Chapter 8: Air Distribution Systems

 

Chapter 8: Air Distribution Systems

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🔹 8.1 What is Air Distribution?

Air Distribution* is the process of delivering conditioned air (cooled or heated) to different parts of a building evenly and efficiently using ducts, diffusers, grilles, and fans.

It ensures:

Proper room temperature

Uniform airflow
Ventilation and IAQ
Energy efficiency

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🔹 8.2 Components of an Air Distribution System

Component	Function
Ducts	Channels that carry air from HVAC unit to different rooms
Diffusers	Distribute air evenly across room surfaces
Grilles/Registers	Return or supply air through walls, floors, or ceilings
Dampers	Control air volume in ducts
Fans/Blowers	Push air into ducts (supply) or pull air out (return/exhaust)
Plenums	Central chambers where air is gathered before distribution

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🔹 8.3 Types of Duct Systems

Type	Description
Single Duct System	Most common; one duct carries air to all zones
Dual Duct System	Separate ducts for hot and cold air; mixed at terminal
VAV (Variable Air Volume)	Airflow volume is adjusted to maintain set temperature
CAV (Constant Air Volume)	Airflow is fixed; temperature is varied
Underfloor Air Distribution (UFAD)	Air is supplied through raised floors

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🔹 8.4 Types of Ducts by Shape and Material

✅ By Shape:

Rectangular – Common in commercial buildings

Round – More energy efficient
Oval – Hybrid of both

✅ By Material:

Material	Used For
Galvanized Steel	Common in HVAC; durable
Aluminum	Lightweight and corrosion-resistant
Fabric	Temporary or spot cooling systems
Flexible Ducts	Short runs in tight spaces

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🔹 8.5 Duct Design Principles (SMACNA Standards)

1. Friction Loss Control – Sizing to minimize resistance

2. Noise Reduction – Smooth bends, acoustic insulation

3. Air Balancing – Dampers & VAV boxes to balance airflow

4. Leakage Prevention – Proper sealing, duct mastic/tape

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🔹 8.6 Diffusers, Grilles, and Registers

Device	Function
Supply Diffuser	Delivers air into room; directs airflow
Return Grille	Pulls air back into ductwork
Registers	Combination of grille + damper

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🔹 8.7 Air Balancing and Zoning

Air Balancing: Adjusting dampers and controls to ensure all rooms receive proper air quantity.

Zoning: Dividing the building into separate zones with individual controls for temperature & airflow.

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🔹 8.8 Static Pressure and Fan Selection

Static Pressure: Resistance in ductwork due to bends, length, filters

Fans must overcome static pressure to maintain proper airflow

Use Fan Laws to calculate:

$$Q_2=Q_1\times \left(\frac{RP{M}_2}{RP{M}_1}\right)$$ $$P_2=P_1\times {\left(\frac{RP{M}_2}{RP{M}_1}\right)}^2$$

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🔹 8.9 Duct Insulation

Thermal Insulation: Prevents heat gain/loss

Acoustic Insulation: Reduces noise

Use insulation in:

• Outdoor ducts

• Unconditioned spaces (e.g., basements, attics)

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🔹 8.10 Common Problems in Air Distribution

Problem	Cause
Uneven cooling/heating	Poor balancing or duct design
Noise from vents	Undersized ducts or sharp turns
Low airflow	Dirty filters or clogged ducts
Duct leakage	Poor sealing or damaged ducts

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🛠️ Practical Applications

• Design ductwork layout using AutoCAD or Revit

• Calculate required air flow for each room

• Use anemometers to test velocity from diffusers

• Seal ducts using proper mastic or UL-rated tape

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📄 Assignment Questions

1. Explain the importance of duct design in HVAC.

2. What are the types of air distribution systems?

3. Differentiate between CAV and VAV systems.

4. What is the role of dampers in ductwork?

5. List the causes and solutions of uneven air distribution.

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💼 Interview Questions

1. What factors influence duct sizing?

2. What is static pressure and why is it important?

3. How do you balance airflow in a multi-zone building?

4. Which material is best suited for flexible ducting?

5. Describe the process of designing a duct layout for a hospital.