Study On Evaluation And Optimization Of Thermal-humid Environment And Gaseous Pollutants In Underground Parking Lots Of Commercial Buildings

With the rapid economic development in China,the number of automobiles has been consistently increasing.The congestion of surface spaces and the shortage of parking spots have made the construction of underground parking lots an indispensable measure for urban development.However,underground parking lots often remain in a semi-enclosed state with poor air circulation,leading to unfavorable thermal-humidity conditions and severe air pollution,which negatively impact the health of indoor occupants.Moreover,commercial building underground parking lots are characterized by their large scale and high utilization rates,resulting in frequent human activities.Therefore,studying the current status of thermal-humidity environment and gaseous pollutants in commercial building underground parking lots is of great significance in reducing the potential harm to human health caused by indoor environments.This paper focuses on a commercial building underground parking lot in Guilin and conducts field measurements and subjective questionnaire surveys to investigate the thermal-humidity environment（temperature,relative humidity,air velocity）and thermal comfort.The measurement results indicate that the indoor temperature in the underground parking lot ranges from 26.37℃to 29.95℃with a small variation range.The overall relative humidity is relatively high,ranging from 55%to 91.17%,and the deepest area of the parking lot has higher relative humidity compared to the entrance and central area.The air velocity ranges from 0.016m/s to 0.198m/s without a clear pattern of change.The questionnaire survey reveals that 48.4%of the indoor occupants perceive the indoor thermal environment as uncomfortable,primarily due to high temperature and poor air circulation.Based on the measured data and questionnaire results,the PMV thermal comfort model shows a neutral temperature of 25.4℃and an acceptable temperature range of 21.1℃to 27.9℃,while the MTS thermal comfort model shows a neutral temperature of 26.9℃and an acceptable temperature range of 23℃to 30.8℃.Furthermore,gaseous pollutants（CO₂,TVOC,formaldehyde）inside the parking lot are measured to study their distribution patterns.The results indicate horizontal variations in the concentrations of CO₂,TVOC,and formaldehyde,with the lowest concentrations at the entrance,followed by the central area,and the highest concentrations at the deepest part of the parking lot.While CO₂ concentration does not show significant vertical variation,TVOC and formaldehyde exhibit vertical distribution patterns,generally being lower at the bottom and higher at the top.Pearson correlation analysis reveals a significant positive correlation between CO₂ and TVOC concentrations.Both CO₂ and TVOC concentrations show a significant positive correlation with traffic volume,with the number of vehicles exiting the parking lot having a greater impact on pollutant concentrations.Additionally,pollutant concentrations show a positive correlation with temperature and a negative correlation with relative humidity.Based on these findings,the indoor air quality is evaluated using grey relational analysis,showing that CO₂ and TVOC have a significant impact on indoor air quality,with certain areas experiencing heavy air pollution.Using the measured data,the PHOENICS software is utilized to simulate the thermal-humidity environment and CO₂ concentration distribution in the parking lot under natural ventilation conditions,yielding results that closely match the measured values.The ventilation performance of different mechanical ventilation schemes is compared and analyzed.The results demonstrate that an evenly distributed exhaust system placed at the top of the parking lot with sidewall supply ventilation exhibits the best ventilation effect.Based on the optimal ventilation scheme,a temperature of 20℃at the mechanical supply air outlet achieves better thermal comfort satisfaction.Finally,comprehensive evaluation results and simulation analysis are used to propose optimization strategies for the underground parking.