## 1 Introduction
Their results showed that during the night, the lower outdoor air temperature, and the higher supply airflow rate increase the efficiency of the NV. Additionally, the importance of thermal mass was clearly revealed in the experiments by increasing the buildings thermal inertia in cooperation with effective NV that produced a lower temperature development and delay in the peak indoor air temperature. [PERSON] et al. [27] verified these conclusions in an experimental study that the key parameters for NV efficiency are the airflow rate, differential indoor-outdoor temperature and the thickness of the PCM layer, which is equivalent to an increase in thermal mass. Simulations and experimental work on PCM wallboards installed in lightweight buildings are performed by [PERSON] et al. [28; 29]. They reported the air flow rate to be effective and one reaches a point of diminishing returns between 4 and 8 ACH. [PERSON] et al. [30] simulated the effect of natural NV in a multilayered building with PCM and concluded that the number of ACHs should be as high as possible, where up to 40 ACH was tested. Whenever hybrid NV strategies are used, most studies report a critical value of airflow rates where the energy savings are starting to drop due to fan usage [27]. In the recent study of [PERSON] et al. [31], the authors presented the climatic and seasonal suitability for the combination of PCM and NV. However, an important factor is the control mechanism for the NV strategy. [PERSON] et al. [32] analyzed three different control schemes in a similar climate and office building as in this report. It was reported that the most efficient strategy was the one which ventilated the office space excessively, where the NV control was not deactivated until the surface temperatures dropped below the outdoor air temperatures. Moreover, it was concluded that a strategy which prolonged the operational hours as long as possible, from 21:00-07:00 had a second-best effect. [PERSON] et al. [33] explored a custom control, which aimed at using NV until a certain set point temperature inside the building was reached. Setpoint temperatures of 13, 15, 17 and 19 \({}^{\circ}\)C was tested, and it was found that the strategy reaching the lowest indoor temperature was best for energy performance. However, this can lead to problems with overcooling in regards to thermal comfort for early working hours. They concluded that 15 \({}^{\circ}\)C could be the optimum set point temperature, but further research is needed. Upon researching more studies on control schemes, it's noticed that no one-fits-all solution exists. Researchers explore different ideas based on the particular climate and building conditions of study. There is also a lack of recommendations in national standards on the details of NV control mechanisms. Studies related to quantification of the energy efficiency of buildings equipped with PCMs are not abundant in literature. This is partly due to the novelty of PCM enhanced building materials where few products are in a state to be readily incorporated in building applications, and partly due to the extent of study needed to properly analyze the energy efficiency. A sufficiently long time period with dynamic weather conditions should be investigated to produce reliable results. We summarize some relevant studies addressing the effectiveness of the PCMs for passive cooling in dynamic weather conditions in Table 1. Note that the results are seldom directly comparable as the outcomes are dependent on many variables linked to the PCM, climatic conditions and test setup. The works presented in [23; 34; 35; 36] showed high improvements to either cooling load power draw or reduction of accumulative energy usage by the combination of PCMs and natural NV. Mechanical cooling (air conditioning (AC) or heat pump) were used at night in [37; 38; 39] to charge the PCMs. Although the results are lower in comparison with NV, significant improvements to the energy efficiency were still achieved.