## 3 Results and Discussion
### The Impact of the Climatic Zone on Energy Consumption
Losses through the HVAC system lose their preponderance and the losses through windows and ventilation assume a prominent position. The losses  
Figure 7: Heat losses during the heating season. through the opaque envelope take values that can justify their improvement with losses ranging from ca. 12% in Paris and London to ca. 18% in Oslo. Regarding heat gains, it is possible to conclude the high influence of solar gains for all the 15 cities, ranging from ca. 18% in Oslo to ca. 38% in Lisbon. The solar gains take the main place of heat gains in Lisbon, Oporto, Madrid and Rome. The gains through the HVAC system to heat the room vary widely according to the cities: in Lisbon, Seville and Athens less than 10% of the gains are obtained by this source, while for example in Amsterdam, Copenhagen, London, Berlin, Krakow, Vienna and Oslo, heating gains accrue more than 40% of total gains. The gains from the opaque envelop take also a prominent role. This can be justified by the high thermal inertia of the elements and the tightness of the indoor climate control which makes the surface temperature of the opaque elements often higher than the air temperature, triggering heat flows over large periods. Data referring to Lisbon are presented in Figure 9: the comparison between the indoor air temperature and the internal surface temperatures of the southern wall, the three internal walls, the floor and the ceiling in (a) and the density of the heat flow rates in the surfaces in (b). The density of the heat flow rate in the surfaces was obtained from Equation (1) [57]:  
\[q_{x}=\frac{\left(T_{amb}-T_{surface,x}\right)}{R_{s}} \tag{1}\]  
Figure 8: Heat gains during the cooling season. where \(q\) is the density of heat flow rate (W/m\({}^{2}\)) of the element \(x\); \(Rs\) means the internal surface resistance (m\({}^{2,\circ}\)C/W); \(T_{amb}\) means the indoor air temperature (\({}^{\circ}\)C) and \(T_{surface,x}\) means the internal surface temperature of the element \(x\) (\({}^{\circ}\)C). Following the standard EN 6946 [57], for the walls, an internal surface resistance of 0.13 m\({}^{2,\circ}\)C/W was adopted. For the floor and the ceiling, surface resistances of 0.1 and 0.17 m\({}^{2,\circ}\)C/W were considered, respectively. The influence of internal gains varies between 14% in Oslo and 21% in Oporto. The gains from ventilation and windows are practically negligible for all the cities. This analysis allows us to conclude that energy reduction can be obtained firstly by changing the climate control strategy, since conservation and comfort are not compromised. In warmer cities, considerable reductions may be achieved by reducing the solar heat gain coefficients of the windows or by including openings in the interior walls to reduce heat storage. In these cases, where the cooling needs are higher than the heating needs and where the contribution of the opaque envelope in the losses is reduced, the implementation of thermal insulation can be hardly seen as an efficient way to reduce the energy demand. In cases where heating needs are the main contribution to global energy consumption, the solution may be the refurbishment of the windows, increasing the SHGC and the implementation of thermal insulation in the opaque envelope. However, it is necessary to consider that the increasing incident radiation causes important hygothermal variations and may compromise the artefact's conservation. A situation like this must be carefully studied.