Airflow Measuring With Piezometer Ring 2d1n71

Airflow Measuring System Using Piezometer Ring

ES-105 August 2011

INSTALLATION, OPERATION & MAINTENANCE MANUAL

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 out in CFM directly. By testing fans in the laboratory,

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.

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:

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:



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

For standard air (ρ = 0.075 lb/ft3): 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.)

Table 1: C1 Values Product EPFN/EPQN (Arr. 1 or 4), Sizes 122-165 EPFN/EPQN (Arr. 1 or 4), Sizes 182-982 EPF/EPQ (Arr. 3), Sizes 122-165 EPF/EPQ (Arr. 3), Sizes 182-982 MPQN, Sizes 122-165 MPQN, Sizes 182-490 APF/APQ BC/BCS/BAF SWSI BC/BCS/BAF DWDI TSL QSL BAE-SW ** BAE-DW** RB (Std. Inlet Bell) HIB/RTF

C1 Free Inlet 753.06 692.03 726.39 667.52 753.06 692.03 753.06 735.42 1470.84 735.42 696.00 720.40 1440.80 913.33 727.94

C1* Ducted Inlet 794.06 740.14 765.94 713.93 794.06 740.14 794.06 786.56 1573.12 753.56 735.83 735.80 1471.60 997.49 785.07

* 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.

©2011 Twin City Fan Companies, Ltd.

Table 2: EPF/EPQ (Arrangement 3) and EPFN/EPQN (Arrangement 1 & 4) Size 122 150 165 182 200 222 245 270 300 330 365 402 445 490 542 600 660 730

EPF/EPQ Free Inlet F 911.46 1163.68 1464.80 1757.39 2108.38 2617.81 3168.67 3856.03 4770.07 5757.23 7032.01 8555.41 10444.42 12669.80 15541.11 19004.71 22994.79 28128.04

EPFN/EPQN Free Inlet F 944.92 1206.40 1518.58 1821.92 2185.80 2713.93 3285.02 3997.61 4945.21 5968.62 7290.21 8869.55 10827.92 13135.01 16111.75 19702.52 23839.12 29160.84

EPF/EPQ Ducted Inlet F 961.07 1227.04 1544.56 1879.58 2254.97 2799.81 3388.97 4124.12 5101.71 6157.51 7520.92 9150.23 11170.58 13550.69 16621.62 20326.03 24593.53 30083.67

Table 5: QSL EPFN/EPQN Ducted Inlet F 996.36 1272.08 1601.26 1948.58 2337.76 2902.60 3513.39 4275.53 5289.01 6383.56 7797.03 9486.16 11580.68 14048.16 17231.84 21072.24 25496.41 31188.11

Size A 0.344 0.439 0.552 0.721 0.865 1.074 1.300 1.582 1.957 2.362 2.885 3.510 4.285 5.198 6.376 7.797 9.434 11.54

105 122 135 150 165 182 200 222 245 270 300 330 365 402 445 490 542 600 660 730 807 890 982

SWSI Free Inlet F 641.87 872.90 1058.21 1305.20 1587.21 1936.99 2321.58 2883.02 3491.62 4247.77 5254.03 6342.73 7747.97 9426.99 11507.43 13957.43 17121.05 20938.50 25334.37 30991.88 37901.44 46079.00 56192.01

DWDI Free Inlet F 1283.74 1745.81 2116.41 2610.39 3174.41 3873.98 4643.16 5766.04 6983.24 8495.55 10508.05 12685.46 15495.94 18853.98 23014.86 27914.86 34242.10 41877.00 50668.73 61983.75 75802.87 92158.01 112384.00

SWSI Ducted Inlet F 686.51 933.61 1131.79 1395.96 1697.58 2071.69 2483.02 3083.50 3734.42 4543.16 5619.38 6783.80 8286.75 10082.53 12307.64 14928.01 18311.62 22394.53 27096.08 33147.00 40537.05 49283.27 60099.52

DWDI Ducted Inlet F 1373.01 1867.21 2263.58 2791.92 3395.16 4143.38 4966.04 6167.00 7468.84 9086.32 11238.86 13567.59 16573.50 20165.06 24615.28 29856.02 36623.24 44789.06 54192.16 66294.01 81074.09 98566.54 120199.04

Size 121 141 161 181 201 221 251 281 321 351 391 441 491 551 631 711 791

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Size A 0.239 0.325 0.394 0.486 0.591 0.721 0.865 1.074 1.300 1.582 1.957 2.362 2.885 3.510 4.285 5.198 6.376 7.797 9.434 11.54 14.11 17.16 20.93

122 150 165 182 200 222 245 270 300 330 365 402 445 490 542 600 660 730 807 890

Free Inlet F 872.75 1305.09 1587.06 1936.15 2322.85 2884.09 3490.99 4248.26 5255.28 6342.85 7747.30 9425.66 11506.83 13958.57 17121.95 20937.86 25333.82 30989.22 37890.63 46081.02

Ducted Inlet F 894.27 1337.28 1626.20 1983.91 2380.14 2955.23 3577.10 4353.05 5384.90 6499.31 7938.40 9658.16 11790.66 14302.88 17544.28 21454.32 25958.71 31753.60 38825.25 47217.66

Table 7: BAE-SW/BAE-DW Size

Table 4: APF/APQ Free Inlet F 944.92 1206.40 1518.58 1929.92 2378.68 2979.06 3779.67 4792.02 6093.21 7719.69 9514.73 11916.25 14881.53 18668.71 24372.82 30836.22 38058.92

Ducted Inlet F 1937.23 2324.14 2885.70 3492.93 4250.63 5258.21 6346.39 7751.62 9430.92 11513.24 13966.36 17131.49 20949.54 25347.94 31006.49 37911.75 46106.71

A 0.721 0.865 1.074 1.300 1.582 1.957 2.362 2.885 3.510 4.285 5.198 6.376 7.797 9.434 11.54 14.11 17.16

Table 6: TSL

Table 3: BC/BCS/BAF Size

150 165 182 200 222 245 270 300 330 365 402 445 490 542 600 660 730

Free Inlet F 1832.36 2198.32 2729.48 3303.84 4020.52 4973.55 6002.82 7331.98 8920.36 10889.96 13210.27 16204.06 19815.41 23975.70 29327.92 35859.36 43610.67

Ducted Inlet F 996.36 1272.08 1601.26 2035.00 2508.19 3141.26 3985.45 5052.92 6424.95 8139.98 10032.75 12565.02 15691.74 19685.12 25699.79 32515.09 40131.02

A 0.344 0.439 0.552 0.702 0.865 1.083 1.375 1.743 2.216 2.807 3.460 4.334 5.412 6.789 8.864 11.21 13.84

182 200 222 245 270 300 330 365 402 445 490 542 600 660 730 807 890 982

SWSI Free Inlet F 1896.61 2275.41 2825.19 3419.69 4161.50 5147.95 6213.31 7589.08 9233.16 11271.82 13673.49 16772.25 20510.23 24816.41 30356.30 37116.76 45139.88 55056.97

DWDI Free Inlet F 3793.22 4550.82 5650.38 6839.38 8322.99 10295.89 12426.62 15178.15 18466.31 22543.63 27346.98 33544.50 41020.47 49632.82 60712.61 74233.52 90279.75 110113.94

A 0.325 0.486 0.591 0.721 0.865 1.074 1.300 1.582 1.957 2.362 2.885 3.510 4.285 5.198 6.376 7.797 9.434 11.54 14.11 17.16

(Sizes smaller than 182 use Table 3: BC\BCS\BAF) SWSI Ducted Inlet F 1937.16 2324.05 2885.58 3492.79 4250.46 5257.99 6346.13 7751.31 9430.53 11512.77 13965.79 17130.79 20948.68 25346.91 31005.23 37910.21 46104.83 56233.92

DWDI Ducted Inlet F 3874.31 4648.10 5771.16 6985.58 8500.91 10515.99 12692.26 15502.62 18861.07 23025.55 27931.57 34261.59 41897.36 50693.82 62010.46 75820.42 92209.66 112467.85

A 0.721 0.865 1.074 1.300 1.582 1.957 2.362 2.885 3.510 4.285 5.198 6.376 7.797 9.434 11.540 14.110 17.160 20.930

Twin City Engineering Supplement ES-105

Table 8: MPQN Size 122 150 165 182 200 222 245 270 300 330 365 402 445 490

Free Inlet F 944.92 1206.40 1518.58 1821.92 2185.80 2713.93 3285.02 3997.61 4945.21 5968.62 7290.21 8869.55 10827.92 13135.01

Table 9: HIB/RTF Ducted Inlet F 996.36 1272.08 1601.26 1948.58 2337.76 2902.60 3513.39 4275.53 5289.01 6383.56 7797.03 9486.16 11580.68 14048.16

A

Size

0.344 0.439 0.552 0.721 0.865 1.074 1.300 1.582 1.957 2.362 2.885 3.510 4.285 5.198

180 200 220 240 270 300 330 360 400 450 490 540 600 660 730 800

Free Inlet F 1917.29 2297.97 2853.70 3456.11 4204.57 5200.59 6278.22 7669.16 9338.47 11390.39 13824.42 16946.91 20725.53 25076.69 30676.66 37530.69

Table 10: Industrial Ducted Inlet A F 2067.76 0.721 2478.32 0.865 3077.66 1.074 3727.35 1.300 4534.55 1.582 5608.74 1.957 6770.95 2.362 8271.05 2.885 10071.37 3.513 12284.33 4.285 14909.38 5.201 18276.93 6.376 22352.11 7.797 27044.75 9.434 33084.21 11.541 40476.16 14.120

Size 905 907 909 911 913 915 917 919 921 923 926 929 933 937 941 945 949 954 960

Free Inlet F 410.40 828.77 1392.65 2102.04 2956.96 3957.39 5103.34 6394.80 7831.78 9311.11 11944.07 14904.43 19360.90 24399.43 30020.04 36222.71 43007.45 51820.34 64125.64

Ducted Inlet F 448.22 905.13 1520.97 2295.74 3229.43 4322.05 5573.59 6984.06 8553.45 10169.10 13044.67 16277.82 21144.93 26647.75 32786.27 39560.50 46970.43 56595.39 70034.58

A 0.123 0.249 0.418 0.630 0.887 1.187 1.530 1.917 2.348 2.792 3.581 4.469 5.805 7.316 9.001 10.861 12.896 15.538 19.228

Transducer Sizing for Piezometer Ring Selecting a pressure transducer with the appropriate range is critical in order to get accurate measurements using the piezometer ring. Since most transducers list accuracy as a percent of full scale, if the range selected is too high, this can have a significant impact on the accuracy of the flow measurement. If the range is too low, there is risk of damaging the instrument and/or getting inaccurate readings or no reading at all. The following steps are for sizing the pressure transducer for use with the piezometer ring flow measurement system: 1. Determine the maximum flow rate in CFM that the fan is expected to produce. This maximum should be the greater of normal, maximum, and/or emergency conditions. 2. Find the formula for calculating the actual flow rate from page 1 of this document for the corresponding size and type of fan being used. 3. Calculate the pressure drop corresponding to the maximum flow rate determined in Step 1. 4. Select the pressure transducer with the smallest range that includes the pressure drop calculated in Step 3. 5. Now take the maximum range from the pressure transducer selected in Step 4 and use that to calculate the maximum flow rate that could be measured with this transducer. 6. Determine an acceptable safety factor for sizing the transducer. 7. Multiply the maximum flow rate from Step 1 by the safety factor. If the maximum flow rate from Step 5 is less than the result, bump up the transducer to the next largest size. Otherwise, the transducer from Step 4 should be used.

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Example: Company XYZ has a size 270 BC SWSI fan to be installed with design conditions of 12,000 CFM at 5 inches w.g. and standard density. What size transducer should be used? 1. After speaking to the design engineer, it was determined that 12,000 CFM is the actual maximum and most of the time the fan will be running closer to 10,000 CFM. Therefore, 12,000 CFM will be used for the calculations. 2. The calculation for this fan type and size is: ACFM = 4247.77 * (∆P) for standard density Note that if the density was other than standard air, the formula would be different. 3. By rearranging the formula in Step 2, the following formula is obtained: ∆P = (ACFM/4247.77)^2 so, ∆P = (12000/4247.77)^2 = 7.98 inches w.g. 4. For the pressure transducer models being considered, the ranges are 0-3, 0-6, 0-10, and 0-20. Therefore, for this flow rate the transducer model is the 0-10 inches w.g. model. 5. The maximum for this transducer is 10 inches, which corresponds to the following flow rate: ACFM = 4247.77 * (10) = 13433 CFM 6. Since 12,000 CFM is the maximum and normal operating conditions are 10,000 CFM, a 10% safety factor should be plenty for this application 7. From step 1, 12000 CFM * 1.1 = 13200 CFM. This is less than 13433 CFM, so the 0-10 inch pressure transducer is acceptable.

Twin City Engineering Supplement ES-105

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