1. Introduction to Energy Management

2. Week/Lesson 10 Air Moving Equipment: Fans and Ducts

3. After completing this chapter, you will be able to:  State how fans add kinetic and potential energy to air  Identify features and drive arrangements of centrifugal fans  Identify the features of axial fans Air Moving Equipment: Fans and Ducts

4.  Explain fan performance characteristics including pressure, flow rate, horsepower, efficiency and speed  Use a fan’s performance tables to check a fan’s capability  Evaluate pressure changes within a duct system Air Moving Equipment: Fans and Ducts

5. Fan basics  Centrifugal fans Force air in a direction perpendicular to the motor shaft  Axial fans Force air in a direction parallel to motor shaft Air Moving Equipment: Fans and Ducts

6. Types of centrifugal fans  Forward-curved-very noisy  Backward-curved  Backward-inclined  Air foil Air Moving Equipment: Fans and Ducts

7. Centrifugal drive arrangements  Air movement and control association  Single or double width  Single or double inlet  Direct connection  Belt and pulley connection Air Moving Equipment: Fans and Ducts

8. Tubular and roof ventilator centrifugal fans  Tubular Straight line air flow Fan mounted transversely in the housing  Roof ventilators Packaged units Air Moving Equipment: Fans and Ducts

9. Types of axial fans  Propeller Move large volumes of air Create very small pressure increases  Tube axial Propeller mounted in a tube  Vaneaxial – low air turbulence Air Moving Equipment: Fans and Ducts

10. Performance characteristics of fans  Volume  Pressure  Horsepower  Speed  Efficiency Air Moving Equipment: Fans and Ducts

11. Volume (capacity)  Amount of airflow through the fan  Expressed in cubic feet per minute (cfm) Pressure  Potential and kinetic energy  P t = P s + P v (total, static, velocity) Air Moving Equipment: Fans and Ducts

12. Pressure sensing  Static, P s  perpendicular to airflow  Velocity, P v  parallel to airflow  Total, P t = Static, P s + Velocity, P v  Pitot tube Air Moving Equipment: Fans and Ducts

13. Horsepower  Brake horsepower  Energy required to operate fans Speed  Determines air volume  Expressed in rotations per minute (rpm) Air Moving Equipment: Fans and Ducts

14. Efficiency  Ratio of output to input  Input is greater than output  Friction losses effect efficiency  Low friction losses  high efficiency Air Moving Equipment: Fans and Ducts

15. Performance tables and curves for fans  Compilation of fan characteristics  Often called multi-rating tables  Helps designers evaluate fan choices  Horsepower, efficiency and pressure Air Moving Equipment: Fans and Ducts

16. Describing air flow in ducts  Continuity principle Q = V x A Conservation of air mass  Air velocity changes with duct size  Larger ducts  lower air velocity Air Moving Equipment: Fans and Ducts

17. Duct characteristics – ideal  Increase in duct cross section Velocity pressure drops Static pressure increases Total pressure remains constant Air Moving Equipment: Fans and Ducts

18. Duct characteristics – ideal  Decrease in duct cross section Velocity pressure increases Static pressure drops Total pressure remains constant Air Moving Equipment: Fans and Ducts

19. Duct characteristics – actual  Friction causes pressure drops  Larger ducts  lower pressure drops  Lower velocity  lower pressure drops  Turbulence causes pressure drops  Static pressure drops as air flows Air Moving Equipment: Fans and Ducts

20. Duct design and evaluation  CFM = Q s / (1.08 X Δ T)  Constant pressure drop method  Velocity reduction method  Static regain method Air Moving Equipment: Fans and Ducts

21. System performance and fan selection  Airflow varies, duct system is fixed  Friction increases at the square of flow rate  System characteristic curve  Operation point  fan selection Air Moving Equipment: Fans and Ducts

22. Types of Fan Demo Two basic types of fan are: Centrifugal - rotating impeller to increase velocity of an airstream. Axial - air is pressurized by the aerodynamic lift of the fan blade.

23. Centrifugal Fan Components

24. Axial Fan Components

25. Vaneaxial fan shown

26. Centrifugal Fans - Blade Designs

27. Centrifugal - Airfoil Blade curves away from direction of rotation Highest efficiency Relatively low noise High structural strength Power reaches max near peak efficiency, then reduces twoards free delivery (self-limiting). For given duty, has highest speed of centrifugal design

28. Centrifugal - Backward Inclined Efficiency slightly less than airfoil design Pronounced region of instability where low efficiency and pulsations (stall, surge, bi- stable flow) Power reaches max near peak efficiency, then reduces t0wards free delivery (self- limiting). Consideration for use in applications where airfoil blade erosion concern

29. Centrifugal - Backward Curved Power reduces towards free delivery (self-limiting). Promote smoother flow than BI fan Operate at higher speeds and therefore require sturdier construction than FC Less susceptible to flow/fan instabilities due to less pronounced instability region

30. Centrifugal - Radial Rugged blade design, self-cleaning Lowest efficiency centrifugal Used for material handling due to blade strength Moderate to high pressure industrial applications Power rises continually to free delivery (overloading).

31. Centrifugal - Radial Tip Blade is radial at outer edge of wheel, curved in direction of flow as it moves inward More efficient than Radial blade Used for mildly erosive environments Higher pressure than Airfoil

32. Centrifugal - Forward Curved Also called “ Squirrel Cage ” Blade curved forward in direction of rotation Low pressure HVAC applications (residential, etc.) Lower speed than other centrifugals Single thickness blade, lightweight construction

33. Axial Fans - Types Propeller - generally operate at < 1/2 inch water gauge, inefficient, steeply rising power curve (overloading). Tubeaxial - propeller mounted in cylindrical tube, ranges up to ~ 4 inches water gauge, overloading. Vaneaxial - utilizes guide vanes to recover rotational energy, up to 10 inches (single stage), overloading.

34. Axial Fan - Guide Vanes Function - reduce the helical flow pattern of the fan. Inlet - vanes guide airflow into a rotational pattern opposite to fan rotation to provide neutralize deflection by blades and result in axial flow Outlet - vanes take rotational pattern from blades and redirects it to an axial flow, converting some rotational velocity into static pressure.

35. Centrifugal Fan Volume Control Generally 3 methods: Variable speed – changing fan speed results in a change in fan flow. Outlet damper – functions by changing system resistance, forcing the fan to operate against higher backpressure and reducing the flow. Inlet damper – combination of resistance change and potential flow characterisitic change (spin, reduced turbulence) at fan inlet.