An experimental setting is devised to investigate the behaviour of a novel type of horizontal ground heat exchanger (HGHE). The HGHE is coupled with a hydraulic closed loop in which warm water is circulating to express the cooling mode of a reversible-cycle heat pump. Several digital thermal sensors are employed in the experimental field to monitor the soil temperature distribution and the plan. The behaviour was tested during the summer 2011, in continuous and discontinuous operating. The HGHE behaviour was monitored in dry and wet conditions, owing to the trench flooding with water. The heat power for unit trench drop down from 140 W/m² to 40 W/m², moving from the start-up to the last period; the minimum was reached at very hard conditions after six months of continuous operating (700 kWh exchanged), late in summer, and with an outdoor temperature still over 38°C. When the working mode was switched in discontinuous, the power increased quickly up to 60 W/m². Finally, the soil temperature appeared modified up to 3 meters far from the HGHE, and without over-heating conditions at soil surface. The flat panel showed to be able to involve a large soil volume, and this behaviour enables high energy performance, at least in cooling mode.