LCA of Passive Smart Windows

Abstract

The building sector is increasingly acknowledging the necessity to mitigate its environmental impact in response to the challenges posed by climate change. Adaptive facades specifically are used to develop a dynamic control of the envelope’s properties, modifying their behaviour in response to outdoor conditions and indoor stimuli. Thermochromic and photochromic technologies, also known as Passive Smart Windows (PSW) are passive solutions that aim to regulate solar gains through the integration of an Auto-Responsive (AR) layer, particularly for cooling purposes, to reduce energy consumption and minimize the operational impact of buildings.
Existing literature predominantly concentrates on the performance aspects of these technologies, mainly due to their early development stages. However, there remains a gap in assessing the overall environmental impact, both in terms of impact perspective, thus considering several possible effects
on the environment, and from a life cycle perspective, thus including both embodied and operational dimensions. The embodied impact, in particular, lacks comprehensive examination beyond considerations of Global Warming Potential (GWP). Furthermore, the dynamic landscape of materials and principles utilized in these technologies adds complexity to their evaluation.
This thesis project aims to bridge these gaps by establishing a comprehensive framework for evaluating the total impact of PSW, encompassing both embodied and operational stages. Through comparative analysis with alternative Dynamic Window Systems (DWS), comprising static windows paired with dynamic shading devices, the framework facilitates a thorough examination. Operational energy calculations are grounded in energy simulations of a standard office space with an exposed facade, while the description of the embodied stages gives an overview of the life cycle of PSW, with focus on different possibilities integrating the AR layer and their consequences.
The application of the framework in a case study reveals nuanced findings. While the GWP of PSW decreases of 1,1%, most of the other impact of PSW increase, including a growth of 0,1% of the Single Score. PSW has a lower impact compared to DWS due to the increased energy demand of the latter but, contrary to the initial expectations, the PSW does not consistently outperform static glazing due to conservative assumptions in energy simulation and a higher replacement rate, which significantly escalates embodied impact. Notably, challenges arise in defining materials for the AR layer, necessitating collaboration with manufacturers to improve data availability.
The study identifies replacement as a critical factor in determining overall impact, underscoring the importance of extending the lifespan of PSW or to consider a detachable layer to enhance its environmental sustainability. However, criticisms regarding the partial nature of the analysis emerge, particularly in neglecting user comfort and control over the facade, as well as the temporal flexibility of the technology. Future research directions should incorporate these aspects for a more comprehensive evaluation.
Ultimately, this thesis emphasizes the interdependency between the LCA approach, the energy simulation and the context of the PSW’s application. This highlights that the environmental impact assessment of such building elements can not leave the contextual application out of consideration in order to provide a sufficiently reliable result, thus limiting the use of this framework mainly to defined projects rather than to the estimation of generic impact for a PSW product.