## 2 Materials and Methods
### Problem Setup  
To investigate the performance of the spackling material for a representative office building in connection with different NV strategies with the simulation tool IDA-ICE discussed above, we consider the following setup as shown in Figure 4. The default settings for dynamic simulation are used, where the calculated variables are solved through a variable timestep integration scheme with a tolerance of 0.02. An EnergyPlus weather file with climate data from Oslo, Norway, is used in the model, where the months of June, July and August are simulated. The location is subject to a temperate cold climate, and has a Koppen-Geiger classification: Dfb. The building is modelled to comply with the energy efficiency criteria set by the Norwegian building code, TEK-17 [45]. The choice of the materials and building layout are made in accordance with the modern building techniques and guidelines in Norway. The thermal properties of the building envelope are listed in Table 3. We consider that the cubicles are equipped with diffusive window screens and if the solar flux exceeds 100 W/m\({}^{2}\) on the facade a draw signal is invoked to inhibit the overshoot from the allowed net energy demand according to TEK-17 regulations. The total g-value of the windows with and without screens drawn are assigned as 0.53 and 0.27, respectively. Figure 4: Office building modelled in IDA-ICE. Figure 3: Comparison of average air temperature between experiment and simulation. (**a**) Without PCM, (**b**) With PCM. To reduce the computational cost, only the south facing part of the upper floor is considered to be fitted with a detailed interior layout (see Figure 4). This is a multi-zone model with 318 m\({}^{2}\) floor area, consisting of multiple single celled cubicles, a hallway, and a technical space above the suspended ceiling. The PCM-spackle is added to the walls and ceiling surfaces of each cubic. The spacing layout and multi-layered construction elements are detailed in Figure 5 and Table 4. The cubicles and the hallway are equipped with a constant air volume (CAV) ventilation system, supplying air with a temperature of 19 \({}^{\circ}\)C whenever active. The air flow rates are prescribed with a min/max schedule based on the working hours of 08:00-18:00, as shown in Table 5. Each cubicle and the hallway are fitted with an ideal cooler activated at 26 \({}^{\circ}\)C operative temperature, as this is the upper limit for the thermal comfort set by the Norwegian national standards. This would reveal the surplus heat needed to be evacuated or prevented from entering the occupied space to maintain the thermal comfort criteria. To reveal the benefit of the careful consideration of the combination of NV strategies with the PCM-spackling we considered both fully natural NV system and a hybrid NV system. The aim is to study the effect on cooling load reduction and energy savings with varying NV air flow rates and PCM layer thickness. In the natural strategy, CAV is shut off and the windows are opened by a varying amount to provide the desired air flow rates. In this strategy, each cubic is ventilated with single sided window opening, while the hallway is ventilated with window openings in each end. On the other hand, for the hybrid strategy, the windows are opened by a limited and fixed amount, and only the exhaust fan of the CAV system is triggered to extract air from the building by varying amounts. The specific fan power (SFP) of the ventilation system is set as \(SFP_{Sup}=1.5\) kW/(m\({}^{3}\)/s) and \(SFP_{exh}=1.0\) kW/(m\({}^{3}\)/s). Both strategies are made active between 21:00-07:00 every day. A minimum allowed indoor set point temperature of 16 \({}^{\circ}\)C is used during NV to avoid over-cooling issues leading to thermal discomfort at the morning working hours. It is evident that only a fixed amount of window opening does not produce a constant ventilation rate and the flow rate depends additionally on the pressure differential between the indoor and outdoor environment.