✅ Fresh Air Supply Methods
Ventilation and air conditioning system can add fresh air (Fresh Air)
There are many types, depending on the type of building and the level of air quality control.
⭐ 1) Add fresh air to the AHU / FCU (Direct to Mixing Section)
Bring outside air into the Mixing Box of the AHU or FCU.
• AHU: Frequently used.
• FCU: Must pass FA box + Filter + Damper.
Advantages
• Economical, no need to install OAU/FAU separately.
• AHU bears the burden of humidity and heat instead.
Limitations
• Humidity control is more difficult than DOAS.
• Hot, moist air entering the AHU → high coil load.
⭐ 2) Add fresh air to the front of the Return Duct (Induced Fresh Air).
Outside air is drawn into the Return Duct by negative pressure from the AHU.
Advantages
• Low cost
• Suitable for general buildings.
Limitations
• मात्रा FA is unstable (depends on Return pressure).
• Manual or Motorized Damper must be installed.
⭐ 3) Add air through FAU (Fresh Air Unit).
It is a special pure air inflator. Usually consists of
• Filter
• Fan
• (Some models have Pre-cool Coil)
Advantages
• Can be inflated according to standards.
• System to push air in the building to Positive Pressure.
Limitations
• Not suitable for strict humidity control work.
• Must control ESP value and internal wind direction.
⭐ 4) fill through OAU – Outdoor Air Unit (100% Fresh Air)
The wind from outside was Full conditioning before sending into the building
• Cooling + Dehumidification
• Reheat (some models)
Advantages
• Best humidity control.
• Suitable for critical areas such as ICU, OR, Lab.
• Reduce the load on the AHU inside.
Limitations
• High equipment costs.
• Energy load is greater than FAU.
⭐ 5) Add Fresh Air through DOAS (Dedicated Outdoor Air System)
Fresh air is conditioned by a separate system.
And the AHU/FCU inside only adjusts the temperature.
Advantages
• Very good humidity control.
• Highest efficiency for large buildings.
• Suitable for Net Zero / energy saving buildings.
Limitations
• High design and installation costs.
• Requires additional machine space.
⭐ 6) Add fresh air directly into the space (Direct to Room Diffuser)
FAU or OAU sends air directly into the diffuser, not through the AHU.
Advantages
• Used in specific rooms such as conference rooms, factories.
• Easy to manage chamber pressure.
Limitations
• Temperature may differ from wind. AHU → Draft occurs.
• Fan noise must be controlled.
⭐ 7) Fill through the Heat Recovery Ventilator (HRV / ERV)
Use Exhaust wind to exchange energy with Fresh Air wind.
Reduce the cooling load
Advantages
• Save energy.
• Suitable for buildings that require a lot of ventilation.
Limitations
• Higher investment than general FAU.
• The energy exchange plate must be maintained.
🟦 Summary of actual use (Prof. Thep can use it to teach immediately)
Air filling system, installation price, humidity control Suitable for the area
Fresh Air entering AHU, low, medium, general buildings
Fresh Air Enter Return Low Low Old Building, Retrofit
FAU Medium Medium Office, School
High OAU Best Hospital, Lab
Very high DOAS, very good, Grade A building
Direct to Room Low–Medium Low Factory, Meeting
HRV/ERV Medium–High Medium Energy efficient building
