| In recent yeas,the deterioration incidents of indoor air quality continue to occur inthe living environment, damaging to human health. The building natural ventilation hasgradually attracted people’s attention. Domestic and foreign scholars have done a lot ofresearch on the various forms of natural ventilation.Natural ventilation mainly has twofunctions of cooling and exhausting heat and ventilation and air exchange, so as toimprove the indoor thermal comfort and indoor air quality.It’s a kind of ventilation way,which saves energy and protects environment.Natural ventilator, which is made byusing the principle of natural ventilation can achieve indoor ventilation and airexchange and improve air quality. Such natural ventilation products start to use in theresidential buildings.However, the main driving force of natural ventilator are hotpressing and wind pressure, whose force are limited by the outdoor weatherconditions.Meanwhile academic circles are lack of research data from the actual useeffect of natural ventilation. Therefore, people gradually begin to question this kind ofproduct’s actual use effect on the improvement of the indoor air quality. It also makesnatural ventilator not be effectively promoted.In this paper, Computational Fluid Dynamics software Fluent has been used toestablish natural ventilation model for the numerical simulation. In the calculationprocess, by selecting the boundary conditions of different hot pressing and windpressure to simulate, we get the indoor concentration field distribution and theconcentration change process with time, in order to judge the natural ventilation effectof ventilator.Then a natural ventilation experiment system is established in a standardunit of residential building in Chongqing area. The experiment has totally set up9conditions of “ventilator close”, ventilator open and curtain open”,“ventilator open andcurtain close”under the6℃,8℃and10℃indoor and oudoor temperature differencefor testing the indoor carbon dioxide’s concentration changes with time.On one hand,the test results and the simulation results are compared to analyse, in order to verify themodel;On the other hand, as the index of the concentration of carbon dioxide the paperfurther analyzes the ventilation effect on the improvement of the indoor air quality.Based on indoor concentration changes and used micro environmental quality balanceformula, the paper has calculated and analysed indoor ventilation rate under differentworking conditions to check if it can meet the requirements of the current specification.The last part of the article also studys on the outdoor wind pressure factor,which greatly affect the natural ventilator’s performance.The main research results ofthis thesis are as follows:1) Wind pressure and hot pressing natural ventilation model are established.Usingthe Fluent software does simulation and analysis of natural ventilator’sairexchangeeffect under different conditions, and the simulaton results are gotlike indoorconcentration field and the change of the indoor carbon dioxide’s concentration withtime. Simulation research proves that under the effect of hot pressing and wind pressure,the natural ventilator can effectively eliminate indoor carbon dioxide and improve airquality.As improving the hot pressing (temperature difference) and wind pressure(windspeed), ventilated effect is getting better and better.And the influence of wind pressureis greater than hot-pressing.2) According to the measurement of CO2concentration changing in the rooms, theauthor paints the curve between CO2and time under different actionof hot pressing andwind pressure and calculates the ventilation rate of the room.From two indicators ofstandard CO2concentration in the room and ventilation rate which stipulated in thecodes, they are used to judge the performance of ventilator.In the winter heating season,under the pure hot pressing action of8℃and10℃difference in temperature, whenventilator open and the curtains open or closed, Research results show that indoorcarbon dioxide concentration can be controlled effectively and room ventilation ratemeet requirements.Natural ventilation has a practical effect in improving indoor airquality. The effect also will be strengthened as outdoor wind pressure is improved. Inthe summer air-conditioning season without wind pressure, the indoor CO2concentration and room ventilation rate meet the basic requirements of the standardvalue under10℃difference in temperature.3) During the experiment, through contrasting test and analysis of switching thecurtain, it is found that the blocking of the curtain has no significant impact on theventilation effect of ventilator. When indoor and outdoor temperature difference keeps6℃, indoor CO2concentration rises by only80ppm and ventilation rate decrease by3.8m3/h after curtains in the master bedroom close.From another side, the curtain isgenerally used in the night when people rest. People are in a state of sleep and rest withmetabolism droping with low carbon number.It expands the application range of naturalventilatior at night.4) Based on the experimental results, the author analyzes the wind pressure (type, wind speed and direction) on the influence law of indoor carbon dioxide.The stablevalue of indoor concentration follows the law of “sustained wind<intermittent wind <nowind”,and ventilation rate follows the law of “sustained wind>intermittent wind>nowind”.Experimental results show that the action of sustained wind (>1m/s)only exists,even if the wind is back to the ventilator, indoor concentration and the ventilation raterespectively meet requirements of the1000ppm standard value and ventilation rate of1times/h in the master bedroom.Because outdoor wind pressure is variable anduncontrollable and hot pressing and wind pressure often influence each other. Study onwind pressure effect on indoor CO2concentration must need a lot of experiments andmulti-condition to improve. |
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