# Demand Control Strategies of a PCM Enhanced Ventilation System for Residential Buildings
## 2 System Description
The PCM stores solar energy during the day when solar radiation is high. The ventilation air flows through the VW before being supplied to the room, and is heated up in the window cavity. 2. The heat release mode (Figure 5b). It operates when the indoor air temperature is low and ventilation pre-heating is needed. The ventilation air flows through the PCM energy storage and the VW before being supplied to the room, and is heated up in both the PCM energy storage and the VW cavity. 3. The overheating preventing mode (Figure 5c). This mode is turned on when the indoor environment is overheated. The ventilation airflow is provided by bypass ventilation, where outdoor air is supplied directly to the room. Meanwhile, the VW is cooled by self-cooling natural ventilation. The PCM energy storage facade works similarly to the PCMVW in winter. It has three operation modes:
4. The heat storage mode (Figure 6a). In this mode, outdoor solar radiation is high. The PCM energy storage has a temperature rise due to solar radiation. 5. The heat release mode (Figure 6b). When the indoor air temperature is low, the ventilation air flows through the PCM facade before it is supplied to the room, and is heated up by the warm PCM energy storage. 6. The bypass ventilation mode (Figure 6c). When the room is overheated, the bypass ventilation airflow is operated, where the relatively low-temperature ambient air is supplied directly to the room. Figure 4: The working principle of the PCM facade in summer. (**a**) PCM discharge mode, when (hour \(<\) 7) or (hour \(>\) 20:00). (**b**) Ventilation pre-cooling mode, when T\({}_{\text{indoor}}\)\(>\) 24 °C. (**c**) Bypass ventilation, when T\({}_{\text{indoor}}\)\(<\) 24 °C. The PCM used is paraffin wax, which has a melting range of 16-23 \({}^{\circ}\)C and a freezing range of 14-21.5 \({}^{\circ}\)C. The PCM changes its phase in the melting range and freezing range. The melting peak of the PCM is 21.5 \({}^{\circ}\)C and freezing peak is 20.7 \({}^{\circ}\)C. The total heat capacity is 117 kJ/kg in the temperature range of [10-30 \({}^{\circ}\)C], which is measured by Differential Scanning Calorimetry (DSC) with a heating/cooling rate of 0.5 \({}^{\circ}\)C/min. The specific heat of the material is 2.3 kJ/kg/\({}^{\circ}\)C. The density of the PCM is 820 kg/m\({}^{3}\). Please refer to [15] for more details on PCM thermal properties. The PCM energy storage is made by parallel PCM fiberboards. The thickness of the fiberboards is 12.5 mm. The depth is 90 mm. The thickness of the gaps between the two boards is 5 mm. The PCM amount for each room is shown in Table 2.  
Figure 5: The working principle of the PCMVW during winter [14]. (**a**) Heat storage mode, when I \(>\) 200 W/m\({}^{2}\)). (**b**) Heat release mode, when T\({}_{\text{indoor}}\)\(<\) 24 \({}^{\circ}\)C. (**c**) Overheating preventing mode, when T\({}_{\text{indoor}}\)\(>\) = 24 \({}^{\circ}\)C.  
Figure 6: The working principle of the PCM facade in winter. (**a**) Heat storage mode, when I \(>\) 200 W/m\({}^{2}\)). (**b**) Heat release mode, when T\({}_{\text{indoor}}\)\(<\) 24 \({}^{\circ}\)C. (**c**) Bypass ventilation mode, when T\({}_{\text{indoor}}\)\(>\) = 24 \({}^{\circ}\)C.  
The ventilation window (VW) is made by a double glazing pane, a single glazing pane, and a ventilated cavity with solar shading integrated into the cavity. A double glazing pane is also used for the surface of the PCM energy storage both for the VW and the facade and is equipped with an external shading device. The rest of the windows and glass doors are made by triple glass panes with integrated solar shading devices. The window properties and shading properties are shown in Tables 3 and 4. The Energyplus model uses Conduction Finite Difference (CondFD) heat balance algorithm for phase change material, which allows shorter time steps and changeable thermal properties than the conduction transfer function (CTF) algorithm. The model was verified by the experiment, which can be found in [14]. The house is equipped with a Packaged Terminal Heat Pump.