Fan Design MSYS4480 Fan Definition ASHRAE A fan is an air pump - - PDF document
Fan Design MSYS4480 Fan Definition ASHRAE A fan is an air pump that creates a pressure difference and causes airflow. The impeller does work on the air, imparting to it both static and kinetic energy, which vary in proportion, depending on
MSYS4480
ASHRAE “A fan is an air pump that creates a pressure difference and causes airflow. The impeller does work on the air, imparting to it both static and kinetic energy, which vary in proportion, depending on the fan type.”
2000 ASHRAE Systems and Equipment Handbook Chapter 18
“A fan is used to move air through ducts and to induce air motion in the space.”
Satwinder Singh - Tag Engineering 30/01/2019 2
3 30/01/2019 Satwinder Singh - Tag Engineering
STP - standard temperature (70° F) and pressure (29.92 in Hg) with gas density of 0.075 lb/ft3.
30/01/2019 Satwinder Singh - Tag Engineering 4
30/01/2019
Satwinder Singh - Tag Engineering 5
Two basic types of fan are: ▪ Centrifugal: (Low Pressure / High Volume)
▪ Discharge air perpendicular to the axis of the impeller rotation. ▪ Preferred for higher pressure ducted systems. ▪ Backward Inclined, Airfoil, Forward Curved, & Radial Tip.
▪ Axial: (High Pressure / Low Volume)
▪ Discharges air parallel to the axis of the impeller rotation. ▪ Preferred for high volume, low pressure, and non-ducted systems. ▪ TYPES: Propeller, Tube Axial and Vane Axial.
Satwinder Singh - Tag Engineering 30/01/2019 6
30/01/2019 Satwinder Singh - Tag Engineering 7
Satwinder Singh - Tag Engineering 30/01/2019 8
Satwinder Singh - Tag Engineering 30/01/2019 9
Satwinder Singh - Tag Engineering 30/01/2019 10
Vane axial fan shown
Satwinder Singh - Tag Engineering 30/01/2019 11
▪ 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
30/01/2019 Satwinder Singh - Tag Engineering 12
▪ 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 towards free delivery (self- limiting). ▪ Consideration for use in applications where airfoil blade erosion concern
30/01/2019 Satwinder Singh - Tag Engineering 13
▪ 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
30/01/2019 Satwinder Singh - Tag Engineering 14
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).
30/01/2019 Satwinder Singh - Tag Engineering 15
▪ 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
30/01/2019 Satwinder Singh - Tag Engineering 16
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
30/01/2019 Satwinder Singh - Tag Engineering 17
Propeller - generally
gauge, inefficient, steeply rising power curve (overloading).
Tube axial - propeller
mounted in cylindrical tube, ranges up to ~ 4 inches water gauge, overloading.
Vane axial - utilizes guide
vanes to recover rotational energy, up to 10 inches (single stage), overloading.
30/01/2019 Satwinder Singh - Tag Engineering 18
Propeller Tube axial Vane axial
30/01/2019 Satwinder Singh - Tag Engineering 19
Source: ASHRAE Handbook
30/01/2019 Satwinder Singh - Tag Engineering 20
These kinds of curves can be used to help choose a fan.
Satwinder Singh - Tag Engineering 30/01/2019 21
Source: Burmeister
Satwinder Singh - Tag Engineering 30/01/2019 22
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.
Satwinder Singh - Tag Engineering 30/01/2019 23
Definition AMCA 99 - An established minimum performance level for fan aerodynamic performance in terms
Simply put in general terms - the higher the Class, the greater mechanical strength (and price).
Satwinder Singh - Tag Engineering 30/01/2019 24
Ensure gaps and clearances set per Vendor Manual
Satwinder Singh - Tag Engineering 30/01/2019 25
The inlet box damper (positioned properly) and both types of inlet vane dampers pre-spin the air in the direction of fan
in the direction of fan rotation, the airflow, pressure and horsepower
resulting in a new fan performance curve.
30/01/2019 Satwinder Singh - Tag Engineering 26
Satwinder Singh - Tag Engineering 30/01/2019 27
A centrifugal fan is operating as shown below at point 1. Estimate the capacity, total pressure, and power requirement when the speed is increased to 1050 rpm. The initial power requirement is 2 hp.
30/01/2019 Satwinder Singh - Tag Engineering 28
Satwinder Singh - Tag Engineering 30/01/2019 29
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 characteristic change (spin, reduced turbulence) at fan inlet.
30/01/2019 Satwinder Singh - Tag Engineering 30
A fan is a constant volume machine. For a fixed speed, the fan will move the same volume of gas irregardless of gas density.
Satwinder Singh - Tag Engineering 30/01/2019 31
▪ Most manufacturer’s rate the fan based upon tests conducted using AMCA 210. ▪ Testing uses ideal configurations (i.e straight duct runs, 10 duct diameters, no
30/01/2019 Satwinder Singh - Tag Engineering 32
30/01/2019 33
Satwinder Singh - Tag Engineering
Installation Type A: Free Inlet, Free Outlet Installation Type B: Free Inlet, Ducted Outlet Installation Type C: Ducted Inlet, Free Outlet Installation Type D: Ducted Inlet, Ducted Outlet
30/01/2019 Satwinder Singh - Tag Engineering 34