# NZEB Renovation Definition in a Heating Dominated Climate: Case Study of Poland
## 5 Cost-Optimal Building Renovation Variant
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Symbol of** & & **Total Renovation** & **Total Renovation** \\
**Renovation** & & **Costs 1-S, EUR** & **Costs 2-S, EUR** \\ \hline W1/G & \begin{tabular}{c} Variant I of building’s envelope renovation \\ Modernization of natural ventilation \\ \end{tabular} & 20,089 & 16,957 \\ \hline W1/G/S & \begin{tabular}{c} Variant I of building’s envelope renovation \\ Modernization of natural ventilation \\ Solar collectors for DHW \\ \end{tabular} & 22,470 & 19,338 \\ \hline W1/H & \begin{tabular}{c} Variant I of building’s envelope renovation \\ Hybrid ventilation \\ \end{tabular} & 20,983 & 17,850 \\ \hline W1/H/S & \begin{tabular}{c} Variant I of building’s envelope renovation \\ Hybrid ventilation \\ Solar collectors for DHW \\ \end{tabular} & 23,364 & 20,231 \\ \hline W1/R & \begin{tabular}{c} Variant I of building’s envelope renovation \\ Balanced ventilation with heat recovery \\ Solar collectors for DHW \\ \end{tabular} & 25,885 & 22,695 \\ \hline W1/R/S & \begin{tabular}{c} Variant I of building’s envelope renovation \\ Balanced ventilation with heat recovery \\ Solar collectors for DHW \\ \end{tabular} & 28,265 & 25,076 \\ \hline W2/G & \begin{tabular}{c} Variant II of building’s envelope renovation \\ Modernization of natural ventilation \\ Solar collectors for DHW \\ \end{tabular} & 21,929 & 18,884 \\ \hline W2/G/S & \begin{tabular}{c} Variant II of building’s envelope renovation \\ Modernization of natural ventilation \\ Solar collectors for DHW \\ \end{tabular} & 24,310 & 21,265 \\ \hline W2/H & \begin{tabular}{c} Variant II of building’s envelope renovation \\ Hybrid ventilation \\ Solar collectors for DHW \\ \end{tabular} & 22,823 & 19,777 \\ \hline W2/H/S & \begin{tabular}{c} Variant II of building’s envelope renovation \\ Hybrid ventilation \\ Solar collectors for DHW \\ \end{tabular} & 25,204 & 22,158 \\ \hline W2/R & \
\begin{tabular}{c} Variant II of building’s envelope renovation \\ Balanced ventilation with heat recovery \\ Solar collectors for DHW \\ \end{tabular} & 28,265 & 24,622 \\ \hline W2/R/S &
\begin{tabular}{c} Variant II of building’s envelope renovation \\ Balanced ventilation with heat recovery \\ Solar collectors for DHW \\ \end{tabular} & 30,105 & 27,003 \\ \hline \hline \end{tabular}
\end{table} 
Table 16: Renovation variants matrix and costs. The variants with the lowest cost have energy need for heating between 45-70 kWh/m\({}^{2}\) year. The base case model needed between 208-320 kWh/m\({}^{2}\) year of energy. The cost-optimal variants (with the lowest discounted cumulative cost) of renovation of the two model buildings are presented in Table 17. The choice of variant depends to a decisive extent on two factors: the price of energy per 1 GJ and the building's location (climate). The calculations have shown that:  
* For both building types at a low energy cost of EUR 4.7 per GJ, the renovation variant W1/G was optimal. It is a variant including improved natural ventilation and the following heat transfer coefficients (U) of external buildings elements: external walls: 0.19-0.21 W/m\({}^{2}\) K, suspended floor: 0.24 W/m\({}^{2}\) K, flat roof: 0.22 W/m\({}^{2}\) K, pitched roof: 0.18 W/m\({}^{2}\) K, floor above unheated basement: 0.25 W/m\({}^{2}\) K, windows: 0.9 W/m\({}^{2}\) K, and external doors: 1.3 W/m\({}^{2}\) K;
* At the energy cost of EUR 9.5 per GJ, the renovation variant W2/G was optimal for both building types. In this case the variant involves improved natural ventilation and the following heat transfer coefficients (U) of external buildings elements: external walls: 0.12 W/m\({}^{2}\) K, suspended