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

Table 39. Variation of Outlet Wind Velocity by Floor Level: Combined Wind-Buoyancy CasesStacks OpenStacks Closed1 m/s 0.7 m/s 0.5 m/s 1 m/s 0.7 m/s 0.5 m/sWindow Inlet 1.1 0.7 0.5 1.1 0.7 0.5Second Floor Upper 0.5 0.4 0.3 0.5 0.4 0.4Lower 0.4 0.3 0.1 0.5 0.3 0.2First Floor Upper 0.5 0.3 0.1 0.5 0.4 0.3Lower 0.3 0.1 0.1 0.4 0.2 0.1The three smallest wind velocities for the stacks open and stacks closed cases along with theexiting velocities at each window level showed that the exiting air velocity increased with height.This did not occur in the wind-only case, where the exiting velocities were uniform at allwindow heights. This difference was due to the effect of buoyancy combined with the wind flowin the model. Though not a substantial difference, only varying by 0.1-0.2 m/s per floor level,and as much as 0.3 m/s from the second floor to the first floor, the change in exiting velocity wasrepeatable and distinct. The simulation results illustrating the temperature distribution for the 0.5m/s wind case are provided in Figure 69, while the airflow patterns for the same wind speed areshown schematically in Figure 70 and the CFD in Figure 71.The scaled temperature variation was calculated using the reference temperature difference forthe reduced-scale air model and full-scale prototype building, as shown in equation 7.3. Thetemperature stratification for the experiments showed that the stratification pattern changedbased on the inlet air velocity. As shown in Figure 72 and Figure 73 for the ground floor, at thecolumn and in the heated zone, the temperature distribution was distinct for those cases withentering air velocities above 1-1.5 m/s and those with entering air velocities below 1-1.5 m/s. Atthe column, there was a linear temperature variation that increased with height for the enteringair velocities below 1 m/s, and was virtually constant in the 1 m/s case. For all of the othercases, at 1.5 m/s and above, the temperature variation caused a reduction in overall temperatureand a decrease in the temperature difference from floor to ceiling. This demonstrated theinfluence of higher, wind-dominated flow on the interior temperature stratification. Within theheated zone of the ground floor, there was a reduction in overall temperature, and thetemperature became increasingly uniform for a larger portion of the space as the wind velocitywas increased.At the first floor level, the cooler ambient air initially entered the model at the south façade,increased in temperature due to the heaters, and entered into the atrium space. Figure 74 andFigure 75 graphically present the temperature distribution for the south half of the first floor atthe column and within the heated space. In the heated space, the temperature measurements hadsome minimal variation in the lower half of the space and then were consistent in the upper halfof the heated zone. The similar temperatures for each case in the upper half of the heated zoneindicated that the air was well-mixed within this portion of the space. The lower temperaturepoints were due to the airflow patterns, with some amount of cooler air reaching thethermocouples at the mid-point within the heated zone remaining at the floor level. The air wasslowly heated by a small but measurable amount at a location 9.5 centimeters above the floor.At the column location, the temperatures were virtually uniform from floor to ceiling, indicatinga well-mixed condition. This well-mixed condition occurred for all of the wind speeds used in142