In-situ performance evaluation of historic box-type windows with vacuum glazing

Climate protection objectives and energy efficiency targets imply stricter performance expectations from both new and retrofit building projects. Given the related important role of the building envelope, there is a need for a holistic approach to the design, construction, as well as laboratory and field testing of buildings' window and wall systems. In this context, the present contribution reports on recent efforts regarding the thermal retrofit of box-type windows. In the course of an actual research project, vacuum insulated glass (VIG) elements were integrated with ten existing box-type windows at six locations in Austria. To facilitate empirical testing and evaluation of these windows, a detailed concept for a continuous in-situ performance monitoring concept was designed and implemented together with the required monitoring infrastructure. This infrastructure involves the deployment of regular state-of-the-art IoT (Internet of Things) technology and enables the continuous monitoring of the salient performance indicators (including temperature, relative humidity, and heat flow). The derived values of performance indicators (such as the f_Rsi-value) can facilitate, among other things, the assessment of water vapor surface condensation risk. Collected data since mid-2020 cover both hot and cold weather periods have been analysed to capture performance differences between alternative vacuum glass settings at the testing locations. The alternative implementations pertain to different positions of the glazing layer (inside versus outside), different opening directions of the casements, and different positions of box-type within the opaque wall. Moreover, for comparison purposes, monitoring equipment was integrated into a comparable regular box-type window (with float glass or insulation glass) at each of the demonstration sites. Occurrences of potential visible or functional defects (including surface condensation) have been documented as well. The paper presents, analyses, and discusses the preliminary findings of this effort in detail.