Study On Measurement And Calculation Of Natural Ventilation In Typical Residential Buildings And Its Related Influencing Factors

As a ventilation mode without any energy consumption,natural ventilation is a well-known technology which is commonly used in buildings to improve the building environment and save energy cost.It is of pratical significance to master the measurement method,calculation theory and explore the factors affecting the characteristics of natural ventilation.In this paper,field measurement,numerical simulation and multi-zone network model,e.g.EnergyPlus are used to study the accuracy of the measured and calculated natural ventilation rate and explore the influence of balcony on ventilation performance in order to provide more basis for natural ventilation design,energy consumption prediction and measurement of residential buildings.First,the theory of natural ventilation calculation is introduced in detail,including the physical description of multi-zone network model and the introduction of specific ventilation branch units.The ventilation branch units include infiltration model and natural ventilation opening model.For infiltration model,the power law equation and equivalent area model are elaborated.And the opening model which includes horizontal opening,vertical opening and rotating opening is driven by buoyancy or wind.This chapter is the theoretical basis for the calculation of natural ventilation rate in the following chapters.Second,the tracer gas decay method is used to measure the ventilation rate in transitional season,plum rain season,summer and winter.Two kinds of tracer gases,i.e.CO₂ and SF₆,are selected here as the tracer gases.It is found that the relationship of the ventilation rate measured by decay method is n?CO₂?=1.006n?SF₆?+0.125 and the goodness of fit is 0.99.Comparing with the decay curves of benzene,toluene and xylene in transitional season,it is found that with the increase of gas diffusion coefficient,the ventilation rate increases as well.In general,the larger the window openings,the greater the ventilation rate.It shows that although ventilation rate depends on indoor and outdoor meteorological parameters,window opening can improve the ventilation rate to a large extent.Then,EnergyPlus is used to calculate the ventilation rate.It is found that the ventilation rate obtained by single-zone model is generally smaller than the measured data,which indicates that the infiltration has a greater impact on the results,which can not be ignored.Considering the infiltration area of doors and windows in multi-zone calculation,it is found that a set of effective infiltration areas cannot be applied for different seasons.Therefore,consider the thermal expansion coefficient of the window and door frame material.On the basis of this,the large opening error of the multi-zone calculation is about 16%,and the error of small opening is 28%.Considering the influence of screen on ventilation rate,the empirical equation in literature is used to obtain the discharge coefficient.The error between calculated results and measured results is less than 20%.It shows that the empirical equation is also applicable to the screen of common residential buildings to some extent.Wind pressure coefficient is an important parameter in natural ventilation calculation.Comparing with the experimental data of wind tunnel,it is proved that CFD can simulate the wind pressure coefficient accurately.On this basis,two kinds of balcony types,square and circular,are set up for comparative study.Large and small rooms are built in CFD to explore the influence of balcony on single-sided and cross ventilation.It is found that on the windward side when there is no balcony,the wind pressure coefficient is 15%²7%larger than the square balcony and 17%²5%larger than the circular balcony.On the leeward side when there is no balcony,the wind pressure coefficient is 4%²5%larger than the square balcony and 5%²2%larger than the circular balcony And the wind pressure coefficient in the middle part of the windward is greater than that on both sides of the wall,which increases first and then decreases with the height.And the values of the left and right sides are nearly symmetrical.On the other hand,the ventilation effect of cross ventilation is much better than that of single-sided ventilation.The existence of the balcony has a certain shielding effect on the cross ventilation,however,it is not obvious for single-sided ventilation.The difference of wind pressure coefficient and ventilation effect between the two types of balconies is not significant.Users can choose the types of the balcony according to their preferences.