General Information
GDH Series Direct Fired Ducted Heater
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C
ONSTRUCTION
The LU Models are constructed from 3mm galvanized steel cabinets complete with internal or external fan
motor drive, access doors and heavy base frames.
The GDH furnace is constructed from 1.0 mm galvanized steel and is basically an open ended duct with
galvanized iron frames on both ends for rigidity and ease of mounting; one extra angle iron frame is supplied
fitted to the air leaving end of the furnace for simple attachment to new or existing ductwork. A large quick
release access panel is fitted to the rear of the duct for easy service access to the burner. On the control
side of the duct, an inspection port is provided for flame observation.
Main Burner Assembly
The direct fired burner consists of a solid cast iron manifold frilled to suit the burner rating, fitted with
stainless steel flame retention plates specially formed to give excellent air gas mixing through the low to
high fire range and still achieving combustion results well within the limits of 10 ppm and 3000 ppm CO
2
as laid down by Australian Gas Association (AGA) regulations.
The burner retention plates line up with a profile plate which is fitted around the inside perimeter of the
duct which also adds to the overall strength of the unit. When the air handling fan is turned on, air is
squeezed through the profile plate and over the burner providing an air velocity in the order of 12 – 16
metres per second.
Burner Control
The programmed burner control system sets the sequence for lighting and supervising the flame. This
control provides the pre-purge sequence, energizing the ignition transformer which provides a high
tension spark at the tip of the ignition electrode. The controller energizes the pilot burner safety shut-off
valve (when pilot fitted) and main burner shut-off valves. Flame supervision is by signals directly back to
the burner control. No flame or a loss of flame will cause the burner control to lockout and shut off all
gas valves within 1 second. A red light will indicate when flame failure lockout) has occurred.
Valve Train
One or two separately controlled valve lines make up the valve train depending on whether a pilot is
fitted or whether direct low fire start is used.
a.
The pilot line (when fitted) consists of a small gas cock, regulator and a solenoid valve.
b.
The main burner line consists of a much larger gas cock, regulator, two safety shut-off valves and
a modulating valve.
Solenoid valves and safety shut-off valves will only operate on command from the burner control in
their correct sequence.
Safety controls
a.
The air pressure switch connects in such a way as to detect air pressure differential across
the profile plate and will detect a fall in air volume over the burner.
b.
The high limit switch mounted in the control box has a remote bulb which is field mounted
and will detect any abnormal increase in air temperature.
