Utilizing solar energy for anti-icing road surfaces using hydronic heating pavement with low temperature

Doktorsavhandling, 2019

During summer, the surface temperature of an asphalt road pavement can rise up to 70°C due to absorbed solar radiation. The high temperature degrades the performance of the asphalt concrete by accelerating the thermal oxidation and plastic deformation, especially under heavy traffic loads. On the contrary, during winter, the temperature of road surfaces can reduce below the temperature of the ambient air due to the radiative heat loss. The low temperature hardens the asphalt pavement and makes it more susceptible to thermal cracking. Moreover, the low temperature causes the road surface to get slippery and hereby increases the risk for traffic accidents. A potentially environmental-friendly method to overcome the abovementioned problems is to use a Hydronic Heating Pavement (HHP). The HHP system consists of embedded pipes in the road. A fluid as thermal energy carrier circulates through the pipes. During sunny days, when the road surface is warm, the energy is harvested and saved in seasonal thermal energy storages. During cold days, the warm fluid from the storage is pumped back to the pipes to increase the surface temperature.

The aim of this study is to investigate the feasibility of the HHP system for harvesting solar energy during summer and anti-icing the road surface during winter. The study is done in five different steps: (i) determining the thermal properties of three typical asphalt concrete used for the construction of roads in Sweden using experimental tests and numerical simulation models, (ii) developing a 2D numerical simulation model of the HHP system to find out the most suitable boundary condition equations associated with the heat transfer interactions between the road surface and surrounding climate as well as the initial results related to the required energy for anti-icing the road surface and remaining number of hours of the slippery condition on the road surface, (iii) developing a hybrid 3D numerical simulation model of the HHP system to obtain the fluid temperature decline along the pipes and the effects of the fluid flow rate on the performance of the HHP system, (iv) calculating the minimum required energy for anti-icing the road surface using optimization tools so no slippery condition remains on the road surface and (v) investigating the feasibility of the coupled HHP system to a Horizontal Ground Heat Exchanger (HGHE) for harvesting solar energy and anti-icing the road surface. The numerical simulation model of the HHP system is made based on the finite element method and validated by the experimental results and analytical solutions as well as by the results of the other numerical simulation models from literature.

The results associated with the thermal properties show that the thermal conductivity of asphalt concrete can vary from 1 W/(m·K) to 3 W/(m·K). The results associated with the 2D numerical simulation model shows that the annual required energy for anti-icing is about 75  and the remaining number of hours of the slippery condition after heating the road surface is 128 hours. The results associated with the hybrid 3D numerical simulation model show that the annual required energy for anti-icing is about 84  and the remaining number of hours of the slippery condition after heating the road surface is 217 hours. The results associated with the optimization show that the minimum annual required energy for anti-icing the road surface is 107  which results in remaining only 3 hours of the slippery condition on the road surface. Furthermore, the results associated with the coupled HHP system to the HGHE show that the annual required energy for anti-icing is about 75  and the remaining number of hours of the slippery condition is 580 hours.