RP-1118 -- Investigation of Methods for Determining Soil and Rock Formation Thermal Properties from Short Term Field Tests PDF

A critical need in the design procedure of closed-loop GSHPs, or ground-coupled heat pumps (GCHPs), is an accurate knowledge of soil/rock formation thermal properties. These properties can be estimated in the field by installing a loop of approximately the same size and depth as the heat exchangers planned for the site. Heat is added in a water loop at a constant rate and data is collected. From this information the thermal conductivity of the soil and/or rock formation can be estimated.

ASHRAE has supported this project to investigate details associated with these tests by collecting and added scientific information to items currently being debated in this industry. These issues include the length of test, required heat input level and quality, analysis procedures, specifications of test methods, equipment and instrumentation, corrections for deviations from fundamental assumptions, and validation of results.

The objective of this project is to evaluate the validity of the models, estimate the accuracy and costs of the test methods, and propose a set of recommended practices to be used for field tests to determine soil and rock formation thermal properties at ground coupled heat pump installation sites.