Shading boards with smaller lower-surface thermal emissivity perform better cooling effect

- We propose a theoretical model for the thermal balance of shading boards.
- The thermal balance of the shading boards during nighttime is validated.
- Decreasing the board lower-surface thermal emissivity enhances the cooling effect.

Roadway embankments over permafrost stratum are susceptible to thawing damage. Installing shading boards on the embankment side slope reflects solar irradiance back to the sky and thus has been deemed as a roadbed cooling technique. Research on the cooling effect of shading boards has centered on the temperature evolution of the roadbed under the board and on the optimum design of the board. Few researches, however, have been dedicated to understand the heat balance between the board and the embankment and to adapt the board's thermal properties to maximize the cooling effect. This study models the heat flux balance between the board and the embankment side slope and validates the model with measured data logged from an in situ shading board experiment. The validation of the model reveals that shading boards with smaller lower-surface thermal emissivity perform stronger cooling effect. Further outdoor experiments are expected to paint the shading board upper surface with differential albedo to understand the influence of board albedo on the cooling effect.