1. Objectives
Duct Design AND Diffuser Selection

2. Relationship Between Static and Total Pressure

3. Duct Design
Total and static pressure drops are proportional to square of velocity
Plot of pressure drop vs. volumetric flow rate (or velocity) is called system characteristic

4. System Characteristic

5. Electrical Resistance Analogy

6. Frictional Losses

7. Non-circular Ducts
Parallel concept to wetted perimeter

8. Dynamic losses Losses associated with Two methods
Changes in velocity
Obstructions
Bends
Fittings and transitions
Two methods
Equivalent length and loss coefficients

9. Loss Coefficients
ΔPt = CoPv,0

11. Example 18.7
Determine total pressure drop from 0 to 4

12. Conversion Between Methods

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

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

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

16. 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

17. Low mixing Diffusers Displacement ventilation

20. 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)

21. Find Characteristic Length (L)

22. 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)

23. Ideal and Reasonable Throws

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

25. 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

26. Reading asignement
Chapter 18
(including 18.4)