Optimization of jet fan layout in the underground utility tunnels for enhanced temperature and humidity distribution: A numerical and response surface methodology study

• Utility tunnels face thermal-humidity stratification and terminal overheating. • Jet fans are validated to effectively enhance ventilation in utility tunnels. • The installation position of jet fans is the most critical parameter. • Optimal and feasible installation range for jet fans is obtained. Utility tunnels in hot-humid climates are prone to adverse temperature and humidity conditions due to moist intake air, cable heat gains, and limited ventilation, posing significant threats to operational safety. This study evaluates mechanical exhaust with natural intake (MENI) against jet fan-enhanced ventilation, using metrics including the not guaranteed rate and nonuniform coefficient of temperature (TNGR, K t ) and relative humidity (RHNGR, K RH ). The jet fan scheme was further optimized via response surface methodology (RSM). Results show that integrating jet fans effectively improves temperature and humidity distributions. In the section equipped with jet fans, the line temperature decreased by 4–5°C, with relative reductions of 55.4% in average TNGR, 15.1% in average RHNGR, and 11.5% in average K RH . RSM optimization yielded optimal configurations for different air changes per hour ( ACH ) values, with installation position ranging from 240.0 m to 250.3 m, upper/lower wall angle at 0°, and left/right wall angle between 30.0° and 38.4°. The optimal scheme at ACH = 4 h⁻¹ was validated via simulation, achieving an average TNGR of 0.030 and an average K RH of 0.133—a relative reduction of 59.5% in average TNGR and 14.7% in average K RH compared to the MENI scheme. The proposed framework—integrating multi-parameter coupling optimization, response surface prediction, and simulation validation—offers a methodological reference for the ventilation design of utility tunnels and similar underground infrastructure.