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Operation - VAV Units (optional)
Blower Start-Up, as shown on page 14, should be
performed before the blower is run.
For maintenance issues associated with variable
frequency drives, consult the drive's manual supplied
with the unit. The drives are programmed at the
factory and should not need any adjustment during
installation and start-up. For kitchen applications, the
drive may be located in the kitchen or in the unit.
Variable Volume Operation
The variable volume option is recommended when
a building's exhaust volume may vary. This option
enables the make-up air volume to track with the
exhaust volume, providing only the amount of make-
up air required. Control strategies include 2-speed and
modulating blowers. Before the unit is left in service, the
variable volume control system should be tested.
2-Speed
A variable frequency drive (VFD) is used to control
air volumes. The VFD 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
Potentiometer Control — a variable frequency drive
is controlled by input from a remote
speed selector (potentiometer). This
unit allows easy manual adjustment
of make-up air volumes. To test
potentiometer operation, turn the
potentiometer to the two extremes.
With variable volume, make sure the
fan goes to maximum and minimum
speed.
When the potentiometer is at 0, the
fan speed will be at its minimum.
When the potentiometer is at 100,
the fan will be at its maximum speed.
®
NOTE
NOTE
BLOWER
EXHAUST
(OPTIONAL)
SUPPLY
MAIN VALVES
HEAT
DIRTY FILTERS
70
75
65
80
(OPTIONAL)
60
85
55
90
GREENHECK
®
Potentiometer
Control
Building Pressure Control —
a variable frequency drive is
controlled according to input from
a pressure sensing device.
Turn both knobs to the upper
most pressure setting. You may
have to remove the outdoor
pressure tap tubing. VAV systems
should go to maximum speed. Set
both knobs at the lowest setting
and the VAV systems should go to
minimum speed.
Reset the correct pressure limits
before starting the unit.
This picture depicts a typical
photohelic setting. Typical
settings are 0.0 in. wg for
the lower pressure setting
and 0.10 in. wg 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 variable frequency drive 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 blower to low
speed. The blower will go to maximum speed with a 10
VDC or 20 mA signal.
Variable Kitchen Control — A variable frequency
drive is controlled by input from a remote speed control.
This unit allows automatic adjustment of make-up air
volumes based on varying cooking loads.
Burner Bypass Damper (optional)
The self-adjusting burner bypass damper is a device
used in variable
volume units. Its
function is to maintain
proper combustion by
providing a constant
airflow over the burner
when outside air
volumes are changed.
It is located underneath
the burner as shown in
the picture.
WARNING
The burner bypass damper is set-up at the factory.
The weights should not be adjusted in the field. The
damper may not fully close during minimum outside
air mode.
BLOWER
EXHAUST
(OPTIONAL)
SUPPLY
MAIN VALVES
HEAT
DIRTY FILTERS
75
70
65
80
(OPTIONAL)
60
85
55
90
PHOTOHELIC
GREENHECK
®
Building
Pressure Control
Pressure Indicating
Pressure Setting
Needle
Needles
Pressure Setting Knobs
Photohelic Gauge
Burner
Bypass Damper
Burner Bypass Damper
Model VSU Make-Up Air
19
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