Notes on ventilation in industrial systems

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Notes on ventilation in industrial systems

Principles of ventilation    

Ventilation   is a measure used to control concentrations of chemicals in the working environment,

including those hazardous to health and those presenting physical hazards, such as explosions  

and fires. Ventilation also   reduces heat that causes fatigue and

discomfort, while controlling problems   with odors, humidity and indoor air quality.

Ventilation is divided into 2 categories:  

1) General ventilation ( General Exhaust Ventilation)  also called

    dilution ventilation  (Dilution Ventilation)  

2) Local exhaust ventilation ( Local Exhaust Ventilation)

General ventilation    This category is divided into 2 types:  

1) Mechanical ventilation ( Mechanism ventilation)  and  

2) Natural ventilation ( Natural ventilation)

Mechanical ventilation   uses devices or machinery such as fans to help

air move and circulate. Natural ventilation relies on naturally occurring differences in atmospheric pressure

between two areas, causing air to move from a higher-pressure area to one with lower

atmospheric pressure.

Components and functions of local exhaust ventilation                       

Local exhaust ventilation is designed to collect contaminants at their source or in a production process before they

disperse or evaporate into the workers' breathing zone. Therefore,   local exhaust ventilation provides contaminant control

at the source with high efficiency and saves energy because the exhaust flow rate is low, reducing the energy required

to move the air. The main components of industrial ventilation are:

 -  Hood ( Hood)

 -  Air duct ( Duct)

 -  Air-cleaning equipment ( Air Cleaner)

 -  fan ( Fan)

Hood design and selection

The main ventilation system design principles are:

1. Minimize elbows and fittings to reduce duct losses.

2. Use a suitable pollutant capture velocity to prevent turbulence in the contaminants.

3. Design for negative pressure at the system inlet and fan inlet, and

    positive pressure downstream of the fan at all times.

Hood selection depends on the following factors:

1. Type of pollutant

  For particulate pollutants, a hood capable of capturing particles from

  below can reduce ventilation-system energy use.   For pollutants consisting of

  toxic chemical vapors, the hood   should be installed at the side, with airflow directed away from the air

  being breathed,  (Breathing Zone)  for example.

2. Work characteristics / worker position

        The installed hood should enclose the pollution source without obstructing the worker's activities.

3. Work frequency / duration

  These affect calculations of pollutant quantity and system energy use.

4. Direction of air movement

  Particle movement depends on factors such as the speed of air circulating around the area, which

  affects   the specified air velocity and hood design.

5. Particle capture velocity ( Capture velocity)  and hood face velocity ( Face velocity)