GEOFIT is optimizing compact geothermal heat exchangers systems (GHEX) with a more compact design based on a helix. To help establish heat transfer behavior, experiments are being conducted by consortium partner AIT. This poster shows the objective, approach and set-up for this experiment, which belongs to WP3. The subsequent CFD-simulations based on this experimental data will help establish a reliable engineering design tool for the helically based GHEX systems.