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fan operation continues to circulate air until the
Morning Warm Up command is removed. Heat
capacity will re-enable if space temperature falls 1.5°F
below Morning Warmup Setpoint.
Pre Cool
Pre Cool is a feature of the unit and can be Enabled, or
Disabled. Pre Cool is a mode often used during
building unoccupied periods and optimal start
applications to rapidly decrease the space temperature,
as efficiently as possible, before building occupancy.
Ventilation air is not provided during Pre Cool.
Space temperature control units must be in Cool or
Auto mode to allow Pre Cool operation. Discharge air
control units also evaluate Pre Cool operation on
transition from Off/Shutdown to Occupied.
All equipment types, a transition from Unoccupied to
Occupied mode, if a valid space temperature input is
above the Pre Cool Se 1.5°F, Pre Cool Mode will
initiate. Symbio 800 operates in a discharge air control
mode providing discharge air per Discharge Air
Cooling Setpoint Active until space temperature drops
equal or below the Pre Cool Setpoint. In this cooling
mode the outdoor air damper minimum position is 0%,
but the controller will use compressor and/or
economizer cooling when suitable.
Multi Zone-VAV units will modulate fan speed and
manage to the duct static pressure setpoint. All other
unit types, the supply fan will operate at max speed.
Pre Cool mode can also be commanded via Heat Cool
Mode Request. In this case, the Symbio 800 remains in
Pre Cool indefinitely until the commanded mode is
removed. When space temperature is equal or less
than Pre Cool Setpoint, cooling capacity is disabled but
the supply fan continues to circulate air until the Pre
Cool command is removed. Cooling capacity control
will enable if space temperature rises above Pre Cool
Se 1.5°F.
Night Purge
Night Purge mode is typically applied in building
unoccupied periods when conditions are suitable for
economizer cooling; all other forms of cooling capacity
are disabled. This mode is only supported via a
commanded Heat Cool Mode Request. The controller
will not use local inputs and assume outdoor air is
suitable for economizing. The outdoor air damper
minimum position setpoint will be overridden to 0%.
When active, the Symbio 800 operates in a discharge
air control mode, modulating the outdoor air damper
to provide cooling capacity per Discharge Air Cooling
Setpoint Active. Night Purge operation is terminated
when the Night Purge, Heat Cool Mode Request is
removed.
Daytime Warm Up
Daytime Warm Up is a feature of Constant Volume and
Multi Zone-VAV Discharge Air Temperature units that
can be Enabled, or Disabled. Daytime Warm Up is
available with any heat type installed. Daytime Warm
Up is a mode used during building occupied periods to
recover a critical zone that is too cold. Ventilation air is
provided while in Daytime Warm Up mode.
When the Heat Cool Mode Status is Cool (the unit is
providing cooling), if a valid space temperature is 3°F
below the adjustable Daytime Warmup Setpoint,
daytime warm up operation initiates. The unit will
operate in a discharge air control mode delivering
heating capacity per Discharge Air Heating Setpoint
Active. The supply fan operates at max speed on
Constant Volume Units. Variable air volume discharge
air control units will operate the supply fan to the duct
static pressure setpoint and report Heat Cool Mode
Status as Heat, if the installed heat type allows
modulating air flow. Else if the heat type requires full
air flow, Maximum Heat is reported.
When the space temperature rises above the Daytime
Warmup Setpoint, daytime warm up operation
terminates and the Symbio 800 will transition back to
Cool mode. See Maximum Heat for details. If the
requested operating mode is no longer Cool, Daytime
Warm Up terminates.
Idle
Idle is a sub-mode of Space Temperature Control units
configured for supply fan cycling. When there is no
demand for heating or cooling the supply fan will cycle
off and Idle will be displayed.
Table 29.
Summary of heat cool modes and sub
modes
Heat Cool Modes
Sub Modes
Heat
Morning Warm Up
Maximum Heat
Morning Warm
(a)
Daytime Warm Up
Cool
Cool – Dehumidification
Cool – Economizing
Cool – Econo DX
Cool – Tempering
Daytime Warm Up
(a)
Pre Cool
Night Purge
All modes
Idle
Demand Limit
Ventilation Override Mode X
Emergency Override Mode X
External Supply Fan Control
External Relief Fan Control
Demand Control Ventilation
(a)
CV and MZ-VAV Discharge air temperature units only
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