Abstract
There is currently no widely accepted on-site method to directly
measure the overall thermal performance of a window as a system [glass, frame,
and thermal bridges]. For historic windows, relying only on simulation often leads
to insufficient accuracy, while laboratory hot box testing [EN ISO 12567-1]
requires removing the window, which is invasive and frequently unfeasible. This
work advances the testing of the WUM-box [Window U-value Measurement Box],
a portable calorimeter for on-site use, by addressing the measurement of a historic
window. The prototype was first tested in controlled laboratory conditions. A
second campaign, presented here, applied the WUM-box to a historic window
under controlled conditions. Two tests were executed in the laboratory under
different boundary setups [static and dynamic]. This paper describes the test
methodology and the calculation steps used to obtain the results. Findings confirm
that this preliminary stage is successful: WUM-box results are in close agreement
with the reference method [hot box], with U-values matching within the expected
measurement uncertainty. The analysis highlights dominant error sources and
points to improvements in both hardware and data analysis. The WUM-box should
still be regarded as a research tool, but it shows strong potential for non
destructive in-situ assessment of historic windows. Next steps include tests with
an uncontrolled exterior boundary, moving towards true on-site application in
case study buildings.