  Computational fluid dynamics (CFD) is frequently used to support the design
of naturally ventilated buildings; however, the model accuracy should be
thoroughly assessed, ideally through validation with full-scale measurements.
The present study aims to (1) validate transient CFD simulations with
uncertainty quantification (UQ) for buoyancy-driven natural ventilation against
full-scale experiments in an operational atrium building, and (2) quantify the
sensitivity of the CFD results to the thermal boundary conditions. The UQ and
sensitivity analysis consider uncertainties in the initial and boundary
conditions for the temperatures. Considering the volume-averaged air
temperature on each floor, the predictions and measurements agree well with
discrepancies less than 0.3 {\deg}C. When considering the temperature averaged
over smaller zones on each floor, two trends can be observed. First, in zones
not adjacent to windows, the discrepancies between the CFD and measurements can
be explained by uncertainty in the boundary conditions and the measurements.
Second, in zones adjacent to windows, higher discrepancies are observed due to
oscillations in the inflow jets just downstream of the windows, and due to
geometrical simplifications in the CFD model. The sensitivity analysis
demonstrates that the boundary conditions for the thermal mass surface
temperature and the outdoor temperature have a dominant effect on the indoor
air temperature predictions, with their relative importance varying as function
of proximity to the windows.
