Winter Road Maintenance using Renewable Thermal Energy

Licentiate thesis, 2017

Winter road maintenance is costly but it is inevitable since it is necessary to keep roads accessible and safe during winter. Current winter road maintenance methods use annually 600 000 tons of salt, in the Nordic countries. The salt ends up in the environment along the roads and results in environmental challenges. This thesis proposes an alternative, winter road maintenance concept for critical parts of the road infrastructure. The proposed concept consists of a hydronic pavement (HP), utilised as solar collector, which is connected to a borehole thermal energy storage (BTES). The combination of an HP and a BTES (called renewable HP) means that the solar radiation will be harvested in the summer time and the stored energy will be used for winter road maintenance at critical parts of a road infrastructure. In existing hydronic pavements district heating or other high temperature energy sources are currently used, however, high temperature energy sources limit the implementation of HP systems. Research on using low temperature energy sources can result in a reduction of primary energy need 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 HP. The renewable HP systems are mostly suitable for areas with mild winters. For locations with harsher climates there is 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 annual number of hours with risk for ice formation from 400 hours and 855 hours, to 6 hours and 23 hours respectively. However, in order to reach low risk levels, further development of control systems will be needed.