Trane Horizon OADG Series, Installation, Operation And Maintenance Manual

Page: 83 / 96

Sequence of Operation
OAU-SVX006E-EN 83
Space Control or Single Zone VAV Control,
with Energy Recovery Wheel or has Mixed
Air
Cooling Mode is enabled according to the graph shown in
Figure 51, p. 82 . Using the graph, setpoint is Space
Temperature Setpoint Active, offset is Occupied Offset,
and temperature is
Space Temperature Active .
Dehumidification Mode takes priority over Cooling Mode.
Space Control or Single Zone VAV Control
with No Energy Recovery Wheel and 100%
Outdoor Air
Cooling Mode is enabled whenever the Outdoor Air
Temperature Active rises above the Outdoor Air Cooling
Enable Setpoint . When this occurs, heating is not allowed,
regardless of space conditions.
When the Outdoor Air Temperature Active is above the
Outdoor Air Heating Enable , but below the Outdoor Air
Cooling Enable Setpoint , Cooling Mode is enabled
according to the graph shown in Figure 51, p. 82 . Using
the graph, setpoint is Space Temperature Setpoint Active ,
offset is Occupied Offset , and temperature is Space
Temperature Active .
Compressor Low Ambient Lockout
On units without head pressure control, the compressors
will be locked out if the
Outdoor Air Temperature Active
falls below the Compressor Low Ambient Lockout
Setpoint and there is a demand for cooling. When this
occurs, the unit will display Compressor Low Ambient
Lockout Active as an informational diagnostic.
Evaporator Frost Protection
Circuit 1 refrigeration pressure is monitored, and Cooling
Capacity will be limited to prevent the indoor coil from
freezing. If the unit has digital scroll on the second circuit,
then both circuits will be monitored.
Dehumidification Mode
Outdoor Air Dewpoint is calculated using Outdoor Air
Temperature Active and Outdoor Air Humidity Active .
For Dehumidification Temperature Active , OAN Rev. 6
(OANG) cabinet uses Discharge Air Dewpoint (calculated
using Discharge Air Temperature Local and Discharge Air
Humidity Local ), all other cabinets use Indoor Coil Leaving
Air Temperature Local .
Discharge Air Control
Dehumidification Mode is enabled whenever the Outdoor
Air Dewpoint rises above the Outdoor Air Dewpoint
Enable Setpoint . The Outdoor Air Temperature Active
must be above Outdoor Air Heating Enable Setpoint .
During Dehumidification Mode, Cooling Capacity is
adjusted to maintain the Dehumidification Temperature
Setpoint Active , which is written to by Dehumidification
Temperature Setpoint (adjustable). Hot Gas Reheat Valve
Command (if installed) is adjusted to maintain Discharge
Air Temperature Setpoint Active .
Multi-Zone VAV Control
Dehumidification Mode is enabled whenever the Outdoor
Air Dewpoint rises above the Outdoor Air Dewpoint
Enable Setpoint .
During Dehumidification Mode , Cooling Capacity is
adjusted to maintain the Dehumidification Temperature
Setpoint Active , which is written to by Dehumidification
Temperature Setpoint (adjustable). Hot Gas Reheat Valve
Command (if installed) is adjusted to maintain Discharge
Air Temperature Setpoint Active .
Space Control with Energy Recovery
Wheel or has Mixed Air
Dehumidification Mode is enabled whenever the Space
Dewpoint rises above the Space Dewpoint Calculated
Enable Setpoint.
During Dehumidification Mode , the Dehumidification
Temperature Setpoint Active is reset by comparing Space
Dewpoint to Space Dewpoint Calculated Enable Setpoint
minus 2°F. Hot Gas Reheat Valve Command (if installed) is
adjusted to maintain Discharge Air Temperature Setpoint
Active .
Space Control with No Energy Recovery
Wheel and 100% Outdoor Air
Dehumidification Mode is enabled whenever the Space
Dewpoint rises above the Space Dewpoint Calculated
Enable Setpoint , or when the Outdoor Air Dewpoint rises
above the Outdoor Air Dewpoint Enable Setpoint .
During Dehumidification Mode , the Dehumidification
Temperature Setpoint Active is reset by comparing Space
Dewpoint to Space Dewpoint Calculated Enable Setpoint
minus 2°F. Hot Gas Reheat Valve Command (if installed) is
adjusted to maintain Discharge Air Temperature Setpoint
Active .
Hot Gas Reheat Purge
Hot Gas Reheat Purge Mode is initiated if the Hot Gas
Reheat Valve Command is between 10% and 50% for thirty
continuous minutes. During Hot Gas Reheat Purge Mode
the signal first goes to 80% for one minute, then to 10% for
one minute. The
Hot Gas Reheat Valve Command returns
to its previous position and will begin to modulate after a
30-second delay.
Supplemental Electric Reheat (Not
Included in Standard Operation)
If the Hot Gas Reheat Valve Command is at 100%, the SCR
electric heat is enabled Heat Capacity at 0%. If Heat
Capacity rises above 0%, the Hot Gas Reheat Valve
Command will be locked at 100% and the electric heat will