Chapter 10: Air Distribution Systems
Air distribution is a core component of HVAC systems — it ensures that conditioned air is delivered efficiently and uniformly to various spaces.
🔹 10.1 What is an Air Distribution System?
It refers to the network of ducts, diffusers, grilles, dampers, and fans used to distribute air from the HVAC unit to the conditioned space.
The goal is to:
Maintain thermal comfort
Distribute air evenlyControl temperature, humidity, and air quality
🔹 10.2 Components of Air Distribution System
| Component | Description |
|---|---|
| Ductwork | Pathways (metal or flexible) that carry air |
| Diffusers | Discharge air into the room (uniformly) |
| Grilles | Allow air to enter or leave rooms |
| Registers | Grilles with dampers for air control |
| Dampers | Regulate airflow (manual/automatic) |
| VAV Boxes | Variable Air Volume boxes for zone-wise control |
| Fans (Blowers) | Create air pressure to move air through system |
| Filters | Clean air before supply |
🔹 10.3 Types of Air Distribution Systems
| Type | Description |
|---|---|
| Constant Air Volume (CAV) | Supplies a constant airflow with varying temperature |
| Variable Air Volume (VAV) | Airflow varies to maintain temperature, more energy-efficient |
| Dual Duct System | One duct for hot air, one for cold, mixed at zone terminal |
| Multi-zone System | Separate ducts for different zones from a central unit |
| Underfloor Air Distribution (UFAD) | Air comes through floor diffusers, used in modern office buildings |
🔹 10.4 Duct Design
🧮 Basic Terms:
CFM (Cubic Feet per Minute): Airflow rate
Velocity (fpm): Speed of air (feet/min)Static Pressure: Resistance to airflow inside ducts
✅ Design Considerations:
Minimize bends and turns
Choose correct duct size (based on velocity and CFM)Proper insulation to reduce heat loss/gain
Sound attenuation (reduce noise)
🔹 10.5 Duct Types and Shapes
| Shape | Advantages |
|---|---|
| Rectangular | Easy to install in tight spaces |
| Round | Less pressure drop, more efficient |
| Oval | Balance between round and rectangular |
| Material | Use Case |
|---|---|
| Galvanized Steel | Common in commercial and residential |
| Aluminum | Lightweight, corrosion-resistant |
| Flexible Duct | Quick installs, less durable |
| Fiberglass | Insulated, absorbs noise |
🔹 10.6 Airflow Patterns
Mixing Type: Supply air mixes with room air (common)Displacement Type: Cool air enters at low velocity near the floor and displaces warm air upwards
🔹 10.7 Balancing Air Distribution
Balancing ensures that each room receives the right amount of air.
Tools used:
Balancing hood
AnemometerFlow meter
Adjust:
Dampers
DiffusersVAV controls
🛠️ Practical Applications
Designing duct layout for a 3-story hospitalRetrofitting old duct system in a heritage building
Using VAV system in a commercial mall
Balancing airflow in open-plan office zones
📄 Assignment Questions
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What are the main components of an air distribution system?
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Compare Constant Air Volume (CAV) and Variable Air Volume (VAV) systems.
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Draw a basic layout of a duct system for a two-bedroom house.
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What is the role of dampers and where are they installed?
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Explain the importance of duct insulation.
💼 Interview Questions
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How do you calculate duct size for a given airflow?
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What is the difference between a diffuser and a grille?
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What problems arise due to unbalanced air distribution?
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Explain the duct static pressure and how it affects the system.
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What are the advantages of round ducts over rectangular ducts?