RT-SVF69C-EN
17
Sequence of Operation
Failure and Override Modes
Certain failure and overriding conditions require special
handling of the Supply Fan Speed on units configured with
Single Zone VAV. See below for a list of these conditions:
•
Supply Fan Proving Failure - If a Supply Fan Proving
failure is detected, the Supply Fan will be de-energized
after 40s of run time and the Fan Speed output will go
to 0 Vdc (0%).
•
Ventilation Override Mode - If a VOM goes active in
which the Supply Fan is commanded ON (Purge,
Pressurize, etc.), the Supply Fan will be energized and
the Fan Speed output will ramp to 100%.
•
Zone Temperature Sensor Failure - If the Active Zone
Temperature input goes out of range, the unit will
discontinue all Heating, Cooling, and Dehumidification
operation.
•
Supply Air Temperature Sensor Failure - If the Supply
Air Temperature input goes out of range, the unit will
revert back to Full Airflow, Traditional CV control. The
unit will call out a Supply Air Temperature Sensor
Failure Alarm, the RTRM System LED will flash the 2-
blink error code, and the Zone Sensor Heat
(Modulating Heat Only) and Cool LEDs will flash.
•
Frostat Failure - If a Frostat failure occurs, all active
Heating, Cooling, and Dehumidification will be de-
energized immediately and the Supply Fan will ramp
up to 100%.
•
Heat Failure (High Temp. Limit Trip) - If a unit
configured with Gas Heat has a High Temp. Limit trip,
the Supply Fan will be requested to remain ON and the
Fan Speed output will ramp to full speed.
Variable Air Volume Applications
(Traditional VAV)
Supply Air Temperature Control -
Occupied Cooling and Heating
The RTRM is designed to maintain a selectable supply air
temperature of 40°F to 90°F with a +/- 3.5°F deadband.
Note:
To reduce the risk of coil freezing, it is not
recommended to set the supply air temperature
below 50°F.
In cooling, if supply air temperature is more than 3.5
degrees warmer than the selected temperature, a stage of
cooling will be turned “On” (if available). Then if the
supply air temperature is more than 3.5 degrees cooler
than the selected temperature, a stage of cooling will be
turned “Off”. At very low airflows the unit may cycle stages
“On” and “Off” to maintain an average discharge air
temperature outside the 7 degree deadband.
If the unit has modulating heat, the unit can be made to do
discharge heating with VAV control. This is done by
placing a contact closure across the “Changeover Input”
on the RTAM. During this mode, the unit will heat to the
Supply Air Heating Se/- 3.5°F. During low load or
low airflow conditions the actual temperature swing of the
discharge air will likely be greater.
The RTRM utilizes a proportional and integral control
scheme with the integration occurring when the supply air
temperature is outside the deadband. As long as the
supply air temperature is within the setpoint deadband,
the system is considered to be satisfied and no staging up
or down will occur.
Supply Air Temperature Control with an
Economizer
The economizer is utilized to control the supply air cooling
at +1.5°F around the supply air temperature setpoint range
of 40°F and 90°F providing the outside air conditions are
suitable. While economizing, the mechanical cooling is
disabled until the economizer dampers have been fully
open for three minutes. If the economizer is disabled due
to unsuitable conditions, the mechanical cooling will cycle
as though the unit had no economizer.
VHR Relay Output
During unoccupied mode, daytime warm-up (DWU) and
morning warm-up (MWU) the VFD will open to 100%. All
VAV boxes must be opened through an ICS program or by
the VHR wired to the VAV boxes. The RTRM will delay
100% fan operation approximately 6.5 minutes when
switching from occupied cooling mode to a heating mode.