Outdoor Air Damper Fault Detection And Diagnostics (Fdd); Dehumidification Control - Occupied; Relative Humidity; Dew Point - Trane IntelliPak 3 with Symbio 800 Installation, Operation And Maintenance Manual

Outdoor Air Damper Fault
Detection and Diagnostics (FDD)
The outdoor air damper fault will have two fault detection
components, faults that are generated when operating in
minimum ventilation mode and another set when the
damper is being controlled by the economizer:
FDD: Excessive Outdoor Air
In minimum ventilation mode and the damper feedback
position is >10% of the damper commanded value for 5
continuous minutes.
FDD: Outdoor Air Damper Not Modulating
In minimum ventilation mode and the damper feedback is
<10% of the damper commanded value for 5 continuous
minutes.
FDD: Unit Economizing When It Should Not
In economizer cooling mode and the damper feedback is
>10% of the damper commanded value for 5 continuous
minutes.
FDD: Unit Not Economizing When It Should
In economizer cooling mode and the damper feedback is
<10% of the damper commanded value for 5 continuous
minutes.

Dehumidification Control -

Occupied
Dehumidification control is a sub-mode of Cool when hot
gas reheat is configured and the dehumidification feature is
enabled. There are two methods for controlling
dehumidification: space relative humidity or space dew
point. A valid Evaporator Leaving Air Temperature sensor
(s) is required for either method.. Two circuit, split coil units
will have an Evaporator Leaving Air Temperature sensor
installed in each airstream. When a valid space relative
humidity value is above the Space Dehumidification
Setpoint, dehumidification control is invoked. Economizer
cooling disables. The sub-mode Cool – Dehumidification is
reported on the user interface Operating Modes screen.
Dehumidification control disables when space relative
humidity is less than Space Dehumidification Setpoint
minus the Occupied Dehumidification Offset, Heat Cool
Mode Status is not Cool or a sensor required for
dehumidification control is invalid.

Relative Humidity

When a valid space relative humidity value is above the
Space Dehumidification Setpoint, dehumidification control
is invoked. Economizer cooling disables. The sub-mode
Cool – Dehumidification is reported on the user interface
Operating Modes screen.
Dehumidification control disables when space relative
humidity is less than Space Dehumidification Setpoint
minus the Occupied Dehumidification Offset, Heat Cool
RT-SVX080A-EN
Mode Status is not Cool, or a sensor required for
dehumidification control is invalid.

Dew Point

If space dew point is greater than the space dew point
setpoint (default = 60F) and outdoor air dew point is greater
than the outdoor air dew point threshold (default = 60F),
the unit enters dehumidification.
In addition to a space humidity sensor, an outdoor air
humidity sensor is also required.

Discharge Air Control Units

When Dehumidification is active, cooling capacity is
controlled by Evaporator Leaving Air Temperature relative
to Evaporator Leaving Air Temperature Setpoint. This
setpoint is suitable to satisfy the space humidity load.
Cooling capacity will first load on circuit 1 to provide hot gas
reheat capacity. The Hot Gas Reheat valve modulates to
manage reheat capacity to satisfy the Discharge Air
Temperature Setpoint.
Optionally, a building automation system can set the
Discharge Air Reheat Setpoint. This then becomes the
target setpoint for hot gas reheat control, when
dehumidification is active. Likewise, Evaporator Leaving Air
Temperature Setpoint can be written for dehumidification
control.

Space Temperature Control Units

Space temperature units internally use dew point to
manage space humidity control. When hot gas reheat is
inactive, the cooling control calculates a suitable setpoint to
manage both space temperature and space humidity. If
space temperature falls below the space cooling setpoint
minus a fixed differential, the hot gas reheat valve
modulates to maintain space temperature control. The
evaporator leaving air temperature setpoint is calculated to
control humidity independent of space temperature.
Optionally, a building automation system can set the
Evaporator Leaving Air Temperature Setpoint to control DX
cooling capacity.
Dehumidification Control -

Unoccupied

Unoccupied Dehumidification control sequence of
operation is the same for all unit types when the controller
is in unoccupied mode, hot gas reheat is configured and
the unoccupied dehumidification feature is enabled.
Typically, dehumidification control will start unit operation
under the following conditions:
• When a valid space relative humidity value rises above
the Space Dehumidification Unoccupied Setpoint, and
Space Temperature is above a fixed 64°F threshold.
• Or, when Space Dew Point is greater than Space Dew
Point Unoccupied Setpoint AND Outdoor Air Dew Point
is greater than Outdoor Air Dew Point Threshold.
Sequence of Operation
89