Choosing an air distributor (Air Diffuser / Grille / Register)

Article details

Air diffusers (Air Diffuser / Grille / Register) come in many forms. and actual selection time

You must look at the type of work + function + air distribution pattern + wind speed that residents can accept.

+ The level of beauty of the area

Summary of worksite usage + selection method + advantages and disadvantages to be “Engineering + actual worksite”
1. Types of air dispensers found in actual work.

(A) Square / Round Ceiling Diffuser
Apply to: shopping malls, offices, hotels, office buildings, classrooms, etc.
Features
 • Radial air distribution / 360° / 4-way / 3-way / 2-way
 • Throw value is longer than slot type.
 • Suitable for stable cool air and good air mixing.

Advantages
✔ Beautiful
✔ The wind spreads well.
✔ Works well with Plenum

Disadvantages
✖ If the wind is too cold + humidity is high, condensation may form. The surface of the head can be dispensed.
—> Use with: CAV, VAV, DOAS + FCU + AHU

(B) Slot Diffuser (Linear Slot) used with: meeting rooms, hotels, lobbies, premium areas
Features
 • Look “beautiful and modern”
 • Long continuous form.
 • Often has a deflector that can adjust the wind direction.

Advantages
✔ High beauty
✔ Attaches together with a smooth plaster ceiling.
✔ Wind does not hit people directly.

Disadvantages
✖ Throw value is not as far as Square.
✖ Higher price
✖ The air volume must be designed clearly, suitable for: middle-high level decoration work.

(C) Jet Nozzle / High Induction Nozzle used with: high warehouses, airports, high halls 8–20m
Features
 • Throw very far.
 • Use with High Ceiling areas.

(D) Bar Grille / Linear Bar / Drum Type used with: shopping malls, factories, high halls, gyms
Features
 • Focus on accelerated wind direction.
 • Can be used as Supply / Return.


(E) Return Air Grilleused with: all jobs
common type
 • Eggcrate
 • Bar type
 • Perforated panel

Function:
 • Mix air return to AHU/FCU.
 • There is no high pressure like Supply.

(F) Louver / Intake Grille for OA (Outside Air):
 • Has a rain cover.
 • There may be a Filter.
 • There may be a Damper to adjust the air volume.

2. How to choose an air nozzle (step by step)
When choosing an air nozzle, you must consider this 6 factor:

STEP 1 : Area type Ask first, what kind of area is this? Area should be selected
Square / Slot Office
High Lobby Slot / Jet Nozzle
Meeting room Slot / Square 3-Way
Jet Nozzle / Drum / Duct Direct Factory
Slot/Linear hotel
Human rooms, avoid wind blowing (Low velocity)

STEP 2 : Ceiling Height Recommended Height
2.6–3.0 m Square / Slot
3–6 m Square + High Induction>6 m Jet / Nozzle / Drum

STEP 3 : Air velocity (Face Velocity) standard used.
Air comes out of the Velocity nozzle.
People don't get wind 150–200 fpm
250–350 fpm office
Warehouse 400–600 fpm
Jet Nozzle 800–1200 fpm
Meeting rooms/office rooms must be careful of drafts.

STEP 4 :Throw Distance
It is the distance that the wind travels until the speed decreases until it is acceptable, for example, an office (comfort) must be lower than 50 fpm at the end of the Throw.

STEP 5 : Acoustics (NC Level) The loudness value of the wind, e.g.
NC area
NC work room 25–30
Meeting room NC 20–25
NC Hall 35–40
NC factory is not critical.

STEP 6: Beauty (Architectural)
Slot has the highest score

3. Example of real work site — Supply for Office
For example, Office room, ceiling 2.7m

The problem requires:
 • beautiful
 • No Draft
 • The wind spreads evenly.
Choose:Square 4-Way + Plenum or Slot Diffuser

4. Example of work site — Lobby 2 Ceiling floor 6m Required: Select Jet Nozzle.
Reason:
 • Throw Far
 • Has Adjust wind field
- Mistakes frequently encountered at work
- Select the dispenser that “hits people sitting” → People complain of being cold/dry throat.
- No insulation → Water droplets on dispenser head
- Throw design is not enough → The room is not cool.
-  Choose a beautiful design but the pressure doesn't reach → the air doesn't come out.
- Not checking NC → The conference room has wind noise.

💡 Short summary
Choosing an air nozzle, you must answer 3 questions first:
 1. What type of area?
 2. How high is the ceiling?
 3. What level of beauty do you want and check the values:
➡ Throw
➡ Velocity
➡ NC
➡ Draft
➡ Condensation