AIRFLOW IN A SYSTEMAIRFLOW IN A SYSTEM

Presented by:Presented by:

Bill Howarth, Illinois Blower, IncBill Howarth, Illinois Blower, Inc..

AMCA International Technical AMCA International Technical Seminar 2009Seminar 2009

The Air Movement and Control The Air Movement and Control Association International (AMCA), has Association International (AMCA), has met the standards and requirements of met the standards and requirements of the Registered Continuing Education the Registered Continuing Education Providers Program. Credit earned on Providers Program. Credit earned on completion of this program will be completion of this program will be reported to the RCEPP. A certificate of reported to the RCEPP. A certificate of completion will be issued to each completion will be issued to each participant. As such, it does not include participant. As such, it does not include content that may be deemed or content that may be deemed or construed to be an approval or construed to be an approval or endorsement by NCEES or RCEPP.endorsement by NCEES or RCEPP.

Learning ObjectivesLearning Objectives

• Describe the elements of an air systemDescribe the elements of an air system• Know the physical properties of airKnow the physical properties of air• Describe the effects of system components on Describe the effects of system components on

airflowairflow• Understand the concept of pressureUnderstand the concept of pressure• Understand how the conservation of energy Understand how the conservation of energy

relates to airflowrelates to airflow• Understand an air systems operating pointUnderstand an air systems operating point

MOVING AIRMOVING AIR

Air at Air at “A”“A”

Air at Air at “B”“B”

AirAir AirAir

AIR SYSTEMAIR SYSTEM

AirAir

Air at Air at “A”“A”

Air at Air at “B”“B”

AiAirr

SystemSystem

•Properties of AirProperties of Air•Conservation of EnergyConservation of Energy•Friction And Friction Friction And Friction LossesLosses

•Fan CharacteristicsFan Characteristics

AIR SYSTEM DESIGNAIR SYSTEM DESIGN PARAMETERSPARAMETERS

PROPERTIES OF AIRPROPERTIES OF AIR

•Standard AirStandard Air•DensityDensity•PressurePressure•TemperatureTemperature

STANDARD AIRSTANDARD AIR

The Reference GasThe Reference Gas

forfor

Air System DesignAir System Design

Ingredients:Ingredients:• 1.105 X 101.105 X 102525 Molecules of Nitrogen (N Molecules of Nitrogen (N22))

• 1.480 X 101.480 X 102323 Molecules of Oxygen (O Molecules of Oxygen (O22))

• 6.558 X 106.558 X 102121 Molecules of Argon (A) Molecules of Argon (A)• 2.190 X 102.190 X 102020 Molecules of Carbon Molecules of Carbon

Dioxide (CODioxide (CO22))

• Pinch of other trace gasesPinch of other trace gases

RECIPE FORRECIPE FORSTANDARD AIRSTANDARD AIR

Mix Well in a sealed box one Mix Well in a sealed box one foot on a side and one foot foot on a side and one foot deep. Heat to 68deep. Heat to 68F. Warning! F. Warning! if you are in a vacuum, it will if you are in a vacuum, it will take 2117 pounds of force to take 2117 pounds of force to hold the lid on the box. hold the lid on the box.

2inlbs14.7

in. 12 x in. 12lbs 2117

RECIPE FORRECIPE FORSTANDARD AIRSTANDARD AIR

If you followed the If you followed the instructions properly, the instructions properly, the container will have gained in container will have gained in weight by 0.075 lb. The weight by 0.075 lb. The density of standard air is: density of standard air is:

3ftlb0.075

VolumeWeight

Density

RECIPE FORRECIPE FORSTANDARD AIRSTANDARD AIR

STANDARD AIRSTANDARD AIR DEVIATIONSDEVIATIONS

Due To:Due To:•Change In PressureChange In Pressure•Change in TemperatureChange in Temperature•Addition of other Addition of other Component(s), such as WaterComponent(s), such as Water

STANDARD AIRSTANDARD AIR

PressurePressure

PRESSUREPRESSURE

Air molecules are in continuous random Air molecules are in continuous random motion. The average impact of the motion. The average impact of the molecules against the sides of a molecules against the sides of a container result in the phenomenon container result in the phenomenon known as pressure.known as pressure.

1 Cubic Foot1 Cubic Foot

at 68at 68F.F.

PRESSUREPRESSURE

Forcing the same number of Forcing the same number of molecules to occupy a smaller volume molecules to occupy a smaller volume (compressing the air) will increase the (compressing the air) will increase the frequency of the molecular impacts, frequency of the molecular impacts, which is an increase in pressure.which is an increase in pressure.

1 Cubic Foot1 Cubic Foot

at 68at 68F.F.

PRESSUREPRESSURE

Increasing energy raises the random Increasing energy raises the random motion and the temperature. motion and the temperature. Pressure also increases. But; a cubic Pressure also increases. But; a cubic foot of air at 600foot of air at 600F and 14.7 lb/inF and 14.7 lb/in22 has has fewer molecules - It is less dense. fewer molecules - It is less dense.

1 Cubic Foot1 Cubic Foot

at 600at 600F.F.

BAROMETRIC PRESSUREBAROMETRIC PRESSURE

The weight of our The weight of our atmosphere atmosphere compresses air to compresses air to a pressure of 14.7 a pressure of 14.7 lb/inlb/in22 or 29.92 in. or 29.92 in. Hg (average at Hg (average at sea level with sea level with 50% relative 50% relative humidity).humidity).

AIRAIR

PRESSUREPRESSURE

•Absolute PressureAbsolute Pressure•Any Pressure referenced Any Pressure referenced to absolute zero to absolute zero pressure.pressure.

•Barometric Pressure is Barometric Pressure is an absolute pressure.an absolute pressure.

AIR DENSITYAIR DENSITY

Density at a given temperature Density at a given temperature and barometric pressure:and barometric pressure:

Temp. F460F70 F460

xHg in. 29.92

press. Abs.x

ftlbm 0.075 3

EFFECT OF HUMIDITYEFFECT OF HUMIDITY

The addition The addition of water of water vapor to air vapor to air will decrease will decrease the density the density of the air.of the air.

PSYCHROMETRIC CHART PSYCHROMETRIC CHART

28.5 29.0 29.5 30.0 30.5 31.065 .07145 .07272 .07398 .07525 .07651 .07777 .00026 .00002866 .07130 .07256 .07382 .07508 .07634 .07760 .00026 .00002967 .07114 .07240 .07366 .07492 .07618 .07744 .00026 .00002968 .07098 .07224 .07350 .07475 .07601 .07727 .00026 .00003069 .07083 .07208 .07333 .07459 .07584 .07710 .00026 .000030

70 .07067 .07192 .07317 .07442 .07568 .07693 .00026 .00003171 .07051 .07176 .07301 .07426 .07551 .07676 .00025 .00003172 .07035 .07160 .07285 .07410 .07534 .07659 .00025 .00003273 .07020 .07144 .07268 .07393 .07517 .07642 .00025 .00003374 .07004 .07128 .07252 .07377 .07501 .07625 .00025 .000033

75 .06988 .07112 .07236 .07360 .07484 .07603 .00025 .00003476 .06972 .07096 .07220 .07343 .07467 .07591 .00025 .00003477 .06956 .07080 .07203 .07327 .07451 .07574 .00025 .00003578 .06940 .07064 .07187 .07310 .07434 .07557 .00025 .00003679 .06925 .07048 .07171 .07294 .07417 .07540 .00025 .000036

80 .06909 .07032 .07155 .07277 .07400 .07523 .00025 .00003781 .06893 .07015 .07138 .07261 .07383 .07506 .00025 .00003382 .06877 .07000 .07122 .07244 .07366 .07489 .00024 .00003983 .06861 .06983 .07105 .07227 .07349 .07472 .00024 .00003984 .06845 .06967 .07089 .07211 .07333 .07454 .00024 .000040

85 .06829 .06950 .07072 .07194 .07316 .07437 .00024 .00004186 .06812 .06934 .07056 .07177 .07299 .07420 .00024 .00004287 .06796 .06917 .07039 .07160 .07281 .07403 .00024 .00004388 .06780 .06901 .07022 .07143 .07264 .07385 .00024 .00004389 .06764 .06885 .07005 .07126 .07247 .07368 .00024 .000044

90 .06748 .06868 .06989 .07109 .07230 .07351 .00024 .00004591 .06731 .06852 .06972 .07092 .07213 .07333 .00024 .00004692 .06715 .06835 .06955 .07075 .07195 .07316 .00024 .00004793 .06698 .06818 .06938 .07058 .07178 .07298 .00024 .00004894 .06682 .06801 .06921 .07041 .07161 .07280 .00024 .000049

95 .06665 .06785 .06904 .07024 .07143 .07263 .00024 .00005096 .06648 .06768 .06887 .07006 .07126 .07245 .00024 .00005197 .06632 .06751 .06870 .06989 .07108 .07227 .00024 .00005298 .06615 .06734 .06853 .06972 .07091 .07209 .00024 .00005399 .06598 .06717 .06835 .06954 .07073 .07191 .00024 .000054

100 .06581 .06700 .06818 .06937 .07055 .07174 .00024 .000055Note: Approx. average decrease in density per 0.10F rise in dry-bulb temperature equals .000017 lbm/ft3.

Dry-Bulb Temp.

°F

Density of Saturated Air for Various Barometric and Hygrometric Conditions—Ibm/ft3

Approx. Average

Increase in Density Per °F Wet-Bulb Depression

Td-Tw

Barometric Pressure in. Hg

Increase in Density Per 0.1 in. Hg

Rise In Barometer28.5 29.0 29.5 30.0 30.5 31.0

30 .07703 .07839 .07974 .08110 .08245 .08380 .00027 .00001731 .07687 .07822 .07957 .08093 .08228 .08363 .00027 .00001732 .07671 .07806 .07940 .08075 .08210 .08345 .00027 .00001733 .07654 .07789 .07924 .08053 .08193 .08327 .00027 .00001834 .07638 .07772 .07907 .08041 .08175 .08310 .00027 .000018

35 .07621 .07756 .07890 .08024 .08153 .08292 .00027 .00001836 .07605 .07739 .07873 .08007 .08141 .08274 .00027 .00001837 .07589 .07723 .07856 .07990 .08123 .08257 .00027 .00001938 .07573 .07706 .07840 .07973 .08106 .08239 .00027 .00001939 .07557 .07690 .07823 .07956 .08089 .08222 .00027 .000019

40 .07541 .07674 .07806 .07939 .08072 .08205 .00027 .00001941 .07525 .07657 .07790 .07922 .08055 .08187 .00026 .00002042 .07509 .07641 .07773 .07905 .08038 .08170 .00026 .00002043 .07493 .07625 .07757 .07889 .08021 .08153 .00026 .00002044 .07477 .07609 .07740 .07872 .08004 .08135 .00026 .000020

45 .07461 .07592 .07724 .07855 .07986 .08118 .00026 .00002046 .07445 .07576 .07707 .07838 .07970 .08101 .00026 .00002147 .07429 .07560 .07691 .07822 .07953 .08084 .00026 .00002148 .07413 .07544 .07674 .07805 .07936 .08066 .00026 .00002149 .07397 .07528 .07658 .07788 .07919 .08049 .00026 .000022

50 .07381 .07512 .07642 .07772 .07902 .08032 .00026 .00002251 .07366 .07496 .07625 .07755 .07885 .08015 .00026 .00002252 .07350 .07479 .07609 .07739 .07868 .07998 .00026 .00002353 .07334 .07464 .07593 .07722 .07852 .07981 .00026 .00002354 .07318 .07447 .07576 .07706 .07835 .07964 .00026 .000023

55 .07302 .07431 .07560 .07689 .07818 .07947 .00026 .00002456 .07287 .07415 .07544 .07673 .07801 .07930 .00026 .00002457 .07271 .07399 .07528 .07656 .07784 .07913 .00026 .00002558 .07255 .07383 .07512 .07640 .07768 .07896 .00026 .00002559 .07240 .07367 .07495 .07623 .07751 .07879 .00026 .000025

60 .07224 .07352 .07479 .07607 .07734 .07862 .00026 .00002661 .07208 .07336 .07463 .07590 .07718 .07845 .00026 .00002662 .07193 .07320 .07447 .07574 .07701 .07828 .00026 .00002763 .07177 .07304 .07430 .07557 .07684 .07811 .00026 .00002764 .07161 .07288 .07414 .07541 .07668 .07794 .00026 .000028Note: Approx. average decrease in density per 0.10F rise in dry-bulb temperature equals .000017 lbm/ft3.

Increase in Density Per 0.1 in. Hg

Rise In Barometer

Approx. Average

Increase in Density Per °F Wet-Bulb Depression

Td-Tw

Barometric Pressure in. Hg

Dry-Bulb Temp.

°F

Density of Saturated Air for Various Barometric and Hygrometric Conditions—Ibm/ft3

1 in. wg1 in. wg

GAGE PRESSUREGAGE PRESSURE

Gauge Pressure is a Gauge Pressure is a Differential Pressure.Differential Pressure.

BarometricBarometricPressurePressure

WaterWater

STATIC PRESSURESTATIC PRESSURE

Fan Static Pressure is a Fan Static Pressure is a gage pressure, indicating gage pressure, indicating compression of the air.compression of the air.

1 in. wg1 in. wg

Static Static PressurePressure

BarometricBarometricPressurePressure

WaterWater

AiAirr

VELOCITY PRESSUREVELOCITY PRESSURE

Velocity pressure is a measurement of the energy Velocity pressure is a measurement of the energy needed to accelerate air to a given velocity.needed to accelerate air to a given velocity.

1 in. wg1 in. wg

Velocity Velocity PressurePressure

BarometricBarometricPressurePressure

WaterWater

AiAirr

VolumeEnergy Kenetic

Pressure Velocity VP

Density x 1097

Velocity

2

VP

TOTAL PRESSURETOTAL PRESSURE

Total Pressure=Total Pressure=

Static Pressure + Velocity Static Pressure + Velocity PressurePressure

ororVPSPTP

ACFM vs. SCFMACFM vs. SCFM

Actual Cubic Feet Per Minute (ACFM)Actual Cubic Feet Per Minute (ACFM)

Standard Cubic Feet Per Minute (SCFM)Standard Cubic Feet Per Minute (SCFM)

ACFM ACFM SCFM SCFM

1 Cubic 1 Cubic FootFoot

at 600at 600F.F.

1 Cubic 1 Cubic FootFoot

at 68at 68F.F.

1 Cubic 1 Cubic FootFoot

at 600at 600F.F.

CONSERVATION CONSERVATION OF OF

ENERGYENERGY

BERNOULLI'S LAWBERNOULLI'S LAW

For ducted airflow which is:For ducted airflow which is:• Constant with timeConstant with time• IncompressibleIncompressible• Without frictionWithout friction

Constant VPSPTP

(If we neither add nor subtract (If we neither add nor subtract energy, energy is constant.)energy, energy is constant.)

FLOW THROUGH A NOZZLEFLOW THROUGH A NOZZLE

1097 xDensity

Velocity2

5.0

2

VP

212

2221

SPTPVP

VPSPTPTP

AirflowAirflow

TPTP11

SPSP

11

Area Area

22

Pitot TubePitot Tube

22 Area x VelocityMinute

Feet CubicCFM

•May be used in system May be used in system calculations wherever friction calculations wherever friction can be can be ignoredignored. .

•Do Do NOTNOT use for: use for:

BERNOULLI'S LAWBERNOULLI'S LAW

•Abrupt Abrupt ExpansionExpansion

•Abrupt Abrupt ContractionContraction

FRICTIONFRICTION

ANDAND

FRICTION LOSSESFRICTION LOSSES

TOTAL PRESSURETOTAL PRESSUREIN AN AIR SYSTEMIN AN AIR SYSTEM

Total Pressure declinesTotal Pressure declinesas duct length increases.as duct length increases.

TotalTotalPressurPressur

ee

DuctDuctLossLoss

Duct LengthDuct Length

FRICTION LOSSFRICTION LOSS

•Caused by non-uniform Caused by non-uniform velocities across the ductwork, velocities across the ductwork, coupled with the viscosity of air.coupled with the viscosity of air.

•Always results in the conversion Always results in the conversion of Total Pressure to Heatof Total Pressure to Heat

•Turbulence (irregular or chaotic Turbulence (irregular or chaotic air flow) will amplify the friction air flow) will amplify the friction loss.loss.

LOSS FACTORS FORLOSS FACTORS FOR ROUND ELBOWSROUND ELBOWS

VP x CLoss

RR

DD

Coefficient

C0.50 0.710.75 0.331.00 0.221.50 0.152.00 0.132.50 0.12

R/D

Coefficient

C per 100 Ft.

0.25 9.35

0.33 6.53

0.50 3.95

0.67 2.78

0.75 2.40

1.00 1.69

1.33 1.19

1.67 0.91

2.00 0.73

2.50 0.56

3.00 0.45

3.50 0.38

4.00 0.32

5.00 0.25

D

LOSS FACTORS FORLOSS FACTORS FOR STRAIGHT DUCTSSTRAIGHT DUCTS

VP x CLoss

100100

DD

SYSTEM LOSSESSYSTEM LOSSESDuct Friction ChartDuct Friction Chart

• Based on standard Based on standard air, 0.075 lbm/ftair, 0.075 lbm/ft3 3 ..

• This chart based This chart based on galvanized on galvanized ducts with Beaded ducts with Beaded slip joints every slip joints every 48” (48” (=0.0003).=0.0003).

• Other charts Other charts available.available.

LOSSES IN A REALLOSSES IN A REALAIR SYSTEMAIR SYSTEM

• Add losses for each component.Add losses for each component.• Add a safety factor to all for the Add a safety factor to all for the

impact of one component impact of one component connected directly to the next.connected directly to the next.

Example:Example:

AIR SYSTEMSAIR SYSTEMS

Basis for Basis for development of an development of an Air SystemAir System

• Ventilation RateVentilation Rate• Air Changes/HourAir Changes/Hour• Face VelocityFace Velocity• Exhaust RequirementsExhaust Requirements

• References:References:• Fan Application ManualFan Application Manual• ASHRAE HandbooksASHRAE Handbooks• Industrial Ventilation Industrial Ventilation

GuideGuide

AIR SYSTEMAIR SYSTEM

Convert Ventilation Rate in to Flow Rate (CFM)Convert Ventilation Rate in to Flow Rate (CFM)

Develop a detailed duct system layout.Develop a detailed duct system layout.

AIR SYSTEMSAIR SYSTEMSDo:Do:

• Calculate:Calculate:• Actual Cubic Feet Per Actual Cubic Feet Per

MinuteMinute• Static Pressure Static Pressure

RequirementRequirement• Air DensityAir Density

• Include all entrance Include all entrance and discharge pointsand discharge points

• Pay careful Pay careful attention to fan attention to fan entry and exit entry and exit conditionsconditions

Don’t:Don’t:• Simplify Simplify

component lossescomponent losses• Abruptly change Abruptly change

velocity through velocity through the air systemthe air system

• Neglect Neglect System System EffectsEffects on the fan on the fan• Inlet and OutletInlet and Outlet• DensityDensity

SYSTEM CURVESYSTEM CURVE2

2

CFM x Constant 0.075 x 1097 x Area

CFMC x C

VP

SystemSystemLossLoss

System Resistance CurveSystem Resistance Curve

System Losses PlottedSystem Losses Plotted

CFMCFM

Pre

ssu

reP

ressu

re

THE FAN’S JOBTHE FAN’S JOB

The purpose of a fan is The purpose of a fan is to supply an air to supply an air system with energy (in system with energy (in the form of pressure) the form of pressure) necessary to maintain necessary to maintain airflow.airflow.

FANFAN

CHARACTERISTICSCHARACTERISTICS

FANSFANS

• There are many types of fans.There are many types of fans.• For each type, there may be many For each type, there may be many

sizes.sizes.• All fans have one thing in common:All fans have one thing in common:

Accurate prediction of aerodynamic Accurate prediction of aerodynamic performance requires a test.performance requires a test.

THE AERODYNAMICTHE AERODYNAMIC PERFORMANCE TESTPERFORMANCE TEST

At:At:

Constant Constant Speed,Speed,

Known Known DensityDensity

Pre

ssu

rP

ressu

ree

Pow

er

Pow

er

AirflowAirflow

THE FAN LAWSTHE FAN LAWS

•Are used to calculate Are used to calculate fan performance at:fan performance at:•Other SpeedsOther Speeds•Other DensitiesOther Densities•Other Fan SizesOther Fan Sizes

First Law:First Law:

1

2

3

1

212 RPM

RPM

DIA

DIACFMCFM

THE FAN LAWSTHE FAN LAWS

Second Law:Second Law:

1

2

2

1

2

2

1

212

RPM

RPM

DIA

DIASPSP

THE FAN LAWSTHE FAN LAWS

Third Law:Third Law:

1

2

3

1

2

5

1

212

RPM

RPM

DIA

DIAHH

THE FAN LAWSTHE FAN LAWS

THE FAN LAWSTHE FAN LAWSPPrreessssuurree

PPoowweerr

AirflowAirflow

Changes in SpeedChanges in Speed

FAN SELECTIONFAN SELECTION

Select a fan which will generate Select a fan which will generate the required pressure at the the required pressure at the desired airflow.desired airflow.

AirflowAirflow Desired Desired CFMCFM

FAN SELECTIONFAN SELECTION

•There is only one intersection There is only one intersection

between the fan curve and between the fan curve and

system curve. system curve.

•Fans are load matching Fans are load matching

devices.devices.

•Fans handle ACFM only.Fans handle ACFM only.

OPERATING POINTOPERATING POINT

Fan - Air System InteractionFan - Air System Interaction

FAN SELECTIONFAN SELECTION COROLLARIESCOROLLARIES

• Any air system fan which generates Any air system fan which generates the required system pressure will the required system pressure will also deliver the required airflow.also deliver the required airflow.

• If an air system fan generates the If an air system fan generates the specified static pressure but not specified static pressure but not the desired airflow, the system the desired airflow, the system resistance has been mis-calculated.resistance has been mis-calculated.

FAN PERFORMANCEFAN PERFORMANCE TOLERANCESTOLERANCES

•Account for:Account for:

•Test UncertaintyTest Uncertainty

•Manufacturing Manufacturing

ImperfectionsImperfections

AMCA TOLERANCESAMCA TOLERANCES• The fan must perform within 2.5% of The fan must perform within 2.5% of

its air performance rating and within its air performance rating and within

5% of its power rating.5% of its power rating.

• To meet rated performance, the fan To meet rated performance, the fan

RPM might have to be increased up to RPM might have to be increased up to

2.5%, and the power increased up to 2.5%, and the power increased up to

5% of the rated power.5% of the rated power.

• The AMCA Tolerances DO NOT account The AMCA Tolerances DO NOT account

for for System EffectSystem Effect or for errors in the or for errors in the

system calculations. system calculations.

Questions?Questions?