Impacts Of Dynamic Relationships Between Contaminants On Indoor Air Quality In Air-Conditioning Rooms

The most important environment in relation to our health is the indoor environment. The main purpose of HVAC systems is to provide a healthy and comfortable environment for the occupants of the space. The energy crisis of the 1970s was responsible for an approach, which emphasized energy savings. The results of such an approach were decreased volume flow rates of fresh air into building and thus worse indoor air quality than before the crisis.The typical contaminants in building are presence in the form of gases and particles. Ventilation plays a key role in the dilution and removal of gaseous contaminants within indoor environment. The amount of outdoor air delivered indoors should be increased in order to reduce the concentration of gaseous contaminants (such as CO₂ and TVOCs). But most ventilation and air conditioning systems are designed without much concern about how separating particles behave in ventilation air flow, and many epidemiological studies showed that air pollution related health problems have extensive relation to inhalable particles (PM10). For office and other similar work-related environments, hospitals, schools etc, the main source of pollutants is often outdoor air. These premises are usually ventilated mechanically with an HVAC system, providing air ventilation and filtration. When the outdoor concentration was relatively high, the strategy recommended to minimize the risk associated with outdoor pollutants would be to reduce the amount of outdoor air delivered indoors.In order to comprehensively study the time related dynamic variations of office room indoor air qualities, the CFD techniques were used for the numerical simulation of CO2 dispersion caused by breathing of people present in the office. Two different ventilation systems and three different outdoor air flow rate were taken into account. The geometry considered was three-dimensional and the k-εmodel was selected as the turbulence model. According to the simulation results, the minimum outdoor air flow rate required for the metabolic needs of occupants were determined theoretically.As the one of the primary pollution sources, indoor particle concentration and its variations were also simulated and analyzed. Two typical cities, Chengdu and Taiyuan, are selected as main background for the investigation, and the outdoor particle concentrations in the two cities were monitored continuously under typical summer climate conditions, respectively. The air flow in air-conditioned office rooms and the variations of indoor contaminants were also simulated by employing the similar CFD techniques. The results of the discussion and analysis show the acceptable ways for simultaneous cleaning of gaseous and particulate pollutants in northern and southern cities under different pollution levels, respectively, and some theoretical recommendations were suggested for the indoor ventilation designs by comparing with the related national standards of ambient and indoor air qualities.