Thermal inertia as an integrative parameter for building performance

Abstract

Traditionally, the energy efficiency properties of building envelope components are prescribed world-wide using the steady-state “U-value” where the insulation capabilities rely on the thermal conductivity of construction materials only. However, the heat flow through the building envelope is also restricted by the effect of other material properties combined in the form of the thermal inertia, a widely used parameter that can be controlled in the building environment through transient-state parameters such as the cyclic transmittance “u-value”. By controlling the thermal inertia of the building envelope components key aspects of the building performance such as the building thermal, energy efficiency and fire performance can be evaluated in a holistic manner so that balanced design solutions are obtained without detriment affecting each other. Herein, it is proposed a holistic assessment method that uses a numerical model to obtain the thermal inertia of building components from their thermal insulating parameters to ultimately predict reaction-to-fire performance. The method includes a complementary thermal test to achieve reliable and realistic assessments that enable the analysis of aspects like the effect of construction imperfections. Two wall assemblies were built first to illustrate the method including the thermal test and finally to verify the method by conducting reaction-to-fire tests.