Verification of thermal conductivity measurements using guarded hot plate and heat flow meter methods

The guarded hot plate (GHP) and the heat flow meter (HFM) methods are two widely used techniques to measure the thermal conductivity (λ) of insulation specimens. In this study, the λ measurement of the two methods was validated using the certified reference material (CRM) IRMM-440 and an expanded polystyrene (EPS) board at temperatures from − 10 to 50 °C. The GHP apparatus was a commercially available apparatus for 300 mm × 300 mm specimens, and the HFM apparatus for 900 mm × 900 mm specimens was built in-house. The λ of the CRM measured using the GHP was within 2% of the certified λ value. Subsequently, the λ values of specimens of nominally identical EPS with 20 mm thicknesses were measured using both the GHP and the HFM methods. A comparison of the λ measurements showed that the two methods were consistent to within 3%. Finally, the λ values of EPS specimens of various thicknesses from 50 to 200 mm were measured using the HFM method. Although the specimens were nominally identical, values of λ for the specimens with thicknesses of 20−150 mm were increased by 0.09% mm−1 at − 10 °C and by 0.07% mm−1 at 10 °C.