Trane ReliaTel - Outdoor Air Flow Compensation for VAV Units; Set up; Operation for RTRM 7.0 and Earlier with RTEM or Any RTRM with Honeywell ECA

158 RT-SVD03G-EN
Outdoor Air Flow Compensation for VAV Units
Outdoor Airflow Compensation (27½ - 50 Ton VAV only)
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.
Note: 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.
Set up
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).
Note: 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%.