Formation Thermal Conductivity | Overview

Thermal conductivity is the physical property of a material that determines how easily heat can pass through it.  The average thermal conductivity of a formation that a geothermal ground-loop heat exchanger is installed into is important in order to develop a properly sized heat exchanger for a particular application.  The information that is obtained from a formation thermal conductivity (FTC) test can be input directly into most of the popular design software programs.


The thermal conductivity of a formation is a prerequisite for a properly designed geothermal ground-loop heat exchanger.  The thermal conductivity of the formation determines how easily heat can be conducted to and from the circulating fluid in the heat exchanger piping. For example, in a formation with high thermal conductivity, the loop temperature required to reject a given amount of heat to the ground would be less than the loop temperature for a formation with a lower thermal conductivity. Higher loop temperatures for cooling translate into reduced heat pump performance and higher operating costs.

Why Consider FTC Testing?

  • Proper testing enables ground loops to be sized to match the existing formation conditions.
  • The obtained information provides for a better estimate of installation cost.
  • Precision designs save money on drilling, grouting and pipe costs.
  • Proper designs allow the system to run more economically.
  • Multiple tests can be conducted which would allow the comparison of different grouts.
  • Test parameters can be set up to simulate loop response under cooling design conditions.


  • Un-surpassed Experience
    • Over 14 years of experience in measuring and calculating thermal conductivity or various formations and soils.
    • Over 200,000 hours of accumulated data has been analyzed from more than 4,500 separate tests.
  • Data analysis performed by Mechanical Engineers with research backgrounds.
  • Long test times provide a reliable value for average formation thermal conductivity.
  • Dedicated to quality testing and data analysis.
  • Follows ASHRAE recommended procedures as found in the ASHRAE Handbook, HVAC Applications, Geothermal Energy Chapter.
  • GRTI offers a variety of approaches to obtain an analysis (see various FTC options).