The project’s aim was to demonstrate how a school of 16 classrooms (7,500 m³) can be heated from solar energy which is stored in an aquifer (aquifer des sables de Fontainebleu) during summer and is extracted by an intermediary heat pump in winter. Apart from showing that the energy collected in summer can be used in winter, the optimum system management was investigated. The process could have been reproduced using an industrial waste heat source, if successful. It was expected that about 200 MWh could be extracted from the aquifer giving a payback of 18 years.
Bearing in mind the intermittent use of the classrooms, the most appropriate form of heating appeared to be pulsed air. Since a certain level of ventilation is necessary, a static recuperator was used to recover heat from the exhausted air. Total heat requirements were 260 MWh per year of which 55 were furnished by the recuperator. The remaining, were extracted from the hot water store in the Fontainebleau sands, which is found beneath the school. This storage was charged during summer. Solar panels, functioning as a cold source for a heat pump, supplied heat to the underground "nappe"; water was extracted by way of a "cold" well and its temperature increased from 12°C (first year) to 50°C by passing through the heatpump’s condensor before being re-injected into the nappe through the hot well. The heat pump allowed the reinjection temperature to be maintained at a constant level thereby guaranteeing higher efficiency. In winter, the warm water was pumped out and heat was transferred to air. The storage was dimensioned to cover all the needs of an average year, however if the temperature of the nappe is too low the water can be used as the cold source of the heat exchanger.