Variation of Thermochromic Glazing Systems Transition Temperature, Hysteresis Gradient and Width Effect on Energy Efficiency

Abstract

Due to increasing pressure to reduce the energy demand in buildings, thermochromic thin film based glazing has become a recognized potential solution due to the intrinsic ability to modulate the solar heat gain of a window as a function of the materials temperature. These "intelligent" glazings have been investigated for several years, and it has been found that, through variation of synthetic route, the thermochromic properties (transition temperature, hysteresis gradient and width) can be altered; however, less attention has been applied to how such alterations affect the overall energy savings attributed to the materials. In this study the building simulation software EnergyPlus TM has been used to model a series of idealized thermochromic spectra in a series of different environments to evaluate their energy saving potential against both clear glass systems and industry standards. The idealized spectra are used to see what effect each of the materials thermochromic properties and therefore elucidate which are the most important with respect to the energy saving properties. It was found that the best thermochromic materials were those with a narrow sharp hysteresis and a low transition temperature and result in an increase in energy saving between 30%-45% across the different environments compared to clear glass systems.

Thermochromic Oxide-Based Thin Films and Nanoparticle Composites for Energy-Efficient Glazings

“…This type of variation in T(λ,τ) clearly is the desired one, and a glazing with a VO 2 -based TC thin film transmits more energy below τ c than above τ c . Similar properties have been recorded many times [31][32][33][34][35][36][37][38][39][40][52][53][54]. Figure 3 also demonstrates that corresponding data on R(λ) increase monotonically towards long wavelengths for the metallic-like state above τ c , which is the expected behavior.…”

Mitigation of hysteresis due to a pseudo-photochromic effect in thermochromic smart window coatings

“…In the non-absorbing case, as in previous work 3,7 , this modulation is assumed to occur by changes in reflectance, where the solar absorption is 0% in both high and low solar transmitting states. In the absorbing case, it is assumed that in the low temperature state 20% of incident solar radiation is absorbed whilst in the high temperature state 40% of incident solar radiation is absorbed, which is representative of optimised nanoparticle composites 12 .…”

“…The absorbing and non-absorbing coatings investigated are both assumed to have a solar transmittance modulation of 20% ( T max = 0.8; T min = 0.6) which is a target theoretical performance for thermochromic window coatings 8 , 12 . In the non-absorbing case, as in previous work 3 , 7 , this modulation is assumed to occur by changes in reflectance, where the solar absorption is 0% in both high and low solar transmitting states. In the absorbing case, it is assumed that in the low temperature state 20% of incident solar radiation is absorbed whilst in the high temperature state 40% of incident solar radiation is absorbed, which is representative of optimised nanoparticle composites 12 .…”

“…1b for definitions). Previous investigations into the effects of transition gradient width and hysteresis width have focused on idealised cases, where films modulate solar transmittance solely via changes in reflectance, such that they are non-absorbing and do not re-radiate thermal energy into the building 3 , 7 . In these cases it has been found that the switching temperature should be at room temperature, transition gradient sharp, and hysteresis width narrow.…”

Environmental Benefits of Thermochromic VO2Windows: Life Cycle Assessment from Laboratory Scale to Industrial Scale

“…[10] In order to fit with the smart window application, W-doped VO 2 is considered rather than VO 2 to lower the transition temperature because a transition temperature around 25 C was found to be the most efficient for building energy efficiency. [12,30] The process consists in a hydrothermal synthesis using vanadium pentoxide (V Europe without Switzerland.…”