Orion System VCM Controller - Manual (Page 5)

VCM Controller
Technical Guide
5
Air to Air Heat Pump Unit
The VCM can be configured to control an Air to Air Heat Pump. The
compressors are used for both Heating and Cooling. With the VCM
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 configured to activate during
Cooling operation for equipment that is built to fail to Heating opera-
tion.
Auxiliary Heating Stages are configured 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 con-
figured 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 Dehumidification Modes operate in the same manner
as described under the Cooling and Dehumidification titled sections of
this manual. In the Heating Mode, the VCM activates the Reversing
Valve and stages compressors to provide Heating if the Outdoor Air
Temperature is above the OAT Cooling Lockout Setpoint. The com-
pressor heating stages are activated as needed to achieve the Active
Supply Air Setpoint. Staged or Modulating Auxiliary Heat can be acti-
vated 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.
PAC (Precision Air Control)
This control scheme can only be used on Constant Volume HVAC
units that are equipped with a Return Air Bypass Damper and use a
Space Temperature Sensor as the Controlling Sensor.
PAC Control provides improved moisture removal capabilities while
utilizing internal space loads for reheat by redirecting the Return Air
path from the upstream side of the DX Evaporator Coil to the down-
stream side of the coil.
For PAC configured units, the Return Air Bypass Damper is only used
during the Dehumidification Mode. When the VCM controller is in De-
humidification Mode, the Return Air Bypass Damper will modulate
open as the Space Temperature falls below the Cooling Setpoint. Modu-
lation of the Return Air Bypass Damper is controlled using a propor-
tional range from 0% (when the Space Temperature is equal to the Cool-
ing Setpoint), up to 100% (when the Space Temperature falls to the
halfway point between the Cooling and Heating Setpoints). A separate,
Return Air Damper Actuator will modulate the Return Air Damper
slightly further towards its closed position as the Return Air Bypass
Damper opens. This is to ensure that enough Return Air is bypassed
around the Evaporator Coil through the Return Air Bypass Damper to
raise its temperature. The rate which the Return Air Damper closes while
the Return Air Bypass Damper is open is user adjustable.
DPAC – Digital Precision Air Control
This control scheme can only be used on Constant Volume HVAC units
that are equipped with a Return Air Bypass Damper, a Digital Com-
pressor and use a Space Temperature Sensor as the Controlling Sensor.
The DPAC control scheme provides improved moisture removal capa-
bilities over the PAC control scheme and provides for tighter tempera-
ture control by combining a Digital Compressor with the Return Air
Bypass Damper. See the Cooling Mode section of this manual for de-
tailed Digital Compressor operation. See the PAC Control previously
described in this section for detailed Return Air Bypass Damper opera-
tion.
The Digital Compressor is used during both Cooling and Dehumidifi-
cation Modes. The Return Air Bypass Damper is used only during the
Dehumidification Mode.