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Duct Design Air Flow Velocities

HVAC System and Components Design and Engineering Data
Engineering Fluid Flow Design and Engineering

Duct Design Air Flow Velocities - Typical

HVAC - air conditioning and heating systems usually require some form of duct system to channel air to places where the conditioned air is needed. A poor HVAC dust design, faulty installation installation job will result in poor performance, bad air flow, leaky duct systems, and higher than usual energy costs. It is important that the installation process is to make sure the duct work is sized properly. An over sized duct system will cost more and may not not maintain the desired air flow and an undersized duct system can cause the system to inadequately flow the HVAC air to the desired destinations.

The following should be considered in an effective duct system design.

  • Tradeoff's between the costs of the duct system and the energy cost of the air distribution system.
  • space available,
  • noise level requirements,
  • capacity for expansion,
  • maintainability
  • Ductwork system be designed for the air conditioning load.
  • Each room or space should be evaluated and a determination of how much air flow will be required

Table - HVAC Ducts Air Velocities

Intake Louvers Velocity (FPM)
  • 7000 cfm and greater
400
Exhaust Louvers
  • 5000 cfm and greater
500
Panel Filters
  • Viscous Impingement
  • Dry-Type, Pleated Media:
    • Low Efficiency
    • Medium Efficiency
    • High Efficiency
    • HEPA

200 to 800

350
500
500
250

Renewable Media Filters

  • Moving-Curtain Viscous Impingement
  • Moving-Curtain Dry-Media

 

500
200

Electronic Air Cleaners

  • Ionizing-Plate-Type
  • Charged-Media Non-ionizing
  • Charged-Media Ionizing

 

300 to 500
250
150 to 350
500 to 600

Steam and Hot Water Coils 200 min
1500 max

Electric Coils

  • Open Wire
  • Finned Tubular

 

Refer to Mfg. Data
Refer to Mfg. Data

Dehumidifying Coils 500 to 600
Spray-Type Air Washers 300 to 600
Cell-Type Air Washers Refer to Mfg. Data
High-Velocity, Spray-Type Air Washers 1200 to 1800


Adapted from ASHRAE “Pocket Guide” 1993


Typical Air Design Velocities for HVAC Components (Ducts)

Duct Element
Face Velocity,
m/s
Louvers
Intake
7000 cfm3300 L/s and greater
2
Less than 7000 cfm3300 L/s
See Figure 1.0
Exhaust
5000 cfm 2400 L/s and greater
2.5
Less than 5000 cfm 2400 L/s
See Figure 1.0
Filters
Panel filters
1 to 4
Viscous impingement
Dry-type, extended-surface
Duct velocity
Flat (low efficiency)
Pleated media (intermediate efficiency)
Up to 3.8
HEPA
1.3
Renewable media filters
Moving-curtain viscous impingement
2.5
Moving-curtain dry media
1
Electronic air cleaners
Ionizing type
Heating Coils
Steam and hot water
2.5 to 5
1 min., 8 max.
Electric
Open wire
Refer to mfg. data
Finned tubular
Refer to mfg. data
Dehumidifying Coils
2 to 3
Air Washers
Spray type
Refer to mfg. data
Cell type
Refer to mfg. data
High-velocity spray type
6 to 9

 

Louver Area vs Flow Chart

Parameters for Figure
Intake
Louver
Exhaust
Louver
Min. free area (1220 mm2 test section
45
45
Water penetration, mL/(m2 · 0.25 h)
Negligible
(< 0.3)
N/A
Max. static Pressure Drop, Pa
35
60

Figure 1.0 (Table + Chart Data) Criteria for Louver Sizing ( 2017F, Ch 21, Fig. 19)

Adapted from: ASHRAE Pocket Guide for Air Conditioning, Heating, Ventilation, Refrigeration SI 9th Edition

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