## 2 Methodology  
### Thermal Comfort Models: Adaptive and Static  
Static comfort models (i.e., PMV-based) were originally based on the theory of thermal comfort developed by [PERSON] [27], and later on, standards were developed through extensive fieldwork conducted in air-conditioned office buildings with some limitations; occupants were considered to be engaged in sedentary activities, and their level of clothing was between 0.5 CLO during summer and 2 CLO during winter; therefore, the mechanisms of thermal adaptation were scarce, especially regarding the operation of the building and the interaction with the external climate [28]. This model and the subsequent standards have been considered a keystone for assessing thermal comfort over the last 40 years, although their applicability has been being reconsidered in recent times. As an example, previous research has highlighted that caution should be exercised when using those standards in the design of air-conditioned buildings because, indeed, those were intended to be applied under very specific conditions [29]. Furthermore, uncertainty in measurements must be also considered as well as in surveys of subjective occupant's evaluation [30]. On top of that, the recent advance in computational capacity has brought a catalogue of calculation tools for the PMV not only for personal computers, but also for smartphones, whose oversimplification in both the input data and the calculation procedure might lead to wrong results [31]. In contrast, adaptive comfort models have been developed in offices without HVAC systems (i.e., free-running offices), where occupants can freely interact with the building to achieve thermal comfort, either by opening or closing windows, changing their clothes or having cold drinks; in short, occupants are able to adapt, to a certain extent, to the internal ambient temperature [31; 32]. At the present time, the adaptive thermal comfort model in Europe, which is also used in this research, is that from the EN 16798-1:2019 standard [33], which supersedes its predecessor EN 15251:2007 [24]. This standard defines three different categories according to occupants' expectations and the type of building (e.g., category I should be used in spaces for people with special requirements, such as old people or ills; category II should be used in new buildings; and category III should be used in existing buildings). These three categories also differ in the amplitude of the comfort zone: category I has an amplitude of 5 \({}^{\circ}\)C; category II has an amplitude of 7 \({}^{\circ}\)C; and category III has an amplitude of 9 \({}^{\circ}\)C. This study deals with an existing building, so category III is adopted. Adaptive comfort limits are established by linear correlations (Equations (1) and (2)). The independent variable is the running mean outdoor temperature (RMOT), which is obtained by the weighted average of the daily external average temperatures of the previous days (Equation (3)). Therefore, if the RMOT is between the upper applicability limit (30 \({}^{\circ}\)C) and the lower applicability limit (10 \({}^{\circ}\)C), the adaptive thermal comfort model is applicable and the adaptive comfort limits can therefore be established. The operative internal temperature should be within these limits to achieve thermal comfort.