## 4 Conclusions  
This paper presents an optimization study of the supply air inlet spacing in a room with SV. Experiments and numerical simulations were performed to study the influence of air inlet spacing on the air distribution in the occupied zone. The air velocity and temperature distributions were analyzed with different air inlet spacings. Evaluation indices (ADPI, LMAA, and EUC) were used to evaluate the effect of air inlet spacing on the ventilation performance of the SV. In addition, six axial velocity attenuation formulas for the jet were verified using experimental data. After a comprehensive analysis of the evaluation index results, the optimal air inlet spacing was studied using the multi-objective optimization method TOPSIS, and the optimal spacing under the simulated condition was obtained. The main conclusions are summarized as follows. * Analysis of the experimental results showed that the flow characteristics in the occupied zone of the room were significantly different with different spacings of the supply air inlets, and the thermal comfort may be different at the same location. The position close to the air inlet was directly affected by the air inlet spacing. For locations away from the air inlets, the change in air temperature with spacing was more obvious than that of air velocity owing to the blocking effect of personnel. * The attenuation formula for the jet axial velocity was verified using the measured data. The RMSE between the measured data and the predicted values for the three cases were 0.23 m/s, 0.09 m/s, and 0.18 m/s, respectively. Thus, the modified Abramovich formula is the most suitable for attenuation of the axial velocity of multiple parallel jets in SV rooms. * Numerical simulation results showed that inappropriate air inlet spacing was not conducive to the performance of indoor air distribution. The distance between the merge point of the parallel jet and the air inlet depended on the spacing between the adjacent air inlets. A small air inlet spacing led to a concentration of the conditioned supply air in the middle of the room, and the indoor thermal environment on both sides could not be guaranteed. A large spacing resulted in areas that could not be covered by the supply air. The velocity profile showed strong asymmetry in its center downstream of the horizontal non-isothermal jet, mainly caused by the strong mixing of the lower part of the jet. * By analyzing the influence of air inlet spacing on the three evaluation indices, it was found that the optimal value of ADPI corresponded to an air inlet spacing of 800 mm; the optimal LMAA and EUC corresponded to an air inlet spacing of 950 mm. The multi-objective optimization method TOPSIS was used to optimize the air inlet spacing. The optimal spacing was 800 mm. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Spacing of Air Inlet** & **Relative Fit Degree** & **Ranking** \\ \hline
500 & 0.0476 & 6 \\
650 & 0.1001 & 5 \\
800 & 0.8560 & 1 \\
950 & 0.9010 & 2 \\
1100 & 0.4019 & 4 \\
1250 & 0.5283 & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Calculation results of TOPSIS evaluation method. **Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13074143/s1](https://www.mdpi.com/article/10.3390/app13074143/s1)]([https://www.mdpi.com/article/10.3390/app13074143/s1](https://www.mdpi.com/article/10.3390/app13074143/s1)), File S1: The detailed procedure for TOPSIS. Data curation, Y.J. and J.M. ; formal analysis, Y.J. ; investigation, Y.J., J.M. and Y.C. ; methodology, J.M. and Y.C. ; project administration, Y.C. ; software, J.M. ; supervision, Y.C. ; writing--original draft, Y.J. ; writing--review and editing, Y.C. All authors have read and agreed to the published version of the manuscript. This research was supported by the National Key Research and Development Program of China (2018 YFC0704405). Not applicable. **Data Availability Statement:** All data included in this study are available upon request by contact with the corresponding author.