# Building Energy Savings by Developing Complex Smart Windows and Their Controllers
## 5 Conclusions  
In this study, a system was developed to reduce the lighting and cooling energy consumption in an office building during the summer period. Prior to the experiments, we developed a control algorithm to derive the optimal SPD transmittance and dimming values. The system simultaneously applied dimming control and smart skin with variable transmittance, and an optimal control method was devised to maximize energy savings. An experimental site was constructed to compare and study the actual energy consumption. The experimental period was from June to September, and the cooling period and lighting operation time were monitored from 9:00 am to 6:00 pm, aligned with the working hours of office workers. As a result of this study, it has been confirmed that the application of the developed complex smart window significantly reduces lighting and cooling loads during the summer season. The major findings are as follows:  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Energy Consumption** & & **June** & **July** & **August** & **September** & **Sum** & **Savings** \\
**(kWh)** & & & & & & & \\ \hline \multirow{3}{*}{Cooling} & Test & 48.4 & 36.8 & 45.4 & 7.8 & 138.61 & \multirow{3}{*}{36.9\%} \\  & Reference & 71.8 & 55.0 & 80.6 & 11.7 & 219.76 & \\ \cline{1-1}  & Test & 43.3 & 31.8 & 27.0 & 21.5 & 124.07 & \\ \cline{1-1}  & Reference & 74.5 & 67.6 & 65.6 & 64.7 & 272.66 & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Experimental glass compositions.  
1. A complex smart window system was developed by combining SPD, LGG, and dimming LED to simultaneously reduce cooling and lighting loads and address the increasing energy consumption in offices during the summer period.
2. An algorithm that can control the transmittance and dimming in parallel was developed to effectively control complex smart windows. The cooling load and lighting energy were optimized by determining a function that controlled the transmittance over time.
3. To increase the effectiveness of the control and application of the complex smart window, an optimal control function was developed for each region using representative solar radiation data for each area. To control the complex smart window in an office, we developed HW and FW for the wireless controller using the LoRa-based wireless communication method, which supports LGG, SPD, and LED control.
4. Based on experimentation, it was shown that energy efficiency can be achieved in parallel with dimming control when complex smart windows are used. By combining LGG and dimming, the lighting load was reduced by 54.5%.
5. An experimental site was constructed to monitor the energy consumption in the test and reference rooms. In the test room with the smart skin system, the cooling energy consumption was reduced by approximately 36.9% compared with the reference room.  
Conceptualization, S.-K.H. and S.-H.C.; methodology, S.-K.H.; software, S.-K.H.; validation, S.-G.J. and S.-H.C.; investigation, S.-K.H.; data curation, S.-H.C.; writing--original draft preparation, S.-K.H.; writing--review and editing, S.-G.J.; visualization, S.-K.H.; supervision, S.-G.J.; funding acquisition, S.-K.H. All authors have read and agreed to the published version of the manuscript.  
This study was supported by the Korean Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry, and Energy (MOTIE) of the Republic of Korea (No. 2019271010015C). Additionally, this research was supported by the \"Regional Innovation Strategy (RIS)\" through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (MOE) (2021 RIS-004).  
Not applicable.  
The authors declare no conflict of interest.