DOE EERE Research Reports

Electrically-Driven Heat Pumps

Geothermal Heat Pumps

Soil and Backfill Thermal Properties

The design and performance of geothermal heat pumps depends on the thermal properties of the material surrounding the ground-coupled heat exchanger. This includes backfill as well as the soil near the heat exchanger. Ground coils in damp or saturated soil have greater heat transfer capacity than equal length coils in dry soi or rock, consequently soil moisture properties are of great importance in sizing coils and consequently on the cost of an installation. Coil design is further complicated by the fact that rejecting heat to the ground causes moisture to migrate away from the vicinity of the heat exchanger and reduces capacity. Projects were undertaken to enhance the understanding of soil properties, including moisture, in order to improve coil sizing methods and design more efficient and cost effect geothermal heat pumps.

Links to Publications:
  1. Determining Effective Soil Formation Thermal Properties from Field Data Using a Parameter Estimation Technique
  2. Effect of Backfilling Material on Ground Coil Performance
  3. Models of Simultaneous Heat and Moisture Transfer in Soils
  4. A New Method to Determine the Thermal Properties of Soil Formations from In Situ Field Tests

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