## 6 Results  
The energy efficiency of the existing building, along with the models for Scenario 1, Scenario 2, and Scenario 3, was simulated using the Integrated Environmental Solutions Virtual Environment 2017 software package (IES VE) for the climatic conditions of Belgrade. Climatic factors such as the annual variation in air temperature and relative humidity, solar insolation, radiation intensity, and wind patterns are characteristics of the location where the building is situated. When renovating this building and its technical systems, it is very important to understand the climatic characteristics of the area. These data serve as input for calculations of energy consumption as well as for assessing comfort conditions within the building [59]. For the examination of a building's energy efficiency through simulations, i.e., for determining thermal and energy behavior with the aim of optimizing energy performance, it is necessary to have data on the climatic and hydrometeorological conditions of the building's location--in this case, Belgrade. The optimization of a building's energy performance was carried out using an appropriate Typical Meteorological Year for Belgrade (a thirty-year period). The average mean, daily maximum, and minimum temperatures and humidity values for Belgrade are provided in Table 4 [59]. The case study model was initially created in SketchUp and subsequently transferred to IES VE 2017, as illustrated in Figure 2. The sports center features a total heated floor area of 6098.85 m\({}^{2}\), and the overall heated volume of the building is 35,529.56 m\({}^{3}\). \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multicolumn{13}{c}{Average Temperature Values} \\ \hline \({}^{\circ}\)C & January & February & March & April & May & June & July & August & September & October & November & December \\ \hline mean & \(-\)1.72 & 0.78 & 5.17 & 9.83 & 16.83 & 21.83 & 24.72 & 22.94 & 20.22 & 13.50 & 7.78 & 2.67 \\ \hline max. & 1.56 & 4.00 & 8.72 & 13.89 & 21.06 & 26.39 & 28.33 & 26.56 & 23.17 & 17.17 & 10.44 & 5.28 \\ \hline min. & \(-\)5.22 & \(-\)3.22 & 1.72 & 6.67 & 12.72 & 17.50 & 21.22 & 19.56 & 16.89 & 9.94 & 4.83 & \(-\)0.06 \\ \hline \multicolumn{13}{c}{Average humidity values} \\ \hline Before & 60.6 & 57.1 & 61.1 & 58.2 & 60.8 & 57.4 & 55.6 & 60.6 & 65.7 & 59.5 & 65.2 & 66.1 \\ \hline Afternoon & 58.3 & 54.6 & 53.5 & 47.3 & 52.4 & 49.8 & 48.0 & 52.6 & 58.6 & 51.6 & 59.2 & 59.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Table of average mean, daily maximum, and minimum temperatures and average humidity for Belgrade. Figure 2: Model of the Vózdovac Sports Centre SC2 IES VE model. The operating hours, as summarized in Table 1, differ between the main sports hall and the other parts of the building. These two segments are treated as separate thermal zones due to distinct thermal requirements. For the simulation of the existing situation, the infiltration rate was set at 0.2 air changes per hour (ACH). In terms of air exchange, there is no natural ventilation in the main sports hall, while it exists in other parts of the building [61]. Simulated indoor air temperatures during the heating period (mid-October to mid-March) are maintained at 16 \({}^{\circ}\)C for the main sports hall (ranging from 12 \({}^{\circ}\)C to 18 \({}^{\circ}\)C for sports activities) and 20 \({}^{\circ}\)C for the rest of the building (with a comfort range of 24 \({}^{\circ}\)C for locker rooms and 26 \({}^{\circ}\)C for administration), as per CIBSE Guide A, 2015 [62]. From mid-May to mid-October, the simulated indoor air temperature is set at 20 \({}^{\circ}\)C for the main sports hall and 26 \({}^{\circ}\)C for all other spaces, following the Rule book on the Energy Efficiency of Buildings (Official Gazette of RS, No. 61/2011) [40]. However, in line with European standards, thermal comfort during summer should not exceed 10% of occupancy hours above 25 \({}^{\circ}\)C throughout the year [59].