Determination of core thermal resistance errors of reflective multifoil insulation products measured in a hot box depending on evaluation accuracy of its low emissivity surfaces

Abstract

The multilayer reflective insulation is relatively new product on a construction market, used as efficient insulation and continuously improved. The thermal resistance of this product has to be determined according to the standard EN 16012+A1 [1], which not defines product's sample installation procedure into a hot box and indicates only rough requirement for emissivity values of surfaces of a tested sample and of adhesive tape for fixing the thermocouples must be similar, but it does not specify allowed differences and its effect on the accuracy of the measurement result. These standard's shortcomings do not ensure reliable and comparable results of the thermal resistance of multilayer thermal insulation. Therefore, a study was conducted and the method for installation and fixing of these products into hot box using frame was created. The influence of the frame on the measured thermal resistance was evaluated as a linear thermal bridge. The research of the influence of the difference between emissivity values of the sample and adhesive tape surfaces on the measured thermal resistance was performed using a calibration standard with known R-value. The research results showed that the linear thermal bridge value of frame was increasing with the increment of emissivity value of adhesive tape. Significant difference between sample and adhesive tape emissivity values can create more than 20% relative difference between both measured and calculated R-values from the known real R-value of the calibration standard. In order to avoid more than 3% relative errors, the limits of difference between emissivity values were set.