# Demand Control Strategies of a PCM Enhanced Ventilation System for Residential Buildings
## 3 Constant Ventilation Airflow Rate
### Results
#### 3.2.2 Winter Solar Energy Storage Application  
Similar to summer night cooling application, the ventilation energy-saving potential of the PCM energy storage in winter solar energy application is calculated by comparing the electricity consumption of the building for ventilation systems with and without PCM energy storage. The PCM energy storage solution is compared to two other reference cases: using either stand-alone ventilated windows (VW) as shown in Figure 17, or standard windows with direct air supply from outdoors to the rooms.  
Figures 18-20 show the electricity consumption of each room under three different ventilation flow rates during the winter period. With increase in ventilation airflow rate, the electricity consumption for each month increases. For all the winter months, the model with PCM energy storage has the least electricity consumption, and the model with the standard window solution has the highest electricity consumption. Bedroom 3 has a relatively high electricity consumption. It has one external wall, which faces north; thus, the room heat gain during the winter is much lower.  
Figure 16: The PCM energy-saving potential during the summer period compared to the two reference cases.  
Figure 17: Winter reference case 1 using stand-alone ventilated windows (VW) [14]. (**a**) Bypass ventilation, when T\({}_{\text{indoor}}\)\(>\) 24 \({}^{\circ}\)C. (**b**) Heat mode, when T\({}_{\text{indoor}}\)\(<\) 24 \({}^{\circ}\)C.  
Figure 19: The electricity consumption of each room during the winter period at a ventilation airflow rate of 180 m\({}^{3}\)/h.  
Figure 20: The electricity consumption of each room during the winter period at a ventilation airflow rate of 300 m\({}^{3}\)/h.  
Figure 21 shows the winter total electricity consumption per air-conditioned area with different ventilation flow rates. The ventilation system with PCM energy storage has the lowest electricity consumption compared to the other two systems. The standard window system has the highest electricity consumption. The VW system has less electricity consumption than the standard window system. The VW is more energy saving in winter than in summer because the heat accumulated in the window cavity heats up the ventilation air. With a higher ventilation airflow rate, the electricity consumption of the house is higher. The electricity consumption is the highest when the airflow rate is 300 m\({}^{3}\)/h.  
The winter energy-saving percentage of the ventilated windows with PCM energy storage with three different ventilation airflow rates is shown in Figure 22. The energy saved compared to the standard window system (SW) is much higher than that compared to the stand-alone ventilated window system (VW). When the ventilation airflow rate increases from 102 m\({}^{3}\)/h to 300 m\({}^{3}\)/h, the total energy-saving percentage decreases. With a ventilation airflow rate of 102 m\({}^{3}\)/h, the energy-saving of the PCM energy storage solution is 26.6 % compared to the standalone VW system, and 32.8 % compared to the standard window system.  
In both summer and winter, the ventilated window and facade system with PCM energy storage are efficient to decrease the house electricity consumption. In summer, a high ventilation rate should be applied, while in winter, a low ventilation rate should be adopted, to decrease the heat pump electricity consumption of the house.  
Figure 21: The winter total electricity consumption of the house (six-month period) under different ventilation flow rates.  
Figure 22: The PCM energy-saving potential during the winter period compared to the two reference cases.