Harmonisation of test and calculation methods to evaluate the heat transfer across building components

Draft CEN (and ISO) standards for hot-box U value measurements of windows and insulated glazing units require calibration measurements to be carried out with glazed calibration panels of known thermal conductance. This panel design has been validated by five European partner laboratories (under the leadership of the National Physical Laboratory, Middlesex, UK) which each made panels to an agreed specification and carried out the calibration procedures specified in prEN 12412-1. The panels were then circulated to the other partner laboratories who measured their thermal transmittance, U, values using the CEN procedure. The work demonstrated that the uncertainty of the subsequent U value measurements made by the calibration data were within ±7%, The sensitivity of the CEN measurement procedures to the calculated conductance and temperature measurement accuracy is discussed and some improvements are suggested for the draft standards. The experience gained from the comparison on the calibration panels provides the chance to establish improved measurement as well as calibration procedures.