Science
Chapter 8 AMCA Fan Selection and Operation Research Paper

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Study Guide Chapter 8: Fan Selection and Operation ©Miaozong Wu Read textbook chapter 8, and make sure you understand the following questions and the body of knowledge (BOK). 1. Fan functions and types:  Ch5: LEV components ‐ Fan function (SP & air movement)  Fan basic components (p8‐1): electric motor, fan blade, housing, air inlet and outlet, etc.  Fan types:  Axial fan: used for higher flow, lower SP systems  Propeller‐type blades  Tube axial  Vane axial  Centrifugal fan: used for lower flows and higher SP system  Radial impeller: LEV; rugged but low efficiency.  Backward‐inclined fans: LEV; less rugged but flat hp  Forward‐curved (squirrel cage): quiet but not rugged 2. Pressure: ABIH: FTP = TPoutlet – TPinlet; FSP = SPout – SPin – Vpin  Positive or negative pressure:  at the upstream of fan is _____, and at the downstream of fan is _____.  on the back side of blade is ____, and on the forward side of blade is _____.  on the inlet of fan (LEV) is ____, and on the inlet of fan (LEV) is _____.  FTP:  Represents all energy requirements for moving air through the ventilation system.  FTP = TPoutlet – TPinlet , different from TP = SP + VP (at a point)  Fan total SP drop (FTP) = (SPout+VPout) – (SPin+VPin) = SPout – SPin (when VPin = VPout) Practice: Exercise 8‐1  FSP:  FSP = SPout – SPin – Vpin, because of FSP = FTP – VPin  Represents the system losses (the amount of static pressure converted to useless heat or noise): FSP = SPout – SPin – Vpin = Fan total SP drop ‐ Vpin Practice: Exercise 8‐2 Updated on Apr 2020 (©Miaozong Wu) 1 3. Fan curve vs system curve:  Fan RPM (revolutions per minute) can be adjusted  Measure SP and Q on fan only (Fan curve) or on the duct system (system curve)  Under AMCA rules, fans are tested under ideal conditions (air enters and leaves the fan wheel in the smooth, uniform, balanced manner) and given the rated capacity.  To prevent the system effect loss occurring when fan operated under non ideal condition, the length of straight duct needs to be “six in and three out” of duct diameters.  Measure pressure (VP, SP and/or SP) and V at about _____ duct diameters downstream, and ____ duct diameters upstream from any non‐straight section point (page 7‐3).  Measure SP at _____ duct diameters downstream from the hood (p 6‐2). 4. Fan laws: ொଶ ௗଶ ோ௉ெଶ 1 ABIH equations: = ( )3 * ( ) ; ொଵ ௗଵ ோ௉ெଵ ௉௥௘௦௦௨௥௘ଶ ௉௥௘௦௦௨௥௘ଵ ௗଶ = ( )2 * ( ௗଵ ோ௉ெଶ 2 ) ; ோ௉ெଵ ௉ௐோଶ ௉ௐோଵ ௗଶ = ( )5 * ( ௗଵ ோ௉ெଶ 3 ) ோ௉ெଵ  Q, pressure (SP) and power are related to fan impeller/ wheel diameter (d) and fan speed.  Avoid running the fan at a speed above 10% of rated rpm: change SP and overload motor Practice: If you run the fan at a speed above 10% of rated rpm, how will Q, SP and power change. Assume the fan wheel diameter remain the same. Solutions: RPM2/RPM1 = (100%+10%)/(100%) = 1.1 ொଶ ௗଶ ோ௉ெଶ = ( )3 * ( ) =1.1 (+10%) ொଵ ௗଵ ோ௉ெଵ Updated on Apr 2020 (©Miaozong Wu) 2 ௉௥௘௦௦௨௥௘ଶ ோ௉ெଶ 2 ) = 1.1^2 = 1.21 (+21%) ௉௥௘௦௦௨௥௘ଵ ௗଵ ோ௉ெଵ ௉ௐோଶ ௗଶ 5 ோ௉ெଶ 3 =( ) *( ) = 1.1^3 = 1.33 (+33%) ௉ௐோଵ ௗଵ ோ௉ெଵ  If d2 =d1: ொଶ ொଵ ௗଶ = ( )2 * ( =( ோ௉ெଶ ௉௥௘௦௦௨௥௘ଶ ோ௉ெଵ ௉௥௘௦௦௨௥௘ଵ ); ொଶ ௉ௐோଶ ொଵ ௉ௐோଵ = ( ) 2; ொଶ =( )3 ொଵ Practice: Exercise 8‐8 to 8‐9 5. Fan power:  aph (Air horsepower): the minimum power to move Q against FTP  bhp (Brake horsepower): also consider the fan loss (up to 75% power; radial fan efficiency = ~60%), so it is the actual power fan needs. bph = aph / fan efficiency  shp (Shaft horsepower): represent all powers needed. sph = bph * Kdl (1.05, 1.1 or 1.3)  rhp (Rated horsepower): marked on fan nameplate  Apply 33% power / 10% rpm when motor ≤ 25 hp: order a fan with rhp > 1.33 shp Note: this material is developed by Miaozong Wu, Ph.D. CSP, ARMTM, especially for 4160/5160 course. Under copyright, you must not distribute it to any other individual or parties (including posting it online), without a permission from the developer. Updated on Apr 2020 (©Miaozong Wu) 3 • When selecting a fan for ventilation system, why should you know about AMCA? • What are the functions of fan? • Use your own words to briefly describe the advantages and disadvantages of radial, forward- and backward-inclined fans, if you want to use them in LEV system. • Please indicate the positive (+) or negative (-) pressure: Static pressure at the upstream of fan is _____, and at downstream of fan is _____. Pressure on the back side of blade is ____, and on the forward side of blade is _____. Static pressure on the inlet of fan (LEV) is ____, and on the inlet of fan (LEV) is _____. • Why can FSP represent the system losses (p 8-4)? • The inlet of fan has SP of -5 "w.g. and VP of 2 "w.g., while the outlet of fan has SP of +1 "w.g. and VP of 2 "w.g. Show your calculation for FTP and FSP. • Why shouldn't you have the fan running on the "backside" of fan curve (that is, not run on the left of the peak SP, but on the steep part of the curve)? • 1) Why should you avoid running the fan at a speed above 10% of rated rpm (that is at 110% rated rpm)? 2) Please calculate the % of changes in power (assume fan wheel diameter remains the same) if RPM increases 10%. • According to the six in and three out rule, what are the lengths of straight duct that should be provided into and out of a fan which will be connected to 10" round ductwork? You need to specify which duct into or out of the fan for full credit • You are designing a ventilation system with the following parameters. What is the required shaft horsepower (sph) for the ventilation system, and what rated power motor (rhp) would you like to choose? FTP = 15.0 inch w.g.; Q = 1,300 scfm; ME = fan efficiency = 0.65; Kdl = 1.05; STP (d = 1); c = 6356. https://www.cincinnatifan.com/manuals/HowToSelectAFanOrBlower.pdf INSTRUCTIONS FOR HOW TO PROPERLY SELECT A FAN OR BLOWER The instructions that follow are to assist you in completing the information required when making a fan or blower selection. If you need additional assistance, please contact our local Cincinnati Fan sales engineer for your area. To locate the Cincinnati Fan sales engineer for your area, go to: www.cincinnatifan.com/rep-lookup.htm Individual product catalogs and our Engineering Data catalog can found at: www.cincinnatifan.com/product-catalogs.htm Thank you for choosing Cincinnati Fan Page 1 of 5 How To Properly Select a Fan or Blower Steps 1. Choose fan type ___ Centrifugal blower ___ Axial flow fan 2. Total airflow ____________ ACFM 3. Static Pressure ________ in. SPWG Explanation A centrifugal blower wheel draws air into the inlet of the blower housing, through the wheel, and discharges it at 90° out through the discharge of the blower housing. An axial fan uses a propeller to draw the air into the fan and discharges the air in the same axial direction. A centrifugal blower housing has a "scroll" whereas a axial fan is an "in-line duct type" fan or a "wall" fan. Do not use an axial flow fan to convey material. There is a variation of axial flow duct fan that uses a blower wheel instead of a propeller. It is referred to as a Tubular Centrifugal. We do not make any tubular centrifugal fans at Cincinnati Fan. Airflow is rated in cubic feet of air per minute (CFM) or in metric equivalent, it is rated in cubic meters per hour (M³/Hr). To convert M³ /Hr to CFM multiply your M³ /Hr x .58858 If you will be conveying material, make sure you have enough CFM for the duct, pipe or hose size so the material will maintain the required velocity to carry it completely through the system and not settle in the duct, pipe or hose. See STEP 2 on page 4. Static Pressure is the resistance to airflow (friction) caused by the air moving through a pipe, duct, hose, filter, hood slots, air control dampers or louvers. Static pressure is rated in inches of water gauge (SPWG) or in metric equivalent, it is rated in Pascal's (Pa). This should include the pressure drop through all of the ductwork on the inlet and outlet of the fan or blower plus the pressure drop through any filters, control dampers, louvers and other system components that restrict airflow. 1 Pa = .004 inches SPWG NOTE: If the static pressure on the inlet side of a blower will exceed 15" SPWG, a correction for suction pressure (called Rarefication) should be made. See Static Pressure Corrections For Suction Pressure in STEP 3 on page 4. Density, Altitude and Temperature Corrections Please contact our sales office for your area if you are not comfortable with making the corrections in the following steps. They will be more than happy to assist you. http://www.cincinnatifan.com/rep-lookup.htm 4. Density _________ @ Standard Conditions 5. Air Temperature _________° F. _______° F to ______° F 6. Altitude _________ Feet above sea level Standard air is based on a temperature of 70° F., 29.92" barometric pressure and .075 pounds per cubic foot. Density changes resulting from temperature and/or barometric pressure variations, such as higher altitudes, must be corrected to standard conditions before selecting a fan or blower based on standard performance data. If your density is in kilograms per cubic meter (kg/m³), make the following correction: 1 kg/m³ = .0624 lb/ft³ For Altitude and Temperature Correction Factors, see STEP 4 on page 5. NOTE: If you make the correction for density, you do not need to show the temperature and altitude in Steps 5 and 6 below. If the fan or blower will be handling a gas or vapor with a density that is less or greater than standard air, contact our sales office for your area for fan sizing assistance. The temperature of the air going through the fan or blower will affect the performance of the fan or blower. Temperature should be shown in degrees Fahrenheit (F). Make the following correction for degrees Centigrade (C). °F = 1.8 x °C + 32 If the air temperature will vary, what are the minimum and maximum temperatures in degrees F? The altitude the fan or blower will be operating at will also affect the performance of the fan or blower. The altitude should be given in feet above sea level. Continue onto next page for Steps 7, 8 and 9 regarding Fan or Blower Construction. Page 2 of 5 Special Conditions That May Affect A Fan Or Blower Construction 7. Material Handling □ YES □ NO □ YES □ NO □G □P □ YES □ NO □ YES □ NO □ YES □ NO Will you be conveying any material through the fan or blower or will it be clean air? Clean air? (If YES, move on to Step 8 below). Dirty air? (Only a fan or blower with a Radial type wheel should be used) If dirty air, the four models below come with radial type wheels: Model PB Cast Aluminum Blowers at: www.cincinnatifan.com/centrifugal-pb.htm Model PBS Fabricated Steel Blowers at: www.cincinnatifan.com/centrifugal-pbs.htm Model SPB Die Formed Steel Blowers at: www.cincinnatifan.com/centrifugal-spb.htm Model RBE Radial Blade Exhauster at: www.cincinnatifan.com/centrifugal-rbe.htm If dirty, is material granular (G) or powdery (P)? (A Shrouded or Non-Shrouded Radial wheel can be used) If dirty, is material long and stringy like paper trim or fibers? (Use only a Non-Shrouded Radial wheel) For any material, will the material be wet or moist? For any material, will the material be dry? _________ lbs./cu ft. If conveying material, what is the weight of the material in pounds per cubic foot ? _________ lbs./hr. If conveying material, how many pounds will you be conveying in pounds per hour ? 8. Ambient Temperature _________° F. _______° F to ______° F 9. Safety Conditions □ YES □ NO □ YES □ NO Class: ____________ Groups: ____________ AMCA Type: _______ The ambient temperature is the temperature of the air outside the fan or blower. This can affect the operation of the motor and the fan bearings and/or belts for any belt driven fans or blowers. If the outside air temperature will vary, what are the minimum and maximum temperatures in degrees F? Is there anything going through the fan or blower or outside the fan or blower that is explosive and/or flammable? Will the airstream of the fan or blower be explosive or flammable? Will the area outside the fan or blower be explosive or flammable? If you checked YES for either of the above, what Class and Groups of Explosion Proof (EXP) motor will you require? If you checked YES for either of the above, what AMCA Type spark resistant construction will you require? (AMCA Type A, B or C?) WARNING All fans and blowers have rotating parts and pinch points. Severe personal injury can result if operated without OSHA required guards. Stay away from rotating equipment unless it is disconnected or properly locked out from it's power source. Read all operating instructions prior to installing, inspecting, moving, performing maintenance or operating any fan or blower equipment. Page 3 of 5 STEP 2 . Total Airflow (CFM): STEP 3 . Static Pressure (SP): Selecting the proper airflow (CFM) for your system can be very critical. If you will be exhausting contaminated air such as engine exhaust fumes, not having enough CFM can lead to asphyxiation and even an explosion. If you will be conveying material such as wood chips, too low a CFM will allow the chips to settle somewhere in the system thus clogging the duct, pipe or hose. That leads to down time to disassemble the ducting to clean it out. Too much CFM can cause a blow out in the system. The correct CFM must take the material conveying velocity into consideration for the material you are wanting to move to another location. The Total Static Pressure for your system must include the static pressure of the total airflow (CFM) moving through the entire system. This should include the static pressure of the CFM going through ducting, piping, hose, filters, hood slots, airflow control dampers and louvers. To select the correct static pressure through smooth wall pipe or duct you will need to refer to pages 11 and 12 in the: Cincinnati Fan Engineering Data catalog. It will show you the friction loss per 100 feet of duct or pipe for the total CFM for your system. Now, add the additional static pressure loss for any dampers, filters, etc. for the Total Static Pressure. SCFM and ACFM (SCFM and ACFM are not interchangeable) Static Pressure Correction For Suction Pressure: SCFM stands for Standard Cubic Feet per Minute. It is the total CFM at standard density conditions. These are the CFM values typically listed in fan manufacturers catalogs. When a large amount of static pressure is on the inlet of a blower, it requires additional suction to move the air. That is because it is easier to blow air than it is to suck air. This is called Rarefication . If you have more than 15" SP on the blower inlet, you need to correct f for suction pressure per the chart below. If you also have to make corrections for altitude and/or temperature, make them first and then correct for Rarefication. ACFM stands for Actual Cubic Feet per Minute. It is the mass flow rate divided by the density of the air or gas being moved. Since fans and blowers handle the same volume of air at any density, the ACFM value should be used when selecting a fan or blower. The total airflow (SCFM) should also meet or exceed the minimum CFM required by any regulating authorities for the application. This sometimes only requires you to meet the minimum CFM as recommended by a "standards" organization. If you are not sure how much CFM will be required for your specific application, do not hesitate to contact our Cincinnati Fan sales engineer for your area. They will be very happy to assist you in making the correct sizing recommendation for your system. You can locate our local sales office for your area by going to: www.cincinnatifan.com/rep-lookup.htm Other Static Pressure Estimating Factors: 1. For flexible hose, use 2-3 times the pressure drop for smooth wall duct or pipe. 2. Each 90° elbow is equal to 10 feet of straight duct or pipe. Example: 125 feet of straight pipe + 2: 90° elbows = 145 feet of straight pipe The Cincinnati Fan Engineering Data catalog will also provide you with very helpful recommendations for material conveying, air changes required for good ventilation, velocities for exhaust hoods, and guidelines for good duct installations. STATIC PRESSURE CORRECTIONS FOR SUCTION PRESSURE Based on standard air at 70° F, 29.92" Hg Barometric Pressure, .075 lbs. Per cubic feet density. Suction Pressure in Inches W.G. 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 Corrected Static Pressure 16.6 17.7 18.8 20.1 21.1 22.2 23.3 24.3 25.5 26.8 27.8 28.9 30.1 31.6 32.4 33.7 34.7 Suction Pressure in Inches W.G. 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 Corrected Static Pressure 35.9 37.1 38.5 39.5 40.8 41.9 43.0 44.4 45.9 46.8 48.1 49.3 50.3 51.9 53.4 54.4 55.7 Suction Pressure in Inches W.G. 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 Corrected Static Pressure 57.0 57.9 60.0 61.2 62.3 63.5 64.6 65.8 68.0 69.1 70.3 71.5 72.7 75.0 76.2 77.4 78.5 Suction Pressure in Inches W.G. 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 Corrected Static Pressure 79.7 82.3 83.5 84.7 85.9 87.1 88.3 91.0 92.3 93.5 94.7 95.9 98.8 100.0 101.2 102.6 104.3 NOTE: 1. With 45" of suction pressure on the blower inlet and no discharge pressure on the blower discharge, yourtotal static pressure = 50.3" Total SPWG. 2. With 45" of suction pressure on the blower inlet and 12" of discharge pressure on the discharge, yourtotal static pressure = 50.3"+12" = 62.3" Total SPWG. 3. With 0" of suction pressure on the blower inlet and 12" of discharge pressure on the blower discharge, yourtotal static pressure = 12" Total SPWG. There is no correction required for discharge pressure. Page 4 of 5 STEP 4 . Corrections For Altitude and Temperature: Safe Operating Speeds: Fan performance tables are developed using standard air which is 70° F., 29.92" barometric pressure (at sea level) and .075 lbs. per cubic foot. Density changes resulting from temperature and/or barometric pressure variations (at higher altitudes) must be corrected to standard conditions before selecting a fan or blower based on standard performance data. Temperature and/or altitude conversion factors are used in making the corrections to standard conditions. Example: For this example, we will be selecting a Model PB, cast aluminum pressure blower. You need to select a blower to deliver 1500 CFM at 7" SP at 250° F. and at 6500 feet altitude. When a blower or fan will be moving air at temperatures substantially above 70° F, the safe operating speed of the blower wheel or fan propeller must be taken into consideration. Most metals become characteristically weaker at higher temperatures. There are maximum operating temperatures listed in suppliers catalogs for various blowers and fan types. The wheel or propeller speeds shown are the maximum for that blower or fan construction. Bearings: The weakest part of a fan or blower is the bearing system, whether in a pillow block design on belt driven fans or located within the motor on direct driven fans. Temperatures above the fans maximum operating range can break down the lubricant in the bearings and cause bearing failure. The location of the bearings on a fan or blower must be considered when moving high temperature air. Fans with bearings located in the air stream have lower temperature limitations. Fans or blowers with bearings outside the air stream h ...
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Fan selection and operation
• When selecting a fan for ventilation system, why should you know about AMCA?
AMCA, being the primary association for fans outlines the conditions and specifications required
to be met by all fan manufacturers. As such, a fan is accepted for use if it meets the AMCA
specifications.


What are the functions of fan?

Fans have two main functions:
i. They physically move air.
ii. They supply needed static pressure.
• Use your own words to briefly describe the advantages and disadvantages of radial,
forward- and backward-inclined fans, if you want to use them in LEV system.
Radial, forward-inclined fans have a unique property from all other fans; quietness. The only
problem with this type of fun is that clogs easily because it is never very rugged. Backwardinclined fans on the other hand are popularly used becau...

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