## 3 Results
### Question 3: Which Aspects and Indicators Should IEQ Models Include?
#### 3.3.2 IEQ Indicators Involved in Existing IEQ Models  
In terms of thermal comfort, air temperature, radiant temperature, humidity, and air movement are the four fundamental indicators that define physical and thermal environments. Apart from these factors, the occupants' metabolic heat and clothing insulation were often also collected in previous thermal comfort-related studies. Using these six indicators together, the occupants' thermal sensations can be determined in an indoor environment; furthermore, the PMV and predicted percentage of dissatisfaction (PPD) can be calculated based on [PERSON]'s thermal comfort equations [70]. However, the PMV and PPD indexes are limited in an air-conditioned environment. The Top measure was proposed and has been widely used in previous studies to better reflect occupants' thermal sensations in naturally and mechanically ventilated buildings since it was closely related to the occupants' thermal sensation votes (TSVs) [71]. Besides these objective indicators, to collect the occupants' thermal sensations directly, the thermal sensation vote was also investigated as a subjective indicator of thermal comfort in many studies.  
IAQ-Related Indicators  
IAQ assessment can be established based on ventilation or the concentration of pollutants in an indoor environment. Therefore, two indicators were used to evaluate IAQ: ventilation rate and pollutant concentrations. [PERSON] and [PERSON] [15] proposed three ways to calculate the IAQ index using three different indicators, i.e., ventilation rate, CO\({}_{2}\), and decipol (pollution perceived in the presence of an ordinary subject in an environment with ventilation equal to 10 L/s of clean air). Similarly, [PERSON] et al. [48] also developed three models to evaluate the IAQ index. Still, with the three different indicators of CO\({}_{2}\), PM\({}_{2.5}\), and TVOC (total volatile organic compounds), only the minimum value of the three indicators was used in the final IEQ model. [PERSON] [52] also used three IAQ indicators--CO\({}_{2}\), TVOC, and formaldehyde (HCHO)--but considered them together in one evaluation model. Among these IAQ indicators, CO\({}_{2}\) was the most widely used indicator since it can be seen as a proxy for ventilation as well as the surrogate of human bio effluents [13; 14; 39]. Besides, occupants' perceptions of air quality (such as freshness or odors) were also widely used as a subjective indicator to evaluate IAQ in previous studies [39; 71; 72; 73].  
Acoustic Quality-Related Indicators  
To evaluate the acoustic quality in an indoor environment, SPL-related indicators, including the A-weighted equivalent sound pressure level, Eq(A) [13; 15; 74], and background noise level [5; 60; 75] were often used. These indicators were the same as those used to test the presence of noise sources. In addition, there are some indicators that are used to describe the sound insulation of an investigated environment (such as reverberation time (RT) and sound absorption coefficient) [76] and the intelligibility of speech (such as the signal-to-noise ratio and speech transmission index (STI)) [56; 77]. However, considering the complexity of measurement, these indicators were not commonly used. Moreover, to subjectively evaluate the acoustic quality in an indoor environment, occupants' perceptions of acoustic quality (such as noisy/quiet or speech intelligibility ratings) were often investigated [10; 13; 14; 15; 50; 56; 75; 75].  
Visual Quality-Related Indicators  
Compared to other IEQ aspects, few alternate objective indicators are used to evaluate visual quality. In terms of visual quality, illuminance (E) was the most widely used indicator to assess lighting performance [10; 13; 14; 58; 64]. However, more subjective visual indicators have been used in previous studies, for example, the perception of artificial light/daylight, the occurrence of glare, etc. [56; 64; 69].