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

model case using CFD simulations was completed with the stacks open and stacks closed, todetermine the resulting airflow patterns and temperature distributions. The stack openings werea design characteristic that affected the airflow in the building, reducing the temperatures in theupper-most floor. The wind and wind-buoyancy driven cases were carried out over a widerangeof wind speeds. The wind-driven cases were used to determine the percentage of air thatexited through the stack without any buoyancy effects. A uniform velocity was achieved at thesouth façade for each of the wind speeds from 1 to 5m/s for the wind-driven case and the exitingair velocities at the north façade were uniform as well. A wide range of wind speeds were used,from 0.5 m/s to 5.0 m/s, to determine when the flow was dominated by wind versus a more equalbalance between wind and buoyancy flows through analysis using the Archimedes number.The key results from the experiments were presented in chapter seven. Temperaturedistributions, both measured from the physical model and the numerical simulation werecompared. The data were presented for all of the experimental cases as the scaled buildingtemperatures, using calculated reference temperatures. The temperature distributions and airvelocities for each case were shown, along with descriptions of the flow phenomena.Comparisons of the resulting reduced-scale air model and selected data from the full-scaleprototype were discussed. The reduced-scale model showed comparable results for conditionswith stacks open when evaluated with data recorded from the prototype building for the summercase. The comparisons of the experimental data to the numerical simulations provided insightinto some of the modeling attributes of computational fluid dynamics simulations.8.2 ConclusionsThe validation of this reduced-scale air model through comparisons with data obtained from theprototype building and numerical simulations provides an additional tool for the prediction ofairflow and temperature distribution in naturally ventilated buildings. With careful attention torequirements of similitude to ensure scalability between the results recorded in the reduced-scalemodel and the prototype building, this experimental reduced-scale model was able to predictaverage temperatures in each zone.Modeling airflow and temperature distribution in buildings is a complex problem that researcherscontinue to pursue. The variety of techniques available has applicability to the design ofpassively ventilated buildings, but the user must be aware of limitations of each technique.There are several key factors to address when modeling airflow in buildings: Clearly identify the problem Identify the governing phenomena Determine the desired detail of the results Understand limitations of the method usedFirst, the problem must be clearly identified. Whether the goal is to model in detail a specificspace or an entire building the purpose chosen can affect the selection of modeling technique. Ifan entire building is to be modeled, then there are limitations in terms of complexity of the modelthat can be used regarding analytical methods, space required for physical models, and timerequired for numerical models. Important values for modeling, both physical modeling andnumerical modeling, were identified including the boundary conditions and level of detail. It is163