Orion System VCM Controller - Manual (Page 44)

Technical Guide
VCM Controller 44
On/Off Control
If you do not require a Modulating Control Signal, you can also config-
ure one of the Relay Outputs as an Exhaust Fan Relay to activate when-
ever the Building Static Pressure is above the Building Static Pressure
Setpoint plus the Deadband. The Exhaust Fan Relay will deactivate
when the Building Static Pressure falls below the Building Static Pres-
sure Setpoint minus the Deadband. Only one Relay Output should be
configured for this operation. There is no staging of additional Exhaust
Fan Relays.
Reverse Acting
If configured, on a drop in building static pressure below the building
pressure setpoint minus the deadband, the AOUT 1 terminal on the
Analog Input Expansion Board will modulate the 2-10 VDC signal to
open the outside air damper. When this option is selected, no econo-
mizer free cooling or IAQ operation will be available.
IAQ (CO
2
) Operation
If you have configured the VCM Controller to monitor and control CO
2
levels, the Economizer operation will be modified as follows:
1. The Maximum Reset Position the Economizer can open to
is determined by a user adjustable setpoint called the CO
2
Protection Limit Max. Level.
2. The Minimum Position the Economizer can close down to
is Reset higher as the level of CO
2
increases above the CO
2
Protection Limit Max Level programmed by the user. As
the CO
2
level increases above the adjustable CO
2
Setpoint,
the Outdoor Air Damper will start opening beyond its
Minimum Position. At the CO
2
Protection Limit Reset
Range above Setpoint, the Economizer will be held to its
Maximum Reset Position and not allowed to open any
further.
Pre-heater Operation
In colder climates where freezing temperatures are sometimes experi-
enced, it is desirable to preheat the Outdoor Air being drawn into the
HVAC unit before it reaches the Water Coils to prevent freezing. The
Pre-heater control option is available by setting a Low Ambient Protec-
tion Setpoint and by configuring one of the relay outputs as a Pre-Heater.
Only one relay can be configured for this option and therefore staging
of Pre-heater relays is not available.
The Pre-heater sequence operates so that anytime the Outdoor Air Tem-
perature is below the Low Ambient Protection Setpoint and the Supply
Fan is running, the Pre-heater Relay will activate. It will remain on
until the Outdoor Air Temperature rises 1°F above the Setpoint or the
Supply Fan shuts down. If the Proof Of Flow option is installed and
configured, its signal must also be active for the Pre-Heater Relay to
activate. This output will operate during any HVAC Mode that exists.
Outdoor Air Lockouts
The Outdoor Air Cooling and Heating Lockouts Setpoints are designed
to prevent unwanted Mechanical Heating or Cooling operation during
certain Outdoor Ambient Temperature conditions.
When the Outdoor Air Temperature is below the Cooling Lockout
Setpoint, no Mechanical Cooling can operate. However, if the unit is
equipped with an Economizer and the VCM is configured to use the
Economizer, it can be used to provide free Cooling when the Mechani-
cal Cooling is locked out. For Air to Air Heat Pumps the Cooling lock-
out also applies to Compressor Heating, which means it usually will be
a lower setting than on Cooling units that are not Air to Air Heat Pumps.
The Outdoor Air Heating Lockout operates so that when the Outdoor
Air Temperature is above the Outdoor Air Heating Lockout Setpoints,
no Mechanical Heating can operate. This applies to any type of Heating
except Compressor Heating as used on Air to Air Heat Pumps. The
lockout for Compressor Heating is explained in the previous paragraph
regarding Cooling Lockout Setpoints.
Supply Air Cutoffs
The Supply Air Temperature Cutoffs are designed to prevent extremely
High and Low temperature Supply Air from entering the building.
High Supply Air Temperature Cutoff
High Supply Air Temperature Cutoff is initiated when the Supply Air
Temperature rises above the HI SAT Cutoff Setpoint. When this oc-
curs, Heating stages will be deactivated until the Supply Air Tempera-
ture falls 5 °F below the HI SAT Cutoff Setpoint.
Low Supply Air Temperature Cutoff
Low Supply Air Temperature Cutoff is initiated when the Supply Air
Temperature falls below the LO SAT Cutoff Setpoint. If the VCM is in
Economizer Operation, Vent Mode or Heating Mode and the Supply
Air Temperature falls below the LO SAT Cutoff Setpoint for 10 min-
utes, it is assumed a Mechanical Failure has occurred and all Heating
will be deactivated, the Supply Air Fan will shut off and the Outdoor
Air Dampers will close. If the VCM is in the Cooling or Dehumidifica-
tion Mode and the Supply Air Temperature falls below the LO SAT
Cutoff Setpoint, the Cooling Signal or Cooling Stages will immediately
begin deactivating. To restore normal operation, one of the following
three things must occur:
1. The Supply Air Temperature rises above the LO SAT
Cutoff Setpoint by 5 °F
2. The VCM goes from Occupied to Unoccupied or
Unoccupied to Occupied Mode.
3. The VCM’s power is cycled.
Scheduling
The VCM Controller has an internal power source for the Real Time
Clock (RTC) that allows the controller to keep the time and accurately
control scheduling. It can also broadcast the time to the VAV/Zone Con-
trollers if that option is configured.
The VCM Controller has an Internal 7 day Schedule with 2 Start/Stop
Events per day. You can also have 1 Holiday Schedule with 2 Start/Stop
Events per day. This Holiday Schedule can be used for 14 different
Holiday periods.
Sequence Of Operations