Fire Protection Plumbing Quick Reference Guide

Introduction to Air Distribution

Space air distribution systems are designed to deliver conditioned air throughout a space to create comfortable and uniform environmental conditions in the occupied zone.

Primary Goals

Maintain thermal comfort
Ensure good indoor air quality
Provide energy-efficient operation
Minimize drafts and noise

Key Conversion Factors

Air Volume: L/s = CFM × 0.4719

Pressure: Pa = inches of water × 249

System Classification

1. Mixing Systems

Conditioned air is supplied at high velocities to promote mixing with room air, creating uniform conditions.

Key characteristic: High-velocity jets that entrain room air

2. Displacement Systems

Conditioned air is supplied at low velocities from floor level, rising as it warms from heat sources.

Key characteristic: Thermal stratification with cooler air at floor level

3. Localized Systems

Conditioning is provided to specific areas rather than the entire space.

Applications: Spot cooling, task conditioning

Mixing System Outlet Groups

Group A: Ceiling, Horizontal Flow

Mounted in or near ceiling
Discharge air horizontally
Excellent for cooling applications
Examples: Square diffusers, linear bar grilles

Group B: Floor, Vertical Non-Spreading

Mounted in or near floor
Discharge air vertically in narrow jet
Creates stagnant zones outside conditioned area

Group C: Floor, Vertical Spreading

Similar to Group B but with wide-spreading jet
Larger stagnant zone during cooling
Smaller stagnant zone during heating

Group D: Floor, Horizontal Flow

Mounted in or near floor
Discharge air horizontally
Poor for cooling (large upper stagnant zone)
Good for heating (warm air rises naturally)

Group E: Ceiling, Vertical Flow

Mounted in or near ceiling
Project air vertically downward
Critical that air reaches floor during cooling

Specialized Distribution Systems

Underfloor Air Distribution (UFAD)

Air supplied through raised floor plenum
Typical supply temperature: 14°C to 18°C
Excellent flexibility for office layouts
Energy efficient due to higher supply temperature

Displacement Ventilation

Low-velocity supply (≤ 0.5 m/s) at floor level
Returns located at or near ceiling
Creates thermal stratification
Excellent indoor air quality
Energy efficient operation

Critical Environment Systems

HEPA/ULPA filtration
Laminar flow patterns
Applications: Hospitals, cleanrooms, laboratories

Performance Considerations

Heating vs. Cooling Performance

Outlet performance is not symmetric. An outlet perfect for cooling may be inefficient for heating due to natural convection patterns.

Selection Criteria

Primary operation mode (heating vs. cooling)
Ceiling height and space geometry
Thermal load characteristics
Indoor air quality requirements
Architectural constraints

Design Principles

Avoid stagnant zones in occupied areas
Prevent draft conditions
Match return location to supply type
Consider throw distance and drop

Comparison of System Types

Feature	Mixing Systems	Displacement Systems
Supply Velocity	High	Low (≤ 0.5 m/s)
Temperature Stratification	Minimal	Significant
Air Change Effectiveness	Moderate (≈ 1.0)	High (1.2 - 1.5)
Energy Efficiency	Standard	High
Ideal Applications	General comfort cooling	Spaces with high air quality needs

Key Design Insight

The selection of air distribution system is as important as the selection of the HVAC equipment itself. Proper air distribution ensures comfort, air quality, and energy efficiency.