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

minute interval, the model was assumed to have reached steady state. During operation airvelocity and temperature measurements were taken at the entry and exit points of airflow andthroughout the internal space. Air velocity measurements were taken using a hand-held hot-wireanemometer at the window face, and data obtained were used to calculate an airflow balance.Smoke pencils were used to view airflow patterns of air throughout the internal space.The CFD model was created for the full-model case. As with the previous computationalmodels, the effects of both radiation and heat loss were considered in the simulation. All of thewindows were modeled, seven upper and seven lower per half floor plate. The two experimentalcases were considered; stacks open and stacks closed. In the full-model case the heat transferbetween floors had less of an impact than the effect of radiation to the ceiling. The anyadditional heat transfer between floors was considered to be negligible. The model wassimulated using a fine grid size to ensure that there were adequate points to evaluate the modelcorrectly. This was of particular concern near the heaters, both the heaters representing theinternal loads and those representing the radiative effects within the heated zone. The grid sizewas 63x59x72, for a total of over 267,000 points. A κ-ε RNG turbulence model was used for allof the CFD simulations.6.5.2 Wind-AssistedWind effects were found when monitoring of the prototype building, and there were rarely dayswhen pure buoyancy-driven ventilation occurred. Therefore as an additional refinement, researchfocused on the modeling of a more realistic but more complex wind-assisted natural ventilationsituation.Although wind velocities varied with time in the prototype building, and mean wind speeds overa specific period of time, often years or decades (Awbi 2003), a design wind speed was used forthe model experiments.It was decided that in order to model the wind caused by the natural environment, a device wouldbe built that would allow a constant, uniform wind speed. This device was created to provide aconstant air velocity on the south side of the reduced-scale model, as this was the predominantdirection of the wind for the prototype building during the summer months, as seen in Figure 41.112