Orion System RNE Modular Controller - Manual (Page 57)

RNE Modular Controller Field Technical Guide
SEQUENCE OF OPERATION
57
Dehumidifi cation Mode
If the 2 nd VFD Compressor modulates down to 0% for the Stage
Down Delay period, it will stage off. If the 1 st VFD Compressor
modulates down to 0% for the Stage Down Delay period, it will
stage off.
4 Compressor Units (RNE 120-140)
The fi rst two VFD Compressors will be driven out of the Analog
Output (AO) #1, and the second two VFD Compressors will be
driven out of the AO #2. The fi rst two VFD Compressors will
enable and modulate together to maintain the Average Coil Tem-
perature at the Coil Temperature Setpoint. If the signal to those
compressors reaches 100% for the Stage Up Delay period, the
3 rd
compressor will stage on. The signal from AO #1 to the fi rst two
compressors will then be locked at 100% while the
3 rd compres-
sor modulates from AO #2 to maintain the Coil Temperature
Setpoint. If the signal to the
3 rd compressor reaches 80% for the
Stage Up Delay period, the 4 th compressor will enable. The signal
from AO #2 will then be cut in half and the 3 rd and 4 th compres-
sors will modulate together.
With all four compressors on, if the signal from AO #2 goes to
30% for the Stage Down Delay period, then the
4 th compressor
will stage off. If the signal from AO #2 then goes to 0% for the
Stage Down Delay period, the
3 rd compressor will stage off. If
the signal from AO #1 to the fi rst two VFD Compressors then
goes to 0% for the Stage Down Delay period, those compressors
will stage off.
Priority and Night Dehumidifi cation
The Dehumidifi cation Mode can be confi gured to have Dehumidifi cation
Priority. If confi gured, the RNE will enter the Dehumidifi cation Mode
when the Dewpoint or Humidity is above the Setpoint regardless of the
current Heating or Cooling demands. The Reheat is always controlled to
the Active Supply Air Temperature Setpoint. The Active Supply Air Tem-
perature Setpoint will change during Heating, Cooling, or Vent Modes.
During the Vent Mode, the Supply Air Temperature Setpoint will be a
Calculated Setpoint that is halfway between the HVAC Mode Setpoints.
If Dehumidification Priority has not been configured, the RNE
will only enter the Dehumidifi cation Mode and use Reheat during
the Vent Mode. The Reheat will be controlled to a Calculated Supply
Air Temperature Setpoint that is halfway between the HVAC Mode
Setpoints.
Night Dehumidifi cation can also be confi gured and is used primarily
for CAV units that require an Unoccupied Mode of Dehumidifi cation.
Night Dehumidifi cation is only activated when the Indoor Air Humidity
is above the Indoor Air Humidity Setpoint during the Unoccupied Mode.
NOTE: Compressor Lockout Setpoints are ignored during de-
humidifi cation as the compressors are controlled by coil
temperature.
Remote Forced Dehumidifi cation
Dehumidifi cation Mode is normally controlled by using a Humidity
Sensor connected to the VCM-X Expansion Module input AI1 or AI2.
If desired, Dehumidifi cation Mode can also be determined by using a
remote BAS or other user-supplied remote device. The RNE will check
BI8 input on the VCM-X Expansion Module for a 24 VAC signal. If
the signal is present, it will force the RNE into Dehumidifi cation Mode
regardless of the mode it is currently operating in if Dehumidifi cation
Priority Mode has been confi gured. If Dehumidifi cation Priority Mode
has not been confi gured, the unit will only be forced into Dehumidifi ca-
tion Mode if it is operating in the Vent Mode during the time the remote
signal is being supplied to input BI8.
NOTE: When using the Remote Forced Dehumidifi cation func-
tion, set the Dehumidifi cation Spt Indoor RH to 100% for
the Remote Forced Dehumidifi cation feature to function.
Coil Temperature Reset
Any time an Indoor Humidity Sensor is used, the Coil Temperature
Setpoint will be automatically reset as the humidity rises above or drops
below the Indoor Humidity Setpoint. It can reset the Coil Temperature
Setpoint by a maximum of 5ºF. For example, if the Coil Temperature
Setpoint is 45ºF and the Indoor Humidity Setpoint is 50% with an ac-
tual humidity reading of 55%, the new Coil Temperature Setpoint will
be 40ºF. If the humidity is below the Indoor Humidity Setpoint, then
the Coil Temperature Setpoint will be increased by a maximum of 5ºF.
Return Air Bypass Damper Control
The Return Air Bypass (RAB) Damper is only used on constant air
volume units with space temperature confi gured as the HVAC Mode
Enable sensor. The RAB damper is only active during the dehumidifi -
cation mode and is used as the fi rst form of reheat. If the HVAC unit is
equipped with modulating hot gas reheat, the RAB damper needs to be
at 100% before the modulating hot gas reheat can be used. 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 cooling and heating setpoints, the RAB
damper will be at 100%.
If the HVAC unit is equipped with separate actuators for the outdoor
air and return air dampers, the return air damper will proportionally
close more as the RAB damper opens. The rate at which the return air
damper closes is user-adjustable. The purpose of closing the return air
damper more as the RAB damper opens is to allow more air to bypass
the evaporator coil through the RAB damper. If you want more air to
pass through the RAB damper, enter a larger number in the Return Air
Damper Factor setpoint. If you want less air to pass through the RAB
damper, enter a smaller number in the Return Air Damper Factor setpoint.
NOTE: See page 5 for specifi c AAON
® DPAC and PAC
operation.