## 2 Materials and Methods  
One of the reference numerical models designed to test the energy calculations of buildings, Figure 1, was used to assess the effects of neglecting the phase change hysteresis in a full-scale facility. The specification of this very simple reference facility is included in the ANSI/ASHRAE Standard 140 Building Thermal guidelines. An object with the symbol 650 FF was selected for the calculations, designed in accordance with the recommendations of energy-efficient construction. The selected object is characterized by a glazing area on the southern side which is enlarged compared to standard solutions. It is equipped with passive elements that reduce the risk of overheating in the form of roof overhangs, causing periodic shading of large, glazed areas. Intensive nighttime ventilation was put in place, but there is no mechanical interior cooling system in this building. The tested object is a simple cuboid-shaped building with a light structure and low thermal capacity of the building envelope. The dimensions of the building are: length 8 m, width 6 m and height 2.7 m. The building contains only one room, without any internal walls. Glazing consists of 2 windows each with an area of 6 m\({}^{2}\) located on the south side. Above the windows, there is solar shading in the form of a bracket with a projection of 1 m. As before, the simulation calculations were made in the Energy Plus 8.4.0 program. The material data adopted for the basic variant (without layers containing PCM) are presented in Table 1. All data, except for the thickness of the thermal insulation, comply with the technical specification of the original standard [33]. The thickness of the thermal insulation was adjusted to the applicable requirements in Poland [34]. It was assumed that the building would be located in Krakow, which determined the adopted climatic conditions. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
\begin{tabular}{c} wooden floor \\ thermal insulation \\ \end{tabular} & 0.04 & 0.25 & 12 & 840 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Material data of the basic variant of the building. Figure 1: Model of the building used for simulation calculations. In subsequent calculation variants, the model was modified by replacing the standard plasterboard with PCM-containing materials: Dupont boards and PCM plasterboards. The DuPont(tm) Energain(r) thermal mass panel is laminated to aluminum protective foils, the core material is a mix of a copolymer and a paraffin wax 'phase change' material, which provides the panel's functionality. Some key technical data include: thickness 5.26 mm, width 1 m, length 1.2 m, area weight 4.5 kg/m\({}^{2}\), melting point 21.7 \({}^{\circ}\)C, heat storage 515 kJ/m\({}^{2}\) (18-24 \({}^{\circ}\)C). Knauf Comfortboard Properties: board thickness 12.5 mm, board weight 11 kg/m\({}^{2}\), latent heat capacity 200 kJ/m\({}^{2}\), specific heat capacity 13 kJ/m\({}^{2}\)K, phase change temperature 23 \({}^{\circ}\)C. The course of the curve (Figure 2) of Temperature Dependence of Enthalpy was adopted based on the results of calorimetric tests and the literature [35]. On the other hand, for a plasterboard containing 30% phase-change material in the form of microcapsules, the curve shown in Figure 3 was determined on the basis of the results of calorimetric tests performed separately for pure PCM and the plasterboard matrix and then calibrated [36]. Due to the expected high degree of overheating of the interior of the building, the use of two layers of boards containing phase-change material was assumed. Figure 3: Enthalpy curves for the heating and cooling processes of PCM contained in a plasterboard [2]. Figure 2: Temperature dependence of enthalpy for Dupont boards. The assumption of the 650 FF standard is the lack of mechanical cooling and heating systems in the summer. Air exchange during the day (from 8 am to 6 pm) takes place only through infiltration, while in the evening and night hours (i.e., from 6 pm to 8 am), the room is intensively ventilated.