# Improving the Energy Efficiency of an Existing Building by Dynamic Numerical Simulation
## 5 Results  
The simulations using DesignBuilder software show all energy consumption--heating, cooling, lighting, domestic hot water, as well as renewable energy production--for the four presented rehabilitation solutions.  
For the presented scenarios results are being presented in the table below:  
Table 2 presents the results for the energy consumption decrease for every presented scenario analyzed. If only the envelope is thermally insulated, 11.63% of final energy is decreased; then, by adding to Scenario 1, the window replacement a 24.35% specific final energy decrease is obtained. Scenario 3 adds the thermal solar panel implementation to Scenario 2 and determines a 40.78% decrease of the specific final energy consumption. Scenario 4, the most complete one, brings a 44.84% decrease of specific final energy if added PV collectors are added. Concerning primary energy, 55.33% can be achieved for the best studied scenario. Carbon dioxide emissions are decreasing accordingly with maximum 56% for the last case study.  
Figure 7: Heating and hot water supply systems schema used in Designbuilder for the third and fourth scenarios.  
The PV yearly coverage of the electrical energy consumption is 99.5%, a good coverage degree being obtained.  
The total energy class of the initial building is B, and the chosen retrofit scenario has an A energy class, according to Romanian methodology existing in the legislation [17]. According to Romanian Legislation [13] the NZEB (Near Zero Energy Building) situated in the same climate as our building (\(-\)15 \({}^{\circ}\)C conventional temperature for wintertime, climate zone II) should have a yearly primary energy consumption less than 111.0 kWh/m\({}^{2}\) year and specific CO\({}_{2}\) emission of 30 kg CO\({}_{2}\)/m\({}^{2}\) year. For our best scenario, the yearly primary energy target could not be reached by almost 5%, but the specific yearly CO\({}_{2}\) emissions were 7.7 times decreased because of the fact that renewable energies were used (biomass and solar). As a perspective maybe a heat pump should be investigated and taken into consideration; additionally, PV solar collectors can be added for heating and DHW (domestic hot water) purposes, with this renewable energy source.  
An investment of 28 k Euro was taken into account which includes building envelope complete rehabilitation and renewable energy systems implementation for Scenario 4. Concerning the building envelope rehabilitation, we took into account the external walls and windows, roof. The floors could not be isolated as it is an existing building and the free internal level high does not allow it. The economic viability depends on the local costs of energy for internal use and, in some countries, the often higher value per kW to sell back to the power grid. Without the benefits of the different 'efficient energy' programs in progress in Romania, the amortization is around 13 years, less than their life time, but this period can be significantly reduced by applying for one of the National Agency of Environmental Protection programs. The payback time was calculated according to Romanian legislation [17].