# Development of Building CFD Model Design Process Based on BIM
## 5 Validation Results
### Validation Result of CFD Analysis Accuracy  
Tables 6 and 7 show the error rate of the flow velocity and temperature compared with ANSYS simulation. Table 6 shows the average velocity error at each height and the volume average velocity error rate. In the case of A-type, the average velocity error rate at each height was less than 2%. The overall volume average error rate was 0.02%, showing almost no error. The qualitative results also showed almost no difference in flow velocity distribution, as shown in Figure 6. B-type also showed no flow velocity error with the ANSYS simulation results. In the case of C-type, the volume average velocity error rate was 0.42%, but the average velocity error rate at each height was relatively high (around 3%). Unlike A, B, and C types, D-type showed a relatively high-volume average velocity error rate of 3.89%. The average velocity error rate at each height reached a maximum of 4.5%, which was relatively high compared to other conditions. This is because the gap in the original geometry was omitted during the optimization process and affected the flow, as shown in Figure 7. In the original model, as shown in Figure 7a, the flow blocked by the gap escapes through the outlet at a relatively fast velocity. On the other hand, the fluid flows along the wall before escaping through the outlet in the optimization model, as shown in Figure 7b. The velocity error rate was relatively high, due to this difference. Although the error rate was higher than 4% under some of the conditions, the average velocity error rate was less than 5% under all of the conditions, which validates the accuracy of the proposed method. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Surface Average Error at Each Height (\%)**} & \multicolumn{2}{c}{**Volume Average Error (\%)**} \\  & **0.5 m** & **1.0 m** & **1.5 m** & **2.0 m** & **Error (\%)** \\ \hline A-type & 0.39 & 1.79 & 1.97 & 0.82 & 0.02 \\ B-type & 0.27 & 0.73 & 2.03 & 0.73 & 1.25 \\ C-type & 2.42 & 3.63 & 3.39 & 3.15 & 0.42 \\ D-type & 4.50 & 3.15 & 3.58 & 2.78 & 3.89 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Validation result for average velocity. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{3}{c}{**Reduction Rate (\%)**} \\  & **Total** & \begin{tabular}{c} **Maximum** \\ **Non-** \\ **Orthogonality** \\ \end{tabular} & \
\begin{tabular}{c} **Maximum** \\ **Skewness** \\ \end{tabular} &
\begin{tabular}{c} **Maximum** \\ **Aspect Ratio** \\ \end{tabular} \\ \hline A-type & 0.16 & 20.78 & 0.00 & 0.00 \\ B-type & \(-0.18\) & 0.00 & 0.00 & 0.00 \\ C-type & \(-1.20\) & 6.52 & 0.00 & 0.00 \\ D-type & 0.00 & 1.78 & 0.03 & 15.32 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Grid model improvement according to optimization. Table 7 shows the average temperature error at each height and the volume average temperature error rate. The volume average temperature error rate was less than 3% for all four types. In the case of C-type, the average temperature error at each height was less than 1%, showing almost no difference. Figure 8 shows the qualitative results for temperature distributions and velocity vectors. As shown in Figure 8, the original geometry showed higher temperatures in the red area, due to gaps. However, there was no significant difference in the quantitative figures. In the case of B-type, the average temperature error rate at height 0.5 m was relatively high (4.01%). This is because the gap omitted during the optimization process affected the temperature, as shown in Figure 9. As shown in Figure 9, the air flowing along the wall is blocked by the gap, which changes the direction of airflow. This creates congestion on the left side of the gap, which results in a relatively high temperature.