Thermal evaluation of a highly insulated steel stud wall with vacuum insulation panels using a guarded hot box apparatus

This paper presents the results of a Guarded Hot Box (GHB) experiment on a wall assembly made up of both steel stud framing and an external insulating assembly which incorporates vacuum insulation panels (VIPs) for which knowledge of the composition of the VIP barrier foil is not readily available. The purpose of the tests is to provide an experiment result for thermal resistance of a wall assembly containing several sources of thermal bridging, including those due to the barrier foil at the edge of and joint material between the VIPs and the condensation potential on the interior surface due to the steel studs. The steady-state GHB experiments were completed in accordance with ASTM C1363 for an interior air temperature of 20.9 degrees C and an exterior air temperature of -34.9 degrees C; this resulted in a thermal resistance for the wall assembly of 6.8 +/- 0.8 m(2) K/W. Surface temperature measurements on a VIP in the wall assembly indicated that increased levels of heat transfer were occurring at the edges of the VIPs as compared to the center of the panel confirming thermal bridges were present at the panel edge. Measurement of the temperature on the interior surface of the sheathing board around the steel stud indicated that the external insulation effectively minimized the risk of condensation due to the steel studs. Determining the thermal resistance and condensation risk for a wall assembly which contains VIPs for which knowledge of the barrier film is not readily available demonstrates the potential for use of such a wall assembly according to energy and building code requirements. The wall assembly and test details can also be used to compare industry standard calculation methods and detailed 2D and 3D simulations to the GHB test result. The comparison can be used to inform on the validity of using calculations and simulation methods in lieu of testing for energy and building code compliance. The comparison of calculations and simulations is not the scope of the work presented in this paper and will be explored in future publications.