Kees IFG (INDIRECT FIRED GAS) MAKE-UP AIR UNITS - Duct Furnace Installation & Maintenance Manual - Manual (Page 14)

– 14 –
OPERATION continued
Chart 4 - Gas Supply Pressure
Natural Gas Propane Gas
Heating Value 1075 Btu/Ft 3 2500 Btu/Ft 3
(40.1 MJ/m 3 ) (93.1 MJ/m 3 )
Manifold Pressure 3.5 in. W.C. 10.0 in. W.C.
(0.87 kPa) (2.49 kPa)
Minimum Supply Pressure
Single Stage Application 5.0 in. W.C. 11.0 in. W.C
(1.24 kPa) (2.74 kPa)
Two Stage Application 6.5 in. W.C. 11.5 in. W.C.
(1.62 kPa) (2.86 kPa)
CONTROLS
Electronic modulating gas firing is available from the
factory on natural and propane gas units.
Do not use a thermostatic fan control switch when either
two-stage firing or modulated gas controls are used. A
fan time delay switch can be used, however, and is
available as an option on outdoor duct furnaces.
All controls are located on the access side of the unit
(reference Figure 11).
Chart 5 lists orifice sizes for outdoor duct furnaces.
OPERATING HIGH LIMIT CONTROL
The operating limit control is a factory installed
component surface mounted in the inlet air stream end
of the heat exchanger. This surface mounted safety
device must have adequate contact to the rear header
plate of the heat exchanger to insure its function.
When the temperature reaches the limit set point, all
heat is shutoff. The limit control has a built in auto-reset
that comes on when the equipment is sufficiently cooled
down. Reference the unit's wiring diagram.
GAS CONTROLS
SINGLE STAGE CONTROL
Gas heating units are factory provided with an
automatic single-stage gas valve. This valve is an
on/off type control, typically activated by a low voltage
single-stage thermostat.
1.
The thermostat calls for heat.
2. The pilot valve opens.
3. The ignitor sparks continuously to ignite the pilot.
4. The sensor proves pilot ignition and shuts off the
ignitor.
5. With the pilot lit, the main gas valve opens.
PILOT CONTROL
Intermittent pilot ignition is standard on all outdoor unit
sizes. Intermittent pilot ignition contains a solid state
ignition control system that ignites the pilot by spark for
each cycle of operation. When the pilot flame is proven,
the main burner valve opens to allow gas flow to the
burners. Both the pilot and burners are extinguished
during the off cycle.
HIGH GAS LINE PRESSURE REGULATOR
(Natural Gas only)
The pressure regulator is a field installed component
located external of the unit and as close as possible to
where the gas line inlet enters the unit.
The pressure regulator reduces the main gas line
pressure to a minimum of seven inches W.C. (1.74
kPa).
6. Main burners are lit at 100 percent of unit's rated
input.
7. The fan time delay relay (optional) allows the heat
exchanger to come up to operating temperature. At
this time, the fan time delay relay closes and
activates the fan controls.
8. The unit continues to fire until the thermostat is
satisfied and no longer calls for heat.
9. The main and pilot valves close.