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D-GAS HEAT COMPONENTS
036, 048, 060, 074 Std gas heat; 1-stage 65Kbtuh input
036, 048, 060, 074 Med gas heat; 1-stage 108Kbtuh input
036, 048, 060, 074 Med gas heat; 2-stage 81/108Kbtu input
048, 060, 074 High gas heat; 1-stage 150Kbtu input
048, 060, 074 High gas heat; 2-stage 113/150Kbtu input
See Gas Heat Specifications on Page 7 for more detail.
1-Heat Exchanger Figure 10
The ZGB units use aluminized steel inshot burners with
tubular aluminized steel heat exchangers and redundant
gas valve. Burners in all units use a burner venturi to mix
gas and air for proper combustion. Combustion takes
place at each tube entrance. As hot combustion gases are
drawn upward through each tube by the combustion air in-
ducer, exhaust gases are drawn out the top and fresh air/
gas mixture is drawn in at the bottom. Heat is transferred
to the air stream from all surfaces of the heat exchanger
tubes. The supply air blower forces air across the tubes
to extract the heat of combustion. The shape of the tubes
ensures maximum heat exchange.
The gas valves on two stage units accomplish staging by
allowing more or less gas to the burners as called for by
heating demand. Low NOx models are available that meet
the California Air Quality Management NOx requirement
of 40 nanogram/ joule. Stainless steel burner inserts are
used to control flame temperatures to meet this emission
level.
2-Burner Box Assembly Figure 11
The burner assembly consists of a spark electrode, flame
sensing electrode and gas valve. Ignition board A3 con-
trols all functions of the assembly.
Burners
All units use inshot burners. Burners are factory-set and
do not require adjustment. A peep hole with cover is fur-
nished in the heating access panel for flame viewing.
Always operate the unit with the access panel in place.
Burners can be removed as a one piece assembly for ser-
vice. Do not try to separate.
Orifice
Each burner uses an orifice which is matched to the burn-
er input. The orifice is threaded into the burner manifold.
The burner is supported by the orifice and will easily slide
off for service once the mounting screws are removed
from the burners.
NOTE-Do not use thread sealing compound on the orific-
es. Using thread sealing compound may plug the orifices.
Each orifice and burner are sized specifically to the unit.
Refer to Product Zone at www.davenet.com for correct
sizing information.
3-Primary High Temperature Limit S10
S10 is a SPST N.C. high temperature primary limit for gas
heat in all units. S10 is located on the vestibule panel.
See figure 10. Primary limit S10 is wired to the ignition
control A3. Its N.C. contacts open to de-energize the igni-
tion control when excessive temperature is reached in the
blower compartment. If the limit trips the blower relay coil
K3 will be energized by ignition control A3. Limit setpoints
are factory set and cannot be adjusted. See www.daven-
et.com for setpoint and replacement.
4-Flame Rollout Limit Switch S47
Flame rollout limit switch S47 is a SPST N.C. high tem-
perature limit located just above the burner air intake
opening in the burner enclosures (see figure 10). S47 is
wired to the ignition control A3. When S47 senses flame
rollout (indicating a blockage in the combustion air pas-
sages), the flame rollout limit trips, and the ignition con-
trol immediately closes the gas valve. Limit S47 is factory
preset to open at 350F + 14F on a temperature rise on all
units. All flame rollout limits are manual reset.
5-Combustion Air Prove Switch S18
Prove switch S18 is a SPST N.O. switch located to the
right of the induced draft assembly. See figure 11. S18
monitors combustion air inducer operation. Switch S18
is wired to the ignition control A3. The switch closes at
negative 0.25"W.C. + 0.05" (62.2 Pa + 12.4 Pa) on pres-
sure fall. This negative pressure fall and switch actuation
allows the ignition sequence to continue (proves, by clos-
ing, that the combustion air inducer is operating before
allowing the gas valve to open.) The combustion air prove
switch is factory set and not adjustable.
Page 33
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