Study On Buiding Environment PM_2.5 Filtration Model Of High Performance Filter Media And Application

The pollution caused by PM_2.5 in the building environment calls for urgent control concerning its serious effects on people’s health, but at present, there are no efficient ways to eliminate those fine particulate existing in HVAC systems. If adding the air filter according to conventional purification method, this operating system would be under the risk of insufficient dynamic pressure and there will be increase in the resistance of the wind attrition system. Therefore, research on characteristic model of the low resistance and high efficiency filter media for PM_2.5 purification in building environment has a very practical engineering value.By investigation the mean concentration of PM_2.5 in China and overseas and testing the PM_2.5 in typical environment of China and UK besides Shanghai subway station, and on the basis of the ambient air quality standards, the technical requirements of the filtering device for PM_2.5 purification was proposed. Besides, weight concentration method was used to test the characteristics of air filter materials at different filtering levels, including purification efficiency, filtration resistance, dust capacity and combustion characteristic related to building fire protection. After a better understanding of the purification characteristics of the current air filtering material, a filter which meets the demand of building environmental PM_2.5 purification was selected.In solving the problem that the commonly used materials are of low efficiency, the high efficiency filtering materials are of high resistance and the electret filter material is of low resistance and high efficiency but with a decrease in purification efficiency, a purification characteristic model including the step-divergence filtration model and filter-layer design model was provided. This model provides the guidance for the design of the filter material for building environmental PM_2.5 purification and its performance prediction.The filtration model of the step-divergence filter layer, in which purification efficiencies, resistances and dust holding capacities of different fabric materials can be calculated, is improved from the original evenly distributed layer model. After the analysis of the results, it can be found that the improved step-divergence filter layer, which is of the same weight and thickness to the uniform one, has a better and filtering quality factor and dust capacity. The analysis results can also porvide the theoretical evidence for the further design of the filter media with different purification layers which is of a lower filtering level in the front and a higher level after.The design model of the filter layer was set up by the grey correlation analysis theory. This kind of design method can be used for the optimal solution according to different objectives of filter layers. Considering that this project was focused on the filter media of low resistance and high efficiency, a step-divergence filter media with a pre-filter layer of medium efficiency layer and a main filter layer of electret filtering material was proposed. The purification tests result of the step-divergence filter media has a good agreement with the calculation results.According to the technical requirements of the low resistance air filter（such as F7 air filter） in ventilation and air conditioning system and high efficiency（such as H11 air filter） of the environmental air quality standard, a fresh air filtering device for building environmental PM_2.5 purification was designed by the purification characteristic model of filter media. Tests result of the fresh air filtering device shows that the filtration resistance is lower than that of F7 and the purification efficiency is higher than that of H11, which achieves the research objectives. Besides, alternative experimental study of the portable air cleaner filter layer also shows a better purification performance than the original air cleaner layer.