Adaptive Thermal Comfort of Indoor Environment for Residential Buildings

Architects and engineers play a key role in the transformation of the building sector toward energy efficiency and climate change mitigation. Buildings are responsible for 40% of the total energy consumption and 11.9% of the CO₂ emission. In this sense, various international agreements are focused to decarbonize buildings, and the concept of nearly Zero-Energy Buildings (nZEB) as well as the implementation of Energy Performance Certificates (EPCs) have been designed. For that reason, building energy efficiency projects could be a driving force to achieve a low-carbon building stock and Energy Poverty (EP) mitigation. This chapter considers energy improvements and comfortable indoor spaces, in which the most appropriate operational guidelines and the users’ training measures are crucial. With this approach, adaptive thermal comfort models could be an opportunity to guarantee sustainable use of Heating, Ventilating, and Air Conditioning (HVAC) systems without affecting users’ thermal comfort. This paves the way for significant reductions in energy consumption with a more responsible use of HVAC systems considering the adaptive thermal comfort models.

Thermal comfort has been widely studied from the middle of the twentieth century to the present. From Fanger’s model based on the neutral thermal state and the development of the Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD) indexes to the adaptive approach based on buildings that operate with natural ventilation, several studies set detailed conditions with strengths and limitations. In this chapter, a review from the international to the specific comfort models is established. In this sense, ASHRAE 55-2017 and EN 16798-1:2019 are the two most used models; both are based on international research projects with large databases. The two models present similarities in terms of applicability, however, some differences are analyzed (e.g., categories considered). In an intermediary state, various countries like the Netherlands (ISSO 74) and China (GB/T50785) have developed specific adaptive thermal comfort models, which present sensible differences with the international standards. Moreover, local studies are carried out in Australia, Chile, India, and Romania, regarding specific building types (e.g., social dwellings in Chile) or for certain climate conditions. To sum up, many research studies at different levels of resolution have presented the potential of adaptive thermal comfort models, to better understand the users’ adaptability.

The use of natural ventilation achieves considerable energy consumption savings and reduces overheating risk in summer; however, it is less effective in regions where heating energy is more demanding. In this sense, the use of adaptive thermal comfort models is an opportunity to use natural ventilation optimally coupled with air conditioning systems when necessary. In this chapter, the use of variable setpoint temperatures has been analyzed, for static and adaptive patterns. Results show energy savings using two approaches with low economic investment and without comprising users’ thermal comfort. This chapter also analyzes the barriers and opportunities to improve energy performance in extant buildings. Results set that the potential of the application of the adaptive strategies on the Earth’s surface is high although it depends on the climatic conditions. Moreover, the applicability could be modified by global warming, considering future climate scenarios, but it still maintains significant energy savings. For that reason, architects and engineers are crucial to identify and apply the most appropriate adaptive measures in specific cases.

Strategies based on adaptive thermal comfort models have great potential for application in most parts of the world. This means that these strategies are appropriate bioclimatic measures for buildings and constitute a tool for architects and engineers. However, it is necessary to know quantitatively the energy savings expected with this type of strategy. For this reason, this chapter analyzes the energy savings obtained in two buildings. The analysis was carried out in different climatic zones in Spain and using an adaptive strategy based on the three categories of EN 16798-1:2019. The results show the total energy savings obtained with the adaptive strategies: Category I ranged from 6.8 to 30.4%, Category II ranged from 23 to 56.3%, and Category III from 35.8 to 74.6%. Furthermore, the use of these strategies is adequate to reduce the payback periods of other energy conservation measures (e.g., the increase in thermal resistance of the facade), with reductions of up to 42 years in Category I, 64 years in Category II, and 73 years in Category III.

Adaptive thermal comfort strategies allow to achieve significant savings in the energy consumption of a building. This represents great potential for buildings since it allows to guarantee thermal comfort and reduce energy consumption without the need for economic investments. However, decision-making can make it difficult to implement the most appropriate strategy. For this reason, this chapter analyzes the single criteria and multi-criteria process to determine the most appropriate strategy. For this, fuzzy logic is used. With the fuzzy logic, two expert systems were designed: one for rehabilitation works (affected by the improvement achieved and the investment price) and another for new buildings. These models analyzed four case studies. The results obtained have shown that the systems designed with fuzzy logic have an adequate success rate with respect to the expected decision. Therefore, they constitute an adequate methodology for decision-making with respect to the thermal comfort model. In addition, architects and engineers can make modifications to the structure of the systems to adapt them to different regions.