Numerical Study Of Natural Ventilation In Industrial Workshop With Solar Chimney

Natural ventilation is widely adopted in summer and transitional'season in the workshops in order to save energy in many regions. Solar chimney (SC) is a very effective technology to improve the natural ventilation because it utilizes the solar energy to heat the air and induces improved flow in the SC channel. It is important to study intensively the natural ventilation performance of SC before its commercial application.In this thesis, computational fluid dynamic (CFD) method was used to numerically study the natural ventilation in an industrial workshop with 4 types of SC. A typical workshop of 40m×24m×20m in length, width and height at Shanghai was selected as the model. The SC was attached to the workshop top. The width of the SC channel was 2 meters and its vertical height was 6 meters. A 45°angle of the SC channel was considered in 2 cases. Realizable k-εturbulent model was used to simulate the air flow and DO radiation model was used to calculate the heat transfer between the air and wall surfaces. SIMPLEC algorithm was used for the calculation. The CFD model was first validated by published experimental data and good agreement between the present CFD results and experimental data demonstrated that the present method was reasonable.The flow field, pressure field and temperature field as well as the pollutant distribution in the workshop was simulated. Parameters, i.e., actual fresh airchangeing times and indoor thermal comfort index including Predicted mean vote (PMV) and Predicted percentage of dissatisfied (PPD), were defined to evaluate the thermal comfort and the ability to exhaust pollutant in the workshop with SC. The effect of SC configuration and sizes, solar radiation, etc on the natural ventilation performance was discussed. The following main conclusions can be drawn from the results.(1) Based on the comparison of the CFD results of five different types of SC model, it's believed that the SC vertically attached to the workshop top, as called the SC-III, could improve the natural ventilation in the workshop best. The average air temperatures in the workshop with SC-Ⅰand SC-IV were higher than that of the prototype workshop, while the average air temperatures in the workshop with SC-II and SC-Ⅲwere lower than that of the prototype workshop. The pollutant concentration in the workshop with all of the 4 types of SC decreased with comparison to that in the workshop without any SC. The actual fresh air changing index showed that SC—Ⅲwas most effective to exhaust the pollutant. The PMV/PPD showed that SC—Ⅲcould provide the best thermal comfort in the workshop.(2) Further investigation of SC—Ⅲshowed that the ventilation rate of the workshop and the average air velocity at air outlet increased as the increase of SC width. When the SC-width increased from 1 meter to 3 meters, the average air temperature and pollutant concentration in the workshop obviously decreased, while, as the SC width further increased, both the average air temperature and pollutant concentration in the workshop tended to be constant. The indoor thermal comfort was also improved as the SC width increased. AT the given conditions in the present study, the optimal SC width was 3 meters.(3) As the increase of SC height, the ventilation rate of the workshop and the average air velocity at air outlet increased, which resulted in a better thermal comfort. The air temperature distribution was similar and had very small change at different SC height. The average pollutant concentration in the workshop decreased as the SC height increased. The two eddies in the middle and upper turbulence zone of the workshop gave important contribution for exhausting pollutant.(4) The increase of solar radiation had little effect on the distribution of velocity and temperature field, but it was effective to lower the pollutant concentration in the upper turbulence zone of the workshop. The actual fresh air change times increased with the increase of solar radiation. The thermal comfort index, PMV/PPD almost was not changed at different solar radiation.Results demonstrated that reasonable design and application of SC would improve the natural ventilation performance.