# NZEB Renovation Definition in a Heating Dominated Climate: Case Study of Poland
## 6 Results and Discussion  
The calculations were conducted for two single-family house types, three climate zones, three energy prices, and 13 variants including the base case. It allowed obtaining a large number of results (234 cases), which were thoroughly analysed. The aim was to define the NZEB renovation definition for single-family houses in the heating-dominated climate of Poland. The first stage of the process was determining the difference between cost-optimal and NZEB requirements. The regulations or literature does not define it precisely:  
* According to the EU Regulation [34; 35] \"In cases where the outcome of the cost-optimal calculations gives the same global costs for different levels of energy performance, Member States are encouraged to use the requirements resulting in lower use of primary energy as the basis for comparison with the existing minimum energy performance requirements\" (Annex I, Cap. 6-2). The NZEB level should be higher or equal to the cost-optimal. * The European Commission has published official recommendations, EU 2016/1318 [11], according to which national NZEB definitions should not be below the cost-optimal level of minimum requirements [62]. * According to [30] the NZEB target was obtained incrementing by 10 kWh/m\({}^{2}\)/year the minimum primary energy achieved by the best building variant (from the energy point of view). Figure 4: Primary non-renewable energy demand for different building models, renovation variants, and locations. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Energy Price per 1 G**} \\ \cline{3-5}
**Building Model** & **Localization** & **Qp Index for Base Variant** & **4.7 EUR** & **9.5 EUR** & **14.3 EUR** \\  & & **[kWh/m\({}^{2}\)year]** & **Qp Index for Renovation Variants (kWh/m\({}^{2}\)year)** & **(Percentage Reduction in Regard to Base Variant (\%))** \\ \hline S-1 (one-storey building with an attic) & Warszawa & 574 & 138 (75\%) & 117 (79\%) & 88 (84\%) \\  & Szczecin & 546 & 132 (75\%) & 112 (78\%) & 84 (84\%) \\  & Suwaki & 669 & 160 (75\%) & 135 (79\%) & 105 (83\%) \\ \hline S-2 (two-storey building with flat roof) & Warszawa & 448 & 137 (69\%) & 116 (74\%) & 96 (79\%) \\  & Szczecin & 425 & 130 (69\%) & 110 (74\%) & 90 (79\%) \\  & Suwaki & 527 & 160 (70\%) & 135 (74 \%) & 74 (86\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 19: Change of the primary, non-renewable energy index after renovation to the cost-optimum variant. * [PERSON] et al. [49] show how to find the cost-optimal level for the French single-family building typology. According to the conclusions finding the cost-optimal building configuration is more important from regulatory perspective than NZEB definition. * The cost-optimal is focused on costs while the NZEB prioritizes the energy performance and the use of renewable energy harvested on site [63]. * A significant part of NZEB solutions, for every building and every climate zones, are within the range of 0 to 15 kWh/(m\({}^{2}\) year) [50]. Based on the above literature review, a decision was made to define two types of requirements: cost-optimal and NZEB. Additionally the proposed definition included not primary energy demand but energy need for heating and percentage reduction of non-renewable primary energy in regard to base variant. Only the second parameter includes the RES. Since a large range of values, especially in regard to energy need for heating, was obtained, price analysis of charts for different energy prices was performed. The cost-optimal level was identified as the minimum energy need level with a lowest cumulative cost for a given energy price. For all three prices it was around 60 kWh/(m\({}^{2}\) year). The corresponding percentage reduction of non-renewable primary energy was 75%.