Ventilation & Air Distribution
Ductwork design, airflow measurement, air handling units, filters, building codes, and indoor air quality.
- Describe ductwork design principles and sizing methods
- Explain airflow measurement techniques and system balancing
- Identify air handling unit components and indoor air quality requirements
Leçon 1
Ductwork Design & Sizing
Duct System Purpose
The duct system distributes conditioned air from the HVAC equipment to the occupied spaces and returns air back to the equipment. A properly designed duct system delivers the right amount of air at the right velocity to each space.
Duct Sizing Methods
| Method | Description | Best For |
|---|---|---|
| Equal friction | Same pressure drop per unit length | Most residential and commercial |
| Static regain | Velocity decreases to regain static pressure | Large commercial systems |
| Velocity reduction | Velocity decreased at each branch | Simple systems |
Duct Types
- Rectangular - most common in commercial, easy to fabricate
- Round - lowest friction loss per unit area, best for air flow
- Flexible - used for short connections to diffusers
- Fiberglass board - insulated, used for low-pressure systems
Fittings and Pressure Loss
Duct fittings (elbows, tees, transitions) create more pressure loss than straight duct. Reducing these losses is critical:
- Use turning vanes in rectangular elbows to reduce turbulence
- Keep duct connections smooth - avoid sharp transitions
- Minimize the number of fittings in the system
- Use equivalent length to account for fitting losses in design
Round vs. Rectangular
Round duct has lower friction loss for the same airflow because it has the most favorable perimeter-to-area ratio. It also handles higher pressures better. However, rectangular duct fits better in tight ceiling spaces.
Equal friction is the most common duct sizing method - maintaining consistent pressure drop per unit length. Round duct has the lowest friction loss per unit area. Use turning vanes in rectangular elbows and minimize fittings to reduce system pressure loss.