# Demand Control Strategies of a PCM Enhanced Ventilation System for Residential Buildings
## 4 Demand-Controlled Ventilation
### Results  
The comparison of the room electricity consumptions in summer with/without demand control of ventilation is shown in Figure 29. For all the bedrooms, the electricity consumption with demand-controlled ventilation is lower than with a constant ventilation airflow rate, especially for bedroom 2 and 3 in July and August. Each of the two bedrooms has two external walls, which results in a high energy gain of the room during the daytime. Thus, the electricity consumption of the rooms is quite high without demand-controlled ventilation. The living room has three external walls, but a much larger PCM energy storage in the ventilation system and higher ventilation airflow rates than the bedrooms, which results in lower electricity consumption than bedroom 2 and 3. For the living room, the room electricity consumption with demand control is lower than that with a constant ventilation airflow rate for most of the months, but the difference is not very large. For June and September, the living room electricity consumption with demand-controlled ventilation is even higher than that with constant ventilation airflow rate. The reason could be that the outdoor air temperature in June and September is suitable for not only night ventilation but also day ventilation. With constant ventilation airflow rate, the higher ventilation airflow rate during the day results in lower electricity consumption than with demand control.  
The comparison of the heat pump electricity consumptions with/without demand control in winter is shown in Figure 30. It shows that with demand-controlled ventilation, all of the bedrooms in all the winter months have a lower electricity consumption than with a constant ventilation airflow rate, especially for bedroom 3. The probable reason is that bedroom 3 has an external wall facing north, which results in low solar heat gain and high electricity consumption of the room without demand control. For the living room, the electricity consumption with demand-control is lower than that without demand-control for most of the months, except October and April, where the demand control has slightly higher heat pump electricity consumption.  
The total electricity consumption of the house and the energy-saving potential of demand-controlled ventilation is summarized in Table 5. For both summer and winter, the electricity consumption is much higher without demand-controlled ventilation. The energy-saving potential of demand-controlled ventilation is higher in winter than in summer. In summer, demand-controlled ventilation could not be operated during the night due to the night ventilation requirement of the house, which could be the potential reason for its limited energy-saving percentage.  
Figure 28: The ventilation schedule of each room during winter.  
In summer, the rooms with more external walls and windows should be have larger PCM energy storages due to the high room electricity consumption. Those rooms also have the highest energy-saving potential by demand-controlled ventilation. In winter, the rooms that only have external walls facing north have high room electricity consumption and benefit more from demand-controlled ventilation.