Energy performance of five different building envelope structures using a modified Guarded Hot Box apparatus—Comparative analysis

Abstract

The most of thermal characteristics of buildings are currently calculated by simplified mathematical models of building envelope behaviour. The main parameter needed for these calculations is the thermal transmittance. The aim of this study is to evaluate thermal performance of several building envelopes suitable for thermal insulating purposes and to compare parameters of thermal performance given by national standards or the thermal performance declared by producers. The experimental measurements were conducted with dynamic conditions in the cold chamber of the Hot Box. Dynamic testing was running under weekly temperature cycle using programmable temperature controller in the cold chamber. Hot site temperature was kept steady according to controlled ambient temperature. Behaviour of each system was investigated under similar conditions with room temperature 22–23 °C in the hot chamber and with temperature fluctuation between +6 °C and −13 °C in the cold chamber. This study provides interesting results. Especially heat flow in case of laminated log wall (massive wood) of thickness 200 mm was measured as significantly lower than it would be calculated by currently known thermal conductivity of soft wood. The presented method of thermal transmittance measurements in dynamic conditions might bring increasing accuracy for building envelope energy loss calculations. The difference between result from one-week long test compared with 20 days long test of the same sample was found as 2,3%. Correlation coefficient between experimental values and calculated total energy loss in time was always found higher than 0,997 and accuracy seems to be increasing with length of the measurement.