Variable Volume Discharge Air Control
- Variable Volume Discharge Air (VVDA) control uses the 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 ductwork 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.
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 by 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 has variable speed supply fans and is 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 controller will modulate supply fan speed to maintain Duct Static Pressure relative to the Duct Static Pressure Setpoint.
Duct Static Pressure High Limit
- The controller operates the supply fan to maintain duct static pressure below the Duct Static Pressure High Limit setpoint. In the event that duct static pressure approaches the high limit setpoint, the controller will reduce and limit the supply fan speed.
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WARNING:
Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.