Announcement
Course Exam
October 11th (Tuesday)
In class: 90 minutes long
Examples are posted on the course
website
Objectives
• Duct Design and Diffuser Selection
• Reading assignment: thextbook Chapter 18
Duct design
(part of the HVAC Design successfully integrated into BIM)
Pressures
• Static pressure
• Velocity pressure
• Total pressure – sum of the two above
Relationship Between Static and Total Pressure

2
2
 V1  V2
Pt  Ps 
2

Duct design method
(defines the layout)
Two design methods:
- Equal friction
- Static regain
System Characteristic
Duct Design
• Static pressure drop (friction losses) in a duct is
proportional to square of velocity or flow
L V2
Ps  f 
D 2
It is a function of
- Dynamic pressure
- Length
- Pipe diameter
- Friction coefficient
Frictional Losses
(in a staring round duct section)
Ductulator
Non-circular Ducts
• Parallel concept to wetted perimeter
Dynamic (or local) losses
• Losses associated with
•
•
•
•
Changes in velocity
Obstructions
Bends
Fittings and transitions
• Two methods
• Equivalent length and loss coefficients
Dynamics (Local) Loss
Coefficients
ΔPt = CoPdynamic
Conversion Between Methods
Leq V 2
V2
P  C0 
 f

2
D
2
D
Leq  C0
f
Example 18.7
• Determine total pressure drop from 0 to 4
Diffuser selection
• Defines thermal comfort
• Air quality
Forced driven air flow
Diffusers
Linear diffusers
Vertical
Horizontal one side
Grill (side wall)
diffusers
Diffusers types
Valve diffuser
swirl diffusers
wall or ceiling
floor
ceiling diffuser
Diffusers
Perforated ceiling diffuser
Wall diffuser unit
Linear slot diffuser
Jet nozzle diffuser
Swirl diffuser
DV diffuser
Round conical ceiling diffuser
Floor diffuser
External louvre
http://www.titus-hvac.com/techzone/
http://www.halton.com/halton/cms.nsf/www/diffusers
Square conical ceiling diffuser
Auditorium diffuser
Smoke damper
Low mixing Diffusers
Displacement ventilation