# Improving the Energy Efficiency of an Existing Building by Dynamic Numerical Simulation
## 6 Conclusions  
The initial case of the simulated building had a poorly thermal insulation envelope with high monthly energy consumption. The total energy class of this building according to Romanian legislation of buildings' energy efficiency [17] was labeled \"B\". The purpose of this research is to find measures to improve energy efficiency considering also renewable energy sources. The initial aim was to obtain a Near Zero Energy House (NZEB) but only some few percentage points are delimiting from this purpose, so we can conclude that a low energy house is simulated for the fourth scenario analyzed, the building being classed \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Initial Case** & **Scenario** & **Scenario** & **Scenario** & **NZEB [13]** \\  & **1** & **2** & **3** & **4** & **Romanian** \\ \hline Thermal energy consumption (kWh/m\({}^{2}\) an) & 163.6 & 140.8 & 116.0 & 108.0 & 108.0 & \\ \hline Thermal energy decrease compared to initial case (\%) & - & 14\% & 29\% & 33.95\% & 33.95\% & \\ \hline Electrical energy consumption (kWh/m\({}^{2}\) year) & 32.36 & 32.29 & 32.24 & 7.99 & 0.04 & \\ \hline Electrical energy decrease compared to initial case (\%) & - & 0.21\% & 0.37\% & 75.32\% & 99.88\% & \\ \hline Final energy specific economy (\%) & - & 11.63\% & 24.35\% & 40.78\% & 44.84\% & \\ \hline Conversion to primary energy & 176.7 & 152.1 & 125.3 & 114.1 & 116.7 & \\ \hline Conversion to primary energy & 84.8 & 84.6 & 84.5 & 46.3 & 0.1 & \\ Electric energy (2) (kWh/m\({}^{2}\) year) & & & & & & \\ \hline Yearly primary energy consumption & 261.4 & 236.7 & 209.7 & 160.4 & 116.8 & 111.0 \\ Total (1) + (2) (kWh/m\({}^{2}\) year) & & & & & & \\ \hline Primary energy economy compared to initial case (\%) & - & 9.46\% & 19.78\% & 38.66\% & 55.33\% & \\ \hline CO\({}_{2}\) emission (kg CO\({}_{2}\)/year) & 1892 & 1714 & 1521 & 990 & 837 & \\ \hline Specific CO\({}_{2}\) emission (kg CO\({}_{2}\)/m\({}^{2}\) year) & 8.80 & 7.98 & 7.08 & 4.61 & 3.89 & 30 \\ \hline CO\({}_{2}\) emission decrease (\%) & - & 9\% & 20\% & 48\% & 56\% & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Final energy, primary energy, and CO\({}_{2}\) emissions. in energy label 'A'. The Romanian Government's target for the existing houses in the year 2020 was to improve energy efficiency by 40%, 50%, or 60% primary energy decrease founding by specific programs that are even now available [19]. Starting from the first of January 2021, the Romanian Government's target changed and only NZEB buildings are allowed to be built. A primary energy reduction of 55% is an acceptable savings, attained only by using PV and solar thermal collectors, as well as a thicker thermal insulation for the envelope. The final energy reduction between the initial case and the fourth scenario was 44.85% and the CO\({}_{2}\) emissions decreased by 56%. The PV panels ensure 99.9% of the house's electric energy consumption and the solar thermal collectors determine a 32% decrease in specific final energy consumption. Generally speaking, both the building's envelope and use of renewable energy sources should be taken into account in order to achieve a near NZEB house, according to the dynamical simulations. These results should be further considered by the policy makers for future eligible funding of the government's energy efficiency programs. This study combined experimental work with numerical simulations, proving the importance of both sides in developing an energy strategy. The experimental data obtained by means of thermal images and building's envelope components' conductivity measurements describe the stage of the initial case and represent the incomes for the numerical simulations. Without the help of a dynamical simulation, the real energy consumption cannot be revealed, as the use of stationary heat transfer equations give a maximum instant energy consumption, which is reached few days over the year. Further studies will take place to achieve a passive house with a lower energy consumption, with this case being a close perspective.