ISO DIS 9869-2

Description / Abstract: This international standard describes the infrared method for measuring the thermal performance of opaque building elements on existing buildings with high emissivity diffuse surface using an infrared (IR) camera. This standard is the screening test to identify the thermal performance defect area of building elements. It shall not be used for any certification methods for the performance of thermal insulation of the building components.

The thermal performance of a part of the building element is evaluated by obtaining the heat absorption (heat penetration) at the part of the indoor surface by multiplying the indoor total heat transfer coefficient of the part surface by the difference between the part indoor surface temperature and the indoor environmental temperature. The thermal transmittance (U-value) of the building components for steady state condition can be obtained with the averages of the observed values over the certain period of time.

The indoor surface temperature distribution of the building component is measured using an IR camera. The indoor environmental temperature is measured by installing the environmental temperature sensor (ET sensor) on the surface of the building component, and the indoor total heat transfer coefficient of the surface of the building component is measured using a heat transfer coefficient sensor. Even the indoor measurement should be carried on with less influence of solar radiation so as the standard shall be used on building elements on which indoor sides are not exposed to direct sunlight through adjacent windows.

The standard aims to measure the thermal transmittance (U-value) of frame structure dwelling with light thermal mass, typically with a daily thermal capacity calculated according to ISO 13786 below 30 kJ / (m².K). The U-value may be measured with an extended uncertainty below 50% for typical U-value greater than 0.5 W/(m².K). For a higher level of insulation, expected uncertainty would be much higher.