## 2 Method
### Evaluation of Single Action  
Following the completion of the project definition stage, it is proposed that applicable single renovation actions are evaluated separately. The goal is to obtain an overview and compare how different renovation actions perform in terms of potential energy savings and costs. A methodology for linking cost, energy savings, and lifetime, described in [37], is applied in this paper and further developed to include renewable energy systems. A brief summary of the methodology is provided in the following paragraph. The methodology proposed in [37] evaluates investments in energy efficiency based on a parameter termed cost-effectiveness. It links implementation cost, primary energy savings, and lifespan of the evaluated actions. The cost-effectiveness parameter (CEP) of each action is calculated using Equation (1) and represents the cost of saved kWh primary energy. \[\text{CEP [($\ell$\,|\,Kr.\,$|$\$)/(saved kWh)] = (Implementation cost/lifetime [$\ell$/y])/(Saved energy [$kWh/y$])} \tag{1}\]  
The different lifespan of investigated improvements is taken into account by dividing the implementation cost by the expected lifespan of the action in question. The implementation cost at this stage includes all costs necessary to implement an action. Those can be the removal and disposal of old materials, equipment and person-hour expenses, investment for new materials and components, etc. This way of representation allows the building owner to obtain a direct overview of the value for money that each action yields. Moreover, knowing the implementation cost for different actions grants a possibility of working with the budget, ensuring there is enough funds to implement a given improvement. Applying the CEP parameter results in a rather simplified approach to evaluate the contribution of single actions, comparing to global cost (NPV) obtained using Equation (2)  
\[\mathrm{GC}=\mathrm{CO}_{\mathrm{init}}+\sum_{\mathrm{j}}\left[\sum_{\mathrm{i=1 }}^{\mathrm{TC}}\Bigl{(}\mathrm{CO}_{\mathrm{a(i)}}(\mathrm{j})*\Bigl{(}1+ \mathrm{RAT}_{\mathrm{xx(i)}}(\mathrm{j})\Bigr{)}+\mathrm{CO}_{\mathrm{co2(i) }}(\mathrm{j})\Bigr{)}*\mathrm{D}_{\mathrm{-f}(\mathrm{i})}+\mathrm{CO}_{ \mathrm{fin(TSL)}}(\mathrm{j})-\mathrm{VAL}_{\mathrm{fit(TC)}}\mathrm{f}(\mathrm{ j})\right]. \tag{2}\]  
Equation (2) follows the representation defined in DS/EN 15459 [38], where GC is global cost, while different cost types are denoted with \"CO\" and accompanying subscript that specifies the type of cost (init--initial; a--annual; CO2--emission cost; fin(TSL)--disposal cost). The calculation takes into account possible residual value (VALfit) and discount factor (D_f) for the calculation period (tTC). The CEP parameter includes only implementation cost and disregards price increase, residual value, and discounting, which simplifies the calculation in comparison to LCC. Furthermore, the CEP evaluates the contributions of studied solutions for the duration of their lifespan, while LCC are calculated for a defined calculation period. At this early stage of the renovation process, such simplification can prove valuable to obtain a quick overview and grounds for comparison of different solutions without diving into details of appropriate assumptions for the additional parameters required for LCC analysis. Moreover, determining the NPV for each alternative may prove to be a task requiring extensive time and resources for the purpose of evaluation of individual contributions from renovation measures. Furthermore, the process of determining CEP acquires a solid background of all the parameters necessary for LCC calculations, which is performed in the next step of the method on the package level. To investigate how CEP ranks the different single actions in comparison to ranking based on LCC, single actions investigated in [37] are further evaluated using the LCC approach. A drawback of the methodology presented in [37] is that it is solely applied for energy-saving actions.