A Numerical Study Of Solar Chimney For Enhanced Stack Ventilation In Buildings

Natural ventilation and new sources of energy utilization are the two main means to improve thermal comfort conditionings and reduce the energy consumption of air conditioning, which are widely used in modem buildings for saving energy. The solar chimney system is a natural draft device, which integrates the two means organically. It uses solar radiation to provide upward momentum to a mass of air, thereby converting the thermal energy into kinetic energy. Three kinds of solar chimney models for natural ventilation in buildings were theoretically analyzed and numerically simulated. The three models are Trombe wall solar chimney, vertical roof solar chimney and inclined roof solar chimney.A numerical study has been carried out to predict mass flow rate, temperature field and velocity field for different models and configurations of solar chimney under steady-state conditions, k - e turbulence models and wall function methods were used. According to the flow patterns and calculation characteristics for three models, different k - s turbulence models and wall function methods were used. Grid independent studies were carried out to ensure essentially no changes after doubling the grids numbers. Suggestions for optimum construction design of solar chimney were provided based on large numbers of simulation results. Results showed that, for Trombe wall solar chimney, there is an optimum ratio of chimney gap-to height to achieve a maximum airflow rate, which is dependent on the inlet design and independent of solar radiation. However, for vertical roof solar chimney or inclined roof solar chimney with both ends open, either a large optimum gap-to-height ratio or no optimum chimney gap was found in the range of chimney gaps investigated. The predicted ventilation rate increases with solar radiation and solar chimney height.Meanwhile, temperature field and velocity field of solar chimney were analyzed. Air velocity inside solar chimney decreases with the increase of chimney gap and increases with the increase of solar radiation. Reverse flow can be observed at the outlet when the chimney gap increased to a certain value. Air temperature inside solar chimney increases with the increase of solar radiation and solar chimney height.Satisfactory correlation was obtained with experimental data from other investigations.