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

Table 32. Conduction Heat Loss for Single Heated Zone Model for Various CasesHeat LossW/m 2Total Heat LossWAtrium HeatLossPercent Heat Lossthru Atrium7Window 1Stack 23.36 290.93 90.78 31.2%7Window 2Stack 14.66 182.65 80.18 43.9%7Window 3Stack 8.62 107.39 69.16 64.4%5 Window 1Stack 21.28 265.10 92.83 35.0%5 Window 2Stack 11.81 147.12 80.39 54.6%5 Window 3Stack 8.62 107.40 73.12 68.1%2 Window 1Stack 22.11 275.34 98.64 35.8%2 Window 2Stack 13.30 165.66 85.26 51.5%2 Window 3Stack 9.81 122.17 80.02 65.5%The heat loss due to conduction through the envelope had to be accounted for in the CFDsimulations, since as much as 60 percent of the heat loss was due to conduction in the 7 window,1 stack case. As it was determined that most of the heat loss occurred in the atrium, the CFDmodel was modified to account for heat loss through the atrium walls as a negative heat flux. Byadjusting the CFD model to account for the conduction issues found in the single heated zonemodel, the resulting data for the numerical models were comparable to the experimental ones.Figure 48. Airflow Patterns for Single Heated Zone Case from Airflow Visualization in theModel: a) Lower Windows, b) Upper WindowsThe location of the windows influences the temperature distribution in the heated zone, as wasshown in the experimental and CFD models. The airflow, as measured by inlet and outletvelocities, is not impacted significantly by the small height difference between the lower andupper windows. However, the total size of the inlet and outlet openings does affect the interiortemperature and airflow; restrictive openings caused a higher internal temperature, leading toreduced heat loss due to airflow and increased heat loss due to conduction through the envelope.The heat loss modeled using PHOENICS (Figure 49) showed the impact of the prescribed heatloss at the atrium walls. The overall temperature was reduced by a scaled full buildingtemperature of approximately 0.5°C.124