Research For Evaluation Method Of Harmful Substances Control Of Local Ventilation System In Industrial Building

With the rapid development of industrial production in China, industrialdistributions of harmful substances are increasing, and so are the increasing problems ofthe environmental pollution. These harmful substances not only jeopardize humanhealth, but also seriously affect the product quality. The local exhaust ventilation systemis the powerful tool which is respond to the call of energy-saving and reducing thedischarge, and is also regarded as the most efficient ventilation way.The evaluation index of local ventilation system usually use capture efficiency.However, there is a case that although the capture efficiency of exhaust hood is high, theindoor workers also have serious health risk. What’s more, the evaluation indexes ofindoor ventilation (such as air exchange efficiency and contaminant removal efficiency)are not for local ventilation. So in order to comprehensive evaluate the ventilation effectof the all building environment, in addition to evaluate the removal effect of harmfulsubstances, and also the influence of escaped.First, it is introduced the evaluation indexes of ventilation system at home andabroad，which contain the calculation method, application situation and inappropriate ofeach index. On that basis, it is presented a new index which is suit for the object of thisstudy–normalized concentration in the targeted zone. Targeted zone is a zone whichconcentration gradient is large, and outside of the zone the concentration gradient issmall to near zero. Normalized concentration in the targeted zone is the ratio of averageconcentration of targeted zone to Indoor average concentration. Using this index at thisfoundation on capture efficiency, it its not only obtained ventilation effect of targeted zone, but also the untargeted zone.Next, it is suggested two optimization methods of controlling harmful substancesby local ventilation. One is it is analyzed control effect of breathing area in the differentwork locations when using working area push-pull ventilation to control harmfulsubstances. Second is compared the control effect of working area push-pull ventilationand lateral exhaust ventilation. It is considered three kinds of locations–worker back toair supply outlet, broadside on air supply outlet and face to air supply outlet. It is got theconclusion that although the capture efficiency is the same, the worker feels the lowestformaldehyde concentration when he broadside on air supply outlet. Furthermore, thecontrol effect of working area push-pull ventilation is superior to lateral exhaustventilation, because the formaldehyde is controlled in a smaller area.Last, it is analyzed and evaluated control effect of working area push-pullventilation under two situations—different building bulk and formaldehyde emission. Itis get the conclusion that the lager building bulk, the high formaldehyde concentrationin targeted zone and the lower concentration in untagged zone, so local ventilationeffect is more prominent. As the formaldehyde emission increase, normalizedconcentration in the targeted zone is deduce, that means the less formaldehydeconcentrated in targeted zone and the escaped form targeted zone is increasing. It iswell-proven that although the capture efficiency of exhaust hood is high, the indoorworkers also have serious health risk by the escaped.The normalized concentration in the targeted zone can not only evaluate theventilation effect around work bench, but also the other area. The research result in thispaper plays a certain guiding role in design of local ventilation in industrial buildings.