Effects Of Insect Screens On Natural Ventilation In Residential Buildings

Natural ventilation makes full use of natural conditions to improve indoor environment.Natural ventilation performance in buildings is complex and multifactorial,including building’s surrounding circulation,building shape,the depth of the room,window opening type and so on.Therefore,the prediction of resistance characteristics and natural ventilation rate through opening are very difficult.Insect screens are commonly installed in residential buildings in China,which will affect the ventilation performance of natural ventilation.Therefore,it is of great practical significance to study and analyze the effect of insect screens on the natural ventilation performance,which can provide more basis for the design of natural ventilation,the prediction of ventilation rate and the prediction of energy consumption of residential buildings.First,this paper expounds current natural ventilation models,including single-zone models,multi-zone models and CFD numerical simulation models.Single-zone models include different prediction models of ventilation rate under the effect of wind pressure and thermal pressure.Multi-zone models include CONTAM,COMIS,and MIX models.The turbulence models are mainly introduced in CFD numerical simulation models.Based on the steady-state flow of one-dimensional incompressible fluid through porous media,a prediction model for the discharge coefficient of natural ventilation of the opening with insect screen is installed through theoretical research.Second,the resistance characteristics of 4 different insect screens were tested by wind tunnel experiments in an environmental chamber using two different methods.Combined with statistical analysis and data calculation,the effects of insect screens on natural ventilation performance were investigated.The results show that the discharge coefficient of the opening with insect screen is related to the porosity,thickness and material of the insect screen.Compared with the existing empirical formulas of the penetration coefficient and inertia factor,it is found that they are not suitable for residential buildings in China.Then,based on the relationship,a precise insect screen model is established.A simplified insect screen model is also built according to the experimental results.Comparing the two new established models with existing models in the literature,it is found that the accuracy of the accurate model is improved by about 34% compared with the model in the literature when using the precise model.When the wind speed of the simplified model is greater than 0.1m / s,the accuracy will be improved by 22 %.The two new models of specific openings established in the environmental chamber is extended to the commonly used square openings in actual residential buildings.Field measurements are performed in residential buildings and tracer gas method is used to measure the actual ventilation rate reduction after installing screens.Comparing it with the result calculated by the two new models,it was found that the errors are basically within 20%.After verification,the accuracy of the precise model and simplified model is above 80%,which proves the reliability and applicability of the two new models.