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Unit Startup
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 Setpoint + 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 Setpoint + 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
66
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 33. Summary of heat cool modes and sub
modes
Heat Cool Modes
Heat
Maximum Heat
Cool
All modes
(a)
MZ-VAV Discharge air temperature units only
Supply Fan Control
All IntelliPak units with the Symbio 800 controller have one
or more supply fans installed with VFD drives. All fans are
controlled identically. The fans are sent the On/Off
command at the same time and commanded to the same
speed at all times. It is assumed that the VFDs for each fan
are setup identically. Supply fan operation will be confirmed
via a method of proving airflow which is explained below.
Supply Fan Speed Control
The controller sends a speed command to each VFD as a
value from 0-100%. The VFD interprets the commands as
0% = Minimum frequency and 100% = Maximum
frequency. See Programming Guide, Manual Overrides for
more details.
The supply fan speed requested and commanded value
will remain at 0% any time the Active Supply Fan Run
Command = OFF. Once the Active Supply Fan Run
Command = ON and the unit has transitioned into an active
Heat/Cool state, the supply fan speed will be controlled as
required by unit type.
Sub Modes
Morning Warm Up
(a)
Morning Warm
Daytime Warm Up
Cool – Dehumidification
Cool – Economizing
Cool – Economizing + DX
Cool – Tempering
Daytime Warm Up
(a)
Pre Cool
Night Purge
Idle
Demand Limit
Ventilation Override Mode X
Emergency Override Mode X
External Supply Fan Control
External Relief Fan Control
Demand Control Ventilation
RT-SVX073A-EN
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