Thermo-optic durability of cool roof membranes: Effect of shape stabilized phase change material inclusion on building energy efficiency

Abstract

Cool roofs represent an acknowledged passive cooling technique aimed at reducing the amount of solar radiation absorbed by buildings and producing indoor overheating, particularly, in summer conditions. Cool roofs owe their unique behavior to improved thermo-optic performances which, however, have been shown to deteriorate when exposed to intense atmospheric weathering. In this context, the authors produced a shape stabilized composite with improved heat storage performance, by adding 15, 25, or 35 weight percentage of non-encapsulated phase change materials (PCMs) to the original blend of a liquid waterproof-polyurethane-based cool membrane. The behavior of such composite material, when exposed to accelerated temperature, humidity, and UV radiation cycles by means of standardized long-term weathering tests (QUV test), is investigated. The final aim of the study is to clarify if the PCM inclusion could help the membrane to better behave during the course of the time, because of thermal stress reduction. In order to do so, controlled atmospheric forcing and surface temperature continuous monitoring are used to investigate the degradation of the membrane produced by the imposed weathering stress. Results show that the introduction of 25% PCM in weight optimizes the superficial finishing characteristics of the prototype, allowing to maintain a more stable thermo-optic behavior, reducing both the thermal-induced degradation and the leakage phenomenon.