# Integration of the Adaptive Approach in HVAC System Operation: A Case Study  
[PERSON]  
1 Grupo de Ingenieria de Organizacion, Escuela Tecnica Superior de Ingenieria, Universidad de Sevilla,  
Camino de los Deschurimientos S/N, 41092 Seville, Spain; jragelbus.es (J.C.R.-B. ); [EMAIL_ADDRESS] (E.B.-M.); guadix@us. adaptive approach \"_to explain the range of temperatures people found comfortable in buildings with the variable indoor temperature's characteristic of naturally ventilated buildings_\" offers a complementary solution to the challenge of heat balance. Since then, this approach has gained recognition, consolidating into standards such as ANSI/ASHRAE 55:2023 [2], the reference for thermal comfort in North America, and the European standard UNE-EN 16798-1:2020 [4], which covers both thermal comfort and other indoor environmental parameters. These adaptive approaches are mainly applied to the assessment of the thermal environment in naturally ventilated (NV) buildings where, e.g., the occupants have access to operable windows and have some freedom to adapt the insulation of their clothing. Countries such as the Netherlands [12] and Brazil [13; 14] have also included adaptive models in their national regulations and standards. Utilizing natural ventilation in buildings can lead to considerable electrical energy savings for cooling and fans [15]. While adaptation is described as the gradual decrease in the reaction to environmental stimulation, and can be behavioral (such as clothing [16], windows, fans), physiological (acclimatization), and psychological (expectation) [17], in a practical setting, variations in the perception of the thermal environment were identified between occupants of naturally ventilated or free-running, fully air-conditioned and mixed-mode or hybrid buildings [17]. Adaptive comfort approach have arisen as a sustainable and resilient solution that, according to [PERSON] et al. [18], could reduce the incidence of fuel poverty, in contrast to the static model that relies exclusively on active cooling. [PERSON] [19] described fully conditioned buildings as \"_Buildings as comfort capsules_\" where the heating, ventilating and air-conditioning (HVAC) system is seen as one of the tools contributing to the \"homogenization of people\", resulting in \"thermal monotony\", although early HVAC engineers strived to avoid creating monotonous thermal environments [20]. The building sector is looking for sustainable building solutions, not only with passive heat dissipation capabilities [21] or from an aerothermal point of view [22], but also passive actions are expected to contribute to periods with natural ventilation, such as the adaptation of the clothing insulation level [23]. The application of adaptive comfort control (ACC) as an alternative to fixed setpoint systems (or the paradigm of a single temperature setpoint in each climatic season) would be justified by [PERSON] et al. [24] who explain that \"_after repeated exposure to variation in environmental conditions, a person's expectations of those conditions may become more relaxed--even anticipatory of temporal changes_\" (p. 181). This idea provides insight into why adaptive comfort control is a valid alternative to fixed setpoint systems, as it suggests that people's expectations of environmental conditions can be adjusted and become more flexible over time. This adaptive capacity comes from repeated exposure to such environmental variations, which fosters more flexible expectations and even positive anticipation of temporary changes in the environment. This reinforces the idea that an adaptive control system, by allowing controlled variations in indoor conditions rather than maintaining a fixed setpoint, can not only be more energy efficient, but also promote a natural thermal comfort experience aligned with human expectations. As highlighted in [25] (p. 16), the application of adaptive comfort systems has been shown to improve energy savings, enhance resilience to climate change and increase thermal satisfaction and well-being.