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1. Fume Hood Design
2. Slot Hood Design Studio
3. Kitchen Hood Design

Feb 17, 2017 It recommends hood construction, location, fire protection, specialty hoods, identification, inspection, testing and maintenance and exhaust. SEFA is the Scientific Equipment & Furniture Association. Its publication “Laboratory Fume Hoods Recommended Practices” covers design requirements of hoods, face velocities and testing. '68-'69 Camaro S/S Hood Item No. CRC-099: $7.50: 14. Mini Rectangle Pro Stock Hood Scoop Item No. CRC-102: $5.50: 15. Aero IV Pro Stock Hood Scoop Item No. CRC-103: $6.00: 16. Stock Vega Hood Item No. CRC-104: $7.00: 17. Short Old Style Pro Hood Scoop Item No. CRC-106: $5.50: 18. Cowl Induction Hood Scoop Item No. CRC-107: $5.00: 19.

Hood Design

Problem:

Solution:

C_e = (VP_d / SP_h)^1/2

where C_e is coefficient of entry,

VP_d is duct velocity pressure,

SP_h is hood static pressure.

SP_h = h_e + VP_dwhere h_e is the hood entry loss.

For plain opening hood,

VP_d = SP_h * Ce² = 3” * 0.82² = 2.017” wg

h_e= 3” – 2.017” = 0.983” wg

Percent loss in velocity head = 0.983 / 2.017 = 48.74 %

For flanged opening hood,

VP_d = SP_h * Ce² = 3” * 0.76² = 1.733” wg

h_e= 3” – 1.733” = 1.267” wg

Percent loss in velocity head = 1.267 / 1.733 = 73.11 %

For cone hood,

VP_d = SP_h * Ce² = 3” * 0.93² = 2.595” wg

h_e= 3” – 2.595” = 0.405” wg

Percent loss in velocity head = 0.405 / 2.595 = 15.61 %

With an increase of C_e, hood entry loss and % loss in velocity decreases.

Problem:

Find the static pressure of a hood if the velocity pressure is 4.5 'H₂O and the coefficient of entry is 0.82.

Solution:

C_e = (VP / SP)^1/2

where C_e is coefficient of entry,

VP is velocity pressure,

SP is static pressure.

SP = VP / C_e² = 4.5 / 0.82² = 6.7” of water

Problem:

A 25' wide hood needs a slot velocity of 200 fpm with a 40 cfs volume. What size of slot opening is required?

Solution:

Required area of slot = Q / V = (40 cfs * 60) / (200 fpm) = 12 ft²

Size of slot opening = 12 ft² / (25” / 12) = 5.76 ft = 69.12”

Problem:

Assume the hood static pressure in a 8' duct is 3.0' H₂O and the hood manufacturer indicates that Ce is 0.89. What is the estimated flow rate?

Solution:

Hood entry coefficient, C_e = √ (VP_duct / SP_hood)

So, VP_duct = C_e ² * SP_hood = 0.89² * 3 = 2.376 “wg

V_duct = 4005 * √VP_duct = 6173.42 fpm

Q = V_duct * A = 6173.42 * [π * (8/12)² / 4] = 2154.93 cfm

Problem:

Assume a hood is exhausting 3,000 cfm of air and the hood static pressure was measured at 2.17' w.g. Three months later the hood static pressure is 5.0 ' H₂O. Assume continued standard conditions (55^oF & 29.92' H₂O). Calculate, by how much the air flow through the duct has been reduced?

Solution:

For standard air, Q = 4005 A C_e √ SP_hood

For the same hood, Q is proportional to √ SP_hood

So, Q₂ = Q₁ (√ SP_{hood, 2} / √ SP_{hood, 1}) = 3000 (√ 5 / √ 2.17) = 4553.83 cfm

Increase in air flow rate = (4553.83 – 3000) = 1553.83 cfm

% Increase in air flow rate = (4553.83 – 3000) / 3000 = 51.8 %

Problem:

Compare the flow rate for a lateral hood located at the edge of an open surface tank (4ft*3ft) with the rate for a canopy hood located 3 ft above the tank. The tank contains a solution of ammonium phosphate in water at 250^oF. Ammonia gas is released from the tank. State your assumptions.

Solution:

Lateral Hood:

Q = V (10 X² + A)

where, Q = Air Flow (cfm), V = Centerline Velocity at X distance from hood (fpm)

X = Distance of source from edge along axis (ft), A = Area of hood opening (ft²)

Assumptions: Capture Velocity = 75 fpm, Hood Dimensions = 4 ft by 3 ft (same as tank)

V = 75 fpm, X = 0 (hood at edge of tank), A = 4 * 3 = 12 ft²

Q = 75 * 12 = 900cfm

Rectangular Canopy Hood:

Height of hood above tank = 3 ftLow Canopy Hood required.

Q = 6.2 * b^1.33 * Δt^0.42 * L

where, Q = Air Flow (cfm), b = Width of hood (ft),

Δt = Difference in source and ambient temperature (F), L = Length of hood (ft)

Assumptions: Hood Dimensions = 4 ft by 3 ft (same as tank)

b = 3 ft, L = 4 ft, Δt = (250 – 70) = 180 F

Q = 6.2 * 3^1.33 * 180^0.42 * 4 = 946.75 cfm

The primary goal of an industrial ventilation system hood is to capture and transfer environmental contaminants. A hood’s size and shape is designed specific to its end application but is typically classified within the enclosing hood or exterior hood category.

Hood Types

Enclosing hoods:

An enclosing hood will completely or partially surround the point where contaminants are generated. An enclosing hood is typically preferred but may not be practical due to potential interference with employee workstations.

• A partial enclosing hood has two to three sides where an inward flow of air through the opening will contain the contaminant within the enclosure and prevent its escape. Examples include paint spray booths or grinder station.
• A completely enclosing hood has all sides and is preferred whenever possible. A laboratory hood is an example of this use.

Exterior hood:

Exterior hoods are placed next to the point where contaminants are generated without creating an enclosure. An exterior hood may be an opening on a welding table or slots on the side of a tank. The exterior hood should be located in the path of the emission if transferring larger particulates such as sand.

There are four main types of exterior hoods:

Fume Hood Design

• Canopy: A one- or two-sided overhead hood that receives upward airflow from hot air or gas.
• Close-capture: Mounted directly over the source of a contaminant.
• Push-pull: A hood placed on the side of a push-pull ventilation system.
• Side-draft (also called lateral exhaust hood): This is not as efficient as other containment or down-draft hoods.

Hood Velocity Considerations

A specific velocity is required, depending on the type of contaminant being captured. To achieve the required velocity, carefully consider the hood’s shape, size and location.

• Face velocity: Velocity right at the hood opening.
• Capture velocity: Velocity at the dust generation source to capture the contaminant and transfer it into the hood.

Ergonomic Considerations:

An industrial ventilation system hood is one of the most important components of an individual’s workstation. A worker will be more likely to use the hood and the ventilation system properly if ergonomic elements are considered. Among these considerations are:

Slot Hood Design Studio

• Accessibility to parts within the hood
• Size, design and weight of objects handled
• Safety cables
• Overhead clearance
• Sharp edges
• Lighting
• Ease of cleaning

Kitchen Hood Design

IVI’s engineering and design team has years of experience designing and sizing industrial ventilation systems. IVI can assist in the design of a new system or the redesign of an existing system.