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• BAS input (times out after 15 minutes when the
value is not updated)
• NetSensor
• Zone temperature (ZT)
• Return air temperature (RAT)
When the operational zone temperature for the active
changeover method is less than the operating heating
setpoint, the unit enters an active heating mode.
When the operational zone temperature for the active
changeover method is greater than the operating heat-
ing setpoint by 1.0°F, the unit exits the active heating
mode and returns to satisfied mode.
Once in an active heating mode, the unit controller
regulates stages of heating operation to achieve and
maintain the active DAT setpoint.
The heating sequence in the rooftop unit has the same
discharge air temperature reset selections available as
the cooling sequences.
Discharge Air Tempering
This feature must be user enabled.
Enable discharge air tempering whenever the unit has
staged or modulating gas heat, the DAT is less than the
cooling DAT setpoint, the unit is in OCC mode, and the
outside air damper is at its minimum position.
SZVAV Heating Operation
On a unit configured for SZVAV operation, the heat-
ing sequence differs from units configured for MZVAV
operation.
On a SZVAV unit, heating demand comes from one of
two sources:
• A ZT sensor can either be hard wired or commu-
nicated from a BAS
• A standard 2-stage cooling/heating thermostat
Zone Temperature Sensor
The ZT sensor relies on which of the following sensors
are connected and reliable. When more than one is con-
nected and reliable, they are used in order of priority.
• BAS input (times out after 15 minutes when the
value is not updated)
• NetSensor
• Zone temperature sensor
• Return air temperature
YORK
Start-Up & Operation Guide | 5587001-YSG-A-520
Staged Gas Heat
When the operational zone temperature is less
than the zone heating setpoint, the unit enters an
active heating mode. The unit controller regulates
the DAT setpoint based on ZT demand. The sup-
ply fan is operated at full speed.
Modulating Gas Heat
When the operational zone temperature is less
than the zone heating setpoint, the unit enters an
active heating mode. The unit controller regulates
the DAT setpoint based on ZT demand. The sup-
ply fan operates at the SZVAV heating minimum
speed (user adjustable).
When the DAT setpoint reaches the heating DAT
upper setpoint for 5 minutes, the unit controller
holds the DAT setpoint at the heating DAT upper
setpoint. At this time, the supply fan speed starts
to increase based on ZT demand.
Thermostat Control
The rooftop unit can be controlled by a 2-stage cool-
ing/heating thermostat. The unit responds to heating
demands based on 24 VAC inputs:
• W1: Low heating mode
• W2: High heating mode
Staged Gas Heat
The supply fan operates at 100%.
The heating demands to W1 and W2 require the
building system interface board.
On a demand for W1, the active DAT setpoint is
the DAT heating lower setpoint.
On a demand for W2, the active DAT setpoint is
the DAT heating upper setpoint.
Modulating Gas Heat
The heating demands to W1 and W2 require the
building system interface board.
On a demand for W1, the supply fan controls to
the SZVAV heating minimum speed, and the ac-
tive DAT setpoint is the DAT heating lower set-
point.
On a demand for W2, the supply fan operates at
100% fan speed, and the active DAT setpoint is
the DAT heating upper setpoint.
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