| In recent years,the use of household air cleaners and ventilation systems is more and more popular in China,and filters are the key components that determine their performance.Compared with the initial performance,the efficiency,pressure drop and other performance of filters will change in the process of operation,and even secondary pollution will occur with the increase of operating time,so that filters needs to be replaced regularly.However,replacement interval of filters is usually only determined by experience,lacking scientific theory and verification.Therefore,it is necessary to explore the factors influencing the service life of filters in household air cleaners and ventilation systems,and to propose a scientific calculation method for the maximum service life of filters.In this paper,two experimental platforms were built to explore the two possible factors that determine the service life of filters.One was the emission of secondary VOCs of old filters,and the other was the long-term performance of filters for particle filtration,including the change of efficiency,pressure drop with the operating time and the secondary detachment of particles.Then the system efficiency changes of a actual household air cleaners and a actual ventilation system were monitored for a long time and compared with the performance changes of the filter itself,and got a new method to calculate and predict filters' service life according to the system efficiency.Through systematic theoretical and experimental research,the main conclusions are as follows:(1)The emission of secondary VOCs of filters was related to the dust loading,environmental humidity and environmental VOCs level.The TVOC emission concentration of filters that have been used for more than one year changes presented a single-peak curve over time.The emission duration was less than 1h,and the peak concentration is 0.3-1.6mg/m3 when the storage relative humidity was 30-50%.After exposure in humid environment,the total emitted TVOC generally decreased while the emission rate of Aldehydes,Ketones and Olefins increased.Alkanes,aromatic hydrocarbons,alcohols and esters were the main compounds in the secondary VOCs emitted by indoor air cleaner filters,while aromatic compounds and alkanes were the main compounds in the secondary VOCs emitted by ventilation filters(2)The TVOC emission rate of portable air cleaner filters was between 0.63 mg/m2 and 3.46 mg/m2,which was 2?10 times higher than filters of ventilation systems.However,compared with other indoor VOCs emission sources,the TVOC emission of air cleaner filters only accounted for 2%,and toluene,which had the highest emission,only accounted for 5%.Therefore,secondary VOCs emission of the filters contributed little to indoor VOCs and cannot be used to judge their service life.(3)The long-term efficiency of filters was theoretically affected by particle deposition,particle secondary detachment and air humidity,but it basically did not change with particle deposition and air humidity in actual operation.Particle detachment occured at the early stage of operation,which was an indicator to determine the service life of G-class filters,but had little impact on the performance of H-class and F-class filters.The pressure drop of filters increased obviously with the operating time.(4)The system efficiency of the household air cleaners and ventilation systems declined with the operation time,because the pressure drop of the filter increased,resulting in the increase of bypass air leakage.According to the analysis,a scientific calculation method of by-pass air leakage and system efficiency was proposed,so that the relationship between system efficiency and operation time could be quantitatively calculated and predicted according to the system parameters and operating environment conditions,and it could be used as an important index of the service life of filters in actual use. |
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