On the influence of environmental boundary conditions on surface thermal resistance of walls: Experimental evaluation through a Guarded Hot Box

In this work, a Guarded Hot Box (GHB) was employed to evaluate the effects of environmental boundary conditions on the internal surface thermal resistance of a wall. For this purpose, the study was carried out through an experimental setup to measure temperature - surface and ambient - in the two chambers of the GHB and air velocity near the specimen wall in the hot chamber. The experimental analysis together with the analysis of the dimensionless parameters allowed to determine the internal convective coefficient for different air speeds. To evaluate the results obtained with the proposed methodology, some existing correlations for the determination of the convective coefficient were used. Moreover, the measurement of the emissivity of sample surface and baffle, and the determination of the mean radiant absolute temperature allowed to calculate the radiative coefficient. Therefore, the internal surface thermal resistance with different air velocities, given by the combination of convective and radiative heat transfer, was determined, and compared with the value offered by the standard ISO 6946.