## Two-Stage Building Information Modeling (BIM) Based Lighting Design Method
### Stage 1: Building Desing Optimziation  
#### 2.1.1 Building performance simulation  
This proposed lighting design method was based on a completed initial building design scheme, which integrated specific client requirements and the project environment. Complete information about the initial design was entered into the BIM system to establish a three-dimensional (3D) building information model. Information related to the project, such as geographical coordinates and the project location's climate, must also be entered into the model.  
To ensure all candidate designs could qualify the minimum lighting standard, the first step was to do a basic lighting performance assessment. Lighting performance of a building envelope can be simulated using BIM, and the ones which cannot achieve the daylight factor of 2% will be eliminated.  
Several studies have found that heating, ventilation and air conditioning (HVAC), and lighting systems consume the most energy in a building [35; 36; 37]. The goal of this study was to both improve lighting performance and save energy. As such, both thermal and lighting performance must be discussed. Therefore, when receiving the qualified design, the BIM simulation module was applied to generate the estimates of artificial lighting time and the assessments of thermal performance.  
For a lighting system, the operation time of the lighting facilities was estimated based on daylight autonomy (DA) at a specific illumination level. An analysis grid with a specific dimension was generated to cover the test area; test points were simulated for DA within the workday. Considering that there were plenty of test points, thus the average DA (\(\overline{DA}\)) of all these points was used at this step for the estimates. Consequently, the annual total operation time of lighting facilities (\(T_{lit}\)) can be calculated using Equation (1):  
\[T_{lit}=(1-\overline{DA})\times t_{work} \tag{1}\]  
In this expression, \(t_{work}\) is the annual total working time of the test area.  
Based on \(T_{lit}\), annual total energy required by the lighting system (\(E_{lit}\)) can be estimated using Equation (2):  
\[E_{lit}=\sum\
olimits_{n=1}^{N}(T_{lit}\times P_{lit})_{n} \tag{2}\]  
In this expression, \(n=1\), \(2\), \(3\),..., \(N\) is the number of lighting facilities in the test area; and \(P_{lit}\) is the power of the lighting facilities.  
For the thermal system, the thermal performance of the building envelope was evaluated based on the energy provided to the HVAC system to maintain thermal neutrality. Therefore, the monthly cooling load and heating load were estimated using the thermal simulation engine of the Ecotect Analysis, which was produced by Autodesk Inc. Then, the amount of energy consumed by the thermal system yearly (\(E_{ter}\)) could be computed using the coefficients of performance (COP) for the chiller and heating pump, as shown in Equation (3):  
\[E_{ter}=\sum\
olimits_{k=1}^{12}(\frac{E^{\prime}{}_{c}}{e_{c}}+\frac{E^{ \prime}{}_{h}}{e_{h}})_{k} \tag{3}\]  
In this expression, \(k=1\), \(2\), \(3\),..., \(12\) is the month number; \(E^{\prime}{}_{c}\) and \(E^{\prime}{}_{h}\) are the monthly loads for cooling and heating, respectively; and \(e_{c}\) and \(e_{h}\) are the COPs for the chiller and heat pump, respectively.  
The annual total energy demand of the design (\(E_{sum}\)) is the sum of the energy consumed by the lighting system and thermal system; as such, it can be calculated using Equation (4):  
\[E_{sum}=E_{lit}+E_{ter} \tag{4}\]  
After the simulation process, the annual total energy demand of lighting and thermal systems are entered into the optimization module for further computation.