Thermal Characterization of Different Insulating Materials via Experimental Analysis in a Guarded Hot Box

Abstract

The thermal characterization of building envelope materials is a crucial phase in understanding the building energy performance, and it is commonly evaluated through the thermal transmittance, often synthetically indicated as U-value. There are several ways to experimentally assess the U-value of insulating materials and multi-layers systems, usually defined by means of experimental in-situ heat flux measurements, where, however, a considerable variation of the boundary conditions may occur, making the measurement difficult. In this work, the experimental thermal characterization of different insulating materials applied to an X-lam wall is presented. The analysis is carried out using a Guarded Hot Box, which allowed to reproduce real, repeatable, and controlled operating conditions. Two different insulating materials were selected: expanded polystyrene (EPS) with graphite and hemp. The experimental tests were carried out by imposing a temperature difference reproducing the common operating conditions (0°C in cold chamber and 20°C in hot chamber). Steady-state conditions (constant temperature in the chambers) have been imposed to determine the thermal properties of the multi-layer systems. The tests, lasted 72 hours each, showed U-values equal to 0.15 W/m2K ± 3.1% for EPS with graphite and 0.19 W/m2K ± 3.1% for hemp.