Dehumidification - Hot Gas Reheat; Dehumidification Control; Dew Point - Initiation; Relative Humidity - Initiation - Trane Symbio 700 Controller Application Manual

Dehumidification — Hot Gas Reheat
Dehumidification control is a mode of Cooling when hot gas reheat is configured with a modulating
reheat valve. Symbio™ 700 supports two configurable dehumidification methods: Dew Point (default) or
Relative Humidity control for occupied and unoccupied operation. All unit types require a valid space
relative humidity, space temperature, discharge air temperature sensor and Evaporator Entering
Refrigerant Temperature for dehumidification operation. Dew Point control additionally requires outdoor
air temperature and relative humidity.
Dehumidification is allowed when outdoor air temperature is between 40 and 100°F, but it is disabled
outside this range. Dehumidification can be enabled and disabled directly via the Occupied
Dehumidification Enable and Unoccupied Dehumidification Enable points.

Dehumidification Control

Dew Point — Initiation
Occupied dehumidification Dew Point control initiates when the follow conditions exist:
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Unoccupied dehumidification Dew Point control initiates when:
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The Unoccupied Dehumidification Timer is default to 12 hours. Setting the timer to 0 effectively disables
the timer and, unoccupied dehumidification initiates only according to Space and Outdoor Dew Point.
Relative Humidity — Initiation
Occupied dehumidification control initiates when the Space Humidity is greater than the Space
Dehumidification Setpoint. Unoccupied dehumidification control initiates when the Space Humidity is
greater than the Space Dehumidification Unoccupied Setpoint.

Operation

Compressors are controlled to manage the humidity latent load by staging up as needed to achieve a
Symbio™ 700 determined target evaporator coil dew point, based on space conditions.
Space temperature is managed by modulating the hot gas reheat valve. The valve will not open until the
space temperature is below the space cooling setpoint minus 1.5°F and modulates to achieve the
Reheat Discharge Air Temperature Setpoint to maintain space temperature control.
Anytime during occupied modes of operation, if the space temperature falls 3°F below the cooling
setpoint or less than heating setpoint and the reheat valve is at maximum position for 5 minutes,
dehumidification control terminates.
During unoccupied dehumidification, if space temperature falls below 60°F and the reheat valve is at
maximum position for 5 minutes, dehumidification control terminates.
Dew Point — Termination
Occupied dehumidification Dew Point control terminates when:
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•
Unoccupied dehumidification Dew Point control terminates when:
ACC-APG002A-EN
Space Dew Point is greater than the Space Dew Point Setpoint and
Outdoor Air Dew Point is greater than the Outdoor Air Dew Point Setpoint
Space Dew Point is greater than the Space Dew Point Unoccupied Setpoint and
Outdoor Air Dew Point is greater than the Outdoor Air Dew Point Setpoint and
[Space has been unoccupied for less than Unoccupied Dehumidification Timer and relative humidity
is greater than 65% or
Space has been unoccupied for greater than or equal to Unoccupied Dehumidification Timer]
Calculated Space Dew Point is less than the Space Dew Point Setpoint minus the Dew Point
Setpoint Offset or
Outdoor Air Dew Point is less than the Outdoor Air Dew Point Setpoint minus the Dew Point
Setpoint Offset
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