## 4 A Case Study
### Evaluation and Discussion  
A total of 15 subsystems in HVAC, including fresh air, air supply and exhaust air systems, and 10 subsystems in fire sprinkler systems, including wet pipe sprinkler systems and dry pipe sprinkler systems were described and discussed. Each subsystem contains 20-40 components, with a total number of 763 components in the HVAC and fire sprinkler system. Table 6 summarizes the number of omissions and errors that occurred. The statistical results demonstrate that there are one or more omissions in the process for generating the connection table in six subsystems and one error in the process for generating the logic model in four subsystems. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Subsystem Name**} & **Number of** & \multicolumn{2}{c}{**Generate Connection Table Process**} & \multicolumn{2}{c}{**Generate Logic Model Process**} \\ \cline{3-6}  & **Components** & **Omissions (Pairs)** & **Accuracy (\%)** & **Errors (Pairs)** & **Accuracy (\%)** \\ \hline Return air 1 & 23 & 0 & 100 & 0 & 100 \\ Return air 2 & 19 & 0 & 100 & 1 & 96.8 \\ Return air 3 & 28 & 3 & 88.9 & 2 & 92.6 \\ Return air & 70 & 3 & 95.7 & 3 & 95.7 \\ Supply air 1 & 32 & 1 & 96.8 & 0 & 100 \\ Supply air 2 & 34 & 0 & 100 & 0 & 100 \\ Supply air 3 & 41 & 0 & 100 & 0 & 100 \\ Supply air 4 & 32 & 2 & 96.7 & 0 & 100 \\ Supply air 5 & 23 & 0 & 100 & 0 & 100 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Performance of the algorithms developed for generating MEP logic models. Figure 13: Data structure of a supply air system. \begin{table}
\begin{tabular}{l l} \hline \hline \multicolumn{1}{l}{**No.**} & **Inspection Rules of A Fire Sprinkler Subsystems** \\ \hline
1 & (Component.Name, contains, “Riser”), UpstreamOf, (Pipe.Name, contains, “Valve”) \\
2 & (Component.Name, contains, “Riser”), UpstreamOf, (Pipe.Name, contains, “pipe”) \\
3 & (Component.Name, contains, “Riser”), UpstreamOf, (Pipe.Name, contains, “elbow”) \\
4 & (Component.Name, contains, “Riser”), UpstreamOf, (Pipe.Name, contains, “Transition”) \\
5 & (Duct.Name, contains, “Transition”), UpstreamOf, (Pipe.Name, contains, “sprinkler”) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: _Cont_. From this case study, the following conclusions can be drawn. 1. In 15 subsystems, both the connection table and logic model were generated with 100% accuracy, demonstrating that the approach could generate the right logic chain. 2. There were ten subsystems with 1-5 omissions when generating the connection tables, and the accuracy rates remained higher than 80%. The spatial connection was misjudged for the following reasons in these cases: 1. There were deviations in the position of the component during modeling. When the model was observed under magnification, there was no connection between components that were, in fact, connected to each other in practical engineering. 2. A portion of the information was missing or incorrect in the modeling process. System classification and system name attributes were missing or missing in certain subsystem components' properties, which influenced the inspection of components. 3. The intersection judgment of space triangles was not sufficiently accurate. Because the triangular size was small, improper handling of truncation errors for intermediate calculations considerably affected on the results. Therefore, the algorithm should be improved. Among the three types of problems, missing or incorrect information during modeling occurred most frequently, followed by misjudgments of triangle intersections and then deviations in the component positions during modeling. During the modeling process, information about the system classification and system name were generally inputted in commercial software. Designers or modelers were likely to ignore the accuracy of relevant property information, which, when combined with the lack of relevant modeling standards, led to the problem of missing or incorrect information.