## 2 Method
### Evaluation of Renovation Packages  
The last stage of the method consists of computing energy and LCC calculations for the selected renovation packages. For consistency and comparability reasons, results from the calculations are represented following the cost-optimal methodology introduced in the EPBD [7].  
The cost-optimal method consists of obtaining an overview of energy and financial performance of each selected package by plotting the resulting global cost (NPV) versus the energy performance, as indicated in the bottom part of Figure 1. This visualization allows the designer to see how the different packages compare in terms of global cost and if they satisfy NZEB demands or not. Plotting results for global cost and primary energy savings in the proposed way typically results in a Pareto distribution, as indicated by the dashed line in the cost-optimality plot in Figure 1. In the provided example, NZEB requirements are defined by a maximum limit for primary energy; however, it can be replaced with the parameter valid for the country or region so long as it is not primary energy.  
Energy calculations in this paper are performed using the national Danish compliance tool BE18. The software employs a quasi-steady-state monthly method [42], which is also in accordance with national and European standards. The output of the software is heat balance and primary energy demand for the modeled building, which is compared to limit values for energy classes set by Danish Building regulations 2018 [39]. Results from BE18 are further used as supply demand input to LCC models. The final heating and domestic hot water demand is obtained from the heat balance, which accounts for transmission and ventilation losses as well as solar and internal gains. The electricity demand for operation of the building is also acquired from BE18, while demand for private apartments has been estimated based on historical data and verified with statistical data for households in Denmark [37]. The calculations are limited to cost concerning total energy demand (heat and electricity), improvements to building parts, and the addition of main and secondary supply systems. BE18 is used to assess the contribution from renewable energy sources by applying the investigated solutions to the selected building case study. The model adapts the same technical specifications as in the evaluation of singe actions; however, it accounts for local conditions and limitations such as space, orientation, inclination, etc. The produced renewable energy is calculated in the software and automatically integrated in the primary energy output. The obtained total produced energy is subtracted from the corresponding final energy demand and used for LCC analysis.  
Computation of the LCC calculations in this paper is done with the software LC-CByg [43]. The tool provides pre-set templates with economic assumptions for different projects types. The presented analysis follow guidelines and assumptions set out by standard DS/EN 15459-1:2017 [38]. The suggested calculation period for residential buildings is 50 years. A set of decreasing discount rates and price development assumptions, which are mandatory for public projects in Denmark, are applied in all calculation models. In this set of assumptions, the discount rate is reduced from 4 to 3% after year 36, while individual price developments ranging from \(-0.5\) to 2% are applied for the different energy sources (natural gas = \(-0.5\)%; district heating = \(1\)%; electricity = \(1.5\)%).  
If a satisfactory package is found, the last step of the methodology is to check if the selected package fulfills all primary and secondary targets of the project. If that is in place,the process can continue with optimization and detailed design of the selected package. If some of the requirements and targets are not fulfilled, the designer can perform a second iteration, either by selecting a different package or creating a new set of packages from single actions defined in the previous step.