Study of Fan Pp2003

8/9/2019 Study of Fan Pp2003

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TYPES OF FANThe types of fans are:y Axi aly Centr ifugaly Propeller y Mix ed flowy Cross flow

Commonly there are two types of fans are w idely used ina ir cond ition ing and vent ilat ion systems:y Axi al fansy Centr ifugal fans

TYPESI

These are the type of Axial Fan:y Panel typey Tubeaxial typey Vaneaxial typey Inline Centrifugal type

Axial Fan Panel Type

y Description:One of the most basic fan designs.

y Applications:For low-pressure, high-volumeapplications. O ften used for ventilationthrough a wall.

Axial Fan Tubeaxial Type

y Description:More eff ic ient than the panel fan.Cyl indr ical hous ing f its closely to theouts ide d iameter of the wheel

y Applications:F or low pressure ducted heat ing,vent ilat ing and a ir-cond ition ing systems. A lso used in some low pressureindustr ial appl icat ions

Axial Fan Vaneaxial Typey Description:

H ighest eff ic iency a xi al fan. Cyl indr icalhous ing f its closely to the outs ide

d iameter of the blade t ips. Thestra ighten ing vanes allow for greater eff ic iency and pressure capac ity.

y Applications:F or heat ing, vent ilat ing, and a ir-cond ition ing systems. Good wherestra ight flow and eff ic iency are requ iredfrom an a xi al fan.

Axial Fan Inline C entrifugal Typey Description:

Cylindr ical hous ing is s im ilar to the vanea xi al.Wheel is generally an a irfo il or backwardincl ined type. In th is case, the hous ing doesnot f it close to the outs ide d iameter of thewheel.

y Applications:Mostly used for low and med ium pressure

systems in heat ing, vent ilat ing, a ir-cond ition ing or industr ial appl icat ions, when acylindr ical hous ing is geometr ically moreconven ient than a centr ifugal conf igurat ion.

THE AX I AL F AN TYPIC AL COMPO N E N T

C ENTRIFUGAL FANy Application:

S upply a ir y Ch aracteristics:

A rotating impeller to increase the velocity of an airstream.

y Ability:

Capable to generating relatively high pressures.y C ommon brand:

TYPESC

These are the type of centrifugal fan:y Forward curvey Airfoily Backward inclinedy Radial bladey Radial tip

C entrifugal Fan Forward C urvedy Description:

Less eff ic ient than a irfo il and backwardincl ined. Requ ires the lowest speed of anycentr ifugal to move a g iven amount of a ir.

Blades are curved forward in the d irect ion of rotat ion

y Applications:U sed for low-pressure heat ing, vent ilat ing, anda ir-cond ition ing systems, rang ing from room

a ir-cond itioners to res ident ial furnaces

C entrifugal Fan Airfoily Description:

A centrifugal fan type developed toprovide high efficiency. Its name isderived from the "airfoil shape of itsblade.

y Applications:

U sed on large heat ing, vent ilat ing, a ir cond ition ing and clean a ir industr ialsystems where energy sav ings are of pr ime importance.

C entrifugal Fan Backward Inclined

y Description:Slightly less efficient than the airfoil. The bladesare flat and of single thickness.

y Applications:Used on large heating, ventilating, airconditioning and industrial systems where theblade may be subjected to corrosive or erosiveenvironments

C entrifugal Fan Radial Blade

y Description:Generally the least eff ic ient of thecentr ifugal fans. The blades are "rad ial" to

the fan shaft.y Applications:

F or mater ial handl ing and moderate toh igh pressure industr ial appl icat ions

C entrifugal Fan Radial Tip

y Description:More eff ic ient than the rad ial blade. Theblades are rad ial to the fan shaft at theouter e x trem ity of the impeller, butgradually slope towards the d irect ion of wheel rotat ion.

y Applications:D

esigned for wear res

istance

ildlyeros ive a irstrea ms

THE CE N TRIFU G AL F AN TYPIC AL

COMPO N E N T

PROPELLERS N

y A pplication:vent ilat ing l ivestock bu ildings and a ir c irculat ion.

y Ch aracteristics:The blades of a propeller act asrotat ing w ings and produce force.

y Ability:D es ign to enhances ma intenance toremove dust and d irt accumulat ions

M I ED LOW ANS

y A fan in wh ich the a ir path throughthe impeller is intermed iate betweenthe a xi al and centr ifugal types g iving

the benef it of

increased pressure butcapable of be ing constructed to

prov ide e ither a xi al or rad iald ischarge .

C ROSS FLOW FANSy Th is type normally has a long

cyl indr ical impeller hav ing arelat ively large number of shallowforward curve blades.

y D ue to the shape of the cas ingsurround ing th is impeller, a ir entersall along one s ide of the cyl indr icalsurface of the impeller and leaves

on another side.

S TUD Y O F F AN

TESTING

ADJUSTING

B ALAN CIN G

at is T.A.B.?y Preparation of work that must be done prior to the

actual testing, adjusting, and balancing of the HVACsystems on the job. Confirm that these preliminary procedures have been completed and check listsprepared.

y Do not attempt to balance a system before installationhas been completed and the system is ready to bebalanced

Identify the issue

Define the problem

Determine & validate operating conditions

Compare to previous conditions

Begin detailed troubleshooting

H VAC Testing, adjusting & balancingguidelines

TH E H VAC SYSTEM STARTUPy Fan Ch eck

A fter ver ifying all control dampers are open, start all

related systems, returns, and e x haust fans and takeprel im inary fan stat ic pressure read ings.

y Damper Ch eck

Check all dampers for the system are in correctpos ition. A ll dampers should be set for a full flowcool ing cond ition.

y Flow/Pressure Ch eckConfirm that all related system fans serving each area

within the space being balanced are operating. If they are not, pressure differences and infiltration or exfiltration may adversely influence the balancing. Positiveand negative pressure zones should be identified at this

TH E H VAC SYSTEM STARTUP

y Damper SettingIf a supply fan is connected to a return a ir system

and an outs ide a ir intake, set all system dampersand controls so that the a ir returned from theind ividual rooms or areas suppl ied by the fan isreturned v ia the related return a ir system. Make sure

all systems are operating and all related dampersare set properly for the T A B work.

TH E H VAC SYSTEM STARTUP

FAN TESTING MET H ODPerform the follow ing tests and adjustments pr ior tobeg inn ing the a ir balanc ing:

1) Record nameplate data on fan, motor and airhandling cabinet.

2) Record and measure fan and motor sheavesindicating number and size of belts along with

centre to centre distances.3) Test and record actual operating fan rpm.4) Measure and record actual running

FAN ADJUSTING MET H ODy It is determine by using the Fan Laws equation.y Air flow fan power relationship can be determined by

using the fan laws.y The fan adjustment is to change the drive for the in

order to achieve the specific design.

F AN ADJUST ING M ETHODy F an D rive Ch anges

the balanc ing read ings w ill have a lot to do w ithdeterm in ing the fan dr ive changes

y Fan AmperageRecheck the amperage whenever any rpm change or major damper sett ing change is made.

y Fan Static PressuresS tat ic pressure read ings should be taken at the fansuct ion and fan d ischarge to obta in the current total fanstat ic pressure read ing

FAN BALAN C ING MET H ODy Verify fan and control operation.y Index the VAV box to maximum (cooling ) position.

Some boxes may have to be set to the minimumposition first.y Fan balancing also related to the Building

Management S ystem (B. M.S)y Use the flow measuring hood to balance the air flow with very accurate data.

TH E T.A.B. INSTRUMENTS FOR FANy E lectron ic Rotat ing Vane A nemometer y F low Measur ing H oody P itot Tubey D ig ital Opt ical Tachometer y Clamp On Volt A mmeter

Electronic Rotating Vane Anemometer

Applications:y measurements of a ir veloc ity

through both supply and return a ir term inals

Ability:y It can detect for a very low

veloc ity

F l Measu ri Hood

F low Measu ri Hood

Applic a tion s :y To obtain direct measurement of air distribution

devices.Ability:y To facilitate taking air velocity and airflow.y A very accurate instrument to measure the air

Pitot Tube

Pitot TubeApplication:y Measurement of static pressure by connecting

the outer tube side outlet connector to one sideof a manometer or gage.

Ability:y It can measure the veloc ity pressure, stat ic

pressure and total pressure accurately.

D ig ital Opt ical Tachometer Applications:y For measurement of rotation

speeds when instrument contact with the rotating equipment is not

feasible.Ability:y Measurement of rotation speeds by

direct contact or by counting thespeed of a reflective mark.

y To measure fan rpm.

C lamp On Volt Ammeter

Applications:y F or a mechan ical systems requ ires

the measurement of voltages andelectr ical currents.

F or an accurate measurement of the runn ing current on a certa inmechan ical electr ical dev ice

Ability:y

Clamp on transformer jaws whichperm it current read ings w ithout

interrupt ing electr ical serv ice .

TP = TP tlet TP i let

F an Total Pressure(TP)

y F an total pressure is the

difference between the totalpressure at the fan outlet and

inlet.

y The fan total pressure is ameasure of the totalmechan ical energy added tothe a ir or gas by the fan.

y Th is generally can bemeasured accurately only in atest laboratory.

Fan SP Fan TP (outlet ) - TP (inlet ) - Vp(outlet )

also,TP (outlet ) - SP (outlet ) Vp (outlet )

and substitute,

Fan SP SP (outlet ) - TP (inlet )

F an S tat ic Pressure(S P)

F an stat ic pressure is the fan

total pressure less the fanveloc ity pressure.It can be calculated bysubtract ing the total pressureat the fan inlet from the stat icpressure at the fan outlet

F AN VE LOCITYPR ESSU RE (Vp)

y F an veloc ity pressure is the

pressure correspond ing tothe fan outlet veloc itypressure.

y It is the k inet ic energy per un it volume of flow ing a ir.

Fan Outlet Velocityy In the theoret ical veloc ity of the a ir as it leaves the

fan outlet and;y i

s calculated by div

ing the a

ir volume

in cfm (

L/s)by the fan outlet area in square feet (m²).

y Read ing should be taken downstream in a stra ightduct connected to the fan d ischarge where the flowis more un

iform.

y A lso called per ipheral veloc ity.y Tip speed equals the c ircumference of

the fan wheel t imes the rpm of the fanand is e x pressed in feet per m inute(meters per second)

Tip S peed

Tip Speed EquationEquation (SI)

x d x RPM60 sec /m in

Where:

Tip S peed = meters per m inuteD = Wheel d iameter metersRPM = Revolut ions per m inute

Equation (I-P)

x d x RPM12 in. /ft.

Where:

Tip S peed = F eet per m inuteD = Wheel d iameter inchesRPM = Revolut ions per m inute

Tip Speed Tip Speed

E x ampley F ind the t ip speed of a 30 inch d iameter fan wheel

rotat ing at 954 rpm.

x d x RPM x 30 x 95412 in. /ft. 12

Tip Speed

Tip Speed 7493 fpm

System Curvey D uct system res istance is the sum of all pressurelosses.

y Th is Is a plot of the pressure that is requ ired to move

a ir through the system.y The system curve for any system is represented by a

s ingle curve.

E x ampley cons ider a system handl ing 1,000 cfm (500 L/ s) w ith

a stat ic pressure ( S P) res istance of 1 in. wg (250Pa).y

If the airflow

is doubled, the

SP res

istance w

illincrease by that rat io squared (4) to 4 in. wg (1000

SYSTEM RESISTAN C E C URVE

1000(500)

2000(1000)

F ans Lawsy It is not pract icable to test the performance of

every s iz e of fan in a manufacturer¶s range at all

speeds at which

it maybe des

igned to run and;

y with every gas dens ity maybe requ ired to handle.y By use of the fan laws, the geometr ically s im ilar

fans of d ifferent s iz es or speed can be pred ictedaccurately enough for pract ical purpose.

F an Laws E quat ion

E x ample A fan operates at 9056 cfm, 1478 rpm,requ ir ing 5.08 B H P at 1.0 in. wg S P.

The airflow must be

increased to10,188 cfm to handle an add itional

load. F ind the new S P and B H P.

S olut ionNew static pressure.

p2 = p1 (cfm 2 » cfm1)²

p2 = 1.0 (10188 » 9056)²

= 1.27 in. w.g S P

New brake h orsepower

b p2 = bh p1 (cfm 2 » cfm1)³

b p2 = 5.08 (10188 » 9056)³

= 7.23 B H P

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