Air Terminals in HVAC Systems

 Air Terminals in HVAC Systems

Selecting the proper Air Terminal is essential for achieving good air distribution and occupant comfort in HVAC systems.
-Common Types
Square Diffuser – Round Diffuser – Slot Diffuser – Perforated Diffuser – Swirl Diffuser – Jet Diffuser – Grilles & Registers – Door Cut / Under Cut – Fresh Air Louver – Disk Valve.
-Selection Based on Ceiling Height
1-Square / Round Diffusers: typically used with suspended ceilings up to ~4 m.
2-Swirl Diffusers: suitable for heights up to ~5 m due to better air mixing.
3-Jet Diffusers: used for high ceiling spaces such as halls and large areas.
4-perforated Diffuser: in hospitals and surgery rooms
Understanding L and Throw Distance
L = distance between two diffusers, or half the distance between a diffuser and a wall.
Many engineers assume this is the throw distance, but actually it is the Critical Length (L).
The relationship between L and T (Throw) depends on the diffuser type,and sometimes T = L.
After determining L, we evaluate T50 / L.
❇️T50 is the throw distance where air velocity drops to 50 FPM, which is considered comfortable for occupants at about 1.8 m height (human breathing zone).
⚠️ Note:
Throw distance should be divided by 0.75 to account for the reduction caused by the temperature difference between supply air and room air.
🛠 Diffuser Selection Steps
1️⃣ Determine the required CFM for the room.(Based on the designer)
2️⃣ Decide the number of diffusers.
3️⃣ Divide total CFM by the number of diffusers to get airflow per diffuser.
4️⃣ Use the manufacturer catalog to select the diffuser based on CFM and Throw.
Tip:
Selection is usually based on the neck size, not the diffuser face size, especially with 600 × 600 mm ceiling tiles.
hashtag