LEV Systems: Design, Maintenance, and Performance Analysis

This report provides a comprehensive overview of Local Exhaust Ventilation (LEV) systems, detailing ventilation approaches, design principles, and maintenance considerations. It explores the differences between general and local ventilation, emphasizing the effectiveness of LEV in controlling contaminants at the source. The report covers critical aspects of LEV design, including hood design, capture velocity, and the impact of enclosure design on performance. It also addresses common LEV system problems and offers design guidance, referencing the ACGIH manual for recommended designs. Furthermore, it highlights the importance of periodic inspection and maintenance to ensure system effectiveness, with a focus on planned maintenance, routine checks, and tests. The report concludes by summarizing the key principles of LEV systems and emphasizing the importance of regular inspection and maintenance for optimal performance.

 
LOCAL EXHAUST
VENTILATION (LEV)
SYSTEMS

Outline
 Ventilation systems approaches
 Main features
 Proper design considerations for local
ventilation
 Maintenance and inspection

Main types of Ventilation
General/Dilution
o Control of heat and/or contaminants removal
o Also called dilution ventilation
o Used in controlling contaminants only in cases local
exhaust cant work
o Uneconomical and ineffective
Local ventilation
o Traps contaminants at source
o Is a preferred control method because:
o more economical
o more effective

Local Exhaust Ventilation (LEV)
Characteristics of contaminants:
o particle speed
o source directionality
o gas/fume particles
o particle size
o temperature
o An ideal solution for one is impractical in another
o The solution has to be suited to source

Typical sources of contaminants

Typical sources of
contaminants

LEV: Design Principles of Hood
Key parameters influencing effective
operation
o Design of openings
o Distance for contaminant source
o Design of enclosure

Distance from source of contaminants

Velocity change with
time

Flow rate & Capture Velocity
 Flow is determined to provide the capture
velocity needed during design

Impact of enclosure design
Hood capture velocity having and without
flange
With flange Without flange

Impact of enclosure design
Airflow required to provide adequate
control
• Plain extract opening
• Enclosure added at
sides and above
bench
• Flange added at
rear
• Transparent screen
added at front
1m3/s
0.40m3/s
0.79m3/s
0.75m3/s