Orion System VCM-X Modular E-BUS - Manual (Page 56)

Zone
Zone
SEQUENCE OF OPERATIONS
VCM-X Modular E-BUS Controller Technical Guide 56
For DX Cooling Stages, the VCM-X E-BUS activates the Cooling
Stages based on the actual Evaporator Coil Temperature compared to the
Evaporator Coil Temperature Setpoint. The Evaporator Coil Temperature
is calculated by using the Suction Pressure Sensor and converting the
pressure to temperature.
For Copeland Digital Scroll™ Compressor units, the VCM-X E-BUS
will modulate the Copeland Digital Scroll™ Compressor to maintain
the Evaporator Coil Temperature Setpoint and activate Fixed Capacity
Compressors as necessary.
If the Fixed Capacity Compressor is activated, the Copeland Digital
Scroll™ Compressor will only be allowed to modulate within the range
of 70% - 100% in order to prevent the loss of reheat capacity during low
load conditions. If, with both compressors on, the digital compressor
has modulated down to its 70% minimum and the Coil Suction Tem-
perature falls below the Coil Temperature Setpoint minus the Cooling
Stage Control Window, then the second compressor will stage off once
its Compressor Minimum Run Time and the Stage Down Delay Timers
have been met. At that point, the Copeland Digital Scroll™ Compressor
can modulate down as needed to maintain the Coil Temperature Setpoint.
For Chilled Water units, the VCM-X E-BUS opens the Chilled Water
Valve to a fi xed 100% position to provide full moisture removal capa-
bilities.
If you confi gured your VCM-X E-BUS for Dehumidifi cation control, you
need to install a Humidity Sensor on the optional Analog Input Expan-
sion module. If the VCM-X E-BUS is confi gured as an MUA unit, use
an Outdoor Air Humidity Sensor. If the VCM-X E-BUS is confi gured as
a VAV or CAV unit, use an Indoor Air Humidity Sensor such as a Wall-
Mounted or Duct-Mounted Sensor. If the VCM-X E-BUS is to be used
for MUA/CAV Dual Damper Modes during Occupied hours, use both
Indoor and Outdoor Air Humidity Sensors. As an example, this could
be used in a kitchen application when you have a CAV unit using both
Outdoor Air and Return Air. This unit could be confi gured to operate
using Return Air when the Exhaust Hood is off or 100% Outdoor Air
when the Exhaust Hood is on.
If the unit is equipped with a Modulating Hot Gas Reheat Controller
(MHGRV), it is automatically detected by the VCM-X E-BUS Control-
ler. In Dehumidifi cation Mode, as the Cooling causes the Supply Air
Temperature to drop, the MHGRV will bypass Hot Gas to the Hot Gas
Reheat Coil, raising the Supply Air Temperature back up to the Active
Supply Air Temperature Setpoint.
If the unit is equipped with an On/Off Hot Gas Valve, then one of the
relays will be confi gured for Reheat. The Reheat Relay will be activated
if the Supply Air Temperature is less than the HVAC Mode Enable
Heating Setpoint. The Hot Gas Reheat Relay will remain on during the
Dehumidifi cation Mode regardless of the Supply Air Temperature. This
is to ensure a steady Supply Air Temperature.
The Dehumidifi cation Mode can be confi gured to have Dehumidifi cation
Priority. If confi gured, the VCM-X E-BUS 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 by the Active Supply Air Temperature Setpoint. The
Active Supply Air Temperature Setpoint will change during Heating,
Cooling, or Vent Modes. During the Vent Mode, the Supply Air Tem-
perature Setpoint will be a Calculated Setpoint that is halfway between
the HVAC Mode Setpoints.
If Dehumidifi cation Priority has not been confi gured, the VCM-X E-
BUS 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
dehumidification 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 VCM-X E-BUS
will check BI8 input on the VCM-X Expansion Module for a 24 VAC
signal. If the signal is present, it will force the VCM-X E-BUS into De-
humidifi cation Mode regardless of the mode it is currently operating in
if Dehumidifi cation Priority Mode has been confi gured. If Dehumidifi ca-
tion Priority Mode has not been confi gured, the unit will only be forced
into Dehumidifi cation 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 function,
set the Dehumidifi cation Spt Indoor RH to 100% for the Remote
Forced Dehumidifi cation feature to function.
Coil Temperature Offset for Split Systems
On split systems that have the condensing unit mounted a considerable
distance from the air handling unit, the actual Evaporator Coil Tempera-
ture can be quite a bit different than the Calculated Coil Temperature
based on the Suction Pressure Transducer reading in the condensing unit.
You can put in a temperature offset to the Calculated Coil Temperature
reading so that it will more closely match the actual Evaporator Coil
Temperature. For example, the Suction Pressure Transducer in the con-
densing unit may give you a Calculated Coil Temperature reading of
30ºF, but the actual temperature of the Evaporator Coil in the air handler
may be 45ºF. To compensate, you can put in a 15ºF offset so that the
Calculated Coil Temperature reading will read 45ºF. The maximum
amount of offset allowed is ± 30ºF.
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.
Dehumidifi cation Mode