A numerical and experimental analysis of the aging of the cool roofs for buildings in Greece

Cool roof coatings remain cooler than absorptive roofs and thus predominantly are used in buildings that require the reduction of the indoor temperature and the cooling loads. Cool roofs can also reduce the ambient temperature. A currently contentious aspect of solar reflective cool coatings is the extent to which an initially high solar reflectance decreases with time.
In the present study, the aging effect on the optical and thermal characteristics of two cool roofs is reported. The buildings under investigation are two schools in Greece, in the city of Athens. The research in this field is roughly divided in four phases and includes the assessment of the optical and thermal performance of the cool roof. For each one of the phases the documentation of the building’s profile includes albedo measurements and infrared imaging of the roof. The first phase includes the above measurements on the existing roof. In the second phase the roof was cleaned at the points where the measurements were taken. The third phase includes albedo measurements and infrared imaging at the cleaned points. In order to estimate the change of the albedo and the surface temperature of the cool roof with time, the same cool coating was applied in a part of the roof. In the fourth phase the measurements were repeated for the new part of the cool roof.
With the aim of investigating what may cause this aging of the cool coating, chemical and biological analysis for two samples from the old and the new cool coating was also carried out.
This study also presents simulations of the buildings in order to estimate the effect of the aging of the cool roofs on the thermal comfort and the alteration of the cooling and heating loads using the EnergyPlus simulation Program.