch line, 42 gallons per minute (gpm) was required at the end of the header where the final branch line was attached. Unfortunately, this was impossible to achieve because the pressure required to overcome friction losses through each branch line greatly exceeded the pressure rating of the HDPE pipe used for the ground exchanger.

After discussing the problem with the owner, a decision to excavate the existing header pipes and install a proper step down header was made. After installing the new header pipes, the piping system was pressure tested, purged of air, and antifreeze was added to the Geothermal Heating System.

The home owner now has a working geothermal heating system.