Orion System SA Controller - Manual (Page 43)

SA Controller Technical Guide
Sequence of Operations
43
Heating Mode
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 Controller can be confi gured to have Dehumidifi cation Priority.
If confi gured, the SA Controller will enter the Dehumidifi 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 Setpoint. The Active
Supply Air Cooling Temperature Setpoint will change during Heating,
Cooling, or Vent Modes. During the Vent Mode, the Supply Air Tem-
perature 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 Controller
will only enter the Dehumidifi cation Mode during the Vent Mode. The
Reheat will be controlled to a Calculated Supply Air Temperature Set-
point 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
dehumidifi cation 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 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 Sup-
ply 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 Controller. In Dehumidifi 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
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 Heat-
ing is used in conjunction with Reheat, the SA 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.
Heating Mode
Occupied Heating Mode occurs whenever the HVAC Mode Enable
Temperature falls one deadband below the HVAC Heating Mode En-
able Setpoint. The unit will leave the Heating Mode when the HVAC
Mode Enable Temperature rises one deadband above the HVAC Heating
Mode Enable Setpoint. Unoccupied Heating Mode only occurs if a Space
Temperature Sensor is connected to the SA Controller or a broadcast
of Space Temperature is being received from an General Broadcast
Device (GBD-X).
The Mechanical Heating will be disabled if the Entering Air Temperature
is above the Heating Lockout Setpoint by 1°F. This gives a 2°F hysteresis
around the Heating Lockout Setpoint to prevent unwanted cycling in
and out of Mechanical Heating Mode. If the Entering Air Temperature
disables the Mechanical Heating while it is currently operating, the Me-
chanical Heating will stage off if all staging and run times are satisfi ed.
No matter which Sensor is confi gured for the HVAC Mode Enable, the
Supply Air Temperature is always controlled to the Active Supply Air
Temperature Setpoint while in Heating Mode.
Stage Control Window
In the Heating Mode, as the Supply Air Temperature falls below the
Active Supply Air Temperature Setpoint, the Heating Stages will begin
to stage on based on the Heating Stage Up Delay. The Heating Stages
will continue to run until the Supply Air Temperature rises above the
Active Supply Air Temperature Setpoint plus the Heating Stage Con-
trol Window. For example, if the Supply Air Temperature Setpoint is
140°F and the Heating Stage Control Window is 5
F, as the Supply Air
Temperature rises above 145
F, the Heating Stages will begin to stage
off based on the Heating Stage Down Delay.
Heating Staging Delay
Minimum Off Time
A Heating Stage cannot be activated unless it has been off for this
amount of time.
Minimum Run Time
After a Heating Stage has been activated, it must remain on for
this amount of time.