Filter
Top Products
Controls
PKG-PRC002-EN 73
Sequence of
Operation
• Air-Cooled Condensers
Condenser fans will stage per a user-
defined setting. If the condenser is
equipped with head pressure control (air
modulation on last stage of condenser
capacity), the condenser airflow will
modulate to maintain condensing
temperature setpoint. Condensing
temperature is determined by sensors
located at each condenser coil.
Water Purge
This user-definable feature allows the
user to select a purge schedule to
automatically circulate water through the
economizer and condensers periodically
during non-operational times. This allows
fresh chemicals to circulate in waterside
heat exchangers.
Airside Options
Inlet Guide Vane Control
Inlet guide vanes are driven by a
modulating 0-10 vdc signal from the RTM
module. A pressure transducer
measures duct static pressure, and the
inlet guide vanes modulate to maintain
the supply air static pressure within an
adjustable user-defined range. The range
is determined by the supply air pressure
setpoint and supply air pressure
deadband, which are set through the
human interface panel.
Inlet guide vane assemblies installed on
the supply fan inlet regulate fan capacity
and limit horsepower at lower system air
requirements. When in any position other
than full open, the vanes pre-spin the air
in the same direction as supply fan
rotation. As the vanes approach the full-
closed position, the amount of “spin”
induced by the vanes increases at the
same time that intake airflow and fan
horsepower diminish. The inlet guide
vanes will close when the supply fan is
off.
Variable Frequency Drive (VFD) Control
Variable frequency drives are driven by a
modulating 0-10 vdc signal from the RTM
module. A pressure transducer
measures duct static pressure, and the
VFD adjusts the fan speed to maintain the
supply air static pressure within an
adjustable user-defined range. The range
is determined by the supply air pressure
setpoint and supply air pressure
deadband, which are set through the
human interface panel.
Variable frequency drives provide supply
fan motor speed modulation. The drives
will accelerate or decelerate as required
to maintain the supply static pressure
setpoint.
Bypass control is offered as an option to
provide full nominal airflow in the event
of drive failure. Manual bypass is initiated
at the human interface panel. When in
the bypass mode, VAV boxes will need to
be fully opened. The self-contained unit
will control heating and cooling functions
to maintain setpoint from a user defined
zone sensor. Supply air static pressure
limit will be active in this mode.
Supply Air Static Pressure Limit
The opening of the inlet guide vanes and
VAV boxes are coordinated during unit
start up and transition to/from occupied/
unoccupied modes to prevent
overpressurization of the supply air
ductwork. However, if for any reason the
supply air pressure exceeds the user-
defined supply air static pressure limit
that was set at the human interface
panel, the supply fan/VFD is shut down
and the inlet guide vanes close. Then unit
will attempt to restart, up to three times. If
the overpresssurization condition still
occurs on the third restart, the unit shuts
down and a manual reset diagnostic sets
and displays at the human interface
panel.