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62 RT-SVD03L-EN
compressor that when energized allows the
compressor to operate at full capacity.
When the unit receives a call for cooling, if the
economizer is enabled, the unit will energize the supply
fan at low speed and begin to modulate the OA damper
open above minimum position up to 100% as
necessary to meet the mixed air temperature setpoint.
If the OA damper reaches 100% the supply fan will
increase to maximum speed and remain there for 5
minutes. The unit will then begin to energize the
compressor outputs to meet cooling demand.
If the economizer is not enabled and the unit enters
Cool 1 due to normal cooling control schemes, the
supply fan will energize and will start operation at the
low speed of 1st stage airflow profile. If no other calls
for stage 2 of cooling are present, the unit will remain
in the 1st stage airflow profile and the fan will only
operate up to 70% of the maximum output signal per
user selection.
After the minimum 3 minute inter-stage timer has
expired from the compressor 1 output being energized,
the RTRM will energize the compressor 2 output if
requested, and will shift the airflow profile vertically
into the 2nd stage airflow profile until the call reduces
to Stage 1.
The unit will stage down compressors and modulate
the economizer back to minimum position in the
reverse order that they were staged and the supply fan
will follow the unit mode transitions based on the
defined airflow profiles. Once the supply fan is no
longer requested ON after a cooling call is cleared, the
supply fan will remain energized at low speed for 160
seconds.
Compressor Protection
Special handling of the compressor protection inputs
on the RTRM is necessary for this unit due to the dual
capacity compressor. The compressor 1 proving and
disable inputs will be honored and the associated
counters incremented when the inputs go active. Once
active, both compressor outputs on the RTRM will be
de-energized and inhibited from running until the fault
clears. The compressor 2 disable input will be honored
so customers can disable the high stage operation of
the compressor if desired. No compressor operation
will be locked out based on compressor 2 disable
events.
The evaporator defrost control scheme will be initiated
at an OA temperature of 55°F.
Outdoor Fan Control
This unit control scheme will require no changes in
existing outdoor fan control logic for ReliaTel
™ . The
unit design currently only supports a single outdoor
fan so the Outdoor Fan B output from the RTRM will be
utilized.
Economizer Min Position Handling (w/o
DCV)
Economizer minimum positions will be handled
similarly to how they are handled on other multi-speed
indoor fan units.
The following setpoint potentiometers will be used on
the RTEM:
• Design min at min fan speed PWM command
(RTEM DCV min)
• Design min at medium fan speed PWM command
(RTEM DCV setpoint LL)
• Design min at max fan speed PWM command
(RTEM design min)
The controller will calculate the active OA damper
minimum position linearly between the user-selected
setpoints based on the supply fan speed command.
The range for 'RTEM DCV Min' and 'RTEM DCV
Setpoint LL' setpoints will be 0-100% while the range
for the 'RTEM Design Min' setpoint will be 0-50%.
As the supply fan speed ramps between its minimum
and maximum output signal (based on cooling or
heating modes/steps), the active economizer minimum
position target will be calculated in a linear fashion,
similarly to the OA CFM compensation function, in
order to help maintain a constant OA flow through the
unit and not over/under-ventilate.
Demand Controlled Ventilation
DCV for this unit control will require an additional
module (RTVM) for the 3 additional setpoint
potentiometers necessary with the varying supply fan
speed. The basic control strategy integrates 2 existing
functions which on traditional units are mutually
exclusive: OA CFM Compensation and DCV.
N No otte e:: For all DCV operation, the supply fan will remain
at minimum speed unless requested higher for
heating or cooling operation.
This new scheme will require the setting of 5 OA
damper position setpoints; 3 more than on traditional
units which will be located on the required RTVM:
• Design Min Position @ Min Fan Speed PWM
Command (RTVM R130)
• Design Min Position @ Medium Fan Speed PWM
Command (RTVM R136)
• Design Min Position @ Max Fan Speed PWM
Command (RTEM Design Min Position)
• DCV Min Position @ Min Fan Speed PWM
Command (RTVM R41)
• DCV Min position @ Max Fan Speed PWM
Command (RTEM DCV Min Position)
As the supply fan speed tracks between the minimum
and maximum % of the user selected setpoint, the
active building design and DCV minimum positions will
be calculated linearly between the user selected
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