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Cool
Cool mode is reported when the control objective is to
provide cooling to maintain building comfort. Direct
expansion cooling is the primary cooling source. Cool
mode is also reported when Economizer cooling,
Dehumidification, Pre-Cool, and Night Purge sub-modes of
operation are active.
For Discharge Air Control units, heat is allowed (when
enabled) to temper cold mixed air conditions to the desired
cooling setpoint. See Cool - Tempering sub-mode section
for more information.
Fan Only
This mode disables all forms of heating and cooling
capacity but operates the fan continuously at minimum
speed or modulates to maintain duct static pressure. The
outdoor air damper modulates to damper minimum position
setpoint or flow setpoint to provide ventilation.
Fan Only is also reported in Emergency Override and
Ventilation Override Modes. Heat Cool Mode Request can
also command the Fan Only mode.
Maximum Heat
Maximum Heat is a heating mode of operation with the
supply fan operating at maximum speed. The controller
does not provide maximum heat (as the name infers);
instead, the controller provides heat capacity per the
Operating Mode and unit type.
•
Multi Zone VAV
Multi Zone VAV control units will transition to
Maximum Heat operation in heating modes (for
example Occupied Heat, Morning Warm Up,
Daytime Warm Up) when the installed heating
capacity requires full air flow. Maximum Heat can
also be a Heat Cool Mode Request command,
which Symbio 800 will remain in the mode until the
mode is released. On the transition to Maximum
Heat the Symbio 800 will reduce the supply fan to
minimum speed, energize the VAV Box Relay and
wait the duration of the VAV Box Stroke Time
(adjustable). The VAV Box Stroke Time allows the
VAV boxes in the system to open. The supply fan
speed will then increase to 100% or the maximum
speed subject to high duct static pressure limit.
Once the supply fan reaches its allowed maximum
speed, Symbio 800 will enable heating capacity
control to Discharge Air Heating Setpoint Active.
Ventilation is managed per the operating mode.
The transition from Maximum Heat back to
modulating air flow control modes is as follows:
1. Heat capacity terminates (if active), a 5 minute
post heat timer begins.
2. Supply fan speed slows to minimum speed, a 3
minute minimum speed timer begins
3. VAV Box Relay de-energizes
4. When the 5 minute post heat and 3 minute
minimum speed timer expire, modulating air
RT-SVX063G-EN
flow control is enabled, operating mode
transitions, and capacity control enables.
•
Single Zone VAV (Space Temperature)
Single Zone VAV control units will also accept a
Maximum Heat command via Heat Cool Mode
Request. On this command the Symbio 800 will
transition to a heat mode while operating the supply
fan at 100% capacity. Heat Cool Mode Status will
report Maximum Heat to indicate the mode is
active.
Off
Off is the reported mode when unit operation is shutdown
due to diagnostics, equipment protections or normal unit
operation.
Test
When a Manual Override is Active such that it overrides
normal capacity control or limits the ability to provide
comfort heating/cooling, Heat Cool Mode Status reports
Test. For example, a Manual Override of a relief fan will not
be reported as Test. See Programming Guide (RT-
SVP011*-EN) for more information.
Operating Modes
The user interface Operating Modes screen provides Unit
and Circuit level mode information valuable to
understanding the equipment operating state. Each Unit
and Circuit mode provide sub-mode information with
valuable details to understand active controls and limits
that are affecting operation. For more information, see
Programming Guide (RT-SVP011*-EN).
Figure 38.
Operating Modes
Unit
Unit modes provide a status of the equipment operating
state. Each of the Unit modes will have one or more sub-
modes that provide more details about the functions active
in the mode.
Stopped
Sequence of Operation
67
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