Experimental study on the cooling performance of shading boards with different emissivities at the underside

Abstract

The settlement of roadways in permafrost regions is sensitive to the warming of the permafrost under the roadbeds. Various measurements have been proposed to cool the roadbeds for preserving the underlying permafrost. One of these measurements is to install shading boards over the side slope of the roadway embankment for sheltering the side slope from solar insolation. Under the board, an air gap with a 30-50 cm thickness is left for draining the heat from the side slope via the stack effect. However, boards over such an air gap are rendering to the risk of wind damages, which have limited the application of the shading boards as a popular roadway-cooling method. Here we investigated if the heat gain of the embankment soil can be curtailed by reducing the emissivity of the board's underside (εu). A group of shading boards with different εu was placed side by side in a permafrost region for testing the temperature of the soils under the boards. It is found that the board with a lower εu retains the solar absorption at the board and curtails the heat radiating to the underlying soils. As a result, soils under shading boards with a lower emissivity at the underside stay cooler. Further studies are called to measure the soil temperature under boards with different εu in a long period and to understand how the condenser and icing on the board's underside influence the temperature of the embankment soils.