AIRFLOW IN A SYSTEM Presented by: Bill Howarth, Illinois Blower, Inc. AMCA International Technical...
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Transcript of AIRFLOW IN A SYSTEM Presented by: Bill Howarth, Illinois Blower, Inc. AMCA International Technical...
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
•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
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.
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
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.
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
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.
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.