Ventilation Assessment And Design For Building Environment Using Numerical Simulations

In the process of building energy-saving,the tightness of civil buildings has been enhanced with the amount of fresh air reduced.As a result,indoor harmful pollutants(such as CO2)cannot be effectively diluted which further leads to the increase of pollutant concentration and seriously affects indoor air quality(IAQ),working efficiency along with personal health and comfort.In order to create a healthy and pleasant indoor environment,the building internal space must rely on ventilation to dilute indoor pollutants.At present,the ventilation evaluation methods(such as the number of air changes,ventilation efficiency,etc.)mainly face the following challenges:(1)the spatial distribution characteristics of indoor pollutants have not been fully considered;(2)when indoor pollutant sources and temperature factors have significant effects on airflow organization and pollutant diffusion,traditional ventilation evaluation indicators are not sufficient to effectively remove indoor pollution.Therefore,how to determine the reasonable parameters of supply air and ventilation evaluation index has become an urgent task for the design of indoor environmental ventilation system,aiming at reducing the energy consumption on the premise of ensuring IAQ.In this paper,initial design and evaluation index for indoor ventilation systems is proposed,which provides a theoretical basis for ventilation design and air flow distribution.The indoor temperature setting method considering the thermal comfort and air quality is proposed based on the current civil building ventilation and air conditioning design standards.The results in this research have a certain reference value and guiding significance for improving indoor thermal comfort and air quality as well as reducing building energy consumption.This paper mainly applied the methods of experiments,numerical simulations and subjective questionnaire to study the diffusion and removal of indoor CO2 under different air inlet sizes and air change rates.The spatial distribution characteristics of CO2(concentration stratification)were studied by using dimensionless analysis method.And the initial design and evaluation index of indoor ventilation system was proposed to optimize the building ventilation design and indoor airflow organization,which could optimize the air inlet size.Based on the questionnaire survey about indoor thermal comfort and air quality,the effects of different temperature conditions on the diffusion of CO2 pollutants were investigated in the upper wall-mounted ventilation system.Compared with the existing indoor temperature design standards,better indoor temperature setting was proposed.The main research results are as follows:(1)Dry ice method to quantitatively simulate the CO2 exhaled by indoor humans:when the dry ice bucket reached stable heat transfer between inside and outside,it could release CO2 with a constant rate.That is,the dry ice method could quantitatively and effectively simulate the CO2 exhaled by indoor personnel,which was used as the method of pollution source release in this paper.(2)Initial design and evaluation index for indoor ventilation systems:with the increase of air change rates,the average CO2 concentration at the outlet was decreasing.Blindly increasing the supply air volume cannot significantly improve the air quality,which would consume a lot of energy on the contrary.When Ri/α was up to or below the critical value of 10-3,the mixing of indoor pollutants and air was sufficient to improve indoor air quality.A ventilation strategy with air change rates of 16 and inlet size of 0.2 to 0.4 could achieve better ventilation,respectively corresponding to Ri/a of 0.0008 and 0.0034 with the order of magnitude was 10-3.(3)Temperature adjustment for both indoor thermal comfort and air quality:in winter,when the upper heating ventilation used,the air quality may have certain problems even if the temperature met the requirements of indoor thermal comfort.Subjective survey showed that 94.74%of indoor personnel accepted the current room temperature,but still 27.03%thought that there was a slight smell in the room;8.11%thought there was odor;5.4%felt the fatigue;and 16.22%felt the bad breathing or asthma chest tightness.The higher the indoor temperature was,the more obvious the temperature stratification was,which could cause local thermal discomfort.At the same time,the negative effect of thermal buoyancy was continuously enhanced,which affected the CO2 diffusion and removal in the room,further resulting in the deterioration of indoor air quality.In addition,under acceptable indoor thermal comfort levels(PMV=0),an increase of 1℃ in temperature increased about 1.2%CO2 concentration and 5%energy consumption.