Introduction to Energy Management. Week/Lesson 10 Air Moving Equipment: Fans and Ducts.
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Transcript of Introduction to Energy Management. Week/Lesson 10 Air Moving Equipment: Fans and Ducts.
![Page 1: Introduction to Energy Management. Week/Lesson 10 Air Moving Equipment: Fans and Ducts.](https://reader035.fdocuments.in/reader035/viewer/2022062805/5697bfe21a28abf838cb4947/html5/thumbnails/1.jpg)
Introduction to Energy Management
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Week/Lesson 10
Air Moving Equipment: Fans and Ducts
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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
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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
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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
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Types of centrifugal fans Forward-curved-very noisy Backward-curved Backward-inclined Air foil
Air Moving Equipment: Fans and Ducts
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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
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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
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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
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Performance characteristics of fans Volume Pressure Horsepower Speed Efficiency
Air Moving Equipment: Fans and Ducts
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Volume (capacity) Amount of airflow through the fan Expressed in cubic feet per minute (cfm)
Pressure Potential and kinetic energy Pt = Ps + Pv (total, static, velocity)
Air Moving Equipment: Fans and Ducts
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Pressure sensing Static, Ps perpendicular to airflow Velocity, Pv parallel to airflow Total, Pt = Static, Ps + Velocity, Pv
Pitot tube
Air Moving Equipment: Fans and Ducts
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Horsepower Brake horsepower Energy required to operate fans
Speed Determines air volume Expressed in rotations per minute (rpm)
Air Moving Equipment: Fans and Ducts
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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
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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
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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
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Duct characteristics – ideal Increase in duct cross section• Velocity pressure drops• Static pressure increases• Total pressure remains constant
Air Moving Equipment: Fans and Ducts
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Duct characteristics – ideal Decrease in duct cross section• Velocity pressure increases• Static pressure drops• Total pressure remains constant
Air Moving Equipment: Fans and Ducts
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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
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Duct design and evaluation CFM = Qs / (1.08 X Δ T) Constant pressure drop method Velocity reduction method Static regain method
Air Moving Equipment: Fans and Ducts
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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
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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.
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Centrifugal Fan Components
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Axial Fan Components
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Axial Fan Components
Vaneaxial fan shown
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Centrifugal Fans - Blade Designs
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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
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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
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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
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Centrifugal - RadialRugged 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).
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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
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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
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Axial Fans - TypesPropeller - 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.
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Axial Fan - Guide VanesFunction - 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.
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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.