Sequence of Operation
RT-SVX34F-EN
95
Purge Mode (Comfort and Dehumidification).
Purge cycle operation will operate identically to Purge on
non-Single Zone VAV Dehumidification units; if the Reheat
Circuit operates in one mode (dehumidification or cooling)
for a cumulative 60 minutes the unit will initiate a 3-minute
Purge cycle with all compressors energized, the Cooling
and Reheat Valves at 50%, and the Reheat Pumpout relay
de-energized.
During an active Purge Cycle the Supply Fan Speed will
operate at the appropriate speed based on the active
compressor step. If a dehumidification purge is initiated,
the unit will run at 80%, if performing a cooling purge the
supply fan will track based on the appropriate minimum
speed for the associated number of compressors
energized. After the Purge Cycle is complete, the Supply
Fan will be released to normal control based on the
Cooling/Dehumidification demand.
Dehumidification - Humidistat Operation.
A
humidistat input located on the Options module will be
supported as on non-SZ VAV.
Other Dehumidification Related Topics.
The
following aspects of Single Zone VAV units configured
with Modulating dehumidification will operate identically
to non-Single Zone VAV units:
1.
Outdoor Fan Control.
2. Low Pressure/High Pressure Cutout input handling.
3. Function Enable/Disable Details.
Failure and Overriding Conditions
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:
1.
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%).
2. 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%.
3. Zone Temperature Sensor Failure - If the Active Zone
Temperature input goes out of range, the unit will
discontinue all Heating, Cooling, and Dehumidification
operation.
4. 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.
5. Frostat Failure - If the unit has a Froststat Failure occur,
all active Heating, Cooling, and Dehumidification will
be de-energized immediately and the Supply Fan will
ramp up to 100%.
6. 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.
Low Pressure Control (LPC)
Sequence of Operation (ReliaTel
Control)
When the LPC is opened for one (1) continuous second, the
compressor for that circuit is turned off immediately. The
compressor will not be allowed to restart for a minimum
of three (3) minutes.
If four consecutive open conditions occur during the first
three minutes of operation, the compressor will be locked
out, a diagnostic communicated to ICSTM if applicable,
and a manual reset will be required to restart the
compressor.
High Pressure Control and
Temperature Discharge Limit
(ReliaTel Control)
The Temperature Discharge Limit (TDL) is located in the
Compressor Output circuit and is connected in series with
the High Pressure Control (HPC). The RTRM will register an
auto reset lockout if either the high pressure control switch
or the temperature discharge limit opens during
compressor operation. If the compressor output circuit is
opened four consecutive times during compressor
operation, the RTRM will generate a manual reset lockout.
