Variable Air Movement Applications - Modine Manufacturing DFP Installation And Service Manual

START-UP PROCEDURE
Electronic Modulating Gas Controls
Single Furnace
Utilizes an electronic modulating/regulating gas control,
combination gas valve, an ignition control, modulating amplifier,
and either a modulating room thermostat or modulating duct
thermostat with remote temperature set point adjuster. The
thermostat controls can modulate the gas flow between 40%
through 100% full fire. When the thermostat is satisfied, the amplifier
cuts power to the combination gas valve which prevents gas
flow to both the main and pilot burners.
When duct sensing is utilized, a room override thermostat can
be added. When calling for heat, the room override thermostat
provides full fire operation until the space temperature is
satisfied. Control is then returned to the duct sensing control.
In this situation, either the duct sensor or the room override
thermostat can call for heat.
1. The thermostat calls for heat.
2. The power exhauster relay is energized starting the power
exhauster motor. Once the motor has reached full speed, the
differential pressure switch closes. The power exhauster relay
pre-purge timer closes after 20 to 40 seconds energizing the
gas control circuit.
3. The pilot valve opens and the spark ignitor sparks in an
attempt to light the pilot. (If the unit was not provided with a
time delay relay, the blower starts at this time.)
4. Once the pilot is lit, the flame sensor proves the pilot and
stops the spark ignitor from sparking.
5. The main gas valve is opened and the main burner is lit to
100% full fire.
6. If the unit was provided with a time delay relay, the blower
starts after 30 to 45 seconds.
7. The modulating gas valve can be controlled by either an
electronic modulating room or duct thermostat. The thermostat
can modulate the firing rate between 40% through 100% full fire.
The call for heat is created by a resistance signal (8000 to 12000
ohms) in the thermostat. The amplifier converts this resistance
into a DC voltage (0 to 12 volts DC with 0 volts high fire and 12
volts low fire). The output voltage is applied to the modulating
gas valve to control the gas flow to the main burner. As the
temperature drops, the voltage drops causing the modulating
valve to open further. If the discharge air temperature increases,
the voltage increases causing the modulating valve to close
allowing less gas flow to the main burner. For further information
regarding the operation of the electronic modulating system,
consult the literature provided with the unit.
8. The unit continues to operate in this manner until the
thermostat is satisfied, at which time both the main and pilot
valves close 100%. (If the unit was not provided with a time
delay relay, the blower stops at this time.)
9. If the unit was provided with a time delay relay, the blower
stops after 30 to 45 seconds.
Electronic Modulating Gas Controls - Master/Slave
One Master furnace is provided with up to three Slave furnaces
that utilize electronic modulating/regulating gas controls,
combination gas valves, ignition controls, one multiple furnace
modulating amplifier, and either a modulating room thermostat
or modulating duct thermostat with remote temperature adjuster.
The thermostat controls can modulate the gas flow of all the
furnaces between 40% through 100% full fire. The amplifier
sends a signal to all of the gas valves so that they modulate
at the same percentage. When the thermostat is satisfied,
the amplifier cuts power to the combination gas valves which
prevents gas flow to both the main and pilot burners.
When duct sensing is utilized, a room override thermostat can
be added. When calling for heat, the room override thermostat
provides full fire operation until the space temperature is
satisfied. Control is then returned to the duct sensing control.
In this situation, either the duct sensor or the room override
thermostat can call for heat.
The sequence of operation for Electronic Modulating Gas
Controls - Master/Slave is the same as Electronic Modulating
Gas Controls - Single Furnace.
Electronic Modulating Gas Controls - Building
Management Control (0-10Vdc or 4-20 mA Signal)
Utilizes an electronic modulating/regulating gas control,
combination gas valve, an ignition control, modulating signal
conditioner, and an inverted (0 Vdc or 4 mA being high fire and
10 Vdc or 20 mA being low fire) 0-10 Vdc or 4-20 mA input
signal provided by a Building Management System (BMS). The
signal conditioner can modulate the gas flow between 40%
through 100% full fire. When the BMS thermostat (field supplied)
is satisfied, the BMS heat contact (field supplied) opens to cut
power to the combination gas valve which prevents gas flow to
both the main and pilot burners.
1. The BMS thermostat (field supplied) calls for heat and closes
the BMS heat contact (field supplied).
2. The power exhauster relay is energized starting the power
exhauster motor. Once the motor has reached full speed, the
differential pressure switch closes. The power exhauster relay
pre-purge timer closes after 20 to 40 seconds energizing the
gas control circuit.
3. The pilot valve opens and the spark ignitor sparks in an
attempt to light the pilot. (If the unit was not provided with a
time delay relay, the blower starts at this time.)
4. Once the pilot is lit, the flame sensor proves the pilot and
stops the spark ignitor from sparking.
5. The main gas valve is opened and the main burner is lit to
100% full fire.
6. If the unit was provided with a time delay relay, the blower
starts after 30 to 45 seconds.
7. The modulating gas valve is controlled by the BMS
thermostat. The thermostat can modulate the firing rate
between 40% through 100% full fire by modulating the input
signal between either 0-10 Vdc or 4-20 mA (The signal
conditioner can accept a 0-10 Vdc signal when all the dip
switches are in the "OFF" position and 4-20 mA signal when
all the dip switches are in the "ON" position). The signal
conditioner converts the input signal into a DC voltage (0
to 12 volts DC with 0 volts high fire and 12 volts low fire).
The output voltage is applied to the modulating gas valve to
control the gas flow to the main burner. As the temperature
drops, the voltage drops causing the modulating valve to open
further. If the discharge air temperature increases, the voltage
increases causing the modulating valve to close allowing less
gas flow to the main burner. For further information regarding
the operation of the electronic modulating system, consult the
literature provided with the unit.
8. The unit continues to operate in this manner until the
thermostat is satisfied, at which time the BMS heat contact
opens resulting in both the main and pilot valves closing
100%. (If the unit was not provided with a time delay relay, the
blower stops at this time.)
9. If the unit was provided with a time delay relay, the blower
stops after 30 to 45 seconds.

Variable Air Movement Applications

When the air mover supplied by others can provide variable
air movement (i.e. 2-speed or variable frequency drive units),
the allowable minimum CFM of the duct furnace can be 66% of
the minimum listed CFM in Table 16.1 if the unit is applied as
follows:
1. The unit is provided with 2-stage, mechanical modulation, or
electronic modulating gas controls. (see Model Identification).
2. The unit is provided with a factory installed discharge air
controller.
3. The system does not include a room thermostat.
The factory installed discharge air thermostat will prevent the
unit from firing above the allowable 100°F rise when the unit is
at or above the minimum CFM by monitoring the discharge air
and going to low fire. A room thermostat, because it is located
remote from the unit, could cause the unit to over-fire.
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