## 3 Results and Discussion
### Cooling Load Reduction  
Due to the attenuation effect to the temperature profile, cooling load needed to maintain the thermal comfort is also reduced. When mechanical cooling is activated, all excessive heat in the cubicle must be removed to stop further temperature rise. By delaying the occurrence of the peak temperature to later in the day, the heat gains inside the cubicle can be considerably less which reduces the required mechanical cooling load. A scenario illustrating this is depicted in Figure 8 for a typical day when 26 \({}^{\circ}\)C OT is reached, and mechanical cooling is activated. In Figure 8a, it can be seen that the setpoint temperature is reached at a later time in the day, for higher thickness of the PCM layers. The cooling load is significantly reduced progressively from 2 mm to 4 mm thickness of the PCM (see Figure 8b) and this is in accordance with the delay of the associated peak temperature. Note that the cooling load reduction is dependent on several factors like (i) the total heat gain on a particular day, (ii) quality of the charging of the PCM achieved by the NV and (iii) capability of the PCM to shift the peak temperature. Although the scenario depicted in the figure is typical, a couple of days with extreme climatic conditions is observed during the simulation period where the PCM would not function as desired. This is due to a combination of high outdoor temperatures at night leading to inadequate discharge of the stored heat of PCMs, and the prevailing conditions of high outdoor temperatures and solar gain on the following day. In this scenario, no cooling benefit is obtained.  
Figure 9 shows a cooling load duration diagram for the whole building, comparing the reference case with the cases of hybrid NV at 1, 3 and 5 ACH with and without PCM. The diagram shows the amount of hours a given magnitude of total cooling load is applied to the building. The extreme climatic scenario mentioned above is the reason for the curves being nearly adjoined close to the Y-axis. However, it is a well established procedure to  
Figure 8: Cooling load reduction for a representative cubic on a typical day. Case: Hybrid NV, 3 ACH. (**a**) Operative temperature development. (**b**) Hourly average mechanical cooling load.  
Figure 7: Indoor operative temperature of a representative cubic. Case: Hybrid NV, 3 ACH. (**a**) Maximum observed temperature reduction on a single day. (**b**) The whole simulated period.  
not size the buildings cooling load capacity for the extreme peaks that occur only on rare occasions, but rather allow for a certain amount of over temperature hours. Disregarding the few hours closest to the Y-axis in the figure, it is clear that increase in the air flow rates of NV reduces the peak cooling load for the building significantly. This is in accordance with the findings of [PERSON] et al. [34], showing a less cooling load demand of the building when the air flow rates are increased.  
Moreover, the addition of the PCM to the NV strategies brings a notable boost to the load reduction and the PCM is more effective at higher air flow rates. For example, limiting the buildings cooling load capacity to the 50 hour mark (see Figure 9), NV alone can reduce the cooling load by 11.5% at 1 ACH, 40.2% at 3 ACH and 59.8% at 5 ACH. Incorporating 4 mm of PCM, further reduction up to 19.5%, 78.2% and 95.5% respectively can be achieved. Indeed, the results show that the PCM can provide significant improvements to the cooling load demand of buildings in contrast to only having NV. This can provide some new insights as previous studies of PCM with NV usually report the results as a combined system. The works in [34; 35; 41] reported total cooling load reduction in the range of 24.3-53.8%, but the numerical results are not directly comparable as they are highly linked to the type of PCMs and other various factors. However, the mentioned studies reported significant impact from NV and the PCM which is inline with this study.