# Demand Control Strategies of a PCM Enhanced Ventilation System for Residential Buildings
## 5 Conclusions  
The PCM-enhanced ventilated window has been proven to be effective for building ventilation energy saving for both summer and winter in previous works. In this paper, the influence of ventilation airflow rate on the PCM energy storage saving potential is studied based on the EnergyPlus model of a sustainable low energy house in New York. Based on the optimized ventilation airflow rate, a demand-controlled ventilation strategy is proposed and its energy-saving potential is examined.  
The influence of airflow rate on the PCM energy storage saving potential is investigated by comparing the ventilated window and facade PCM energy storage system with two reference systems: stand-alone ventilation window (VW) system and a standard window (SW) system. The main conclusions are:  
Figure 30: The electricity consumption of each room with/without demand control in winter.  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Summer** & **Winter** \\ \hline No demand control heat pump electricity consumption (kWh/m\({}^{2}\)) & 65.09 & 57.32 \\ Demand control heat pump electricity consumption (kWh/m\({}^{2}\)) & 55.55 & 39.91 \\ Demand control energy-saving potential & 14.7\% & 30.4\% \\ \hline \hline \end{tabular}
\end{table}
Table 5: Total electricity consumption of the house and demand-control energy-saving percentages.  
Figure 29: The electricity consumption of each room with/without demand control in summer.  
The heat pump electricity consumption of the house with the PCM energy storage system \(<\) VW \(<\) SW for both summer night cooling application and winter solar energy storage application.  
In summer, increasing the ventilation airflow rate decreases the electricity consumption of the house; the increasing airflow rate increases the energy-saving potential of the PCM energy storage. With a ventilation airflow rate of 300 m\({}^{3}\)/h, energy-saving of the PCM energy storage is 10.1% compared to the VW system, and 12.0% compared to the SW system.  
In winter, increasing the ventilation airflow rate increases the electricity consumption of the house. The energy-saving potential of PCM energy storage is similar under different airflow rates. With a ventilation airflow rate of 102 m\({}^{3}\)/h, the energy-saving of the PCM energy storage system is 26.6% compared to the VW system, and 32.8% compared to the SW system. The PCMVW has a much higher energy-saving potential in winter than in summer, which indicates the high potential of adopting PCM in solar energy storage applications.  
Based on the optimized ventilation flow rate from Section 3, a demand-controlled ventilation strategy, which personalizes the air supply to each room based on the room demand, is proposed. The setup of ventilation and air conditioning schedules of each room are based on the occupancy and electricity level of each room distinguished by weekdays, weekends, summer, and winter. The conclusions are that both in summer and winter, the room electricity consumption with demand-controlled ventilation is lower than without demand controlled ventilation. With demand control ventilation, the energy-saving percentage of the house is 14.7% in summer and 30.4% in winter.  
The PCM-enhanced ventilated window with a demand-controlled ventilation system has a big building energy-saving potential in comparison with the ventilated window and standard window systems, for both summer night cooling application and winter solar energy storage application in New York climate. Future works include the energy-saving potential of PCM-enhanced ventilated windows in various climate zones, and life cycle accessment of the system.  
Conceptualization, P.K.H. and Y.H.; Methodology, P.K.H. and Y.H.; Writing-Original Draft Preparation, Y.H.; Writing-Review & Editing, P.K.H. and T.S.L.; Supervision, P.K.H. and T.S.L.; Funding Acquisition, T.S.L. All authors have read and agreed to the published version of the manuscript. This research was funded by the project Det cirkulaere trachus grant number 893501.  
The authors declare no conflict of interest.