## 3 Results and Discussion
### How to Choose the Optimal Solution within Each POS? To discuss and clarify the previous results, it is interesting to consider both the holistic efficiency scores (Model#1) together with some characteristics of the solutions. We decided to used Model#1 because the holistic efficiency scores represent a more complete definition of efficiency and the decision of customer is to decide which intervention is the most convenient from different point of views. Scores from Model#2 are also relevant, but they refer specifically to environmental issues. Indeed, for instance, they do not take into account the size of investment that, on the contrary, is considered in LCC estimations used in Model#1. Tables 5 and 6 report, respectively for Single-Family and Multi-Family houses, the amounts of Primary Energy Consumption (kWh/m\({}^{2}\)) (The primary energy consumption is the value of energy consumption of the buildings (for each m\({}^{2}\)) after the implementation of the optimal solution (as defined in report D3.4 of the HAPPEN Project) [2]) and of Life Cycle Cost (\(\mathfrak{C}\)/m\({}^{2}\)) for each solution and climate zone. Data were elaborated from the Deliverable 3.4 of HAPPEN project and the Life Cycle Cost methodology was presented in [36]. To calculate the LCC estimates, the initial investment is considered and, at the same time, the LCC was used as input for the Model#1 applied for computing the holistic efficiency of solutions. On the contrary, the primary energy consumption could were an input for the frontiers, because, together with the LCC, are key variables in finding the optimal solution. However, the sample size does not allow to obtain robust results with an input-output space bigger than that used. For this reason, in both models the good output to maximize was represented by the final energy saving that, together with CO\({}_{2}\) emissions, is the most suitable candidate to catch the effects on consumptions. From the analysis, we can observe that, in general, the obtained efficiency scores do not always match with the minimum values of primary energy consumption. Indeed, considering the case of Single-Family house and W1S2 climate zone, the solution 9 is the best in terms of efficiency (Table 3); however, considering Table 5, it does not correspond to the minimum LCC evaluation, but it is the best solution considering the primary energy consumption. Indeed, the proposed scores measure which solution has the minimum impact on environment, in terms of CO\({}_{2}\), and the maximum capacity in final energy saving, taking equal the LCC (Model#1) or total costs (Model#2). We could conclude that results are contradictory but in truth the meaning of LCC alone and of efficiency scores is different. However, results in Table 5 suggest that considering only LCC, the solution 9 is not the best one (i.e., solution 9 does not present the lowest level of LCC for W1S2 climate zone), but the solution 9 is the most efficient considering the LCC together with the impact in terms of energy savings and emissions (i.e., from Table 3, solution 9 presents the lowest efficiency scores). For this reason, the methodology proposed presents the most complete evaluation of solutions, considering not only costs and investments, but also negative externalities (i.e., CO\({}_{2}\) emissions). Considering this specific case (W1S2), from Table 5 solution 1 (POS1 and POS5) presents the lower LCC values but Table 3 (Model#1) suggests that this solution is not the most efficient because the efficiency score is higher than 0, rather it is the worst in terms of produced outputs and also the primary energy consumption is very high compared with that of other alternatives. Similar results are obtained in the case of multifamily houses and W1S2 climate zone (Table 4 Model#1 and Table 6). Indeed, also in this case, models agree in highlighting solution 8 (POS9 and POS13) as the more efficient. Table 6 shows that this solution does not present the minimum value of LCC estimation but in terms of initial energy consumption is the best choice.