Spectral optical performance of phase-change-material-filled glass-block system: Experimental evaluation and comparative exploration

Research on sustainable building design is pushing boundaries to introduce innovative solutions that enhance energy efficiency and improve user comfort. The integration of phase-change materials (PCMs) into transparent façade elements has gained substantial attention; however, its widespread application in current construction practices remains limited. This study examined the solar/light transmittance of PCM-based materials embedded in transparent façade elements, focusing on providing and comparing the optical properties of modular glass blocks integrated with PCM measured experimentally in a laboratory setting. Optical properties of multi-layer and non-homogeneous systems represent a more complex problem in terms of proper characterisation. To overcome this limitation, more comprehensive approaches can be considered, including integrating spheres to perform measurements on the complex nonhomogeneous glass system. This study employed spectrophotometric measurements within the visible and near-infrared (NIR) spectra by two different measurements methods: a direct method and one using an integrating sphere. Additionally, the investigation was based on a comparison between clear and various PCM-filled glass blocks. The results demonstrated that the direct method facilitated reliable spectral transmittance measurements with deviations not exceeding 3 %. In addition, the results revealed that paraffinic PCM glass blocks in liquid phases could achieve up to 90 % of light transmission and act as a highly transparent system in the visible region compared with conventional air-based glass blocks (up to 77 %). However, in the NIR region, the spectral transmission of PCM glass blocks was reduced by half (around 46 %). Depending on the PCM type in solid phases, the visible transmission is significantly reduced, which is from 5 % to a maximum of 19 %. This study contributes to the expanding knowledge base on adaptive building systems, particularly those related to PCM integration in transparent façade components.