YORK
5587001-YSG-A-520 | Start-Up & Operation Guide
58
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.
Ventilation
The rooftop unit can have several optional factory in-
stalled ventilation systems. Most building codes re-
quire a minimum amount of outside air for ventilation
purposes.
The ventilation options are:
• Fixed minimum
• Supply fan speed
•
Outside airflow measurement
• External control
• Wired control - Set source* to hardware
• BAS communicated control - Set source* to
software
• Demand control ventilation (DCV)
*NOTE -
Source (exhaust damper, exhaust fan, out-
side air damper) can be found under
Com-
mission > Options.
Ventilation Sequences
Fixed Minimum
This is the percentage that the outside air damper
opens to when the unit is in OCC mode and the supply
fan is running.
This position can be overridden by economizer opera-
tion or DCV requirements.
This setpoint can be set in
Details > Economizer >
Setup
menu
.
Supply Fan Speed
The outside air damper opens to a certain percentage
based on the supply fan speed.
When the supply fan is running at 100%, the outside air
damper is at the damper minimum position high speed
fan setpoint.
When the supply fan is running at 50%, the outside air
damper is at damper minimum position low speed fan
setpoint.
When the supply fan is running somewhere between
100% and 50%, the damper is at a position somewhere
between the damper minimum position high speed fan
setpoint and the damper minimum position low speed
fan setpoint
Outside Airflow Measurement
The rooftop unit has the option of having an airflow
measuring station (AMS) installed. The AMS meets
ASHRAE standards for building ventilation
The unit controller modulates the outside air damper
open/closed to maintain the fresh air intake setpoint.
If DCV is installed with an AMS, the outside air damper
position increases above the fresh air intake setpoint
when the CO
2
level goes above the setpoint.
When economizer operation causes the outside air
damper to go above the fresh air intake setpoint, more
outside air is needed to satisfy the cooling demand.
The low ambient minimum position may force the out-
side air damper below the current fresh air intake set-
point and disable the AMS reset.
External Control
This ventilation sequence allows control of the outside air
damper by a BAS for ventilation requirements. This se-
quence takes priority over any other ventilation sequence.
Low Mixed Air Temperature Limiting
This is a safety feature built into the ventilation se-
quences. When all conditions below are met, low
mixed air temperature (MAT) limiting occurs.
• Unit in OCC mode
• Economizer is inactive
• Supply fan output is ON
• The MAT is below the MAT cooling limit
The outside air damper begins to close. When the MAT
becomes equal to/greater than the MAT cooling limit,
the unit controller terminates low MAT limiting.
Demand Control Ventilation
The rooftop unit has the option for factory installed CO
2
sensors.
When CO
2
sensors are installed, the unit controller
monitors the indoor CO
2
and controls the outside air
damper open/closed to keep the amount of CO
2
at an
acceptable level.
The outside air damper position is the greater of the
minimum outdoor air damper reset or the DCV position.
