ISO 16957

Description / Abstract: This International Standard describes a method of measuring the thermal conductivity (diffusivity) of a wet porous building material and a method of evaluating the measurement uncertainty.

While ISO 10051 is the current International Standard, based on a steady-state method, this International Standard proposes a method that makes use of a non-steady-state method which uses a small temperature change with a short period as an input. Along with the measurement, an evaluation of the measurement uncertainty is described, which makes possible a simple and practical measuring method.

This International Standard intends to measure the apparent (effective) thermal conductivity, including latent heat transfer caused by vapour movement. The situation in which moisture and/or air movement occur due to convection or gravity is excluded. The application of this International Standard to high moisture content is excluded so that the gravity effect can be neglected. This International Standard can be applied to a porous material heavier than about 100 kg/m³, in which radiative heat transfer can be neglected.

This International Standard specifies the following:

a) a non-steady-state method of measuring thermal conductivity;

b) an approximation formula for the measurement uncertainty caused by moisture movement and nonuniform moisture distribution (and, thus, a determination of the measuring conditions that satisfy the upper limit of measurement uncertainty);

c) an estimate of the heat transfer caused by moisture (vapour) movement.