CLCH-SVX06A-EN •
T-Series Climate Changer Air Handler IOM
83
Start-Up
Fan Inlet Airflow Measuring System
Wiring
In the absence of a factory-provided control system, consult the transmitter
manufacturer or the factory for wiring.
Note: Ensure that the transmitter has a separate power source.
Transmitter Calibration
The transmitter is factory-calibrated to a specific pressure range with a 0-20 inch w.g.
range being used in most cases. To check calibration and to adjust if necessary, consult
the transmitter manufacturer or the factory for specific procedures.
The transmitter outputs a linear, 4-20 mA signal representing a differential pressure
measurement. With this measurement, the airflow through the fan can be calculated
using the following equation:
Significant differences in elevation and/or temperature will affect the density of air. For
air at a constant, non-standard density, a field-obtained K factor can be used.
Alternatively, the following equation can be used to continuously correct the equation
above:
Note: Alternative units, including SI, can be used in place of the IP units above although
the K-factor must be converted appropriately.
Figure 63. Piezometer airflow
measurement
A fan inlet airflow measuring system with a
piezometer ring is available on many centrifugal and
plenum fans. Each system comes with a differential
pressure transmitter. The piezometer ring is
connected to the LO port of the transmitter and the
reference pressure point is connected to (or actually is)
the HI port of the transmitter.
CFM = K * SQRT(DP)
Where:
CFM = Airflow (ft
3
/min) assuming a standard air density of 0.075 lbm/ft
3
.
K = A constant factor that’s unique for each fan. See next section for more information.
DP = Differential pressure (inches w.g.) being measured by the transmitter.
ACFM = CFM * SQRT(0.075/
ρ
)
Where:
ACFM = Actual airflow (ft
3
/min) corrected for non-standard air density.
ρ
= Density (lbm/ft
3
) of the air at the inlet to the fan.
