## 4 Discussion  
The available information could be used to calculate the correction factors that reflected the deviations from the assumed normative conditions, which were related to three key parameters: space heating, namely during the operating hours, the floor heated areas and the indoor setpoint temperature. The adaptation factors should be used for the different building typologies. The values presented in Table 2 reflect current trends that are coupled with the reduced energy use for space heating. They constitute a conservative result since they capture recent occupant efforts to reduce the heating operating costs of their dwellings. Accordingly, to account for the occupant interactions, the theoretical EUI, estimated following the normative calculation procedures [14], should be multiplied with an adaptation factor of 0.329 for SFHs and 0.127 for MFHs. To illustrate this, consider that the theoretical final EUI for space heating and DHW averaged 318.9 kWh/m\({}^{2}\) in SFHs and 196.2 kWh/m\({}^{2}\) in MFHs, according to the national normative calculations for issuing EPCs [46]. A combined deep renovation scenario could help reach the highest energy savings of 87.2% for SFHs and 91.6% for MFHs [47], which resembles nZEB performance. Accordingly, the anticipated theoretical space heating savings will be 278.1 kWh/m\({}^{2}\) and 179.7 kWh/m\({}^{2}\), respectively. Considering that the average size of Hellenic dwellings is 88.6 m\({}^{2}\)[48], the resulting savings would be 24,640 kWh (2.12 toe) per dwelling in SFHs and 15,921 kWh (1.37 toe) per dwelling in MFHs. This translates to average energy savings of 1.75 toe per dwelling. According to the national energy efficiency action plan, the final energy use allocated to space heating and DHW in the residential sector was set to 3.25 Mtoe for 2020, and the target for 2030 was set to 1.49 Mtoe [49]. This implies that during this decade, the total energy savings should reach 1.76 Mtoe. On this basis, the cumulative potential savings could result from the deep renovations of \(\sim\)1 million dwellings or \(\sim\)100,000 dwellings per year (Figure 9). Considering that the ongoing national financing program on energy savings and autonomy in the residential sector is targeting up to 80,000 dwellings this year, one may claim that it is manageable to hit this target, provided that the eligible dwellings decide to implement deep renovations. However, taking into account the occupant interaction and the more conservative energy use may reveal a different reality that would be more challenging to handle and eventually lead to a trajectory that will miss the national target. Using the adaptation factors of 0.329 for SFHs and 0.127 for MFHs, the theoretical savings become 91.5 kWh/m\({}^{2}\) and 22.8 kWh/m\({}^{2}\), respectively. This limits the anticipated energy savings to 8107 kWh (0.70 toe) per dwelling in SFHs and 2020 kWh (0.17 toe) per dwelling in MFHs, or with  
Figure 9: Final energy use for space heating and DHW in Hellenic residential buildings for 2020 and projection toward the target in 2030 as a result of different renovation scenarios with theoretical and adapted actual estimates. average energy savings of 0.44 toe per dwelling. In order to meet the same total energy savings of 1.76 Mtoe by 2030, this would translate to the need for deep renovations of ~4 million dwellings or ~400,000 dwellings per year (Figure 9). Sustaining this annual renovation campaign that corresponds to ~6% of Hellenic dwellings is an even greater challenge. On the other hand, by continuing with the current trends and a constant number of 80,000 deep renovations of dwellings on an annual basis, the adapted cumulative energy savings would only reach 0.35 Mtoe. This would practically miss the 2030 target altogether, as is illustrated in Figure 9. This example highlights the implications and difficulties that can be encountered if planning and decision-making are solely based on theoretical calculations.