Vacuum Insulation Panels, Modelling Methods, Guarded Hot Box, Experimental Validation, Non-Homogeneous Wall Assmblies
As of 2012, space heating accounted for 62% of Canadaâ€™s secondary residential energy use, the most significant category by a large margin. New strategies and policies to reduce overall energy consumption, with a focus on reducing space heating energy. Voluntary performances standards have been developed for new homes including R-2000, LEED Canada for Homes and Passive House. These standards add a series of performance criteria, in addition to conventional building code, in an effort to reduce a homeâ€™s energy consumption and include a limit on energy and water consumption, and prescribe minimum levels of insulation, ventilation, etc. Generally, extensive modelling, proof of concept and/or builder training are required to obtain the energy efficiency designation. A common method of maintaining a home within the constrained energy budget is to increase the overall air tightness and insulation in the dwelling above conventional construction standards through additional sealing and insulation. The typical industry practice for increasing the insulation value involves simply adding more insulation. However, this practice is not always possible or favorable. For example, adding thickness to the walls will either increase the dwellingâ€™s footprint or reduce the usefulfloor space within the home. As a consequence, many studies are being performed on vacuum insulated panels (VIPs), which offer a high thermal resistance per unit thickness when compared to conventional materials. VIPs consist of a metallic enclosure and a vacuum maintained inside, effectively eliminating the conduction through the center of panel, however a thermal bridge will occur along the edges. There are concerns about whether the fragility and the non-homogenous nature of the panels will cause problems within residential dwellings, as well as how to model VIPs within building assemblies effectively. Currently, there is no method of efficiently modelling the non-homogenous nature of the panels in building applications to meet requirements prescribed in performance standards, hinders the widespread adoption of VIPs. This paper compares two methods of modelling the steady-state heat transfer across a composite, non-homogenous wall assembly containing VIPs validated against measured experimental data. Method 1 is the typical practice used by industry experts and involves creating a thermal model for each unique 2D profile within the wall assembly independently. The effective thermal conductivity (U-value) for the assembly was calculated using weighted averages methodÂ based on proportional coverage area of each profile and involves multiplying the U-value by the ratio of profile height to the overall height of the wall. In method 2, a single profile was created based on the wall composition, coverage area, and layout of non-homogenous sections to represent the entire assembly then modelled in THERM. The results of both methods were compared to an empirically calculated thermal resistance based on measured heat flux across five points in a representative assembly under steady-state conditions in a guarded hot box. The feasibility of using either modelling method to find the thermal resistance of wall assemblies incorporating VIPs and if a single representative profile can accurately determine thermal resistance to avoid modelling all profiles included within the wall was examined.