Status on Reference Material for Guarded Hot Plate Equipment for Thermal Conductivity at Higher Temperatures in Europe

Abstract

This paper gives a short summary of activities in Europe to secure higher accuracy in testing of thermal conductivity at higher temperatures. Official reference material for measuring thermal conductivity for thermal insulation products at temperatures above 50°C is not available in Europe or in North America. Several investigations to find a relevant material have so far only had limited success. When the legal requirement to measure and declare the thermal conductivity at high temperature came into force in Europe (CE marking of thermal insulation products for industrial applications) different actions were taken: 1. FIW found and characterized a material, glass granulate, which can be used both on GHP, pipe tester and the sphere equipment. Intensive documentation was performed to ensure that the material could be used for round robin between the European laboratories. Comparative testing between all commercial 3rd party labs has taken place. The material has not been approved for further documentation as a reference material by IRMM because it is difficult to handle. The comparative testing between the European 3rd party laboratories will be reported officially when all labs have finished measurements. A round robin in Germany with glass granulate using different test methods has been reported. 2. A high temperature round robin was conducted in the period 2007 to 2010 using a silicium-magnesium fibrous board. The results are presented and discussed. 3. The European Union (EMRP, European Metrology Research Programme) has supported a project intended to identify material useful for reference material, EMRP EURAMET SIB52 Thermo under the lead of NPL. In this project, high density calcium silicate (HDCaSi-N) was identified as a potential reference material, however a lot of work is still needed before this (or another) reference material is fully developed and available on the market by IRMM. To overcome the lack of reference material for the annual internal checks of the GHP in the lab, this paper also describes the activity performed within the EFiC laboratory (European Fire & Conductivity Laboratory). Test specimens prepared of high density stone wool lamellas fixed by metal bars have proven stable for many measurements at mean temperatures up to 550°C and have been useful to document the stability of the calibration for 5 years so far. The test specimens are easy to handle and therefore easier and faster to install for testing than the glass granulate for the GHP equipment. The material characterization, the specification for the test specimens as well as test results are shown in this paper.