Field monitoring of the dynamic heat transmission characteristics of residential 2 x 6 wood-frame wall systems thathad been retrofitted using vacuum insulation panels (VIPs) with glass fiber cores and extruded polystyrene foam (XPS)panels were undertaken in 2011-2012 at the Field Exposure ofWalls Facility (FEWF) of the NRC Construction. The mainobjective of this research was to evaluate the steady-state and transient thermal performance of three wall assemblies (4ft x 6 ft), two of which incorporated VIPs within an XPS tongue and groove (T&G) configuration and VIPs within an XPSclip-on (C-O) configuration, and a third assembly incorporating only XPS. The three wall assemblies were installed in theFEWF for one year cycle of exposure to outdoor natural weather conditions. The NRC's hygrothermal model, hygIRC-C,was validated against the measured data. Results showed that the model predictions were in good agreement with the experimentaldata. Given that the VIP could be punctured during the installation process (e.g., inadvertent use of fasteners inwall assembly) or may fail during normal operating conditions or due to imperfection during the manufacturing process,the numerical model was used to conduct parametric analyses in order to predict the thermal resistance (R-value) in caseswhere one or more VIPs failed.

In the final phase of this study, the model was used to predict the yearly cumulative heat losses from the respective wallsystems. It is important to point out that the aging effect and the effect of the thermal bridging due to the envelope (i.e.,skin) of the VIPs are not accounted for in this study. However, sensitivity analysis of the thickness and thermal conductivityof the VIP envelope was conducted in this paper to investigate the effect of these parameters on the effective R-values ofVIP. Results showed that the yearly cumulative heating loads for the XPS retrofit wall specimen was 69.9% and 78.8%,respectively, greater than that obtained for the T&G VIP retrofit wall specimen and the C-O VIP retrofit wall specimen.Furthermore, the results showed that the effect of the furred-airspace assembly in the C-O VIP retrofit wall specimen whenthe emissivity of all surfaces that bounded the airspace was assumed to be 0.9 resulted in a reduction in the yearly heatingload by 5% compared to the T&G VIP retrofit wall specimen without furred-airspace.

Presented at Thermal Performance of Exterior Envelopes of Whole Buildings XII, December 2013