## 3 Results
### Results of the Economic Analyses and Their Discussion  
The LCC provides a comprehensive assessment of the costs of a glazing system from the moment of purchase to the moment of disposal, throughout its entire life cycle. Using this method, the most cost-effective option was identified. To enable this task, a graph (Figure 8) showing the change in the LCC value depending on the discount rate was created. It turned out that the lowest total cost in the long term (30 years) was for Variant B, i.e., windows made in a triple-glazed system in the case of a house located in Bialystok. If inflation constantly remains above 5.2%, choosing Variant A would become a more profitable solution. This is a rather unrealistic scenario for the development of global business and the situation in financial markets. Additionally, a new and quite realistic variant was considered, in which a 2% increase in energy prices is predicted (Figure 9). In this case, triple- and quadruple-glazed windows have a similar LCC value provided that the discount rate is lower than 2.5%. Within the range of 2.5% to 7.5%, triple-glazed windows are characterised by definitely the lowest LCC. In the highly unlikely event of an increase in the return on invested capital to over 7.5%, triple-glazing windows become less profitable. Slightly different LCC analysis results are obtained for the house located in Kiruna. If the discount rate is less than approximately 3%, triple- and quadruple-pane windows will have a similar LCC value. Above this value of \(r\), a triple-glazed system will have the lowest life cycle costs. And after taking into account a 2% increase in energy prices, \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Model**} & \multicolumn{10}{c}{**Month**} \\ \cline{2-13}  & **1** & **2** & **3** & **4** & **5** & **6** & **7** & **8** & **9** & **10** & **11** & **12** & **Sum** \\ \hline \hline \multicolumn{13}{c}{Electricity consumption for artificial lighting [kWh]} \\ \hline \multicolumn{13}{c}{**Bialystok**} \\ \hline A & 73.8 & 65.1 & 67.3 & 52.9 & 49.9 & 43.8 & 48.4 & 51.8 & 59.0 & 69.6 & 70.5 & 74.3 & **726.4** \\ \hline B & 74.1 & 65.4 & 67.6 & 54.2 & 50.3 & 44.6 & 48.9 & 52.7 & 59.6 & 70.4 & 70.9 & 74.7 & **733.3** \\ \hline C & 74.3 & 65.7 & 68.2 & 55.0 & 50.9 & 44.7 & 49.5 & 52.9 & 60.0 & 71.2 & 71.3 & 75.0 & **738.7** \\ \hline \multicolumn{13}{c}{**Kiruna**} \\ \hline A & 80.04 & 67.87 & 64.57 & 43.3 & 31.83 & 21.17 & 23.51 & 39.89 & 54.43 & 72.46 & 76.04 & 80.49 & **655.60** \\ \hline B & 80.11 & 68.04 & 65.29 & 44.28 & 33.26 & 21.56 & 24.83 & 41.01 & 56.19 & 73.07 & 76.18 & 80.49 & **664.31** \\ \hline C & 80.13 & 68.24 & 66.23 & 45.4 & 34.47 & 22.98 & 25.22 & 41.69 & 57.49 & 73.37 & 76.33 & 80.49 & **672.04** \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Monthly energy consumption for artificial lighting. quadruple-glazed windows are the best choice, provided that the discount rate is not higher than about 5%. Therefore, we can see that in more severe climates it is profitable to use windows with the highest thermal resistance. The study considered three variants to estimate the NPV, assuming a 5% discount rate: \begin{tabular}{l} Variant I--replacing a double-glazed window with a triple-glazed one; \\ Variant II--replacing a double-glazed window with a quadruple-glazed window; \\ Variant III--replacing a triple-glazed window with a quadruple-glazed window. \\ \end{tabular}   
In the case of determining NPV, it was assumed that the financial flows were defined as the reduction in energy consumption caused by replacing windows with more energy-efficient ones. A positive NPV value indicates the profitability of the project from a financial perspective.