The impact of ambient temperature difference in subtropical regions on the natural ventilation environment of medium-sized gymnasium
Thermal stratification is a common phenomenon in large space buildings,which has been validated in research related to full-scale measurement and has gradually attracted attention in recent years.This also indicates that the changes in indoor temperature and natural ventilation environment in gymnasiums may be complex and sensitive.The research background and survey data show that the ambient temperature difference of gymnasiums in the subtropical region alternates between positive and negative,an important reason for the instability of natural ventilation efficiency and indoor airflow.The ventilation mechanism of a naturally ventilated gymnasium is diverse.From the perspective of wind pressure ventilation,the horizontal openings'combination mode on the windward and leeward sides can effectively utilize the wind pressure difference environment.In contrast,from the perspective of thermal pressure ventilation,the vertical openings'combination mode that emphasizes the relative height of the inlet and outlet can produce a chimney effect in the large space environment,thus improving the natural ventilation efficiency.In current research,it is necessary to approach related research from the perspective of mixed ventilation driven by wind and buoyancy.To explore the potential impact of ambient temperature difference in subtropical regions on natural ventilation in medium-sized gymnasiums,the coupling mechanism is established in this work,considering the synergy of wind pressure and thermal buoyancy for a natural ventilation environment.Two medium-sized gymnasiums in subtropical regions as the full-scale measurement objects are selected.The influence of thermal boundary conditions on the natural ventilation environment of medium-sized gymnasiums in subtropical regions is evaluated by monitoring the indoor and outdoor temperature and wind velocity in the transition season and using the numerical simulation method of Computational Fluid Dynamics(CFD).A comprehensive investigation is conducted on the coupling effect of wind and buoyancy on the natural ventilation environment of medium-sized gymnasiums in subtropical regions.For the climate temperature measurement results in subtropical regions,taking the analysis data of typical seasons as an example,the ambient temperature difference of medium-sized gymnasiums in subtropical regions often alternates between positive and negative,especially in hotter months such as June to September.The results indicate that the natural ventilation environment of medium-sized gymnasiums in subtropical regions is dominated by mixed convection in various situations,and the transformation of ambient temperature difference is an important reason for the unstable indoor airflow.A reasonable opening combination mode plays a key role in improving the ventilation environment of occupied areas in large spaces.The calculation results can observe the ventilation differences of indoor airflow under different ambient temperature difference environments.For example,due to the lower temperature of the inlet airflow,the airflow will sink in a negative ambient temperature difference,while in a positive ambient temperature difference,the airflow will quickly rise under the buoyancy after entering the space.The natural ventilation environment of medium-sized gymnasiums in subtropical regions is driven by both wind and buoyancy.Based on existing research on wind pressure and thermal pressure,the consideration of ambient temperature difference is crucial for explaining the changes in the airflow environment in large spaces.Airflow in the occupied area in the negative ambient temperature difference is significantly better than that in the positive ambient temperature difference.The inlet wind speed is higher(for example,the research data in this work shows that under the same external wind conditions,the inlet wind speed in a negative temperature difference environment is 0.8～0.9m/s,while the inlet wind speed in a positive temperature difference environment is only 0.4～0.6m/s,with a decay rate of 50%),allowing fresh air to concentrate at the bottom of the large space,improving the ventilation efficiency of the occupied area.It is more conducive to creating a good indoor natural ventilation environment under the situation of lower outdoor temperature,and precooling the inlet air flow may also be an effective measure to improve the thermal comfort of the occupied area(compared to the rapid rise of the inlet airflow in a positive ambient temperature difference,the inlet airflow in a negative ambient temperature difference can reach the occupied area further away from the inlet).The numerical simulation method effectively explains the temperature sensitivity of the natural ventilation environment of medium-sized gymnasiums in subtropical regions,and error analysis of the numerical simulation results is conducted using the measurement data,and effectively reflects the complex natural ventilation phenomena in large spaces,providing a foundation for future related research.The numerical models established in this work can provide an optimization design framework for the evaluation of the natural ventilation efficiency of university gymnasiums in the early design stage.
subtropical regionsmedium-sized gymnasiumnatural ventilationambient temperature differenceCFDgreen building
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