Abstract

Background

Phase change materials (PCMs) have been proposed as a means to increase the thermal inertia of glazing systems. These materials have optical features that need to be investigated and characterised in order to better understand the potential of these systems and to provide reliable data for numerical simulations.

Methods

The spectral and angular behaviour of different PCM glazing samples, characterised by different thicknesses of PCMs, were investigated by means of commercial spectrophotometer and by means of a dedicated optical test bed that includes a large integrating sphere with a diameter of 0.75 m. Such equipment was necessary because of the highly diffusive behaviour of the PCM layer when in the solid state of aggregation.

Results

The paper provides a data set of luminous and solar properties of glazing units with PCMs in gaps; the data set uses results from an advanced optical facility that overcomes the intrinsic limitations of commercial spectrophotometers in measuring the optical properties of the advanced transparent materials. In detail, transmittance, reflectance and absorptance spectra of double glazing units characterised by different PCM layer thicknesses in the gap, measured at different incident beam angles, are reported. Integrated values calculated according to relevant international standards are thus provided. Optical features of PCM glazing systems are also highlighted and issues related to the integration of these systems in buildings are discussed.

Abstract

Sodium tungstate (Na-WO3) nanorods with typical diameters of 10-200 nm and lengths of several microns were prepared via hydrothermal synthesis. X-ray diffraction showed that the material crystallized in a hexagonal phase (space group
P6/mmm) with unit cell dimensions of a = 7.3166(8) Å and c = 3.8990(8) Å. The as-prepared Na-WO3 nanorods showed a distinctive visible-light-driven photochromism related to a proton-electron double injection process. The involved local
structural evolutions were monitored by Fourier transform infrared (FTIR) and Raman scattering spectroscopy. One diagnostic FTIR absorption at 585 cm-1 and one Raman band at 813 cm-1 were identified and assigned to the O-W-O stretching vibration. These two modes were strongly affected by the proton and electron insertion, showing promises for studying the chromogenic properties of hexagonal WO3 materials.