White roof coatings have existed in hot countries for a long time. These coatings help to reflect solar energy back into the atmosphere, rather than heating up the building. To achieve this white finish, pigments and fillers like titanium dioxide and calcium carbonate are used.
This article demonstrates that, with the use of hollow glass microspheres in a coating, one can achieve a high level of total solar reflection with the dry film. This helps to reduce the need for energy-intensive cooling systems.
It is worth noting that there are many coating applications possible with this technology and that it is not just restricted to improving the energy efficiency of buildings. Other examples that would benefit from the use of solar heat reflective coatings include caravans, mobile homes, cold storage distribution centres, refrigerated vehicles, oil and gas storage tanks, cryogenic tanks and tankers, and deck coatings.
Total solar emission comprises UV, visible and IR radiation – the latter responsible for heating. In this article, we will show that hollow glass bubbles offer an excellent level of reflection in both the visible and IR regions of the spectrum.
Testing hollow glass microspheres for Total Solar Reflectance when incorporated into a coating
A waterborne coating was formulated for the subsequent TSR testing. Glass bubbles are compared with calcium carbonate on a volume replacement basis. For this study, 22.5% by volume of glass bubbles or calcium carbonate were used.
A Perkin-Elmer spectrophotometer was used to analyse the Total Solar Reflectance of the subsequent coating at 400 microns. hollow glass microspheres outperformed the reference filler (calcium carbonate). Conventionally filled roof coatings absorb over 50% more solar energy compared to systems containing the novel, small particle size glass bubbles. This correlates to impressive temperature reduction. These coatings can also be applied with an airless sprayer, without breakage of the hollow glass microspheres.
How does Total Solar Reflectance correlate with the reflection of heat?
Each coating was painted onto an aluminium panel and exposed to an IR lamp. A thermocouple on the other side of a supporting polystyrene box was monitored over time, to investigate the thermal barrier presented by the coating.
A good correlation is found between Total Solar Reflectance and the level to which heat transfer is reduced through the coating. with a reduction of 10°C when compared to the coating containing only calcium carbonate.
What other benefits can hollow glass bubbles impart to your coating?
Additionally, hollow glass bubbles reduce microcracks forming in the coating, due to the reduction of shrinkage and warpage under temperature fluctuations. These cracks can form thermal bridges through the coating and areas for water infusion, leading to subsequent algae and fungal growth. Glass bubbles reduce crack formation when using nails or screws.
Author: Adam Morgan , Ph.D.
