## 4 Discussion
### Discussion of Results for the Case Study on a Building  
The experimental study was performed in a BREEAM certified building, and included the determination of formaldehyde concentration, CO\({}_{2}\), and VOCs in the indoor air. The example calculation of the combined \(\Sigma\)IAQ model for three basic pollutants, as components of the IEQ\({}_{\text{index}}\) model, is presented in two variants but the calculated \(PD^{*}\)tvoc values obtained with both calculation methodswere very similar. The first variant of \(\Sigma\)IAQ calculation used \(\%PD=f\!(c_{j})\) curves in \(\%\) sub-indices of IAQ for three pollutants, and the differences in approach in Tables 5 and 8a meant combining them into one IEQ submodel: the \(\Sigma\)IAQ model intended for the IEQ calculation. The second variant used submodels of IAQ for TVOC and HCHO pollutants based on the IAQI system [30] which were then converted into percentages of persons dissatisfied (\(PD^{*}\) in \(\%\)).  
The first conclusion is that CO\({}_{2}\) concentration cannot be used separately for the IAQ\({}_{\text{index}}\) assessment, especially at the pre-occupancy stage (Table 5). The building was polluted with VOC emissions and HCHO from the construction products directly after finishing works were completed.  
The authors confirmed that all three pollutions should be a simultaneously integrated part of the IAQ model, because the importance of TVOC is much greater, representing the main source of pollution--the construction and finishing materials.  
According to the results, we recognized two variants of the combined \(\Sigma\)IAQ\({}_{\text{index}}\) calculation. For the first variant [22], the combined \(\Sigma\)IAQ index of satisfied users was 69.1% and, for the second variant (new approach with converted AQI index), the \(\Sigma\)IAQ index was 70.0% satisfied. The results of the IEQ\({}_{\text{index}}\)(1) (for Variant 1) were within the interval of combined overall uncertainty,\(\pm\)16.24%, and the results of the IEQ\({}_{\text{index}}\)(2) (for Variant 2) were that the overall uncertainty was \(\pm\)16.15%. Therefore, the result was convergent, which confirms the credibility of the proposed approach.  
The results obtained also showed that, in the period immediately after completion of finishing works in indoor spaces, there may be a temporarily increased concentration of TVOC, which systematically decreases over time, as we have shown in other papers. In the case of a building, the research showed that  
Figure 9: \(PD_{TVOC}\) based on conversion from IAQI to the PD\({}^{*}\) scale and study of Weber-Fechner theory.  
tests carried out immediately after finishing works gave results that significantly exceeded the BREEAM limits for TVOC at 300 \(\upmu\)g/m\({}^{3}\) (twice as high). It should be expected that an acceptable level should be reached after a minimum of one month from the completion of the work.  
For correctness of the obtained calculations, the authors are conducting a model credibility analysis that will be provided in the next article--Indoor Air Quality Model Part II: The Combined Model \(\sum\)IAQ\({}_{\text{index}}\) Reliability Analysis. The model uncertainty estimate may be compromised because the model reproduces the discomfort level associated with the dominant component.  
Conceptualization, M.P. and K.B.K.; methodology, M.P. and K.B.K.; formal analysis, M.P. and K.B.K.; investigation, M.P. and K.B.K.; resources, M.P. and K.B.K.; data curation, M.P. and K.B.K.; writing--original draft preparation, M.P. and K.B.K.; writing--review and editing, M.P. and K.B.K.; visualization, M.P. and K.B.K.; supervision, K.B.K.; project administration, M.P.  
This research received no external funding.  
The authors declare no conflict of interest.