Sequence of Operation
RT-SVX26R-EN
47
By default, the Design Minimum Position schedule will be
a linear line through all user selectable Design Minimum
Position setpoints. The user will have the ability to set the
Design Minimum Position at Middle fan speed command
to a point that would be lower than the calculated linear
line between the Design Minimum Position setpoints at
0% and 100% fan speed command in order to compensate
for the non-linear outside airflow through the fan and
damper modulation range. However, if the Design
Minimum Position at Middle fan speed command is set to
a point that would be higher than the calculated linear line
between the Design Minimum Position setpoints at
Minimum and Full fan speed command, the minimum
position will be limited to the point that would make the
Design Minimum Position schedule linear.
Provisions have been made in Service Test Mode to allow
for proper damper minimum position setup:
1. To set the Design and DCV Minimum Position setpoints
at Minimum Fan Speed, set the unit to operate at Step
1 (Fan ON) or Step 2 (Economizer Open) and make the
proper adjustments.
2. To set the Design Minimum Position setpoint at Middle
Fan Speed, set the unit to operate at Step 3 (Cool 1) and
make the proper adjustment.
3. To set the Design and DCV Minimum Position setpoints
at Full Fan Speed, set the unit to operate at Step 4 (Cool
2) and make the proper adjustments.
Economizer Damper Position Set-Up without
DCV
For units not configured with DCV (no CO
2
sensor value
available), additional minimum position setpoints to
increase outdoor airflow accuracy will be supported. The
operation will be similar to OA CFM Compensation on
Traditional VAV units with the addition of a Design
Minimum Position setpoint at Middle Fan Speed
Command. The following setpoint potentiometers will be
used on the RTEM:
1. Design Min at Minimum Fan Speed Command (RTEM
DCV Min)
2. Design Min at Middle Fan Speed Command (RTEM
DCV Setpoint LL)
3. Design Min at Full Fan Speed Command (RTEM Design
Min)
The controller will calculate the active OA Damper
Minimum position between the user-selected setpoints
based on the supply fan speed command. By Default, the
Design Minimum Position schedule will be a linear line
through all user selectable Design Minimum Position
setpoints. As with Demand Controlled Ventilation, if the
Design Minimum Position at Middle fan speed command
is set to a point that would be higher than the calculated
linear line between the Design Minimum Position
setpoints at Minimum and Maximum fan speed
command, the minimum position will be limited to the
point that would make the Design Minimum Position
schedule linear.
Provisions have been made in Service Test Mode to allow
for proper damper minimum position setup:
1. To set the Design Minimum Position setpoint at
Minimum Fan Speed, set the unit to operate at Step 1
(Fan ON) or Step 2 (Economizer Open) and make the
proper adjustment.
2. To set the Design Minimum Position setpoint at Middle
Fan Speed, set the unit to operate at Step 3 (Cool 1) and
make the proper adjustment.
3. To set the Design Minimum Position setpoint at Full
Fan Speed, set the unit to operate at Step 4 (Cool 2) and
make the proper adjustment.
Heating Operation
Heating operation on units configured with Single Zone
VAV control will utilize two separate control
methodologies based on heating configurations. For all
“Staged” Heating types the unit will utilize 100% full
airflow during all active heating periods like traditional
Constant Volume units. For Modulating Gas heat units, the
unit will have the ability to control the discharge air
temperature to the calculated discharge air heating
setpoint in order to maintain the Zone Temperature to the
Zone Heating setpoint.
Staged Heating Operation
For units configured with Staged Heat once the control
determines that there is an active heating capacity
request, the unit will energize the Supply Fan and ramp up
to full speed. The control methodology during Active
Heating on units configured with Staged Heat types will be
identical to traditional Constant Volume units; heating
stages will be energized/de-energized to meet the Zone
Heating demand.
Note:
All heat staging sequences will be identical to
Constant Volume unit staging sequences.
Modulating Heat Operation with SZVAV
Heating
Units configured with Modulating Gas Heat will utilize true
Single Zone VAV control in the same manner as during
Active Cooling.
Heating Sequence
Once the unit control determines that there is a space
heating demand, the unit will transition into zone heating.
Once the Discharge Air Temperature falls below the
calculated discharge air temperature setpoint, the unit will
initiate the Modulating Heat output request and control
the supply fan at minimum speed. At this point, the
Modulating Heat output will be controlled to maintain the
discharge air temperature requirements and the supply
fan speed will be controlled between 63%-100% to meet
the zone heating requirements.
