Study On Efficient Exhaust And Pollutant Distribution Characteristics Of Toilets In Public Buildings

The rapid development of China’s economy has led to a substantial increase in the number of public buildings,resulting in an increasing number of public building toilets.At the same time,it is recognized that the infection of many intestinal and respiratory diseases is closely related to the poor air environment of public building toilets,which has aroused widespread concern about the air quality of public building toilets.Ventilation is considered to be an effective method to improve the toilet environment of public buildings.However,due to the lack of applicable airflow organization forms,the environmental problems of the bathroom are difficult to be effectively improved.’Natural air supply+mechanical exhaust’is a common ventilation method for toilets in public buildings.It uses the natural air supply of doors（windows,gaps）and the suction of exhaust vents to eliminate pollutants.In the form of mechanical exhaust:the top exhaust can effectively remove the ammonia,moisture and other lighter pollutants accumulated at the top.Low exhaust air can eliminate pollutants in time,reduce pollutant retention time,and can also eliminate pollutants with high density such as hydrogen sulfide.Therefore,the combination of top exhaust and low exhaust not only effectively removes pollutants,but also shortens the retention time of pollutants,and avoids the problems of large energy consumption and difficult management of mechanical air supply.Based on the above premise,this paper uses numerical simulation,model test and other methods to discuss a kind of’top exhaust+low exhaust’（upper and lower exhaust combined）public building toilet ventilation mode.The main contents include the following aspects:（1）Through the establishment of CFD calculation model and model test platform for the diffusion of polluted gas in public building toilets,the simulation results and experimental values are compared.The results show that the average relative deviation of wind speed and tracer gas concentration at the measuring point is within the allowable range.The ventilation method is feasible and the calculation model is effective.（2）The average concentration and normalized concentration index of polluted gas in the height section of breathing area（z=0.9 m,z=1.5 m）were introduced to evaluate the air quality of toilets in public buildings.The average concentration of ammonia at the height of the breathing zone z=1.5 m was used as the test index,and the influence of the position height of the exhaust tuyere（0.15 m,0.25 m,0.35 m）,the ratio of the upper and lower exhaust（1:9,2:8,3:7）,and the size of the tuyere（200 mm×200 mm,250 mm×250 mm,300 mm×300 mm）on the performance of the exhaust system was discussed.The results show that the position and height of the exhaust outlet have the most significant influence on the performance of the ventilation system.In addition,the optimal combination parameters of the exhaust system are as follows:the height of the exhaust air outlet is 0.15 m,the ratio of the upper and lower exhaust air is 2:8,and the size of the air outlet is 300 mm×300 mm.（3）Through CFD numerical simulation,the pollutant discharge effect of’combination of upper and lower exhaust air’and other three common airflow organizations was compared and evaluated by different evaluation indexes.The results show that the average pollution gas concentration and normalized concentration of the respiratory height section of the’combination of upper and lower exhaust’are the smallest,and the minimum normalized concentrations of ammonia and hydrogen sulfide are 0.2660 and 0.0023,respectively.This form of pollutant removal effect is the best.（4）Based on the form of’combination of upper and lower exhaust air’,CFD numerical simulation was used to study the influence of the partition form and ventilation rate of the squatting interval on the distribution of polluted gas,and evaluated by different evaluation indexes.The results show that the minimum normalized concentrations of ammonia and hydrogen sulfide are 0.1762 and 0.0023,respectively,in the form of partition to the top and the top and bottom open.Considering the distribution of ammonia and hydrogen sulfide,the form of partition to the top has better ventilation effect.Based on the form of partition to the top,with the increase of ventilation times from 5 h^-1 to 20h^-1,the concentration distribution of ammonia and hydrogen sulfide decreased significantly,but the decrease was also reduced.When the ventilation times increased from 15 h^-1 to 20 h^-1,the average reduction of ammonia and hydrogen sulfide on the two respiratory height sections was only 14.7%and 37.6%,respectively,which was much smaller than 81.1%and 97.2%when the ventilation times increased from 5 h^-1 to 10 h^-1.