Winter Road Maintenance using Renewable Thermal Energy

Sammanfattning: Winter road maintenance is costly but it is an inevitability in order to keep roads, accessible and safe during winter. Current winter road maintenance methods utilises 600 000 tons of salt per year, in the Nordic countries. This salt ends up in the environment along the roads and causes environmental challenges. This thesis propose an alternative, winter road maintenance concept, for critical parts of the road infrastructure. The proposed concept involves a hydronic pavement (HP), utilised as solar collector, and connected to a borehole thermal energy storage (BTES). The combination of an HP and a BTES (renewable HP) means that the solar radiation will be harvested in the summer and the stored energy will be used for winter road maintenance at critical parts of a road infrastructure. District heating or other high temperature energy sources are used in existing hydronic pavements. However, high temperature energy sources limits the implementation of HP systems. Research on using low temperature energy sources can reduce the needed primary energy and makes implementation of HP systems more feasible. The purpose of this thesis is to investigate the feasibility of implementing hydronic pavements using renewable energy, in the Scandinavian countries. This thesis studies how a BTES can be connected to a hydronic pavement, focusing on the design of the BTES.  The studies are based on extensive literature reviews and numerical simulations considering the interaction between the hydronic pavement and the BTES. The studied systems have all been direct connected systems without supplementary heating such as boilers or heat pumps. The results revealed that BTES is a suitable thermal storage technology to be used in combination with renewable hydronic pavements. The renewable HP systems are mostly suitable for areas with mild winters. For locations with harsher climates there are a need for supplementary heating or increased number of boreholes in the BTES. The studied locations of Tranarp and Studevannet revealed that the renewable HP system can reduce the number of hours with risk for ice formation to 6 hours and 23 hours respectively. However, in order to reach low risk levels further development of control systems will be needed.