A Field Experiment to Assess the Influence of Heat and Mass Transfer at the Soil Surface on Shallow Ground Heat Exchanger Performances

Prediction of soil thermal regime is still a difficult task for design of ground-coupled heat pump system units (GCHP). A Field experiment was carried out to study the near-surface and moisture transport effects on soil temperature distribution. Energy balance components at the soil surface was monitored using a meteorological station, that included a pyrgeometer and a pyranometer to measure short and far infrared radiation, and using two heat flux plates installed in the soil at a depth of 0.08 m to measure ground heat fluxes. A 2.5 m deep trench has been dug in order to (i) characterize soil hydraulic and thermal properties at different depths and (ii) install tensiometers and thermocouples allowing continuous measurements of soil water tension and soil temperature. We observed that variations of soil properties along the profile as well as compaction influenced soil thermal properties. Results showed that temporal variations of soil heat flux at 8 cm depth closely followed those of available energy (net radiation), vertical turbulent heat fluxes (latent and sensible fluxes) near the soil's surface.