Orion System VCM Controller - Manual (Page 43)

VCM Controller
Technical Guide
43
setpoint for cooling. When the supply fan VFD signal is at 100%, the
SAT/Reset Source cooling setpoint will the lowest Supply Air Tem-
perature setpoint for cooling. During the dehumidification priority mode,
the Active Supply Air Setpoint is calculated in the same way as the
Heating or Cooling Modes. When the VCM is in the Vent Mode, the
Supply Air Temperature Setpoint will be calculated to be halfway be-
tween the HVAC Mode Enable Setpoints.
If Remote SAT Reset is configured as the SAT/Reset Source, the SAT/
Reset Source Setpoints will be the lowest Supply Air Temperature
Setpoints for both Heating and Cooling when the Remote SAT Reset
Input is at 0 VDC. When the Remote SAT Reset Input is at 5 VDC, the
Remote SAT Reset Setpoints will be the highest Supply Air Tempera-
ture Setpoints for both Heating and Cooling. The supply air setpoint
will proportional between the SAT/Reset Source Setpoints at 0 VDC
and the Remote SAT Reset Setpoints at 5 VDC. During the Dehumidi-
fication Priority Mode, the Supply Air Temperature Setpoints will be
the same as the Heating and Cooling Modes. When the VCM is in the
Vent Mode, the Supply Air Temperature Setpoint will be calculated to
be halfway between the HVAC Mode Enable Setpoints.
Supply Fan Control
Anytime the Supply Fan is requested to start, a timer is checked to
make sure the Supply Fan has been off for at least 1 minute. This 1
minute delay is to protect against rapid cycling of the Supply Fan. Once
the 1 minute delay has been satisfied, the Supply Fan relay is activated
and all other outputs are verified to be in the off condition for a period
of 1 to 2 minutes. This short period of Supply Fan only Operation
serves to purge the stagnant air from the duct before any Heating or
Cooling occurs.
Normally the Supply Fan runs continuously during the Occupied Mode
of operation. If the fan is only required to run in the Occupied Mode
during Heating, Cooling or Dehumidification Modes, the VCM can be
configured for Fan Cycle Mode.
Duct Static Pressure Control
The VCM Controller reads and controls Static Pressure in the duct sys-
tem if the Supply Fan has been configured for Duct Static Pressure
Control. Anytime the Supply Fan is operating, the VCM Controller is
controlling Duct Static Pressure. The Duct Static Pressure Setpoint and
Deadband limits are user adjustable along with a Control Interval. This
Control Interval is the amount of time that elapses between each adjust-
ment to the Duct Static Pressure Control Output Signal. The default
period is 10 seconds and should not be changed unless close observa-
tion reveals that the Supply Fan is hunting and not maintaining a stable
pressure reading. The Static Pressure Control Output Signal can be used
to control a Supply Fan VFD (Direct Acting Operation) or a Zoning
Bypass Damper Actuator (Reverse Acting Operation).
The Duct Static Pressure Control Output Signal is a non-configurable
Direct Acting Signal (0-10 VDC). This Output Signal can be used to
directly connect to a Supply Fan VFD. The Output Signal increases
(Increases VFD Speed) if the Duct Static Pressure is below the Duct
Static Pressure Setpoint by the Deadband amount and the Output Sig-
nal decreases (Decreases VFD Speed) if the Static Pressure is above the
Setpoint by the Deadband amount.
Since the Duct Static Pressure Control Output Signal is a non-
configurable Direct Acting Signal (0-10 VDC), when you are using a
Zoning Bypass Damper Actuator to control the Duct Static Pressure
you must set up the Zoning Bypass Damper Actuator or the Zoning
Bypass Damper so that it is Reverse Acting in operation. The Output
Signal increases (closes Zoning Bypass Damper) if the Duct Static Pres-
sure is below the Duct Static Pressure Setpoint by the Deadband amount
and the Output Signal decreases (opens Zoning Bypass Damper) if the
Static Pressure is above the Setpoint by the Deadband amount.
If the Static Pressure ever rises 0.5” above the Duct Static Pressure
Setpoint, the Duct Static Pressure Control Output Signal will be cut in
half every control period until the Static Pressure is brought under con-
trol. This is to prevent damage to the ductwork if all the VAV boxes are
closed or some other blockage occurs in the ductwork.
Warning: The manufacturer does not assume responsibility
for protecting the equipment from over
pressurization! The user should always install
mechanical high static protection cutoffs to protect
their system!
When the Supply Fans starts, the Duct Static Pressure Control Output
Signal will go to the Minimum % for Heating. Anytime the Supply Fan
is off the Duct Static Pressure Control Output Signal will remain at zero
volts.
If the Supply Fan control is not configured for Duct Static Pressure
Control, you can still monitor the Duct Static Pressure if the Duct Static
Pressure Sensor is installed, however no control will occur.
Building Pressure Control
The VCM can maintain Building Static Pressure anytime the Supply
Fan is operating by activating a Constant Volume Exhaust Fan, a VFD
Exhaust Fan, Modulating Exhaust Damper or by modulating the Out-
door Air Damper. A Building Pressure Transducer must be connected to
the VCM’s Analog Input Expansion Board. For Constant Volume Ex-
haust Fan applications, only an Exhaust Fan Relay needs to be config-
ured for on/off operation of the Exhaust Fan. VFD or Modulating Build-
ing Pressure control must be configured in order to operate. An Ex-
haust Fan Relay can also be configured along with Modulating Build-
ing Pressure control for an Enable output. Building Pressure can be
maintained by either Direct or Reverse Acting control.
Direct Acting
If configured, a VFD Exhaust Fan or Modulating Exhaust Damper will
be controlled by varying a 0-10 or 2-10 VDC control signal on the
analog output of the optional Analog Input Expansion Board. If an en-
able output is required, an Exhaust Fan Relay can also be configured.
The Exhaust Fan Relay and the Modulating Signal will activate when
the Building Static Pressure rises above the Building Static Pressure
Setpoint plus the Deadband. The Exhaust Fan Relay will remain active
until the Building Static Pressure falls below the Building Static Pres-
sure Setpoint minus the Deadband and the Modulating Signal falls to
0%.