Keeping cool with lower emissions: comparing internal to external blinds as solar shading devices

High-performing building envelopes play a crucial role in the sustainable refurbishment of the existing buildings, especially in consideration of an increasing energy demand for cooling. Dynamic external shadings are recognized for their higher energy efficiency as compared to internal blinds, as they effectively block solar radiation, thereby mitigating internal discomfort. However, their life-cycle impact is frequently underestimated, especially regarding material intensity, recycling potential and operational requirements. This study investigates the performance and environmental impact of four commercially available innovative internal blinds as a potential alternative to conventional external venetian blinds, using an office building in Zurich as case study. Through a multidisciplinary analysis and a novel approach that incorporates the thermos-optical properties of the materials, five shading devices are compared in terms of energy savings, thermal comfort, daylighting quality, and carbon emissions. Results suggest that a roller blind with low-e coating, a cellular shade, a high-transparency curtain and a high-reflectivity fabric louvre device offer a 10% greater reduction of overall energy demand compared to aluminium external venetian blinds. Moreover, a 60-year life cycle assessment indicates that the internal blinds analysed exhibit up to 70% lower embodied carbon as compared to the outdoor venetian blinds. Additionally, they offer ease of installation and maintenance, thus providing potential cost benefits. The final SWOT analysis provides practical guidance for performance-oriented design choices. This study demonstrates the effectiveness and environmental benefits of simple, easy-to-install, standardized solutions for retrofit interventions.