Ingersoll-Rand ReliaTel, Manual, Page: 172 / 176

172 RT-SVD03L-EN
Outdoor Air Flow Compensation for MZVAV Units
3 to 50 Tons
When a VAV unit is modulating supply airflow, the
pressure drop across the outdoor air damper changes.
This usually means that the quantity of outside air will
drop as the IGV closes or the VFD slows down. VAV
units have a feature called outside air (OA) flow
compensation to help maintain consistent OA flow
regardless of supply airflow.
N No otte e:: OA flow compensation mode is disabled if the
unit has a CO
2
sensor, min position input from
ICS, or remote min position input at LTB3-1 and
LTB3-2. It is also overridden during all ventilation
override modes. Also, the minimum position can
only be adjusted from 0 to 50% damper position
regardless of OA flow setpoints.
Setup
Once set up, the OA damper position will increase as
the IGV closes or VFD slows down. The 27K resistor
with plug in KIT#PLU00970 provides a signal to the unit
to enable this function. The resistor must be plugged to
the "OAT" input (this is an otherwise unused input) on
the economizer module (ECA) and power reset to the
unit.
Operation for RTRM 7.0 and Earlier with
RTEM or Any RTRM with Honeywell ECA
The potentiometers MIN POS and DCV SETPOINT (DCV
UL setpoint if RTEM) must now each be set in order to
control the OA damper position. The MIN POS setpoint
determines the OA damper position (from 0 to 50%)
when the IGV / VFD is at 100% regardless of DCV
SETPOINT (DCV UL Setpoint).
N No otte e:: This function is disabled if a building
management system (ICS, Tracer®, LonTalk®) is
providing a OA damper minimum position
setpoint to the unit. This function is disabled if
the unit is using a CO
2
sensor input at the DCV
input or if a building management system (ICS,
Tracer
® , LonTalk ® ) is providing a CO
2
sensor
input to the unit.
The DCV SETPOINT (DCV UL Setpoint) determines the
percentage increase of the OA damper position when
the IGV / VFD is at 0%. The percentage of OA damper
increase between 0 and 100% IGV / VFD is linear. To
have no effect on the OA damper position when the
IGV/VFD output is 0%, set the DCV SETPOINT to 0%. To
have the maximum effect on the OA damper position
when the IGV/VFD output is 0%, set the DCV SETPOINT
(DCV UL Setpoint) to 100%. This chart shows the effect
of DCV input vs. MIN POS when the IGV/VFD is at 0%.
Figure 107. Outdoor airflow compensation
EXF
MAT
OAH/
OAE
OAT
RAT
RAH/
RAE
DCV
OPEN
CCW CW
Min. Pos.
Setpoint
0-50%
ABCD
Settings
DCV Setpoint
0-100%
Green
LED
27k Resistor
Goes Here
Remote Minimum
Position Potentiometer
L
T
B
3
-
2
L
T
B
3
-
1
Table 107. OA damper minimum position when IGV
is closed /VFD at min. HZ
MIN
POS 0%
(CCW)
MIN
POS
25%
MIN
POS
50%
(CW)
DCVSP (DCV UL SP)0% 0 (closed)
25% 50%
DCVSP (DCV UL SP)
50%
25% 37.5% 50%
DCVSP (DCV UL SP)
100%
50% 50% 50%
Operation for RTRM 8.0 and Later with
RTEM
Once configured appropriately as described above, the
potentiometers "Design Min Pos" and "DCV Min Pos"
must each be set in order to control the OA damper
position. The Design Min Pos potentiometer
determines the OA damper position (from 0 to 50%)
when the IGV / VFD is at 100%. The DCV Min Pos
potentiometer determines the OA damper position
(from 0 to 50%) when the IGV / VFD is at 0%.
N No otte e:: This function is disabled if a building
management system (ICS, Tracer ® , LonTalk ® ) is
providing an OA damper minimum position
setpoint to the unit. This function is disabled if
the unit is using a CO
2
sensor input at the DCV
input or if a building management system (ICS,
Tracer
® , LonTalk ® ) is providing a CO
2
sensor
input to the unit.