1. Objectives Describe room distribution basics Select diffusers
Supply and return duct sizing

2. Pressures Static pressure – pressure not due to velocity
Velocity pressure – pressure due to velocity
Total pressure – sum of above

3. Relationship Between Static and Total Pressure

4. 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

5. System Characteristic

6. Electrical Resistance Analogy

7. Frictional Losses

8. Non-circular Ducts
Parallel concept to wetted perimeter

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

10. Loss Coefficients
ΔPt = CoPv,0

11. ΔPt = CoPv,0

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

13. Conversion Between Methods

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

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

16. Balance Point

17. Fan Performance

18. Centrifugal fans

21. Axial Fans

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

25. Question
How does fan power consumption vary with volumetric air flow rate?

26. Controlling Air Flow

27. Dampers

28. Effect on Fan Curve

29. VAV Operation

30. Duct Layout Overview Layout and select diffusers
Use maximum air flow rates
Locate air handling equipment and do all connections
Space requirements
Aesthetics
Acoustics
Assign fittings

31. Duct Layout (cont.)
Find pressure drop data for all components and duct fittings
Complete rough sizing using either
Equal friction
Static regain method
Complete second sizing
Check sound levels
Access for maintenance

32. Summary Select diffuser based on ADPI Given a layout of duct system
Calculate total pressure drop
Identify fittings contributing most to pressure drop
Deal with non-circular ducts
Use fitting loss coefficient or equal length method
Next class: fans, duct layout, other equipment