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 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

Fan Performance Tables Satwinder Singh - Tag Engineering 3 30/01/2019

Fan Curves STP - standard temperature (70° F) and pressure (29.92 in Hg) with gas density of 0.075 lb/ft 3. Satwinder Singh - Tag Engineering 30/01/2019 4

Fan Laws CFM varies directly with RPM CFM 1 /CFM 2 = RPM 1 /RPM 2 SP varies with the square of the RPM SP 1 /SP 2 = (RPM 1 /RPM 2 ) 2 HP varies with the cube of the RPM HP 1 /HP 2 = (RPM 1 /RPM 2 ) 3 Satwinder Singh - Tag Engineering 30/01/2019 5

Types of Fan 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

Centrifugal Fan Components Satwinder Singh - Tag Engineering 30/01/2019 7

Axial Fan Components Satwinder Singh - Tag Engineering 30/01/2019 8

Van Axial Fan Components Satwinder Singh - Tag Engineering 30/01/2019 9

Axial Fan Components Vane axial fan shown Satwinder Singh - Tag Engineering 30/01/2019 10

Centrifugal Fans - Blade Designs Satwinder Singh - Tag Engineering 30/01/2019 11

Centrifugal – Forward Inclined ▪ 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 Satwinder Singh - Tag Engineering 30/01/2019 12

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 towards free delivery (self- limiting). ▪ Consideration for use in applications where airfoil blade erosion concern Satwinder Singh - Tag Engineering 30/01/2019 13

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 Satwinder Singh - Tag Engineering 30/01/2019 14

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). 30/01/2019 15 Satwinder Singh - Tag Engineering

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 30/01/2019 16 Satwinder Singh - Tag Engineering

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 Satwinder Singh - Tag Engineering 30/01/2019 17

Axial Fans - Types Propeller - generally operate at < 1/2 inch water 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 18 Satwinder Singh - Tag Engineering

Axial Fans - Curves Tube axial Propeller Vane axial Satwinder Singh - Tag Engineering 30/01/2019 19

Fan Curves Source: ASHRAE Handbook Satwinder Singh - Tag Engineering 30/01/2019 20

Generalized Fan Curves These kinds of curves can be used to help choose a fan. Source: Burmeister Satwinder Singh - Tag Engineering 30/01/2019 21

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. Satwinder Singh - Tag Engineering 30/01/2019 22

AMCA Class Definition AMCA 99 - An established minimum performance level for fan aerodynamic performance in terms of pressure and airflow rate. Simply put in general terms - the higher the Class, the greater mechanical strength (and price). Satwinder Singh - Tag Engineering 30/01/2019 23

Gaps/Clearances Ensure gaps and clearances set per Vendor Manual Satwinder Singh - Tag Engineering 30/01/2019 24

Gaps/ Clearances continued Satwinder Singh - Tag Engineering 30/01/2019 25

Centrifugal Fan Vortex The inlet box damper (positioned properly) and both types of inlet vane dampers pre-spin the air in the direction of fan rotation. By creating spin in the direction of fan rotation, the airflow, pressure and horsepower of the fan are reduced, resulting in a new fan performance curve. 30/01/2019 Satwinder Singh - Tag Engineering 26

Fan Laws Satwinder Singh - Tag Engineering 30/01/2019 27

Example-1 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

Fan – Selection Criteria • Air volume required - CFM • System resistance - SP • Air density (Altitude and Temperature) • Type of service • Environment type • Materials/vapors to be exhausted • Operation temperature • Space limitations • Fan type • Drive type (Direct or Belt) • Noise criteria • Number of fans • Discharge • Rotation • Motor position • Expected fan life in years Satwinder Singh - Tag Engineering 30/01/2019 29

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 characteristic change (spin, reduced turbulence) at fan inlet. Satwinder Singh - Tag Engineering 30/01/2019 30

Fans 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

Fans ▪ 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 obstructions, etc.). Satwinder Singh - Tag Engineering 30/01/2019 32

Fan Testing Satwinder Singh - Tag Engineering 30/01/2019 33

AMCA Installation Types Installation Type A: Installation Type C: Free Inlet, Free Outlet Ducted Inlet, Free Outlet Installation Type D: Installation Type B: Free Inlet, Ducted Outlet Ducted Inlet, Ducted Outlet Satwinder Singh - Tag Engineering 30/01/2019 34