Twin City ES-105 User Manual
Airflow Measuring System
Using Piezometer Ring
INSTALLATION, OPERATION & MAINTENANCE MANUAL
ES-105
September 2014
Twin City Fan now offers an air measuring device as an
option on centrifugal fans. It is based on the principle
of a flow nozzle. The inlet cone of the fan is used as
the flow nozzle. By measuring the pressure drop through
the inlet cone, the flow can be calculated. The system
consists of a piezometer ring mounted in the throat and
a static pressure tap mounted on the face of the inlet
cone. A differential pressure transducer and a digital
display can be provided. The display must be capable
of performing the square root function in order to read
Twin City Fan was able to determine flow coefficients for
various fan types. The flow coefficients were combined
to give the equations listed below by fan type. Based
on testing performed in Twin City Fan’s laboratory, the
accuracy of the system was determined to be +/- 5%.
The pressure drop is measured from the tap located
on the face of the funnel to the piezometer ring in the
throat. The inlet tap is connected to the high-pressure
side of the transducer and the piezometer ring is connected to the low-pressure side.
out in CFM directly. By testing fans in the laboratory,
Measurement of Airflow
The equations below are accurate for flow estimation for flows from 40% to 100% of wide-open volume. According
to testing done previously at Twin City Fan, several factors affect the accuracy of this method of determining flow.
The equations below assume the following:
• There are no vanes or other obstructions in or near the inlet
• Even flow entering the funnel (no pre-swirl)
• Standard wheel to inlet cone overlap
• Accurate determination of air density at the inlet
• Free inlet (consult Twin City Fan for ducted inlet factors)
Non-Standard Density Method Standard Density Method
One of the following equations is used to measure
the flow:
ACFM = C1 * A * (∆P/ρ)
where: A = Actual inlet funnel throat area (square
feet) - from tables on pages 2 and 3
∆P = The differential in static pressure from
the piezometer ring and the front
pressure tap (inches w.g.)
ρ = Air density (pounds mass/cubic foot)
C1 = Value from Table 1 below
Table 1: C1 Values
Product
EPFN/EPQN (Arr. 1 or 4), Sizes 122-165
EPLFN/EPLQN, Sizes 122-165
EPFN/EPQN (Arr. 1 or 4), Sizes 182-982
EPLFN/EPLQN, Sizes 182-982
MPLFN/MPLQN,MPLFS/MPLQS
EPF/EPQ (Arr. 3), Sizes 122-165 726.39 765.94
EPF/EPQ (Arr. 3), Sizes 182-982 667.52 713.93
MPQN, Sizes 122-165 753.06 794.06
MPQN, Sizes 182-490 692.03 740.14
APF/APQ 753.06 794.06
BC/BCS/BAF SWSI 735.42 786.56
BC/BCS/BAF DWDI 1470.84 1573.12
TSL/TFE 735.42 753.56
QSL/QFE/QIFE/TVIFE 696.00 735.83
BAE-SW ** 720.40 735.80
BAE-DW** 1440.80 1471.60
RB (Std. Inlet Bell) 913.33 997.49
HIB/RTF 727.94 785.07
HAF 790.17 760.92
VBC/VAF 1414.00 NA
C1
Free Inlet
753.06 794.06
692.03 740.14
Ducted Inlet
The equations can be simplified by assuming standard
density and assuming funnel dimensions match drawing
dimensions. The following tables show the factor (F) for
each fan size and type. The equation then becomes the
following:
For standard air (ρ = 0.075 lb/ft
3
):
ACFM = F ∆P
where: F = factor from tables on pages 2 and 3
∆P = The differential in static pressure
from the piezometer ring and the
front pressure tap (inches w.g.)
C1*
* Values for ducted C1 factors are based on
duct diameter matching standard inlet collar
diameter.
** BAE sizes smaller than 182 use BC\BCS\BAF
Factors.
©2014 Twin City Fan Companies, Ltd.
Table 2: EPF/EPQ (Arrangement 3),
EPFN/EPQN (Arrangement 1 & 4)
F
EPFN/EPQN
EPL-Series
Free Inlet
F
EPF/EPQ
Ducted Inlet
F
EPF/EPQ
Size
Free Inlet
122 911.46 944.92 961.07 996.36 0.344
150 1163.68 1206.40 1227.04 1272.08 0.439
165 1464.80 1518.58 1544.56 1601.26 0.552
182 1757.39 1821.92 1879.58 1948.58 0.721
200 2108.38 2185.80 2254.97 2337.76 0.865
222 2617.81 2713.93 2799.81 2902.60 1.074
245 3168.67 3285.02 3388.97 3513.39 1.300
270 3856.03 3997.61 4124.12 4275.53 1.582
300 4770.07 4945.21 5101.71 5289.01 1.957
330 5757.23 5968.62 6157.51 6383.56 2.362
365 7032.01 7290.21 7520.92 7797.03 2.885
402 8555.41 8869.55 9150.23 9486.16 3.510
445 10444.42 10827.92 11170.58 11580.68 4.285
490 12669.80 13135.01 13550.69 14048.16 5.198
542 15541.11 16111.75 16621.62 17231.84 6.376
600 19004.71 19702.52 20326.03 21072.24 7.797
660 22994.79 23839.12 24593.53 25496.41 9.434
730 28128.04 29160.84 30083.67 31188.11 11.54
EPFN/EPQN
EPL-Series
Ducted Inlet
F
Table 5: QSL/QFE/QIFE/TVIFE
Size
A
150 1832.36 1937.23 0.721
165 2198.32 2324.14 0.865
182 2729.48 2885.70 1.074
200 3303.84 3492.93 1.300
222 4020.52 4250.63 1.582
245 4973.55 5258.21 1.957
270 6002.82 6346.39 2.362
300 7331.98 7751.62 2.885
330 8920.36 9430.92 3.510
365 10889.96 11513.24 4.285
402 13210.27 13966.36 5.198
445 16204.06 17131.49 6.376
490 19815.41 20949.54 7.797
542 23975.70 25347.94 9.434
600 29327.92 31006.49 11.54
660 35859.36 37911.75 14.11
730 43610.67 46106.71 17.16
Free InletFDucted Inlet
F
A
Table 3: BC/BCS/BAF
Size
SWSI
Free Inlet
F
105 641.87 1283.74 686.51 1373.01 0.239
122 872.90 1745.81 933.61 1867.21 0.325
135 1058.21 2116.41 1131.79 2263.58 0.394
150 1305.20 2610.39 1395.96 2791.92 0.486
165 1587.21 3174.41 1697.58 3395.16 0.591
182 1936.99 3873.98 2071.69 4143.38 0.721
200 2321.58 4643.16 2483.02 4966.04 0.865
222 2883.02 5766.04 3083.50 6167.00 1.074
245 3491.62 6983.24 3734.42 7468.84 1.300
270 4247.77 8495.55 4543.16 9086.32 1.582
300 5254.03 10508.05 5619.38 11238.86 1.957
330 6342.73 12685.46 6783.80 13567.59 2.362
365 7747.97 15495.94 8286.75 16573.50 2.885
402 9426.99 18853.98 10082.53 20165.06 3.510
445 11507.43 23014.86 12307.64 24615.28 4.285
490 13957.43 27914.86 14928.01 29856.02 5.198
542 17121.05 34242.10 18311.62 36623.24 6.376
600 20938.50 41877.00 22394.53 44789.06 7.797
660 25334.37 50668.73 27096.08 54192.16 9.434
730 30991.88 61983.75 33147.00 66294.01 11.54
807 37901.44 75802.87 40537.05 81074.09 14.11
890 46079.00 92158.01 49283.27 98566.54 17.16
982 56192.01 112384.00 60099.52 120199.04 20.93
DWDI
Free Inlet
F
SWSI
Ducted Inlet
F
DWDI
Ducted InletFA
Table 4: APF/APQ
Size
121 944.92 996.36 0.344
141 1206.40 1272.08 0.439
161 1518.58 1601.26 0.552
181 1929.92 2035.00 0.702
201 2378.68 2508.19 0.865
221 2979.06 3141.26 1.083
251 3779.67 3985.45 1.375
281 4792.02 5052.92 1.743
321 6093.21 6424.95 2.216
351 7719.69 8139.98 2.807
391 9514.73 10032.75 3.460
441 11916.25 12565.02 4.334
491 14881.53 15691.74 5.412
551 18668.71 19685.12 6.789
631 24372.82 25699.79 8.864
711 30836.22 32515.09 11.21
791 38058.92 40131.02 13.84
Free InletFDucted Inlet
F
A
Table 6: TSL/TFE
Size
122 872.75 894.27 0.325
150 1305.09 1337.28 0.486
165 1587.06 1626.20 0.591
182 1936.15 1983.91 0.721
200 2322.85 2380.14 0.865
222 2884.09 2955.23 1.074
245 3490.99 3577.10 1.300
270 4248.26 4353.05 1.582
300 5255.28 5384.90 1.957
330 6342.85 6499.31 2.362
365 7747.30 7938.40 2.885
402 9425.66 9658.16 3.510
445 11506.83 11790.66 4.285
490 13958.57 14302.88 5.198
542 17121.95 17544.28 6.376
600 20937.86 21454.32 7.797
660 25333.82 25958.71 9.434
730 30989.22 31753.60 11.54
807 37890.63 38825.25 14.11
890 46081.02 47217.66 17.16
Free InletFDucted Inlet
F
A
(Sizes smaller than 182 use
Table 7: BAE-SW/BAE-DW
Size
SWSI
Free Inlet
F
182 1896.61 3793.22 1937.16 3874.31 0.721
200 2275.41 4550.82 2324.05 4648.10 0.865
222 2825.19 5650.38 2885.58 5771.16 1.074
245 3419.69 6839.38 3492.79 6985.58 1.300
270 4161.50 8322.99 4250.46 8500.91 1.582
300 5147.95 10295.89 5257.99 10515.99 1.957
330 6213.31 12426.62 6346.13 12692.26 2.362
365 7589.08 15178.15 7751.31 15502.62 2.885
402 9233.16 18466.31 9430.53 18861.07 3.510
445 11271.82 22543.63 11512.77 23025.55 4.285
490 13673.49 27346.98 13965.79 27931.57 5.198
542 16772.25 33544.50 17130.79 34261.59 6.376
600 20510.23 41020.47 20948.68 41897.36 7.797
660 24816.41 49632.82 25346.91 50693.82 9.434
730 30356.30 60712.61 31005.23 62010.46 11.540
807 37116.76 74233.52 37910.21 75820.42 14.110
890 45139.88 90279.75 46104.83 92209.66 17.160
982 55056.97 110113.94 56233.92 112467.85 20.930
DWDI
Free Inlet
F
Table 3: BC\BCS\BAF)
SWSI
Ducted Inlet
F
DWDI
Ducted InletFA
2 Twin City Engineering Supplement ES-105
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