Exhaust Hoods
Exhaust hoods are essential in kitchens, laboratories and industrial application for removing
- fumes
- mists
- vapors
- aerosols
- particulates
- hazardous substances
- polluting contaminants
before they "escapes" to from the surrounding air.
In general for an exhaust hood to be efficient
- the height - y - should not exceed 1.20 m (4 ft)
- the distance - x - should not be less than 1/3 y
- the capture velocity - v1 - should not be less than 0.15 - 0.20 m/s (30 - 40 ft/min)
Note! Potential hazardous and polluting applications requires special solutions. Always check local regulations before design.
Capture velocity - v1 - for an exhaust hood can be estimated with the empirical equation
v1 = q / 2 y2 c (1)
where
v1 = capturing velocity (m/s)
q = air volume flow (m3/s)
y = distance between table and exhaust hood (m)
c = circumference of the hood (m)
(1) can be modified to calculate air volume flow
q = 2 v1 y2 c (1a)
Example - Kitchen Exhaust Hood
Required air volume flow for a exhaust hood with circumference 3 m located 1.2 m above a stove can be calculated as
q = 2 (0.2 m/s) (1.2 m2)2(3 m)
= 1.7 m3/s
Note! The units don't match since the equation is empirical (a result of experiments).
Exhaust Hood Calculator
The air flow volume in the exhaust hood can be calculated below
Exhaust Hood with internal Plate
The efficiency of an exhaust hood can be improved by adding an internal plate.
The required air volume for an exhaust hood with an internal plate can in general be reduced to approximately 80% compared to an exhaust hood without a plate.
Exhaust Hood with Side Walls
The exhaust hood efficiency can be further improved by adding side walls.
Related Topics
• Ventilation Systems
Design of systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more.
Related Documents
Convective Air Flow - Single Heat Source
Calculate the vertical air flow and air velocity generated by a single heat source.
Evacuation of Air - minimum Capture Velocities to avoid Pollution products transferred to the Room
Capture velocities to avoid pollution products from galvanic baths, spray painting boxes and more contaminating the surrounding room and environment.
Exhaust Outlets - Capturing Air Velocities
Capturing air velocity in front of an exhaust outlet - online exhaust outlet velocity calculator.