## 1 Introduction  
By 2050, it is estimated that the European building stock will have reduced greenhouse gas emissions by 90% when compared to 1990 [1]. If this reduction percentage is achieved, it will strongly affect climate change control due to the activity of the building stock [2]. In addition, other social and health aspects, such as energy poverty [3; 4; 5] or mortality because of inappropriate thermal conditions [6; 7], could be reduced. The improvement in building energy performance is therefore crucial. For this purpose, attention should be paid on the use of heating, ventilation, and air conditioning (HVAC) systems as they are the main energy consumption source in buildings [8; 9]. The combination of energy conservation measures with smart designs will improve the performance of the building stock. However, the main challenges for a more sustainable use of energy in buildings are not just focused on obtaining buildings with better systems [10; 11], a better envelope [12; 13; 14], and an energy self-production [15; 16; 17], but also on the use of buildings [18; 19]. The influence of users on the behavior of HVAC systems is due to the main goal of such systems: to maintain satisfactory thermal conditions inside the dwelling. One of the possibilities to reduce this energy consumption is by modifying setpoint temperatures [20]. The nudge of the HVAC system setpoint temperatures can strongly impact the energy performance of the building [21], mainly due to its influence on the energy demand required for the HVAC system [22]. In this regard, [PERSON] et al. [23] analyzed the effect of increasing the cooling setpoint temperature by 2 \({}^{\circ}\)C in a field study conducted in an administrative building in 2010. A total of 129 participants were surveyed, and the results showed that the rise in the setpoint temperature did not affect their thermal comfort. [PERSON] et al. [24] studied the energy saving obtained by varying the setpoint temperatures of HVAC systems in office buildings. Significant savings were obtained in the energy consumption, with variations of 1 \({}^{\circ}\)C in heating and of 3 \({}^{\circ}\)C in cooling. A similar study was carried out by [PERSON] and [PERSON] [25]. In this study, the authors studied several Greek bank branches. The use of setpoint temperatures of 20 \({}^{\circ}\)C for heating and of 26 \({}^{\circ}\)C for cooling achieved energy savings of up to 45%. [PERSON] et al. [26] analyzed the effect of increasing the range of the thermostat by 1.1 \({}^{\circ}\)C in heating and cooling, as well as other improvement measures in the HVAC systems of office buildings. Energy savings oscillated between 12 and 20%. [PERSON] et al. [27] studied the possibilities of reducing the energy consumption of a Swiss office building. Increasing the cooling setpoint temperature up to 4 \({}^{\circ}\)C reduced the annual building energy consumption by a third. Additionally, [PERSON] [28] analyzed that the increase in the air conditioning setpoint temperature from 22 to 26 \({}^{\circ}\)C can save by 24% the energy consumption of office buildings in Malaysia. Likewise, [PERSON] et al. [29] evaluated the effect of increasing the air conditioning setpoint temperature by 26 \({}^{\circ}\)C in 13 office buildings in Thailand. The results showed a total saving of 804.60 GWh/year. Finally, [PERSON] and [PERSON] [30] analyzed the effect of gradually increasing the setpoint temperatures in residential buildings in Detroit and Miami. The results reflected that, depending on the type of climate, the modification of the setpoint temperatures influenced heating in cold climates and cooling in hot climates. Most of these research studies considered that HVAC systems are used with static setpoint temperatures. The use of this type of setpoint temperatures has discrepancies with the adaptability of users to real buildings [31; 32; 33]. There is solid evidence, however, that users perceive comfort according to the external thermal variations [34].