Digital Scroll Operation During Dehumidification; Reheat Output; Supply Air Setpoint Reset; Primary Heat Used As Reheat - Emerson iPro.Genius Installation And Operational Manual

calculated dehumidification load. In all units, the first
cooling stage will activate once the load reaches 20%.
As the dehumidification load increases, it will be
distributed proportionally across cooling stages based
on the magnitude of the load and the number of
available cooling stages.
For example, in a two-stage unit, the first cooling
stage will activate at 20% dehumidification load, and
the second cooling stage will activate at 60% load.
Similarly, in a four-stage unit, the first stage will
again activate at 20% load, followed by the second
stage at 40%, the third stage at 60%, and the fourth
and final stage at 80%. Thus, the maximum load will
be distributed across all available cooling stages.
The cooling stage will remain active until the load
drops to the activation point for the prior stage or to
0% in the case of the first stage. The sequence of
activation of additional compressors is similar to the
staging during cooling mode, including using the
same cooling stage delays and the cooling PID
settings.
7.6.2.1. Digital Scroll Operation During
Dehumidification
7.6.2.1.1. Adjusted Minimum Percentage
If additional fixed compressor stages are required
to be brought on during dehumidification, the digital
compressor will only be allowed to modulate down to
a minimum of 70%, even if the minimum capacity
setpoint for the digital compressor is set to a lower
value. This will reduce the loss of reheat capacity
during low load conditions. If the digital compressor
stays at 70% for the duration of the cool stage-off
delay, the fixed compressor will be turned off.
7.6.2.1.2. Multiple Digital Compressors
If two digital compressors are defined and both are
configured to be used for dehumidification, the
second digital compressor will not turn on until the
first digital compressor has reached its maximum
capacity, similar to how digital compressors stage up
in cooling mode. Two suction pressure inputs are
supported, so when the second digital compressor is
activated, the controller will use the second suction
pressure transducer to calculate the coil temperature.

7.6.3. Reheat Output

When dehumidification is active, the Reheat
output will activate when the space temperature drops
1°F below the cooling space temperature setpoint.
However, if a return air bypass damper is configured,
the Reheat output will not be permitted to activate
Discharge Air Controller (DAC) Manual
until the return air bypass damper reaches 100%.
Once activated, the Reheat output will remain active
until the space temperature either rises above the
cooling space temperature setpoint, or falls below the
heating space temperature setpoint (at which point
heating mode will activate).
7.6.3.1.

Supply Air Setpoint Reset

When the Reheat output is active, and the Supply
Air Setpoint Reset output is defined, the Reset output
will modulate proportionally based on the space 
temperature. Specifically, as the space temperature
drops from the Cooling setpoint to the Heating 
setpoint, the Reset output will increase from 0% to
100%

7.6.4. Primary Heat Used as Reheat

Primary heating stages can be used instead of or in
addition to the reheat output in order to maintain a
dehumidification supply air setpoint. When used in
addition to the reheat output, the primary heat will
only stage on if the reheat output has been on for the
Heat On-Delay period. Primary heat stages will then
stage on according to the Heat On-Delay time as long
as the supply temperature remains below the
dehumidification supply setpoint. The heat stages will
stage off if the supply temperature rises above the
dehumidification supply setpoint plus the
dehumidification supply deadband, according to the
Heat Off-Delay setpoint.

7.6.5. Return Air Bypass Damper

The return air bypass (RAB) damper is only used
on constant air volume units and only during
dehumidification mode. When defined, the RAB
damper acts as the first form of reheat. The RAB
damper modulates from 0-100% as the space
temperature falls below the cooling setpoint. When
the space temperature is equal to the cooling setpoint,
the RAB damper will be at 0%. When the space
temperature falls to halfway between the active
cooling and heating setpoints, the RAB damper will
be at 100%.
7.6.5.1. Return Air Damper During Dehu-
midification
If the unit has a separate actuator for the return air
(RA) damper (i.e., not linked to the outdoor air
damper), the return air damper will proportionally
close more as the RAB damper opens during
dehumidification mode. The rate at which the RA
damper will close is determined by the RA Damper
Software Overview • 21