1. Objectives Finish with Duct Design Diffuser Selection
Review the design procedure and explain the theoretical background
Diffuser Selection

2. Frictional Losses

3. Dynamic losses Losses associated with Changes in velocity Obstructions
Bends
Fittings and transitions

5. Air Distribution System Design
Describe room distribution basics
Select diffusers
Supply and return duct sizing

6. Forced driven air flow Diffusers
Grill (side wall)
diffusers
Linear diffusers
Vertical
Horizontal one side

7. Diffusers types Valve diffuser swirl diffusers ceiling diffuser
wall or ceiling
floor

8. Diffusers http://www.titus-hvac.com/techzone/
Perforated ceiling diffuser
Jet nozzle diffuser
Round conical ceiling diffuser
Square conical ceiling diffuser
Wall diffuser unit
Swirl diffuser
Floor diffuser
Auditorium diffuser
Linear slot diffuser
DV diffuser
External louvre
Smoke damper

9. Low mixing Diffusers Displacement ventilation

12. Diffuser Selection Procedure
Select and locate diffusers, divide airflow amongst diffusers
V = maximum volumetric flow rate (m3/s, ft3/min)
Qtot = total design load (W, BTU/hr)
Qsen = sensible design load (W, BTU/hr)
ρ = air density (kg/m3, lbm/ft3)
Δt = temperature difference between supply and return air (°C, °F)
Δh = enthalpy difference between supply and return air (J/kg, BTU/lbm)

13. Find Characteristic Length (L)

14. Indicator of Air Distribution Quality
ADPI = air distribution performance index
Fraction of locations that meet criteria:
-3 °F < EDT < 2 °F or -1.5 °C < EDT < 1 °C
Where, EDT = effective draft temperature
Function of V and Δt (Eqn 18.1)
EDT=(tlocal-taverage)-M(Vlocal-Vaverage) , M=7 °C/(m/s)
ADPI considers ONLY thermal comfort (not IAQ)

15. Ideal and Reasonable Throws

16. Diffuser testing

17. ADPI

18. Select Register Pick throw, volumetric flow from register catalog
Check noise, pressure drop

19. Summary of Diffuser Design Procedure
Find Q sensible total for the space
Select type and number of diffusers
Find V for each diffuser
Find characteristic length
Select the diffuser from the manufacturer data

20. Fans Driving force to move air in buildings
Raise pressure and produce flow
Two main types:
Centrifugal
Axial

21. Relevant Fan Parameters
Total pressure rise
Static pressure rise
Power requirement
Efficiency
Note ηtot does not account for motor efficiency

22. Balance Point

23. Fan Performance

24. Centrifugal fans

27. Axial Fans

30. Fan Laws “Approximate relationships”
Given two aerodynamically similar fans, can extrapolate performance data
Be very careful