Setup and operation cont, Q (cfm) = a * k * p, Position control mode (override) – Greenheck IAQ-42 (467954) User Manual
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Position Control Mode (Override)
The damper will be in position control mode when there is a closed circuit between control box terminals 11 and
12. In this mode of operation the damper will modulate open and closed based on the 0-10 Vdc position setpoint
signal sent to control box terminals 6 and 7. The 0-10 Vdc position setpoint will linearly modulate the damper’s
blade position between 0 and 100% open. For example, a position setpoint of 4 Vdc will drive the damper blades
to the 40% open position.
Setup and Operation for IAQ-42's Without Factory Supplied Controller
1. Plumb the High and Low Pressure ports to a differential pressure transducer to determine the pressure
difference (P) between the upstream and downstream pickups on the damper blades. A pressure transducer
with an approximate span of 0 – 2.5 in. wc is recommended.
2. Wire the damper’s actuator. Wire actuator terminals 1 (power), 2 (common), 3 (position set-point), and 5
(position feedback). Actuator terminal 4 should not be used.
3. Program the field-supplied controller. A field-supplied controller can be programmed to determine the airflow
going through the damper by using one of two methods. Both methods use the following formula to calculate
the airflow:
Q (cfm) = A * K * P
e
Where:
A = Total Damper Area in Sq. Ft.
K = Flow Coefficient that is a function of the damper’s blade position
supplied by the actuator feedback.
P = Differential Pressure across IAQ damper
e = exponent (constant) supplied by Greenheck
The K value, which is a function of actuator feedback, can be determined by using either of the following
methods. Method A is recommended and will result in the most accurate readings.
Method A
The K value can be determined by using a look-up table that is supplied
with every IAQ-42 that is ordered without a factory supplied controller. The
K value is determined by interpolating between the two values that the
actuator feedback falls between. Since every unit is factory calibrated, every
unit will have a unique look-up table. To the right is an example look-up
table.
Method B
The K value can also be determined by using the following formula where x
is the 0-10 Vdc signal from the actuator’s position feedback:
K = Ax4 + Bx3 + Cx2 + Dx + E
The A, B, C, D, and E values are supplied by Greenheck with every IAQ-42
that is not ordered with a factory supplied controller.
Setup and Operation cont....
Point
Act
Feedback (0-
10 Vdc)
K
1
0.00
0
2
1.95
183
3
2.70
280
4
3.58
369
5
4.35
478
6
4.77
551
7
5.23
647
8
5.57
703
9
5.88
770
10
6.18
843
11
6.52
856
12
6.83
879
13
7.19
900
14
7.54
949
15
7.84
1,008
16
8.17
1,092
17
8.45
1,147
18
8.81
1,273
19
9.10
1,376
20
9.52
1,501
21
9.84
1,651
22
10.00
1,721
Coefficient Look-Up Table