A performance case study of energy pile foundation at Rosborg Gymnasium (Denmark)

The Rosborg Gymnasium building in Vejle (Denmark) is partially founded on 200 foundation pile heat exchangers (energy piles). The thermo-active foundation has supplemented the heating and free cooling needs of the building since 2011 (4,000 m2 living area). Operational data from the ground source heat pump installation has been compiled since the beginning of 2015. The heating requirement of the building supplied by the ground source heat pump exceeds the free cooling covered by ground heat exchange. The asymmetric utilization of the soil should in principle, imply a decrease in the long-term ground temperatures. However, operational data show that the temperatures of the heat-carrier fluid do not fall below +4.2oC during the heating season (winter) and that the soil recovers to undisturbed conditions during the summer when heat demand is low. In addressing the consequences of an imbalanced ground heat extraction/injection activity , this paper provides a performance study of the energy pile-based ground source heat pump installation utilising operational data. The study demonstrates that the measured seasonal performance factors so far are lower than expected: 2.7 in heating mode and 4.2 in cooling mode. Nevertheless, there is room for improvement if novel energy management strategies are applied. This highlights the relevance of considering the daily heating/cooling requirements of the building during the design phase of the heating and cooling system. Moreover, this study demonstrates the feasibility of ground source heat pump systems based on energy foundations in heating-dominant buildings.