Variable Volume Discharge Air Control Sequence Of Operation; Supply Air Tempering; Changeover Input; Vav Box Relay Output - Trane Symbio 700 Controller Application Manual

Variable Volume Discharge Air Control Sequence of
Operation
Variable Volume Discharge Air (VVDA) control uses available heating and cooling capacity to deliver the
required temperature at the discharge of the unit. A discharge air temperature sensor is required for
operation.
In cooling modes, the control uses cooling sources to deliver air temperature as required by the
Discharge Air Cooling Setpoint. In heating modes, the control uses heat sources to deliver air
temperature as required by the Discharge Air Heating Setpoint. Primary heat is never used in
conjunction with mechanical cooling.
Symbio™ 700 operates in Discharge Air Temperature Control in all heat, cool, and occupancy modes of
operation. The typical operating mode is Cooling delivering conditioned air to multiple zones of a
building. These units have duct work to supply VAV terminal units. The VAV units modulate to control
space comfort.
VVDA units also change over to provide heat (when installed). A building automation system or the VAV
Box Relay Output can be used when the heat source requires full airflow. See Heat Types for more
information. A valid space temperature input must be provided to perform heating modes such as
Daytime Warm Up and Morning Warm Up (when enabled).

Supply Air Tempering

Supply air tempering is not supported with staged heating capacity.

Changeover Input

Variable Volume Discharge Air units include a binary Changeover Input. An open input requests
discharge air cooling operation. A closed input will request the unit to change to discharge air heating.
This local input is arbitrated with building management Heat Cool Mode Request commands to
determine the active mode of operation.

VAV Box Relay Output

This binary output is provided by the controller to be optionally wired to VAV units in a Multi Zone-VAV
system to coordinate system changeover to full airflow heating. The binary output is de-energized when
the controller is operating in cooling modes. The binary output energizes when the heat type installed
requires full airflow. See Maximum Heat for more details.

Discharge Air Reset

Discharge Air Reset is a method to save energy by resetting the discharge air temperature as heating
and cooling building loads increase and decrease.
When enabled, the controller can independently reset the Discharge Air Heating Setpoint Active and/or
Discharge Air Cooling Setpoint Active based on Zone (space temperature), Outdoor Air temperature or
Return Air Temperature. The new target setpoints are reported as Discharge Air Setpoint Heating Status
and Discharge Air Cooling Setpoint Status. The controller provides settings for the reset type (Outdoor
Air, Zone, Return Air), temperature range to apply the reset, and reset amount. For example: the
discharge air temperature cooling setpoint shall increase 5°F over an outdoor air temperature range of
90°F to 70°F. If Discharge Air Cooling Setpoint Active is 50°F and Outdoor Air Temperature is 80°F, the
reset function calculates and reports Discharge Air Cooling Setpoint Status = 52.5°F. The controller will
provide discharge air at 52.5°F.

Duct Static Pressure Control

Multi Zone-VAV equipment have variable speed supply fans and are often used in Variable Air Volume
(VAV) systems consisting of ductwork serving multiple building zones and VAV boxes that control space
comfort independent of the rooftop air handler. VAV boxes modulate air volume by a damper that opens
and closes to maintain space comfort. In response, duct static pressure increases and decreases. The
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