Iri Modulating - Patterson-Kelley THERMIFIC MODU-FIRE Supplement Manual

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Modu-Fire Gas-Fired Boiler
12. Relay 1 bypasses the purge switch, removes
power from the closed terminal of the damper
motor, and releases the temperature control to
modulate.
13. The unit modulates between the Low fire setting
and the High fire setting to maintain the desired
outlet water temp set point.
14. When the load is below the Low fire rating of
the boiler, the boiler will continue firing and the
outlet water temperature will rise until it reaches
the operating limit setpoint. At this point the
operating control switch opens and the
combustion control is de-energized at Terminal
6 and the indicator for HEAT is turned off. This
action also de-energizes Terminal 9 thus closing
the main gas valve and the air gas ratio control
valve. Relay-1 and 2 are de-energized which
applies power to the close terminal of the air
damper motor. The air damper closes.
15. When the water temperature is reduced by the
load on the system, the operating control switch
will close again. The operating sequence will
recycle to step 5, provided the limits on water
flow, gas pressure, and high temperature are all
met.

5.5.2 IRI MODULATING

1. When the On/Off (Main power) switch is turned
on, the switch illuminates. Power is provided to
the flame safeguard control, the temperature
control, and through the flame safeguard
control to the damper close terminal. Power is
also applied through the proof of closure switch
on the air gas ratio control, and to the "start
logic string" a series of normally closed
switches, including water flow, gas pressure,
high stack temp, high limit temperature, and
operating temperature to the flame safeguard
programmer.
2. The water flow limit switch is closed when
there is water flow through the boiler.
3. When adequate gas pressure is available, the
low gas pressure limit switch is closed. Manual
reset is required following conditions resulting
in low gas pressure.
4. When the temperature sensed by the high limit
temperature control is below the set limit, the
switch is closed. Manual reset is required
following conditions exceeding high limit
temperature.
5. When heat is required as indicated by the outlet
water temperature, power is applied to Terminal
6 of the programmer, which initiates the burner
ignition and operation sequence.
6. The flame safeguard control first energizes
Terminal 5 which supplies power to the motor
contactor for the blower motor and the air flow
switch, which initially shows low air flow with
the "Low Air "indicator. This indicator will
remain on until sufficient air flow is sensed.
Terminal 12 is also energized which drives the
air damper to the open position. When the
damper motor is at the full open position, the
High fire limit switch is made which energizes
the High fire switch input terminal 19 on the
flame safeguard control.
7. Once sufficient airflow is indicated by the air
flow switch, Terminal 7 of the flame safeguard
control is energized. If the High fire switch and
proof of closure switch are in the correct state,
this starts the Prepurge period. The combustion
chamber is Prepurged for 30 seconds.
8. When the Prepurge time period elapses the
flame safeguard control energizes terminal 14,
which drives the damper motor to the Low fire
position.
9. When the damper motor is at the Low fire
position, the Low fire limit switch is made,
which energizes the Low fire switch input
terminal 18 on the flame safeguard control. A
10-second "trial for ignition" period is initiated
with both Terminal 8 and 10 being energized.
Terminal 10 of the combustion control powers
the ignition transformer. The transformer
output creates a spark at the igniter. Terminal 8
powers the pilot gas valve.
10. When a pilot flame is detected by the UV
scanner a signal is sent to the combustion
control. When this signal is detected, Terminal
10 of the combustion control is de-energized
terminating the spark.
14
Maintenance