AIRFOIL FAns - HTS

Flow Measurement System
Piezometer Ring (Airflow Measuring
System)
A piezometer ring is available on model BAE fans, as
well as other Twin City Fan housed and plenum fans,
as part of an airflow measuring system, based on the
principle of a flow nozzle. The inlet cone of the fan is
used as the flow nozzle. The flow can be calculated
by measuring the pressure drop through the inlet
cone. No tubes or sensors are inserted in the high
velocity airstream which could obstruct airflow.
The system, consists of a piezometer ring mounted
at the throat and a static pressure tap mounted on
the face of the inlet cone. A differential pressure
transducer and digital display can also be provided.
The pressure drop is measured from the tap located
on the face of the inlet cone 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.
Based on Twin City Fan laboratory tests, the system
was determined to be accurate within +/-5%.
Refer to Twin City Fan Engineering Supplement ES-
105.
NOTE: Twin City Fan does not recommend placement
of flow measuring probes inside the fan inlet
cone in the path of airflow. These devices create
disturbances and unpredictable performance losses.
Twin City Fan will not be responsible for loss of performance
due to such devices.
Piezometer Ring
Mounted at Throat
of Inlet Cone
Performance Correction for Temperature & Altitude
The performance tables in this catalog are based
on fans handling standard air at a density of 0.075
pounds per cubic foot. This is equivalent to air at
70°F at sea level (29.92" Hg barometric pressure).
When specified performance is at a density different
than standard, it must be converted to the
equivalent standard conditions before the fan can be
selected from the performance tables. The equivalent
standard conditions can be calculated by using the
Temperature and Altitude Density Ratios shown in the
table below.
Temperature and Altitude Density Ratios
ALTITUDE IN FEET ABOVE SEA LEVEL
AIR
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 15000
TEMP
BAROMETRIC PRESSURE IN INCHES OF MERCURY
°F
29.92 28.86 27.82 26.82 25.84 24.90 23.98 23.09 22.22 21.39 20.58 16.89
–50 1.293 1.247 1.201 1.159 1.116 1.076 1.036 0.997 0.960 0.924 0.889 0.729
0 1.152 1.111 1.071 1.032 0.995 0.959 0.923 0.889 0.856 0.824 0.792 0.650
50 1.039 1.003 0.967 0.932 0.897 0.864 0.833 0.801 0.772 0.743 0.715 0.586
70 1.000 0.964 0.930 0.896 0.864 0.832 0.801 0.772 0.743 0.714 0.688 0.564
100 0.946 0.912 0.880 0.848 0.818 0.787 0.758 0.730 0.703 0.676 0.651 0.534
150 0.869 0.838 0.808 0.770 0.751 0.723 0.696 0.671 0.646 0.620 0.598 0.490
200 0.803 0.774 0.747 0.720 0.694 0.668 0.643 0.620 0.596 0.573 0.552 0.453
250 0.747 0.720 0.694 0.669 0.645 0.622 0.598 0.576 0.555 0.533 0.514 0.421
300 0.697 0.672 0.648 0.624 0.604 0.580 0.558 0.538 0.518 0.498 0.480 0.393
350 0.654 0.631 0.608 0.586 0.565 0.544 0.524 0.505 0.486 0.467 0.450 0.369
400 0.616 0.594 0.573 0.552 0.532 0.513 0.493 0.476 0.458 0.440 0.424 0.347
450 0.582 0.561 0.542 0.522 0.503 0.484 0.466 0.449 0.433 0.416 0.401 0.328
500 0.552 0.532 0.513 0.495 0.477 0.459 0.442 0.426 0.410 0.394 0.380 0.311
550 0.525 0.506 0.488 0.470 0.454 0.437 0.421 0.405 0.390 0.375 0.361 0.296
600 0.500 0.482 0.465 0.448 0.432 0.416 0.400 0.386 0.372 0.352 0.344 0.282
650 0.477 0.460 0.444 0.427 0.412 0.397 0.382 0.368 0.354 0.341 0.328 0.269
700 0.457 0.441 0.425 0.410 0.395 0.380 0.366 0.353 0.340 0.326 0.315 0.258
750 0.439 0.423 0.407 0.393 0.379 0.365 0.351 0.338 0.326 0.313 0.303 0.248
800 0.420 0.404 0.389 0.375 0.362 0.350 0.336 0.323 0.311 0.300 0.290 0.237
850 0.404 0.391 0.376 0.363 0.349 0.336 0.324 0.312 0.300 0.289 0.279 0.228
900 0.389 0.376 0.363 0.349 0.336 0.324 0.312 0.300 0.289 0.279 0.268 0.220
950 0.376 0.363 0.350 0.337 0.325 0.313 0.301 0.290 0.279 0.269 0.259 0.212
1000 0.363 0.350 0.338 0.325 0.314 0.302 0.291 0.280 0.270 0.259 0.250 0.205
11
Twin City Bulletin 370