Greenheck Fan Modular Make-Up Air Unit DGX - Manual (Page 4)

VARIABLE MAKE-UP AIR OPTIONS
The variable volume option is recommended when a
building’s exhaust volume will vary. The make-up air
volume will track with the exhaust volume, providing
only the necessary amount of make-up air.
The variable volume option saves energy by reducing
both fan power and gas consumption whenever make-
up air requirements are less than the maximum.
Airflow Control Strategies
Greenheck offers four methods of controlling the
make-up air volume. All four vary the fan speed for
maximum energy savings.
• Variable Frequency Drive controlled by building
pressure.
• Variable Frequency Drive controlled manually with a
remote potentiometer.
• Variable frequency drive controlled by a 2-10 VDC
or 4-20 mA signal.
• 2 speed motor controlled manually with a remote
switch.
Burner By-Pass Damper
The Variable Volume option includes a patented
burner by-pass damper, which maintains the pressure
drop across the burner as air volumes change. This
assures that complete and proper combustion occurs.
The by-pass damper is self-adjusting, designed for
minimal maintenance, and requires no controls.
Outside Air
Supply Air
Variable Volume Variable Volume
There are three temperature control
options for heat: 1) Discharge Control, 2)
Space Control, and 3) DDC Interface
Control. Cooling controls are by others.
Discharge Control
A factory installed modulating system
controls the gas valve to provide the
desired temperature based on a sensor
at the fan discharge. A room override
option is available to boost the discharge
temperature when the space is too cool.
Room Control
Specify this option when the DGX has the primary
responsibility for controlling the room temperature. A
manually adjusted room thermostat provides feedback
to the unit controls, which vary the discharge
temperature in order to maintain desired room set
point.
DDC Interface Control
Allows for an external signal (0-10 VDC or 4-20 mA)
from the building management system to modulate
the burner output to satisfy monitored conditions.
The recirculation option is recommended when the
ventilation equipment provides the primary source of
heating for the space.
Up to 80% of the air from the space can be
recirculated and filtered and then combined with a
minimum of 20% outdoor air for a continuous source
of fresh air. Only outdoor air is used for combustion to
eliminate the possibility of contaminants from the
recirculated air crossing over the burner.
Airflow Control Strategies
Greenheck offers four methods of controlling the ratio
of recirculated air to outdoor air via motorized
dampers.
• Modulating actuator controlled by building pressure.
• Modulating actuator controlled manually with a
remote potentiometer.
• Modulating actuator controlled by a 2-10 VDC or
4-20 mA signal.
• Two position actuator controlled manually with a
remote switch/time clock.
Supply Air
Outside Air
(100-20%)
20%
80-0%
Recirculated Air
(0-80%)
Recirculation Recirculation
Temperature Control Temperature Control
4
Roof Mounted Installation
Thru-Wall Installation