Effect of retro-reflective materials on building indoor temperature conditions and heat flow analysis for walls

• A new material, retro-reflective material, is researched experimentally and numerically.
• The heat flow is reduced by more than 30% due to the covering of retro-reflective material.
• The peak temperature of indoor air is reduced up to 8 °C at natural conditions.
• The peak temperature of outer surface is reduced up to 20 °C at natural conditions.

Reducing the solar heat gain of buildings is an effective way to improve the building thermal conditions in summer and reduce the energy consumption. Although highly reflective materials can reduce the heat gain of the target building by specular reflection, they also increase the heat gain of the surrounding buildings owing to the fact that the reflected radiation is only transferred, not eliminated. In this situation, this study considers retro-reflective materials, which can improve the building temperature conditions by reflecting the solar radiation back in the opposite direction. Comparative experiments were conducted without any conditioning in summer, and the experimental results show that due to the covering of the retro-reflective materials, the peak temperatures of the indoor air and the inner surfaces were decreased up to 8 °C and 10 °C, while the outer surface peak temperature was reduced up to 25 °C. Through a comparison of the walls in different orientations, the top, south and east walls were found to be better choices for covering with the retro-reflective materials. To explore the influence of retro-reflective materials on the inner surface heat flow, a one-dimensional wall heat transfer model was built for four typical walls with an indoor constant temperature of 25 °C, and this model was verified by the experimental data. The numerical results showed that, due to the addition of the retro-reflective materials, the inner surface heat flow can be reduced by more than 30%, and the outer surface peak temperature can be reduced by 10–20 °C, clearly demonstrating that retro-reflective materials can reduce the outer surface temperature effectively.