Orion System VCM-X Modular E-BUS - Manual (Page 59)

VCM-X Modular E-BUS Controller Technical Guide
SEQUENCE OF OPERATIONS
59
Heat Pump Operation
The VCM-X E-BUS can be confi gured to control a Heat Pump. The
compressors are used for both Heating and Cooling. With the VCM-X
E-BUS Controller, the Reversing Valve is activated during Heating
operation as the default because
AAON ® units are typically built to
fail to Cooling operation. The Reversing Valve can be confi gured to
activate during Cooling operation for equipment that is built to fail to
Heating operation.
Auxiliary Heating Stages are confi gured as Heat Relays and are used to
supplement the Compressor Heating Stages. If the unit is not equipped
with Auxiliary Heating Stages, Heating Relays do not need to be confi g-
ured in order for the unit to provide Heating. Auxiliary Heating can also
be Modulating heat in the form of SCR Electric, Hot Water, or Steam.
The Cooling and Dehumidifi cation Modes operate in the same manner
as described under the Cooling and Dehumidifi cation titled sections on
pages 51-53 of this manual. In the Heating Mode, the VCM-X E-BUS
activates the Reversing Valve and stages compressors to provide Heating
if the Outdoor Air Temperature is above the OAT Cooling Lockout Set-
point. The compressor heating stages are activated as needed to achieve
the Active Supply Air Setpoint. Staged or Modulating Auxiliary Heat
can be activated to supplement Compressor Heating in order to achieve
the Active Supply Air Setpoint if the Outdoor Air Temperature is below
the OAT Heating Lockout Setpoint. If the Outdoor Air Temperature is
below the OAT Cooling Lockout Setpoint, only Auxiliary Heating will
occur. If the Outdoor Air Temperature is above the OAT Heating Lockout,
only Compressor Heating will occur.
Emergency Heat stages can also be confi gured. If the Outdoor Air
Temperature is above the Compressor Lockout Temperature, Emer-
gency Heating is disabled. If the Outdoor Air Temperature is below the
Compressor Lockout Temperature, Emergency Heating is enabled and
can stage up after Auxiliary Heat.
Note: If using the VCM-X WSHP (Water Source Heat Pump)
Controller, the Compressor Lockouts are ignored. Since Emergency
Heat can only be used below the Compressor Lockouts, Emergency
Heat is therefore not available.
If a heat pump unit is used in a VAV application using Supply Air Tem-
pering, then Morning Warm-Up mode will only use Auxiliary Heat.
Heating for the Supply Air Tempering operation will only use Auxiliary
Heat (and Emergency Heat if available).
For VCM-X Modular E-BUS applications with an installed Suction
Pressure Transducer, a Head Pressure Module and a Head Pressure
Transducer(s), a Defrost Mode is available during the Heat Pump Heat-
ing operation. The VCM-X Modular E-BUS Controller converts the
Suction Pressure to a Suction Temperature. A user-adjustable Suction
Temperature Setpoint determines when the unit will go into Defrost
Mode during Heat Pump Heating. The unit will operate in Defrost Mode
for 10 minutes or until the Head Pressure reaches 450 PSIG.
Heat Pump Operation
An Adaptive Defrost Adjustment confi guration is available that will
automatically adjust the length of the Defrost Timer (interval between
Defrost Modes) depending on if the unit stays in Defrost Mode for the
full 10 minutes or leaves the Defrost Mode early because of reaching a
Head Pressure of 450 PSIG. If Adaptive Defrost is confi gured and the
Defrost Mode is terminated because the 10 minute timer has elapsed,
this could indicate that the unit needs more Defrost time. In this case,
the Adaptive Defrost Adjustment value will be subtracted from the
original Defrost Timer to shorten the interval between Defrost Cycles.
If the Defrost Cycle is terminated between the 8th and 9th minute, the
Defrost Timer value will not be changed. If the Defrost Cycle is termi-
nated before the 8th minute, this could indicate that the Defrost Timer
is too short. In this case, the Adaptive Defrost Adjustment value will
be inversely proportionally added to the original Defrost Timer as the
termination time shortens from 8 minutes to 0 minutes.
Morning Warm-Up Mode Operation
When the VCM-X E-BUS Controller is confi gured as a VAV unit (Cool-
ing only)and switches to the Occupied Mode of Operation (not Override
Mode), the unit compares the Return Air Temperature to a Morning
Warm-Up Target Temperature. If the Return Air Temperature is below
this Setpoint, the Warm-Up Mode is initiated. This Mode remains in ef-
fect until the Return Air Temperature rises above the Target Temperature
or a user-adjustable Time Period expires. Warm-Up Mode is not initiated
by Push-Button Overrides or Unoccupied Heating demands. The Outdoor
Air Damper remains closed during Warm-Up Mode.
Once the Warm-Up Mode has been terminated, it cannot resume until
the unit has been through a subsequent Unoccupied Mode. Only one
Warm-Up Mode is allowed per Occupied cycle.
If you have stand-alone VAV boxes that need to be forced wide open
during the Warm-Up Mode, you can confi gure one of the relay outputs
to be used during this Mode. If the Warm-Up Mode is active, the relay
is activated. This relay then becomes the Force Open Command for all
VAV boxes to which it is wired.
Off Mode
If the schedule has set the Unoccupied Mode and no Heating, Cooling,
or Dehumidifi cation demands exist, the VCM-X E-BUS Controller
enters the Off Mode. During the Off Mode, the Supply Fan is off and
the Outdoor Air Dampers are closed.