FIW München was one partner in an illustrious group that was involved in a three-year project to improve measurements of the total hemispherical emissivity of reflective films: national metrological institutes, institutions involved in certifying insulation materials, research laboratories, a manufacturer of low-emissivity insulation materials and the manufacturer of TIR-100 emissometers (IN-GLAS).
Alongside improving the accuracy, repeatability and calibration of the industrial measurement technique, one aim of the project was to develop a "best practice guide" for emissivity measurements using the TIR-100 instrument. Important boundary conditions for carrying out the measurement were defined.
Taking measurements with the TIR-100 devices provides an almost normal emissivity, which still has to be converted into the total hemispherical emissivity for use in construction, for example in measuring the thermal resistance of air layers or gas gaps in glazing.
Both the uncertainties in measuring the normal emissivity using the TIR-100 device and the uncertainties in converting it to hemispherical emissivity were analysed in the project.
This yields a combined expanded uncertainty of 0.36 for the total hemispherical emissivity. This conclusion is based on a limited number of emissivity results with relatively large uncertainties. As a consequence, at this time the members of the EMIRIM project recommend against lowering the limit value for the lowest declarable emissivity to 0.05, as is envisaged in the proposed amendments and comments aimed at improving DIN EN 16012.
The project was funded by the European Metrology Programme for Innovation and Research (EMPIR) under grant agreement 16NRM06 "EMIRIM". The
EMPIR initiative is co-funded by the European Union's Horizon 2020 research and innovation programme and the countries participating in EMPIR.