Hokksund school – A plus energy school building with an innovative geothermal heat pump system
Hokksund School is a multi-building project comprising three school wings, a sports hall, and a swimming pool with a total heated area of 11,200 m². The school wing and sports hall are designed as plus-energy buildings according to the Futurebuilt definition, while the swimming pool uses best-available technology to minimize energy use. The thermal supply is based on the Lowex concept – low-temperature heating and high-temperature cooling – combined with a deep closed-loop borehole field (10 wells × 500 m) and six inverter-controlled heat pumps (total 258 kW). Simulations indicate that free cooling from the wells alone should meet cooling demands most of the summer season; however, there is still uncertainty about whether compressor-based cooling (reversal of the heat pumps) will have to be used at the end of the cooling season or under peak load conditions. The paper presents the Lowex system design, borehole field sizing based on in-situ thermal response test (TRT) results, and long-term Superposition Borehole Model (SBM) simulations for the 10-well field. The school was completed and occupied in August 2025; commissioning and tuning are ongoing, so measured verification of the simulated performance is pending.