Thermochromic glazing performance: From component experimental characterisation to whole building performance evaluation

Thermochromic switchable glazing have been gaining increasing popularity among dynamic building envelope solutions aimed at reducing energy demand in tertiary buildings, due to their capability of varying optical properties according to the material temperature. This enables the management of entering solar loads without any need for an active control, hence thermochromic glazing performance relies on effective material design. Nevertheless, to date the development of thermochromic glazing materials has relied on limited building performance evaluations, considering the effect of managing solar radiation on energy use for heating and cooling alone, and without representing in a comprehensive way the variations of the thermochromic optical properties to include hysteresis phenomena. The present paper aims to evaluate the building performance of a ligand exchange thermochromic glazing (LETC), characterised by a wide variation of optical properties in the visible and solar spectra and hysteresis between heating and cooling cycles. To this aim an ad-hoc developed building performance simulation strategy is presented, enabling data integration between dynamic thermal simulation and climate based daylight analysis, including a thermochromic parametrical model describing the hysteretical variation of optical properties as a function of material temperature, derived from experimental measurements. The simulation method is adopted to evaluate the energy uses for heating, cooling and lighting and the visual comfort in an office space integrating the LETC glazing in different climatic contexts. The results show that the LETC glazing is able to optimise multiple building performance aspects simultaneously. Compared to static glazing benchmarks with comparable selectiveness, for the considered locations, the LETC glazing achieves a total energy use reduction from 3% to 10% and daylight availability improvements from 5% to nearly 20%. Increasing the thermochromic hysteresis has shown a positive effect on improving daylight availability (from 5% to 15%) and on reducing probable glare due to direct solar radiation (from 12% to 25%), with negligible effect on total energy use. Finally, the simulation framework presented represents a general method that can be adopted to evaluate the performance of other switchable glazing technologies as well.