## 3 Results and Discussion  
### The Impact of the Climatic Zone on Energy Consumption  
The results of the energy simulation for the 15 cities can be seen in Figure 6. This analysis allowed us to conclude that the cities of Oporto and Lisbon (in Portugal) present the lowest energy requirements with 45 kWh/m\({}^{2}\).year and 64 kWh/m\({}^{2}\).year, respectively, while Oslo and Krakow are at the opposite extreme with consumptions of 135 kWh/m\({}^{2}\).year and 117 kWh/m\({}^{2}\).year, respectively. Separating the analyzed cities into three main groups ordered by the total energy consumption, Oporto, Lisbon, Seville, Rome and Madrid can be  
Figure 5: Sensitivity study to assess the impact of the climate control strategy and window refurbishment on energy consumption. classified in the first group; London, Athens, Amsterdam, Paris and Florence in the second group; and Berlin, Copenhagen, Vienna, Krakow and Oslo in the third group. The first group of cities are all located in southern Europe. Energy consumption in the 15 cities under analysis  
However, this analysis can be reductive since it only focuses on absolute consumption. Consider for example the case of Athens, which, although classified in the second group with 81 kWh/m\({}^{2}\).year, behaves differently to London, also in the second group with a consumption of 78 kWh/m\({}^{2}\).year. In Athens, the cooling demand assumes 71% of the global energy consumption, while heating needs in London account for 80% of the global consumption. This analysis allowed us to conclude that the greatest energy needs in all the analyzed cities are related to the need to maintain the temperature between the imposed set-point. In the most adverse case, the energy requirements to maintain relative humidity in the defined target do not exceed 20% of the total energy consumption. It can be concluded that the use of less demanding climate control strategies can contribute to important energy reductions. By analyzing the energy consumed to maintain the temperature set-point, it can be observed that the cooling needs are higher than the heating needs in three cities, accounting for more than 70% of the total consumption: 71% in Athens, 74% in Lisbon and 89% in Seville. Oporto, Madrid, Rome and Florence show more balanced behavior, while for the remaining cities, the heating needs are responsible for most of the energy consumption. These results allow us to conclude the impossibility of defining a global policy for conser  
Figure 6: Energy consumption in the 15 cities under analysis. vation and energy reduction in Europe, since the necessities of the different locations are quite different. To define an efficient and adjusted rehabilitation strategy for each case, an analysis of heat gains and losses between the building and the surrounding environment was carried out. The results are presented in Figure 7 for the heat losses in the heating season and in Figure 8 for the heat gains in the cooling season. Heat losses from cooling the room (C), from ventilation (V), from the opaque envelope (O.E.) and from the windows (W) were analyzed. Heat gains to heat the room (H), from ventilation (V), from the opaque envelope (E.O. ), from the windows (W), due to internal gains (I.g.) and due to solar gains were also analyzed. As far as losses are concerned, it is possible to observe different behaviors for the 15 cities. For Lisbon, Seville and Athens, the loss of heat through the HVAC system to cool the room plays a prominent role and is responsible for ca. 56%, 64% and 61% of the total losses, respectively. Following this, the losses through the windows and ventilation can be found. The cities of Oporto, Madrid, Rome and Florence present losses relatively well distributed by the HVAC system, the windows and the air exchanges with the exterior. It is interesting to note that for all the cities of southern Europe, the losses through the opaque envelope are practically negligible. For the remaining cities, located in central and northern Europe, the panorama changes.