## 3 Results
### Question 9: How do we Interpret the IEQ Models?  
Although many IEQ models have been proposed and updated, not all provided a matched interpretation method (i.e., appropriate benchmarks) to indicate the significance of their final IEQ index. Some studies merely compared their results with previous, similar studies [15]. The European standard EN15251 (2007) [100] is commonly used among those studies that mentioned comparing the data with the benchmarks. This standard could be seen as the catalyst of studies on the IEQ assessment models since it first advocated an overall index to represent IEQ performance and then provided clear IEQ assessment categories (see Table 3). The determination of classes in this standard is based on occupants' subjective expectations. Therefore, many indexes of the resulting IEQ models involved the occupants' acceptance or satisfaction [14; 39]. Based on this standard, some studies further developed their classification methods. For example, [PERSON] and [PERSON] [15] proposed an IEQ classification with five categories for rating office buildings, while [PERSON] et al. [74] drew up an indoor quality classification with seven scales. However, the researchers' opinions did not coincide with standard EN15251-2007. [PERSON] [101] pointed out several issues regarding this standard, such as its non-applicability to personalized environments  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Conditions** & \multicolumn{3}{c}{**Acceptance of Each IEQ Factor \(i\)***} & \multicolumn{3}{c}{**Occurrence Probability**} & \multicolumn{1}{c}{
\begin{tabular}{c} **Acceptance** \\ **Probability** \\ \end{tabular} } \\ \hline \(j\) & \(i\) = 1 & \(i\) = 2 & \(i\) = 3 & \(i\) = 4 & \(\varphi_{j}\) & \(\rho_{j}\) \\ 1 & 0 & 0 & 0 & 0 & \((1-\delta_{1})\)\((1-\delta_{2})\)\((1-\delta_{3})\)\((1-\delta_{4  
due to its lacking different categories for light and acoustic requirements. Considering the weaknesses of this standard, it was withdrawn and then replaced by EN 16798-1:2019 [47].  
Although the new standard provided more categories for the different indicators, the main IEQ categories did not change greatly; they still have four levels and are based on the occupants' expectations. However, according to [PERSON] and [PERSON] [102], using occupants' expectations as a classification basis might encourage closer control, which usually consumes more energy. Additionally, more categories mean narrower ranges. [PERSON] et al. [103] believed that occupants' acceptance was broader than the range defined by EN15251 (similar to EN16798-1), which will also cause unnecessary energy consumption. Therefore, to avoid these problems, [PERSON] et al. [8] proposed a straightforward classification system with only two categories: compliance and non-compliance.  
Other studies also invented IEQ assessment categories to interpret the results of their IEQ models. For example, based on the percentage of dissatisfaction with total IEQ (i.e., the final index of their model), [PERSON] and [PERSON] [60] proposed a classification with three categories to divide the investigated offices into 'above average', 'average', and 'below average' levels. [PERSON] and [PERSON] [10] divided the measured classrooms into five classes, based on the IEQ indexes calculated using their IEQ model. [PERSON] and [PERSON] [15] also applied a five-category IEQ classification to assess the investigated office buildings with different boundary levels. However, most existing assessment criteria only focused on the overall IEQ index and seldom considered the assessment of individual IEQ aspects (except in the case of [74]). Moreover, almost none of these studies mentioned the reason or offered theoretical support to explain each class's boundary settings, making these classifications appear groundless. Since it is impossible to compare the IEQ performance in a different building without a scientific classification methodology, a set of unified benchmarks with a theoretical basis and a clear definition of boundaries is still needed.