Creating a positive pressure room (Positive Pressure Room) is the heart of HVAC system work.

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Creating a positive pressure room (Positive Pressure Room) is the heart of HVAC system work.

Especially office buildings, hospitals, food factories and cleanrooms.

To prevent dirty air from outside from flowing back into the area.

Below are the clear design principles. In the style of Achan Thep Can be used to teach work 👇

🟦 How to make the "area have positive pressure (Positive Pressure)"?

✅ 1) sends more air in Air that is exhausted (Supply > Exhaust)
This is the most important principle of Positive Pressure.
Basic formula:
Supply\ Air\ (SA) > Return/Exhaust\ (RA/EX)
Example:
 • Design air supply 2,000 CFM
 • Reabsorb or drain. 1,800 CFM
→ The area will immediately have positive pressure.

✅ 2) Increase Fresh Air more than the standard value.

If positive pressure is desired, 5–15 Pa
Add Fresh Air to 10–20% of the supply air volume (SA).
Example:
SA = 2,000 CFM
Appropriate Fresh Air ≈ 200–300 CFM
The space will have positive pressure and better IAQ.

✅ 3) Control leakage (Leakage) of the area.
If the room is leaking, positive pressure will not occur or very little will occur. It must be checked:
 • Leaky gap around the door.
 • Drop Ceiling openings that are not completely sealed.
 • Leaking holes around pipes/wire tracks.
 • Under the door there should be a Door Seal or Drop Seal.

✅ 4) Use VCD / Motorized Damper + DPT Sensor to control pressure.
Use DPT = Differential Pressure Transmitter.
Control the room to be within the desired pressure range, such as +10 Pa.
The control system works as follows:
 • If the pressure drops → Open the Damper to increase Fresh Air.
 • If the pressure is too high → Close the Damper to reduce Fresh Air.
Used to control important rooms such as
 • Dispensary room
 • ICU room
 • Laboratory
 • Operating room
 • Server room

✅ 5) Design Door Airlock / Anteroom (in case of critical room)
 • Inside is Positive.
 • Airlock chamber is center pressure.
 • Outside pressure is the same as normal.
Reduce contamination while opening the door

🟦 What should the positive pressure be?
Area pressure value (+Pa)
Office +5 Pa
Medicine room / clean room +10 Pa
Operating room +15 – 20 Pa
Cleanroom Class 100 – 10,000 +15 – 30 Pa

🧩 Summary in an easy to understand way (Achan Thep version)
Positive pressure = supplying more air than air output + controlling Fresh Air + closing leaks + using DPT to control Damper
Complete all 4 points → positive pressure is definitely stable.