# 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 \multirow{2}{*}{**Building Model**} & \multirow{2}{*}{**Location**} & \multicolumn{2}{c}{**Energy Price per 1 GJ**} \\ \cline{3-4}  & & **4.7 EUR** & **9.5 EUR** & **14.3 EUR** \\ \cline{3-4}  & & **Cost-Optimum Renovation Variants** \\ \hline \multirow{3}{*}{S-1 (one-storey building with an attic)} & Warszawa & W1/G & W2/G & W2/H/S \\  & Szczecin & W1/G & W2/G & W2/H/S \\  & Suwalki & W1/G & W2/G & W2/H/S \\ \hline \multirow{3}{*}{S-2 (two-storey building with flat roof)} & Warszawa & W1/G & W2/G & W2/G/S \\  & Szczecin & W1/G & W2/G & W2/G/S \\ \cline{1-1}  & Suwalki & W1/G & W2/G & W2/R/S \\ \hline \hline \end{tabular}
\end{table} 
Table 17: Cost-optimum renovation variants. Figure 3: Discounted cumulative cost (K\({}_{\text{Rd}}\)) for different renovation variants, base case (W0), locations and buildings models S-1 and S-2 in relation to energy need for heating (Q\({}_{\text{H}}\)). Energy price: 9.5 EUR/GJ. on the ground: 0.14 W/m\({}^{2}\) K, flat roof: 0.12 W/m\({}^{2}\) K, pitched roof: 0.10 W/m\({}^{2}\) K, floor above unheated basement: 0.19 W/m\({}^{2}\) K, windows: 0.9 W/m\({}^{2}\) K, and external doors: 0.9 W/m\({}^{2}\) K; and * In the case of EUR 14.3 per GJ for both building types the optimal variant is W2/S. which takes into account solar collector installations supporting the preparation of domestic hot water. Some differences can be seen in regard to ventilation. In the case of the two-storey building with flat roof, mechanical ventilation with heat recovery is cost-effective in Suwalki (the coldest location) whereas, for the second building, the use of hybrid ventilation is optimum for all locations. Table 18 shows the energy need for heating (Q\({}_{\rm H}\)) (including heating and ventilation) for the cost-optimum variants of renovation of two model buildings, respectively. It can be seen that the energy need ranges from 30.9 to 91.1 kWh/m\({}^{2}\) year correspond to the optimal variants. The high range of values is a result differences in climate (different locations) energy prices and building types. Average energy need at a low energy cost (EUR 4.7 per GJ) is around 62% higher than for high energy cost (EUR 14.3 per GJ). The difference caused by the climate (between Suwalki and Szczecin) is only 16%. The average energy need for heating for all renovation variants is 58 kWh/m\({}^{2}\) year. Based on the energy need for heating, the primary non-renewable energy demand was calculated for the models. At this point renovation of heating and DHW system, auxiliary equipment was included, as well as the use of solar collectors for DHW. The obtained reduction of the primary non-renewable energy demand for heating, ventilation, hot water production, and the work of auxiliary equipment (this includes energy for fans, pumps, electronics, etc.) is shown in Figure 4. In all the variants the demand is reduced significantly. Before renovation buildings have needed from 425 to 636 kWh/m\({}^{2}\) year of primary, non-renewable energy. After renovation it was from 66 to 160 kWh/m\({}^{2}\) year, depending on the variant. Such a high reduction was possible thanks to wide range of improvements, including not only the building envelope, but also the systems. The primary energy demand was, in most cases, higher than requirements for new NZEB single-family house (\(\leq\)70 kWh/m\({}^{2}\) year) [61]. The percentage of reduction of primary non-renewable energy demand was determined in relation to the energy demand of the buildings before renovation only for the cost-optimum renovation variants (Table 19). It ranges from 69% to 86%. The higher reduction in primary non-renewable energy can be achieved by using RES and a better insulated building envelope. Both improvements are used in the case of high energy price. The location does not have a significant effect in this case. The PEF for the main energy carrier was 1.1 before and after renovation.