# Demand Control Strategies of a PCM Enhanced Ventilation System for Residential Buildings
## 3 Constant Ventilation Airflow Rate
### Results  
#### 3.2.1 Summer Night Cooling Application  
The ventilation energy-saving potential of the PCM energy storage in a summer night cooling application is calculated by comparing the heat pump electricity consumption of the building for a ventilation system with PCM energy storage to one without. The PCM energy storage solution is compared to two other reference cases: using either ventilated windows (VW), as shown in Figure 11, or standard windows (SW) with direct outdoor air supply.  
Figure 8: The weather conditions for the simulation. (**a**) Outdoor air dry-bulb temperature; (**b**) Solar radiation.  
Figures 12-14 show the heat pump electricity consumption of each room under three different ventilation airflow rates during the summer period. With the increase in the ventilation airflow rate, the heat pump electricity consumption for each month decreases, except in July. In July, the night cooling potential is too low due to the high outside air temperature, and increasing the ventilation airflow rate increased the cooling heat pump electricity consumption. In the other summer months, an increasing airflow rate increased the pre-cooling ability of the PCM energy storage, because more heat is discharged during the night. For all the summer months, the model with PCM energy storage has the least heat pump electricity consumption, and the model with the standard window has the highest heat pump electricity consumption. Bedrooms 2 and 3 have relatively high heat pump electricity consumption, especially during July and August. The two rooms have more external walls and windows than Bedroom 1; thus, the heat gain during the summer is much higher and the room should be equipped with a larger PCM energy storage.  
Figure 11: Summer reference case 1 using VW [14]. (**a**) Night time ventilation, when (hour \(<\) 7) or (hour \(>\) 20:00). (**b**)Bypass ventilation, when T\({}_{\text{indoor}}\)\(>\) 24 \({}^{\circ}\)C. (**c**) Heat mode, when T\({}_{\text{indoor}}\)\(<\) 24 \({}^{\circ}\)C.  
Figure 12: The heat pump electricity consumption of each room during the summer period at a ventilation airflow rate of 102 m\({}^{3}\)/h.  
Figure 13: The heat pump electricity consumption of each room during the summer period at a ventilation airflow rate of 180 m\({}^{3}\)/h.  
Figure 15 shows the summer total heat pump electricity energy consumption per air-conditioned area with different ventilation airflow rates. The ventilation system with PCM energy storage has the lowest electricity consumption compared to the other two systems. The ventilated system has similar electricity consumption as the standard window system, which indicates that the energy-saving potential of VW is limited during summer. With a higher ventilation airflow rate, the heat pump electricity consumption of the house is lower. However, the decreased amount is not significant.  
Figure 16 shows the energy-saving potential of the ventilated window with PCM energy storage compared to using the stand-alone VW or the standard window (SW) solutions. With increase in ventilation airflow rate, the energy-saving potential increases. With a ventilation airflow rate of 300 m\({}^{3}\)/h, the energy-saving of the PCM energy storage is 10.1% compared to VW and 12.0% compared to the SW.  
In summer, the house should be ventilated by a high ventilation airflow rate, for both purposes of decreasing the electricity consumption and increasing the PCM energy storage saving potential. Rooms with more external walls and windows should be equipped with larger PCM energy storage due to the higher room electricity consumption.  
Figure 14: The heat pump electricity consumption of each room during the summer period at a ventilation air flow rate of 300 m\({}^{3}\)/h.  
Figure 15: The summer total electricity consumption of the house (six-month period) under different ventilation flow rates.