## 4 BIM Simulation
### Life Cycle Cost Analysis  
According to the aforementioned renovation scenarios, costs are analyzed according to the unit price and quantity variation information during renovation by BIM (as shown in Figure 7). In the traditional approach to cost estimation, estimators have to digitize the designer's paper drawings or improve their CAD drawings into an estimating package to conduct quantity take-offs. This process may lead to the potential for human errors and propagate any inaccuracies that there may be in the original drawings [26]. Some studies assert that BIM can increase the accuracy in the quantity take-off, especially at the early stage of the design, and allow for a precise future prediction of the construction costs [27]. The BIM model provides the advantage that when a change is made in the design, the change automatically ripples to all related construction documentation and schedules, as well as takeoffs, counts, and measurements that are used by the estimators [28]. In comparison to the traditional approach, the cost estimation of BIM can be done within Revit and output to a Microsoft Excel program that can effectively enhance cost estimation workflows. As the three proposals have inconsistent timing of renovation behavior, and as different proposals have different costs of renovation behavior, in order to compare the cost benefits objectively, this study uses Net Present Value (NPV) to analyze the life cycle costs. The lowest minimum acceptable rate of return (MARR) is 3%, and the compared time is the 100-year life cycle. The analysis results are shown in Tables 1 and 2. \[\mathrm{NPV}=\sum_{t=1}^{n}\frac{C_{t}}{\left(1+i\right)^{t}}-C_{0} \tag{1}\]  
where \(C_{t}\) is net cash flow during period \(t\); \(C_{0}\) is the total initial investment cost; \(i\) is the discount rate; and \(t\) is the number of time periods. Figure 7: Cost analysis of BIM. [PERSON] [29] indicated that enhancing the elastic design of buildings would be an efficient way to prolong the service life and value of residential buildings, and proposed a relation graph of the designs that accommodate change and building value according to this concept. According to [PERSON]'s \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Time (Year)** & \begin{tabular}{c} **Proposal A** \\ **Traditional Design Cost (NTS)** \\ \end{tabular} & \
\begin{tabular}{c} **Proposal B** \\ **Semi-Open Design Cost (NTS)** \\ \end{tabular} &
\begin{tabular}{c} **Proposal C** \\ **Open Design Cost (NTS)** \\ \end{tabular} \\ \hline
0 & 3,500,000 & 3,850,000 & 4,200,000 \\
15 & 353,000 & 282,000 & 200,000 \\
30 & 3,562,400 & 692,000 & 440,000 \\
45 & 353,000 & 282,000 & 200,000 \\
50 & - & 3,650,000 & - \\
60 & 3,533,800 & - & 365,000 \\
65 & - & 282,000 & - \\
75 & 353,000 & - & 200,000 \\
80 & - & 755,000 & - \\
90 & 3,510,400 & - & 343,000 \\
95 & - & 282,000 & - \\
100 & - & 100,000 & 100,000 \\ NPV & 6,171,000 & 5,358,000 & 4,675,000 \\ \hline \hline \end{tabular} Note: the values in the table only consider the actual construction costs.  
\end{table} 
Table 2: Life cycle cost analysis of the three proposals. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Time (Year)** & \begin{tabular}{c} **Proposal A** \\ **Traditional Design Cost (NTS)** \\ \end{tabular} & \
\begin{tabular}{c} **Proposal B** \\ **Semi-Open Design Cost (NTS)** \\ \end{tabular} &
\begin{tabular}{c} **Proposal C** \\ **Open Design Cost (NTS)** \\ \end{tabular} \\ \hline
0 & 3,500,000 & 3,850,000 & 4,200,000 \\
15 & 353,000 & 282,000 & 200,000 \\
30 & 3,562,400 & 692,000 & 440,000 \\
45 & 353,000 & 282,000 & 200,000 \\
50 & - & 3,650,000 & - \\
60 & 3,533,800 & - & 365,000 \\
65 & - & 282,000 & - \\
75 & 353,000 & - & 200,000 \\
80 & - & 755,000 & - \\
90 & 3,510,400 & - & 343,000 \\
95 & - & 282,000 & - \\
100 & - & 100,000 & 100,000 \\ NPV & 6,171,000 & 5,358,000 & 4,675,000 \\ \hline \hline \end{tabular} Note: the values in the table only consider the actual construction costs.  
\end{table} 
Table 1: Renovation behavior analysis in the life cycles of the three proposals.