## 3 Results and Discussion
### Cooling Energy Reduction  
In Figure 10, the energy saved for cooling (see Equation (1)) during the simulation period is shown for both NV strategies. Only the energy spent locally by the ideal coolers in the cubicles are regarded in these calculations. Both the natural and hybrid strategy show nearly identical results as approximately equal air flow rates are maintained for these strategies to have a good comparative basis. It can be seen that increase in the air flow rates during NV increases the potential for energy savings considerably. As for the case of 5 ACH, \(\approx\)80% reduction is achieved from NV alone without any PCM. A further increased value, \(\approx\)95% is obtained when NV is coupled with 4 mm PCM. Clearly, the slopes of the curves decrease with the increase of ACH and the curves tend to saturate asymptotically. Also, above an air flow rate of 4 ACH, the additional benefits become much smaller. Furthermore, it can be seen that the NV alone is the main contributor to the energy savings, but the PCM adds notable benefits to the savings. At 4 ACH, 2 mm of PCM adds \(\approx\)12% of energy savings to the NV, while 4 mm adds \(\approx\)17%. The maximum benefit from the PCM occurs at 2 ACH where 2 mm of the PCM adds \(\approx\)14% and 4 mm adds \(\approx\)21%. The results correspond well with numerous studies that have confirmed NV air-flow rates and the amount of thermal mass to be some of the key parameters for effective  
Figure 9: Cooling load duration diagram for the whole building. Cases of 1, 3 and 5 ACH with and without PCM are compared to the reference case. NV [26; 27; 30; 32; 49]. Indeed, this is apparent in our results as the energy saved for cooling increases both with higher NV air flow rates and thicker layers of PCM (thermal mass). Moreover, the results are also in line with studies showing diminishing returns occurring around 4-8 ACH [29; 49]. A vast amount of research have found PCMs to provide significant energy savings potential, both for heating and cooling across a wide variety of climates [12; 50]. However, the results vary considerably due to the complexity of multiple parameters which influences the effectiveness of the material. Also, PCMs are developed in numerous configurations with different approaches to building implementation. It's evident that results are heavily reliant on the parameters like, the PCM concerned, the quantity of the PCM, test setup, and the method for calculating energy savings. All of these factors are found to vary by a great deal amongst published reports. Some interesting aspects about our results is that it provides a realistic building scenario case and that it separates the impact of the PCM from the accompanied strategy that is needed to cool the PCM at night. Building engineers needs to solve both energy efficiency and thermal comfort requirements, which are usually conflicting goals. These results can be of great value as the case building is aligned with the local energy efficiency criteria, and the results give a comparative basis for the engineer to evaluate different methods to achieve thermal comfort during summer conditions. Although both strategies are equally effective in reducing the local cooling demand, Equation (2) is used to calculate the cooling energy savings with all energy posts affected by the strategies. The AHU fans are found to be dominant in terms of their energy expenditure besides the mechanical cooling. The main downside with hybrid NV is the increasing energy usage for fans with increasing air flow rates. With natural ventilation, all fans can be shut off which is an additional bonus compared to the baseline case where the CAV system runs through the night at low air flow rates. Figure 11 shows the results for both strategies. The natural NV strategy shows the similar tendency as before but the total energy savings are lower when fan usage is included into the fraction (see Equation (2)).