**2. Research Themes**

Considering the broad scope of this Special Issue's call, the topics and research questions addressed by the submissions are diverse. We have identified common themes and clustered all published papers under three categories: (1) design-based optimization of indoor environment performance, (2) comfort evaluation of IEQ, and (3) the impact of IEQ on psychophysiology. These contributions help to advance the scientific conversation concerning these important issues.

### *2.1. Design-Based Optimization of Indoor Environment Performance*

Improving indoor environmental performance and reducing building energy consumption through active and passive design has become an important research field. The

**Citation:** Wu, Y.; Liu, Z.; Kong, Z. Indoor Environmental Quality and Occupant Comfort. *Buildings* **2023**, *13*, 1400. https://doi.org/10.3390/ buildings13061400

Received: 8 May 2023 Accepted: 12 May 2023 Published: 29 May 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

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articles published in this Special Issue are representative of this research field. Scholars focus on how to effectively improve indoor thermal comfort [7], air quality [8], lighting performance [9–12], and sound insulation performance [13], and reduce building energy consumption by optimizing building equipment [7–9], interior spaces [10–12], and building structures [13]. In addition, the functional types and geographical locations of the research objects are different. Zhang et al. [8] studied a new ventilation system for rural houses in severely cold regions of China in winter. Piraei et al. [10], Ma et al. [11], and Jia et al. [12] explored the optimal design of daylighting performance of heritage buildings in highlatitude areas and classrooms in mid-latitude areas. Qu et al. [13] conducted a study on the sound insulation performance of interior partition structures for a hotel. These studies have provided a reference and evaluation basis for architectural design to improve indoor environmental performance.

### *2.2. Comfort Evaluations of IEQ*

The articles published on this topic are representative of the exploration of comfort evaluations, and researchers have found that the positive design of the environment can significantly improve comfort. They cover a diverse range of occupant types, including studies on the elderly [14], visually impaired individuals [15], and infants [16]. The examined architectural types and geographic locations also vary, including historical residents in Zanzibar [17], school buildings under both severely cold areas in China [18] and mild climate areas in Japan [16], and office buildings in North China and America [19]. These articles have investigated the impact of acoustic [15,20], lighting [14], and thermal [16–19] indoor environmental quality on comfort.

#### *2.3. Impact of IEQ on Psychophysiology*

IEQ has significant impacts on occupants, both psychologically and physiologically. Researchers have conducted studies on public buildings, such as offices [21], schools [22,23], shopping malls [24], hotels [25,26], and elderly facilities [27], by using a variety of methods, including field measurements, simulations, behavioral observations, questionnaires, and interviews, as well as tools such as virtual reality (VR) and electroencephalography (EEG). Some interesting findings deserve attention: interior natural lightscapes can influence physiological indicators [21], whereas colors can impact emotional indicators [22,25]. These findings potentially provide supporting data for further developments in the therapeutic effects of indoor environments on health.

#### **3. Concluding Remarks**

Although the three themes discussed above do not comprehensively cover all the aspects of IEQ and occupant comfort, they highlight some "hot topics" relevant to researchers. It is worth noting that as a research area examining the impacts of the environment on occupants, this field is still evolving and expanding to a certain extent, particularly with the integration of research methods from fields such as neuroscience, computer science, psychology, and sociology into architectural research. Examples of such methods include virtual reality techniques, Heart Rate Variability (HRV) and EEG measurement, on-site investigation, and behavioral observation. The interdisciplinary nature of these approaches helps researchers to better understand how the built environment affects human perception, as well as how architectural design can support better human experiences. In future research, it is important to engage a wider range of stakeholders in the discussion, including the general public, government, investors, building professionals, designers, and artists.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

1. Kong, Z.; Utzinger, D.M.; Freihoefer, K.; Steege, T. The impact of interior design on visual discomfort reduction: A field study integrating lighting environments with POE survey. *Build. Environ.* **2018**, *138*, 135–148. [CrossRef]


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