YORK
5587001-YSG-A-520 | Start-Up & Operation Guide
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• The unit controller monitors the current MAT.
• When the MAT falls below purge DAT low
setpoint, the outside air damper modulates
closed until the MAT reaches the DAT low
limit.
• When the MAT rises above purge DAT high
setpoint, the outside air damper modulates
open until the MAT reaches the DAT high limit.
•
When an IAQ sensor is being used, pre-oc
-
cupancy purge is terminated when the IAQ
control point is satisfied.
Humidification
The rooftop unit can be ordered with an optional fac-
tory installed steam humidifier manifold.
The steam control valve, wye type strainer, and steam
trap are factory provided and shipped loose for field
installation
The steam control valve is a 24 VAC normally closed,
spring return actuator. Steam is field supplied.
Humidification Sequence
• The supply fan must be running
• The unit cannot be in an active cooling/dehumidi-
fication mode
•
When the %RH falls below the humidification
%RH setpoint, the unit controller sends a signal to
the humidifier valve
• The unit controller modulates the steam valve
open/closed to try to raise the %RH value above
the humidification %RH setpoint
• After the %RH of the return air is above the hu-
midification %RH setpoint, the unit controller
stops sending a signal to the valve
Exhaust System
The rooftop unit can be ordered with an optional fac-
tory installed exhaust fan assembly, which maintains
proper building pressure.
There are three types of exhaust fan assemblies avail-
able:
• Modulating exhaust fan
• Modulating exhaust damper with fan
• External control
Modulating Exhaust Fan
This exhaust system sequence has a VFD driven ex-
haust fan and a barometric damper.
A barometric relief damper has no actuator attached
to drive it open/closed. The barometric relief damper
is held closed by spring tension and opens when the
exhaust fan starts.
When the current building pressure rises above the
building pressure setpoint, the exhaust fan analog out-
put starts to increase. The exhaust fan is energized
when the output reaches 10%. This is an adjustable
value.
When the output continues to increase, the VFD con-
tinues to increase the exhaust fan speed.
The exhaust fan will be stopped if the output decreases
to 5%. This is an adjustable value.
• Building pressure setpoint:
Views > Details > Ex-
haust > Setup
menu
• Exhaust fan output to start/stop fan:
Views > De-
tails > Exhaust > Setup
menu
Modulating Exhaust Damper with Fan
This exhaust sequence has an actuator driven exhaust
damper with a single speed ON/OFF exhaust fan
When the current building pressure rises above the
building pressure setpoint, the exhaust damper starts
to open. The exhaust fan is energized when the damp-
er position reaches 10%. This is an adjustable value.
When the output continues to increase, the actuator
continues to open the exhaust damper.
The exhaust fan is stopped if the damper position de-
creases to 5%. This is an adjustable value.
• Building pressure setpoint:
Views > Details > Ex-
haust > Setup
menu
• Exhaust fan output to start/stop fan:
Views > De-
tails > Exhaust > Setup
menu
External Control
This sequence is controlled completely by a BAS. The
BAS is responsible for monitoring the building pressure.
External control can be utilized for either of the above
sequences.
Return Fan
The rooftop unit can have an optional factory installed
return fan assembly.
A return fan assembly is typically used when the HVAC
system has a return duct static that is too great to be
overcome by the supply fan alone.
