# Thermal Comfort and Sustainability in University Classrooms: A Study in Mediterranean Climate Zones
## 1 Introduction  
Thermal comfort, understood as the sensation of thermal well-being experienced by people in a given space [1, 2], has increasingly relevant implications for buildings in the context of climate change [3, 4]. Rising global temperatures and the increasing frequency of extreme weather events increase the demand for energy to maintain adequate indoor thermal conditions [5]. This phenomenon is particularly relevant in Mediterranean regions, whose climate is characterised by very hot and dry summers and cold and wet winters [6, 7]. This type of climate can pose certain challenges, as the interaction between outdoor climatic conditions and indoor thermal environments can profoundly affect energy consumption patterns, contributing significantly to operating costs and greenhouse gas (GHG) emissions, as well as occupant well-being [8]. Energy used for heating, ventilation and air-conditioning (HVAC) systems accounts for a considerable share of global energy consumption [9], with estimates suggesting that it can account for up to 60-70% of total building energy use [10]. In specific spaces, such as schools, thermal comfort becomes even more critical, as an inadequate indoor environment can be detrimental to students' health, concentration and, consequently, learning outcomes [11; 12; 13]. Unlike other types of spaces, classrooms are characterised by the fact that they concentrate large groups of people for prolonged periods in an enclosed environment [14; 15]. This generates particular thermal demands related both to the need to maintain a stable and comfortable temperature and to adequate ventilation to ensure indoor air quality (IAQ) [16; 17]. In this regard, IAQ has become even more relevant since the emergence of COVID-19, as a well-ventilated environment is essential to reduce the spread of respiratory viruses and improve the general well-being of occupants [14; 18]. In many areas with a Mediterranean climate, schools often lack HVAC systems, especially air conditioning (AC), due to the high costs associated with their installation, operation and maintenance [19; 20]. Moreover, it was traditionally considered unnecessary, as the periods of exceptionally high temperatures mostly coincided with the summer holidays outside the school calendar. However, changes in weather patterns, with high outdoor temperatures generally recorded in the early and late months of the academic year, have increased the importance of ensuring adequate thermal comfort in spaces where air conditioning is unavailable or not feasible [21]. In these cases, natural ventilation (NV) strategies can offer effective and sustainable solutions. Designs that encourage cross-ventilation through the strategic placement of operable openings, together with appropriate building orientation, help to maintain more suitable indoor temperatures throughout the year [22]. However, as most classrooms lack cooling systems, the incorporation of shading elements (blinds, curtains, etc.) and other solutions can significantly reduce the thermal discomfort of the occupants [8; 23]. Although these strategies do not always completely replace air-conditioning systems in more extreme weather conditions, they are very effective most of the year, reducing energy dependency [24]. In addition to possible measures taken in buildings, behavioural adaptations among occupants also play a vital role in achieving thermal comfort. Research has shown that people can adjust their clothing, activity levels and comfort expectations depending on environmental conditions [25; 26]. This adaptive approach can be especially beneficial in university classrooms, where diverse student populations may have different preferences and comfort tolerances [27; 28]. Understanding these dynamics is essential to developing effective strategies that not only address the physical aspects of thermal comfort but also take into account the psychological and social dimensions that influence occupant satisfaction [9; 25].