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:

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

This paper deals with the experimental assessment of the energy performance of two Advanced Integrated Façade modules (AIF) characterized by two very similar configurations. The two AIF modules were installed on the south-exposed façade of an outdoor test cell facility (a real-scale mockup of an office building) and continuous measurements were carried out for more than one year. Data collected during the experimental campaign were analyzed to evaluate the energy performance and thermo-physical behaviour of the AIF modules. The performances of the two systems were assessed by comparison and by means of conventional and advanced synthetic metrics.

The results of the activity point out the different performances of the two configurations, which only differs on the inner-side glazing (a stratified single clear glass pane vs a stratified low-e double glazed unit). It was demonstrated that just a single additional glass layer can contribute to substantially improve the energy performance of a quite complex façade technology. On average, the façade configuration with the stratified low-e double glazed unit shows the abatement of heat loss and of solar gain of about 30% during the whole year. Moreover, the reliability of some conventional and less conventional metrics in assessing the performance of dynamic façade technologies was also investigated. The results confirm that conventional metrics are not fully reliable when they are used to assess advanced building envelope components with high level of dynamic.

Façades play an important role in architecture, with deep implications in both the quality of the indoor environment and the appearance of the building. R&D in the field of energy conservation is moving toward advanced integrated façades (AIFs): these are innovative and dynamic façades deeply connected with the building equipment. Their dynamic features allow the energy performance of the façade to be optimized, adapting its behavior to different boundary conditions. The substantial lack of synthetic performance parameters to assess and to characterize the energy performance of AIFs is one of the main limitations to the widespread of these technologies. This inconvenience is due to the fact that conventional synthetic metrics (such as U-value and g-value) cannot be fully applied with these technologies. The research activity presented in the paper is an attempt to investigate new synthetic metrics able to characterize the thermal behavior of an AIF. A multiple linear regression (MLR) approach is adopted to identify synthetic parameters able to replicate the energy performance of the façade as a function of the main boundary conditions, e.g., solar irradiance and thermal gradients.

The optical characteristics of an advanced glazing system are presented in this paper. The investigated glazing system is based on the incorporation of a paraffin-based Phase Change Material (PCM) into a transparent component, made of two extra-clear glass panes and a cavity where the PCM layer is placed. Due to the highly scattering property of the system (when the PCM is in solid state), the use of a large integrating sphere equipment (75 cm diameter) is necessary to obtain reliable results. The spectral transmission, reflection and absorption coefficients of the PCM glazing system are measured between 400 and 2000 nanometers, and the integrated values are calculated according to the relevant standards. The optical properties are determined with a maximum relative error of 4% (on the sum of the transmission, reflection and absorption coefficients), when the PCM layer is either in complete solid state or liquid state. The average error for all the optical properties is 2%. Different thicknesses of the PCM layer are used in order to assess the dependency of the optical properties on the PCM layer thickness. The angular dependency is also investigated for beam angle up to 45 deg

Transparent façades are often used to increase the aesthetic value of the building and to provide visual contact with the outdoor. However, together with several positive features, it should be mentioned that glass façades may reduce the quality of the indoor thermal environment, causing thermal discomfort especially due to overheating in the summer season. The aim of this paper is to compare the implications on thermal comfort of different glazed façades, whose surface temperatures have been monitored during several experimental campaigns. The analyzed glazing systems were double skin façades and non conventional single skin façades integrating different materials (i.e. phase change material, areogel). Starting from the measured internal surface temperatures, a fictitious office room was simulated in order to assess the thermal comfort performance through the calculation of the PMV index. Results show that the choice of the glazing system can strongly affect the thermal comfort of an office.