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H. (23 81 19.13.H.) Gas Heat:
1. General:
a. Heat exchanger shall be an induced draft
design. Positive pressure heat exchanger
designs shall not be allowed.
b. Shall incorporate a direct-spark ignition system
and redundant main gas valve.
c. Gas supply pressure at the inlet to the rooftop
unit gas valve must match that required by the
manufacturer.
2. The heat exchanger shall be controlled by an inte-
grated gas controller (IGC) microprocessor.
a. IGC board shall notify users of fault using an
LED (light-emitting diode).
b. The LED shall be visible without removing the
control box access panel.
c. IGC board shall contain algorithms that modify
evaporator fan operation to prevent future
cycling on high temperature limit switch.
d. Unit shall be equipped with anti-cycle protec-
tion with one short cycle on unit flame rollout
switch or 4 continuous short cycles on the high
temperature limit switch. Fault indication shall
be made using an LED.
3. Standard heat exchanger construction:
a. Heat exchanger shall be of the tubular-section
type constructed of a minimum of 20-gage steel
coated with a nominal 1.2 mil aluminum-sili-
cone alloy for corrosion resistance.
b. Burners shall be of the in-shot type constructed
of aluminum-coated steel.
c. Burners shall incorporate orifices for rated heat
output up to 2000 ft (610 m) elevation. Addi-
tional accessory kits may be required for appli-
cations above 2000 ft (610 m) elevation,
depending on local gas supply conditions.
d. Each heat exchanger tube shall contain multiple
dimples for increased heating effectiveness.
4. Optional stainless steel heat exchanger
construction:
a. Use energy saving, direct-spark ignition system.
b. Use a redundant main gas valve.
c. Burners shall be of the in-shot type constructed
of aluminum-coated steel.
d. All gas piping shall enter the unit cabinet at a
single location on side of unit (horizontal
plane).
e. The optional stainless steel heat exchanger shall
be of the tubular-section type, constructed of a
minimum of 20-gage type 409 stainless steel.
f. Type 409 stainless steel shall be used in heat
exchanger tubes and vestibule plate.
g. Complete stainless steel heat exchanger allows
for greater application flexibility.
5. Optional low NOx heat exchanger construction:
a. Low NOx reduction shall be provided to reduce
nitrous oxide emissions to meet California’s Air
Quality Management District (SCAQMD) low
NOx emissions requirement of 40 nanograms
per joule or less.
b. Primary tubes and vestibule plates on low NOx
units shall be 409 stainless steel. Other compo-
nents shall be aluminized steel.
6. Induced draft combustion motor and blower:
a. Shall be a direct-drive, single inlet, forward-
curved centrifugal type.
b. Shall be made from steel with a corrosion resis-
tant finish.
c. Shall have permanently lubricated sealed
bearings.
d. Shall have inherent thermal overload protection.
e. Shall have an automatic reset feature.
I. (23 81 19.13.I.) Coils:
1. Standard aluminum fin-copper tube coils:
a. Standard evaporator and condenser coils shall
have aluminum lanced plate fins mechanically
bonded to seamless internally grooved copper
tubes with all joints brazed.
b. Evaporator coils shall be leak tested to 150 psig,
pressure tested to 450 psig, and qualified to UL
1995 burst test at 1775 psig.
c. Condenser coils shall be leak tested to 150 psig,
pressure tested to 650 psig, and qualified to UL
1995 burst test at 1980 psig.
2. Optional pre-coated aluminum-fin condenser coils
(3 phase models only):
a. Shall have a durable epoxy-phenolic coating to
provide protection in mildly corrosive coastal
environments.
b. Coating shall be applied to the aluminum fin
stock prior to the fin stamping process to create
an inert barrier between the aluminum fin and
copper tube.
c. Epoxy-phenolic barrier shall minimize gal-
vanic action between dissimilar metals.
d. Corrosion durability of fin stock shall be con-
firmed through testing to be no less than
1000 hours salt spray per ASTM B117-90.
e. Corrosion durability of fin stock shall be con-
firmed through testing to have no visible corro-
sion after 48 hour immersion in a room
temperature solution of 5% salt, 1% acetic acid.
f. Fin stock coating shall pass 2000 hours of the
following: one week exposure in the prohesion
chamber followed by one week of accelerated
ultraviolet light testing. Prohesion chamber: the
solution shall contain 3.5% sodium chloride and
0.35% ammonium sulfate. The exposure cycle
is one hour of salt fog application at ambient
followed by one hour drying at 95°F (35°C).
Guide specifications (cont)
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