# NZEB Renovation Definition in a Heating Dominated Climate: Case Study of Poland
## 5 Cost-Optimal Building Renovation Variant  
On the basis of defining cost-optimum U-values of building elements and solutions referring to the upgrading of the ventilation system and the use of RES, different renovation variants were identified. All of them include upgrading of the existing heating and domestic hot water system with replacement of heating source. The symbols used to differentiate the variants are explained below:  
* W0: baseline variant, existing model buildings and systems before renovation;
* W1: variant I of building envelope renovation; energy price 4.7 EUR per 1 GJ;
* W2: variant II of building envelope renovation; energy price 14.3 EUR per 1 GJ;
* G: natural ventilation, improved base case but with no reduction of the energy loss through ventilation;
* H: hybrid ventilation, it was assumed that the energy loss through ventilation will be reduced by 20%; \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**W1—4.7 EUR per 1 GJ**} & \multicolumn{4}{c}{**W2—14.3 EUR per 1 GJ**} \\ \cline{2-9}
**Building Element** & **d** & **U-Value** & **Renovation** & **Unit** & **d** & **U-Value** & **Renovation** & **Unit** \\ \cline{2-9}  & **cm** & **W/(m\({}^{2}\) K)** & **Cost** & **cm** & **W/(m\({}^{2}\) K)** & **Cost** & **Cost** & **Cost** \\ \hline External wall & 14 & 0.183 & 27.56 & EUR/m\({}^{2}\) & 24 & 0.118 & 32.29 & EUR/m\({}^{2}\) \\ Floor above an & 7 & 0.247 & 12.60 & EUR/m\({}^{2}\) & 10 & 0.187 & 18.00 & EUR/m\({}^{2}\) \\ unheated collar & 14 & 0.235 & 30.82 & EUR/m\({}^{2}\) & 30 & 0.128 & 38.71 & EUR/m\({}^{2}\) \\ Flat roof & 12 & 0.217 & 22.05 & EUR/m\({}^{2}\) & 26 & 0.121 & 26.50 & EUR/m\({}^{2}\) \\ Pitched roof & 20 & 0.177 & 33.73 & EUR/m\({}^{2}\) & 35 & 0.097 & 39.02 & EUR/m\({}^{2}\) \\ Windows & - & 0.9 & 133.90 & EUR/m\({}^{2}\) & - & 0.9 & 133.90 & EUR/m\({}^{2}\) \\ External doors & - & 1.3 & 973.27 & EUR/pcs. & - & 0.9 & 1035.08 & EUR/pcs. \\ \hline \hline \end{tabular}
\end{table} 
Table 13: The cost-optimum renovation variants (depending on the energy price) of building’s envelope—discount rate changed to 3%. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**W1—4.7 EUR per 1 GJ**} & \multicolumn{4}{c}{**W2—14.3 EUR per 1 GJ**} \\ \cline{2-9}
**Building Element** & **d** & **U-Value** & **Renovation** & **Unit** & **d** & **U-Value** & **Renovation** & **Unit** \\ \cline{2-9}  & **cm** & **W/(m\({}^{2}\) K)** & **Cost** & **cm** & **W/(m\({}^{2}\) K)** & **Cost** & **Cost** & **Cost** \\ \hline External wall & 10 & 0.235 & 25.70 & EUR/m\({}^{2}\) & 18 & 0.150 & 29.29 & EUR/m\({}^{2}\) \\ Unheated collar & 3 & 0.438 & 7.71 & EUR/m\({}^{2}\) & 7 & 0.248 & 12.60 & EUR/m\({}^{2}\) \\ Suspended floor & 10 & 0.297 & 28.85 & EUR/m\({}^{2}\) & 20 & 0.179 & 33.78 & EUR/m\({}^{2}\) \\ Flat roof & 10 & 0.245 & 21.35 & EUR/m\({}^{2}\) & 18 & 0.162 & 25.04 & EUR/m\({}^{2}\) \\ Pitched roof & 20 & 0.177 & 33.73 & EUR/m\({}^{2}\) & 30 & 0.115 & 37.11 & EUR/m\({}^{2}\) \\ Windows & - & 1.3 & 108.76 & EUR/m\({}^{2}\) & - & 0.9 & 133.90 & EUR/m\({}^{2}\) \\ External doors & - & 1.3 & 973.27 & EUR/pcs. & - & 0.9 & 1035.08 & EUR/pcs. \\ \hline \hline \end{tabular}
\end{table} 
Table 14: The cost-optimum renovation variants (depending on the energy price) of building’s envelope—discount rate changed to 8%. R: mechanical ventilation with heat recovery, efficiency of heat recovery: 90%; and
* S: solar system used for DHW heating, assumed coverage between 50-60% of DHW energy demand. The precise description of improvements and solutions in baseline variant can be found in Table 15.  
The renovation cost, energy efficiency and auxiliary electrical energy consumption was calculated for each system. The costs of renovation were defined on basis of offers from companies and fixed max prices from existing renovation programmes, e.g., Jawor in Malopolska region. Since both models have similar heated area the absolute vales were given and used each case.