An intercomparison of heat flow meter apparatus within the United Kingdom and Eire

Abstract

The heat flow meter (HFM) technique is widely used for rapid and reliable measurement of apparent thermal conductivity of thermal insulation materials. In the British Isles there is a large number of HFM apparatus of different sizes and forms, mainly in the quality assurance and research laboratories of thermal insulation manufacturers. With the advent of European legislation requiring manufacturers to declare thermal performance values of their products, the National Physical Laboratory organised an intercomparison to assess the comparability and accuracy of industrial HFM measurements in the UK and Eire with the aim of helping to establish consistent measurements. Seventeen HFM apparatus featured in the intercomparison, with NPL using a guarded hot-plate apparatus to provide baseline thermal conductivity values. Measurements were made at 10 °C and 23 °C, on two thicknesses of samples of expanded polystyrene, extruded polystyrene, and high density rock fibre. With few exceptions, the measurements agreed to within ±5%. In a total of 154 data points 69% were within ±3%, and 50% were within ±2%. Measurement differences due to calibration issues and equilibrium time variations are discussed, together with proposals for further reduction of measurement uncertainties.