Experimental and numerical assessment of the impact of increased roof reflectance on a school building in Athens

This paper describes an effort to estimate the impact of a cool roof (characterised by increased solar reflectance compared to the initial roof and high infrared emittance) on the energy performance and thermal behaviour of a non-cooled school building in Athens, Greece. An experimental monitoring campaign has been carried out before and after the application of a white elastomeric coating with a solar reflectance of 0.89 on the roof of the building. The air and surface temperature of the building have been measured and a set of meteorological parameters have been collected. An infrared camera has been used to depict the differences in the surface temperature before and after the cool roof application. The monitoring results are complemented and supported by building simulation. The building has been modelled into TRNSYS software and the model has been calibrated and validated using the experimental data. Simulation results show a decrease in the air temperature in the classes that reaches 2.8 °C and a decrease in the annual cooling load by 40%. The corresponding heating penalty (i.e. the increase of heating load) is 10%. Additionally, the impact of the cool roof on thermal comfort, peak power and surface temperature has been assessed.

► We examine the impact of a cool roof on a 410 m2 school building in Athens Greece.
► The indoor air temperature was reduced by 1–3 °C during summer.
► The annual cooling load reduction was 40% and the heating penalty was 10%.
► The surface temperature was decreased by as much as 25 °C.
► Daily surface temperature fluctuations are reduced suggesting a longer lifespan of the roof.