Mechanical ventilation is the exchange of air that occurs thanks to the use of mechanical devices. Mechanical ventilation can be: vacuum, when it creates a negative pressure in a ventilated room; low pressure, in which the air flow speed is 3 ÷ 9 m / s in the main ventilation ducts and 3.5 ÷ 11 m / s in the branches; diesel, in which the air flow speed is 13 ÷ 30 m / s in the main ventilation ducts and 10 ÷ 24 m / s in the branches.
Mechanical ventilation is the exchange of air with fans driven by an electric motor. The air drawn in or supplied to the rooms is led through ducts (tin plates, plastic, etc.) after cleaning on filters and heating in winter by a heater. Dampers and gate valves are used to regulate the amount of air flowing in the ducts.
The fans together with the drive cause air vibrations, sewers and building structures and unwanted noises. This is prevented by damping the fans and lining the engine room with sound-absorbing materials, and installing special silencers on the ducts.. In these rooms of catering establishments, where people are staying, noise from ventilation devices must not exceed 50 decibels.
Mechanical ventilation is divided into general and local.
General ventilation then apply, when the source of pollution is not concentrated in one place. Its purpose is to reduce the concentration of all pollutants in rooms below the limit value. Channels with holes (bars) supply ventilation are distributed like this, that the air streams cover the entire surface of the ventilated room. In many cases, general ventilation does not give the desired results, and even spreads pollutants throughout the room.
Local ventilation we use for it, to prevent these undesirable effects of general ventilation. Its purpose is to capture harmful pollutants at the point of their formation with the help of suction cups. Hoods are used for local ventilation. The hoods are most often used in the kitchen hot above the cookers, pans and cookers. They draw out moist air along with undesirable odors, and the condensate formed on the planes of the eaves is discharged to the sewage system.
Drawing. Scheme of local and general mechanical ventilation. 1 - air supply lines, 2 - exhaust pipes, 3 - fresh air intake shaft, 4 - air heaters, 5 fans, 6 - dust collector.
The figure shows a schematic view of a combined ventilation system, in which fresh air is supplied through intake ventilation ducts terminated with grilles, and it draws off with hoods connected to the exhaust ventilation ducts (suction).