Methodology for the Evaluation of Natural Ventilation in ... - Cham

height is used for the full-scale building and air model, the Grashof number is 4.5x10 10 and1.1x10 8 respectively.Larger models may reflect better the full-scale prototype building. However, space limitationslimit the use of larger scale models. At the scales presented, both water and air models are ableto achieve turbulent flow regimes within the heated zones, which is critical for the analysis of theflow and makes the models comparable to the full-scale prototype. There are limited sources indetermining the critical values that must be reached for natural ventilation. Critical Reynoldsnumbers found in the literature often use the supply diffuser area, rather than the cross-section ofthe space for their characteristic length. This is appropriate for mechanically ventilated spaces,when the supply jets are of concern, however with natural ventilation; the airflow within theoccupied space is of importance.5.7 SummaryThe governing equations were identified and made dimensionless to use them in comparing thefull-scale prototype to the reduced-scale model through the resulting dimensionless parameters.The key dimensionless parameters identified in the non-dimensionalized governing equationswere the Reynolds number, the Archimedes number, and the Prandtl number. For the buoyancydrivencase, the Grashof number was identified as the critical parameter to match between theprototype and model cases. There are no guidelines in the selection of the characteristic length,but based on the goals for analysis of the flow, characteristic lengths were selected for definingthe Reynolds and the Grashof numbers.91