Orion System VCM-X Modular E-BUS - Manual (Page 57)

VCM-X Modular E-BUS Controller Technical Guide
SEQUENCE OF OPERATIONS
57
Heating Mode
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 evapo-
rator 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 6 for specifi c AAON
® DPAC and PAC
operation.
Heating Mode Operation
Occupied Heating Mode occurs whenever the HVAC Mode Enable
Temperature is below the HVAC Mode Enable Heating Setpoint. Un-
occupied Heating Mode only occurs if a Space Temperature Sensor is
connected to the VCM-X E-BUS or a broadcast of Space Temperature
is being received from an Averaging Broadcast Controller.
The Mechanical Heating will be disabled if the Outdoor Air Temperature
is above the Heating Lockout Setpoint by 1°F. This gives a 2°F hysteresis
around the Heating Lockout Setpoint to prevent unwanted cycling in
and out of Mechanical Heating Mode. If the Outdoor Air Temperature
disables the Mechanical Heating while it is currently operating, the Me-
chanical Heating will stage off if all staging and run times are satisfi ed.
No matter which Sensor is confi gured for the HVAC Mode Enable or
if the Remote BAS sets the Mode through Remote Forced Heating, the
Supply Air Temperature is always controlled to the Active Supply Air
Temperature Setpoint while in Heating Mode.
Stage Control Window
The Heating Stage Control Window Setpoint determines when the Heat-
ing Stages begin to stage up and stage down. In the Heating Mode, as the
Supply Air Temperature falls below the Active Supply Air Temperature
Setpoint, the Heating Stages will begin to stage on based on the Heating
Stage Up Delay. The Heating Stages will continue to run until the Supply
Air Temperature rises above the Active Supply Air Temperature Setpoint
plus the Heating Stage Control Window. For example, if the Supply Air
Temperature Setpoint is 140°F and the Heating Stage Control Window
is 5
F, as the Supply Air Temperature rises above 145F, the Heating
Stages will begin to stage off based on the Heating Stage Down Delay.
Heating Staging Delay
Minimum Off Time
A Heating Stage cannot be activated unless it has been off for this
amount of time.
Minimum Run Time
After a Heating Stage has been activated, it must remain on for
this amount of time.
Staging Up Delay
After the fi rst Heating Stage has been activated, this delay pre-
vents additional stages from activating too quickly before they are
needed to achieve the Active Supply Air Temperature Setpoint.
Staging Down Delay
After a Heating Stage has met its Minimum Run Time and is not
needed, this delay prevents additional stages from deactivating too
quickly in case they are needed to maintain the Active Supply Air
Temperature Setpoint.
AAON ® MODGAS Controller
The AAON ® MODGAS Controller is treated as a single stage of gas
heating when connected to the VCM-X’s expansion port. The Supply
Air Temperature is broadcast from the AAON
®
MODGAS Controller to
the VCM-X. The Supply Air Temperature Setpoint is broadcast from the
VCM-X E-BUS to the AAON
®
MODGAS Controller. When the VCM-X
E-BUS enters the Heating Mode, it broadcasts a command to activate
the MODGAS Controller. The AAON
® MODGAS Controller modulates
the Natural Gas Valve to maintain the Supply Air Temperature Setpoint.
See the MODGAS Controller Technical Guide for detailed operation
information of the AAON
®
MODGAS Controller.
AAON ® MODGAS Controller with Additional Stages
of Heat
The VCM-X E-BUS can activate the AAON
® MODGAS Controller and
additional stages of heating if needed. If this confi guration is needed, a
heating relay must be confi gured on the VCM-X E-BUS for the AAON
®
MODGAS Controller, but it will not be connected to anything. The
AAON
®
MODGAS Controller will always be the fi rst stage of heating
in this confi guration. Additional heating relays can be confi gured and
connected to Staged Heating sources, such as Natural Gas or Electric
Heat. In order for the additional stages to activate, the AAON
® MOD-
GAS Controller must be at 100%, and then the Stage Up Delay begins.
Once the Stage Up Delay expires and the Gas Valve is still at 100%,
another Fixed Stage of Heating will activate. This will be the VCM-X’s
second stage of heat. The AAON
®
MODGAS Controller will modulate
to achieve the Active Supply Air Temperature Setpoint.
If the AAON ® MODGAS Controller modulates to 0% and the Supply Air
Temperature is above the Active Supply Air Setpoint plus the Heating
Stage Control Window, the Stage Down Delay begins. Once the Stage
Down Delay expires and the Supply Air Temperature has remained above
the Active Supply Air Setpoint plus the Heating Stage Control Window,
the Fixed Stage of Heating will be deactivated. The AAON
® MODGAS
will remain active, even at the minimum valve position unless the Supply
Air Temperature remains above the Active Supply Air Setpoint plus the
Heating Stage Control Window. The AAON
®
MODGAS Controller will
be the last stage of heating to be deactivated.