Evaluation of thermochromic elastomeric roof coatings for low-slope roofs

Large cities have significant climatic impacts owing to clustered buildings, high population densities and numerous automobiles. Effects of crowded construction have to this date not been fully studied. Furthermore, there is need to mitigate the urban heat island effect caused by the latter. Researchers have already unveiled a promising means of doing so, which entails conserving energy through cool roof technology, especially in commercial low-slope roofing. For such roofs, energy saving attributes outweigh aesthetics for the obvious reason. Production of such roofs would utilize thermochromic roof membranes were it not for their absence in the market. To this end, there is need to develop a thermochromic material, characterized by a large solar reflectance above the transition temperature and a large change in solar reflectance. The work entails a detailed attempt to fabricate a composite material in a multi-layer system can provide the desired performance in order to minimize energy usage on both hot and cold days.

Dow Chemical Company scientists in the United States: Manish Sharma and colleagues evaluated the performance of a commercially available leuco dye (T_c ∼ 32 ^◦C) as a thermochromic additive in the fabrication of a multi-layered thermochromic roof coating system. The team also aimed at conducting tests for UV stability and energy saving so as to determine the commercial viability of such coatings. Their work is currently published in the research journal, Energy and Buildings.

Briefly, the procedure for the proposed analysis involved the preparation of thermochromic elastomeric roof coatings for low-slope roofs. This was done by incorporating a commercial thermochromic dye into a white acrylic elastomer matrix. Additionally, the research team applied thermochromic coatings in a bid to protect the developed structure. Eventually, weathering studies and cost calculation were undertaken to determine the economic feasibility of the developed material.

The authors observed that under optimal conditions, the smart roof coatings fabricated exhibited a maximum solar reflectance change of 20% with high temperature solar reflectance of 70%. In addition, they also noted that the thermochromic dyes used were photosensitive and displayed an irreversible degradation within 96–144h accelerated aging. Unfortunately, the researchers noted that the barrier coating synthesized were not as effective as anticipated in providing protection to the coatings.

Manish Sharma and colleagues study successfully presented the preparation of multilayer thermochromic smart roof coatings by dispersing a commercial organic thermochromic dye in a conventional elastomeric roof coating. The failure of the barrier coating has been seen to be due to degradation as a result of absorption of visible wavelengths. Worse still, had the thermochromic smart roof coatings emerged stable, their incorporation in roof coating would still have not been viable economically relative to a static cool roof. Therefore, the study has opened the gates for a more in-depth techno-economic analysis of smart roofing technologies that will be technically and commercially viable. In addition, future work in the area of thermochromic pigments/dyes with higher thermal and UV stability is needed.