Constant Volume/Multi-Speed Fan Space Temperature Control (Cvzt); Space Temperature Recovery; Supply Fan Control - Trane SYMBIO 700 Troubleshooting Manual

Constant Volume/Multi-Speed Fan Space Temperature Control (CVZT)

Similar to the Reliatel control system, the Symbio 700 includes a single-loop (space temperature only)
control sequence.
The sequence is PI-based (proportional, integral) and strives to maintain space temperature within 1F of
the Active Cooling and Heating setpoints.
When Space Temperature Active > Space Temp Cooling Setpoint Status, the algorithm will begin
calculating a need for Cooling capacity to be energized.
When Space Temperature Active < Space Temp Heating Setpoint Status, the algorithm will begin
calculating a need for Heating capacity to be energized.
When Space Temp Heating Setpoint Status ≤ Space Temperature Active ≤ Space Temp Cooling Setpoint
Status:
The algorithm will begin calculating a reduction in need for any active Cooling or Heating capacity if ON
If no Cooling or Heating capacity is Active, Cooling and Heating capacity will remain Inactive

Space Temperature Recovery

If the Space Temperature gets 3F out of control (above cooling setpoint or below heating setpoint), a
recovery sequence will be initiated such that the controller will immediately request 1 stage of cooling
or heating to be ON.
Once a stage of cooling or heating is energized due to a space temperature recovery request, that stage
of capacity and any additional stages of capacity will revert to be under the normal PI control sequence.
Recovery will bring on a stage of capacity, but the normal PI controller will be responsible for
maintaining the active capacity once energized.

Supply Fan Control

The supply fan will be controlled "ON" 5 seconds before heating or cooling capacity is energized. When
heating or cooling capacity is de-energized, a supply fan off delay will be applied based on active
capacity.
For Single-Speed supply fan configured systems, the supply fan will be controlled "ON" during all cooling
and heating sequences.
For Multi-Speed supply fan configured systems, the fan will operate per the following:
Low Speed when the Supply Fan is ON without Active Capacity (unless ON due to an override function)
Low Speed when the unit is operating at its minimum cooling stage
High Speed when the unit is operating at its maximum cooling stage, or while any heating stages are
active.
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