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Optional Piezometer Ring Airflow
Measurement Device
Piezometer rings are available as an option on direct drive
plenum fans to measure airflow though the fan. The device
consists of a piezometer ring mounted in the throat of the
funnel and a static pressure tap mounted near the inlet of the
funnel. The pressure drop is measured from the tap located
near the inlet 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.
See the equations and factors required to calculate flow using
the piezometer ring.
NOTE: There are two manufacturer options for the piezometer
ring. Care should be taken to ensure that the
appropriate coefficients are used, otherwise airflow
measurement may be incorrect. Reference
to determine which piezometer ring you have.
Figure 46: Determining the Manufacturer
www.DaikinApplied.com
Non-Standard Density Method
The following equation is used to measure the flow for non-
standard density:
ACFM = C1 × A × √(ΔP/ρ)
where: A = Inlet funnel throat area (square feet) - from
and Table 16
ΔP = The differential in static pressure from the piezometer ring
and the inlet pressure tap (inches w.g.)
ρ = Air density (pounds mass/cubic foot)
C1 = Value from
Standard Density Method
The equation can be simplified by assuming standard
density and assuming funnel dimensions match the drawing
dimensions.
Figure 46
fan size and type. The equation then becomes the following:
For standard air (ρ = 0.075 lb/ft3):
ACFM = F × √ (ΔP)
where: F = factor from
ΔP = The differential in static pressure from the piezometer ring
and the front pressure tap (inches w.g.)
Table 13: DDPL Factors For Free and Ducted Inlet —
Non Standard Density Method, TCF Piezo Ring
Product
DDPL Size 11-16
DDPL Size 18-44
Table 14: DDPL Factors For Free and Ducted Inlet —
Standard Density Method, TCF Piezo Ring
DDPL Size
11 and 12
15
16
18
20
22
24
27
30
33
36
40
44
29
Daikin Applied Fan Array
Table 13
and
Table 15
Table 14
and
Table 16
show the factor (F) for each
Table 14 and Table 16
C1 Free Inlet
753.06
692.03
Ducted
Free Inlet F
Inlet F
944.92
996.36
1206.40
1272.08
1518.58
1601.26
1821.92
1948.58
2185.80
2337.76
2713.93
2902.60
3285.02
3513.39
3997.61
4275.53
4945.21
5289.01
5968.62
6383.56
7290.21
7797.03
8869.55
9486.16
10827.92
11580.68
IM 915-13 • VISION - EXTENDED SIZES
Table 14
C1 Ducted Inlet
794.06
740.14
Wheel
Area A
Diameter
0.344
12.40
0.439
14.00
0.552
15.75
0.721
18.25
0.865
20.00
1.074
22.25
1.300
24.50
1.582
27.00
1.957
30.00
2.362
33.00
2.885
36.50
3.510
40.25
4.285
44.50
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