Orion System SA E-BUS Controller - Manual (Page 45)

SA E-BUS Controller Technical Guide
Sequence of Operations
45
Dehumidifi cation Mode
The First Stage (Digital Compressor) will modulate up. If the First Stage
stays above 100% for the Stage Up Delay and the Coil Temperature is
above the Coil Temperature Setpoint, then the Second Stage (ON/OFF
Compressor) will activate. The First Compressor will modulate between
70-100% to provide energy in the Reheat Coil.
If the Digital Compressor stays at 70% for the Stage Down Delay and
the Coil Temperature is below the Coil Temperature Setpoint minus the
Cooling Stage Control Window, then the Second Stage will deactivate.
Units with 2 Digital Compressors and 2 ON/
OFF Compressors (Dual Unit)
The Compressors will Stage Up and Stage Down similar to 1 Digital
Compressor and 1 ON/OFF Compressor. The two Digital Compressors
modulate together as Stage One. The two ON/OFF Compressors are
considered the 2nd and 3rd Stage of Cooling.
This application requires 2 Suction Pressure Transducers. The lowest
Coil Temperature is used for the Compressor control.
The fi rst Stage (2 Digital Compressors) will modulate up. If the First
Stage stays above 100% for the Stage Up Delay and the Coil Tem-
perature is above the Coil Temperature Setpoint, then the Second Stage
will activate. The First Compressor will modulate between 70-100%
to provide energy in the Reheat Coil. This sequence will repeat for the
Third Cooling Stage.
If the two Digital Compressors stay at 70% for the Stage Down Delay
and the Coil Temperature is below the Coil Temperature Setpoint minus
the Cooling Stage Control Window, then the Second Stage will deacti-
vate. This sequence will repeat for the Third Cooling Stage.
Dehumidifi cation Confi guration Options
The SA E-BUS Controller can be confi gured to have Dehumidifi cation
Priority. If confi gured, the SA E-BUS Controller will enter the Dehu-
midifi cation Mode when the Dewpoint or Humidity is above the Setpoint
regardless of the current Heating or Cooling demands. The Reheat is
always controlled to the Active Supply Air Cooling Temperature Set-
point. The Active Supply Air Cooling Temperature Setpoint will change
during Heating, Cooling, or Vent Modes. During the Vent Mode, the
Supply Air Temperature Setpoint will be a Calculated Setpoint that is
halfway between the HVAC Mode Setpoints.
If Dehumidifi cation Priority has not been confi gured, the SA E-BUS
Controller will only enter the Dehumidifi cation Mode during the Vent
Mode. The Reheat will be controlled to a Calculated Supply Air Tem-
perature Setpoint that is halfway between the HVAC Mode Setpoints.
Night Dehumidifi cation can also be confi gured and is used primarily
for CAV units that require an Unoccupied Mode of Dehumidifi cation.
Night Dehumidifi cation is only activated when the Indoor Air Humidity
is above the Indoor Air Humidity Setpoint during the Unoccupied Mode.
NOTE: Compressor Lockout Setpoints are ignored during
dehumidification as the compressors are controlled by coil
temperature.
Reheat Control
This application requires that at least one Cooling Stage is active. The
Modulating Hot Gas Reheat Valve Controller (MHGRV) will modulate
the Reheat Valve to maintain the Supply Air Setpoint.
During the Dehumidifi cation Mode, the SA E-BUS Controller activates
Cooling to extract moisture from the Supply Air and utilizes either
Modulating Hot Gas Reheat, On/Off Hot Gas Reheat, or Heating to
warm the Supply Air before entering the building. Modulating Hot Gas
Reheat is the standard form of Reheat. The HVAC unit’s Heat Source
or a Heat Source located in the Supply Air Duct can be used for Reheat
if the unit is not equipped with Hot Gas Reheat.
If the unit is equipped with a Modulating Hot Gas Reheat Controller,
it is automatically detected by the SA E-BUS Controller. In Dehumidi-
fi cation Mode, as the Cooling causes the Supply Air Temperature to
drop, the MHGRV will bypass Hot Gas to the Hot Gas Reheat Coil,
raising the Supply Air Temperature back up to the Active Supply Air
Temperature Setpoint.
If the unit is equipped with an On/Off Hot Gas Valve, then one of the
relays will be confi gured for Reheat. The Reheat Relay will be activated
if the Supply Air Temperature is less than the HVAC Mode Enable
Heating Setpoint. The Hot Gas Reheat Relay will remain on during the
Dehumidifi cation Mode regardless of the Supply Air Temperature. This
is to ensure a steady Supply Air Temperature.
When Heating is used for Reheat instead of Hot Gas Reheat, the SA E-
BUS Controller can activate the Heat Source(s) discussed in the Heating
Mode section. Heating can also be used in conjunction with Hot Gas
Reheat to add additional Reheat for applications that require a higher
Supply Air Temperature than what Hot Gas Reheat can provide. When
Heating is used in conjunction with Reheat, the SA E-BUS Controller
restricts the Heating to one form of Modulating Heat or one stage of
External Heat.
Coil Temperature Offset
On systems that have the condensing unit mounted a considerable dis-
tance from the air handling unit, the actual Evaporator Coil Temperature
can be quite a bit different than the Calculated Coil Temperature based on
the Suction Pressure Transducer reading in the condensing unit. You can
put in a temperature offset to the Calculated Coil Temperature reading so
that it will more closely match the actual Evaporator Coil Temperature.
For example, the Suction Pressure Transducer in the condensing unit
may give you a Calculated Coil Temperature reading of 30ºF, but the
actual temperature of the Evaporator Coil in the air handler may be 45ºF.
To compensate, you can put in a 15ºF offset so that the Calculated Coil
Temperature reading will read 45ºF. This offset prevents the unit from
shutting off compressors prematurely based on the fi xed 32ºF Suction
Temperature Low Limit Safety Cutoff Temperature. The maximum
amount of offset allowed is ± 30ºF.