Comparison of Steady-state and In-situ Testing of High Thermal Resistance Walls Incorporating Vacuum Insulation Panels

Abstract

Two standard test methods exist to experimentally determine the effective thermal resistance of a wall: in-situ testing to calibrate a computer simulation and steady-state testing in a guarded hot box. This paper compares results obtained using both methods on a wall assembly incorporating vacuum insulation panels (VIPs) with an experimentally determined effective R-Value of8.21 m2K/W using a guarded hot box. The result using a guarded hot box was lower than that using in-situ measurements paired with computer simulation as a result of the more accurate representation of thermal bridging between VIP panels using this test method. When testing in a guarded hot box, all thermal bridges, including between panels is accounted for. By comparison, an experimentally obtained thermal resistance measured at the center of a VIP panel and assumed as a constant thermal resistance across the complete VIP layer in the computer model does not account for the non-homogenous nature of a VIP layer. As a result, it was concluded that wall assemblies that contain numerous small thermal bridges like those incorporating VIP panels should be experimentally evaluated using a guarded box.