Start-Up: Indirect Gas-Fired Heating; Optional Features; Variable Air Volume - Greenheck IGX Series Installation, Operation And Maintenance Manual

Variable Air Volume (VAV)
Complete the Supply Fan Pre-Start Checks and Start-
Up sections in this IOM before proceeding.
For maintenance issues associated with a variable
frequency drive (VFD), consult the drive's manual
supplied with the unit. The drives are programmed
at the factory and rarely need any adjustment during
installation and start-up. For some applications, the
drive may be located in the building or in the unit.
The VAV option is recommended when a building's
exhaust volume may vary. This option enables the
make-up air volume to track the exhaust volume,
providing only the amount of make-up air required.
Control strategies include 2-speed and modulating
options. Before the unit is left in service, test the
variable air volume control system.
2-Speed Option
A VFD is used on a single speed motor to control air
volumes. The VFD is factory programmed for 2 speed
operation and can be switched to low or high speed
from a remote control panel. Turn the fan speed switch
on the remote control panel to each position and
confirm that the fan speed adjusts accordingly.
Modulating Options
Potentiometer Control
A VFD is controlled by input from a remote speed
selector (potentiometer). This option
allows easy manual adjustment of
make-up air volumes.
To test potentiometer operation,
turn the potentiometer to the two
extremes. Make sure the fan goes
to maximum and minimum speed.
When the potentiometer is at
minimum, the fan speed will be at its
minimum. When the potentiometer
is at maximum, the fan will be at its
maximum speed.
Building Pressure Control
A VFD is controlled according to input from a pressure
sensing device.
On the Photohelic gauge, turn both
®
pressure knobs to the upper most
setting. The VAV system should go
to maximum speed. Set both knobs
at the lowest setting and the VAV
system should go to minimum speed.
Reset the correct pressure limits
before starting the unit.
Typical settings are 0.0 in. wg (0 kPa).
for the lower pressure setting and
®

Start-Up: Indirect Gas-Fired Heating

Optional Features

BLOWERS
EXHAUST
(OPTIONAL)
SUPPLY
MAIN VALVES
HEAT
DIRTY FILTERS
70
75
65
80
(OPTIONAL)
60
85
55
90
Potentiometer
Control
BLOWER
EXHAUST
(OPTIONAL)
SUPPL Y
MAIN V AL VES
HEA T
DIRTY FIL TERS
75 70
65
80 (OPTIONAL)
60
85
55
90
PHOTOHELIC
Building Pressure
Control
Pressure Indicating
Needle
Pressure Setting Knobs
Photohelic
0.10 in. wg (0.02 kPa). for the upper pressure setting.
The needle indicates a negative building pressure.
During correct operation, the indicating needle will
remain between or near the setting needles.
External Signal
A VFD is controlled according to input from an external
2-10 VDC or 4-20 mA signal (by others).
A 2 VDC or 4 mA signal will send the fan to low speed.
The fan will go to maximum speed with a 10 VDC or
20 mA signal.
Variable Kitchen Control
A VFD is controlled by input from a speed control signal
from the kitchen hood. This unit allows automatic
adjustment of make-up air volumes based on varying
cooking loads.
Optional Duct Static Pressure Sensor
The controller will modulate the supply fan based upon
a comparison of the duct static pressure set point to
the actual duct static pressure level reported from the
sensor. Sensor shipped loose.
Optional Building Static Pressure Sensor
The controller will modulate the supply fan based upon
a comparison of the building static pressure set point
to the actual building static pressure level reported from
the sensor. Sensor shipped loose.
Control Voltage
Manufacturer's standard control voltage is 24 VAC.
Control wire resistance must not exceed 0.75 ohms
(approximately 285 feet total (86.9 m) length for
14 gauge wire; 455 feet (138.7 m) total length for
12 gauge wire). If the resistance exceeds 0.75 ohms,
an industrial-style relay must be wired in place of the
remote switch. The relay must be rated for at least
5 amps and have a 24 VAC coil. Failure to comply with
these guidelines may cause motor starters to chatter or
not pull in, resulting in contactor failures and/or motor
failures.
Pressure Setting
Needles
®
Gauge
Model IGX Make-Up Air 29