Organization principles general ventilation
Principles of organization of general ventilation flow from the nature of the spread of harmful substances on the premises. Uniform allocation of pollutant in the area of industrial premises or at its height is rare. As a rule, the hazards highlighted in certain areas, both vertically and horizontally. Currents of air gases and vapors are carried into the room. Dissemination of harmful substances on the premises as there is no uniform, except when the air is stirred by an artificially concentrated inflow jet. Natural extension of hazards on the premises always makes it a relatively "clean" and "dirty" zone.
The greatest role in this play convection currents that cause the vertical, horizontal and recurrent jet. Convection currents blow up not only to gases and vapors, regardless of their weight, but the fine dust. Thus, in the presence of powerful sources of heat in the room most of the hazards imposed by jets to the overlap of the shop.
If these dirty streams immediately removed intensive hood placed over the site the largest concentration of pollutant in a stream, the further spreading of the pollutant in the room is virtually eliminated. If, however, completely removed upstream fails, or if it will be broken by jets of air-supply, the picture is complicated by the spread of harmful substances. There are horizontal and vertical return flow (due to the cooling air from the cold roof) to return the hazards in the working area from which they were removed by an upward heat flux.
Simplifying a complex phenomenon, one can say that in the presence of heat release (a special case), the largest concentration of harmful substances will be in the upper zone, and the smallest - in the work (the upper zone - a "dirty", and the lower, working - "net"). This suggests the scheme of general ventilation of bottom - up ", ie, feed fresh air into the area and extract it from the upper band. Erroneous in this case would be feeding the flow into the upper zone from the top or bottom of the range hood.