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

START-UP PROCEDURE
signal (8000 to 12000 ohms) in the thermostat is converted
by the modulating amplifier to an inverted DC voltage
(0VDC for high fire to 12 VDC for low fire). The output
voltage is applied to the modulating gas valve to control
the gas flow to the main burner. The modulating valve is
modulated open or closed based on the voltage from the
amplifier (less gas flow required = higher voltage, more gas
flow required = lower voltage).
Note: When modulating duct sensing is utilized, a room
override thermostat can be added. When the room override
calls for heat, the burner modulates to full fire operation
until the room override is satisfied. The unit then reverts
back to duct sensing control. When equipped with both,
either the duct sensor or the room override thermostat can
call for heat.
d. BMS Signal: The main gas valve is opened 100% and the
burner firing rate is modulated between 40% and 100% full
fire. A BMS 0-10VDC or 4-20mA signal (inverted, such that
0 VDC or 4 mA is high fire and 10 VDC or 20 mA is low fire)
is converted by the signal conditioner/modulating amplifier
into an inverted DC voltage (0VDC for high fire to 12 VDC
for low fire). The output voltage is applied to the modulating
gas valve to control the gas flow to the main burner. 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 modulating valve is modulated open or closed based
on the voltage from the amplifier (less gas flow required =
higher voltage, more gas flow required = lower voltage),
which correlates to the control signal from the BMS.
Note: For further information regarding the operation of
any of the electronic modulating system options above,
consult the literature provided with the unit.
6. If the unit was provided with a time delay relay, the blower
starts after 30 to 45 seconds.
7. The unit continues to operate until the thermostat is satisfied,
Once satisfied:
a. Single-Stage Units: Both the main and pilot valves close
100%.
b. Two-Stage Units: Once the high stage of the thermostat
is satisfied, the main valve closes to 50% fire. The unit
continues to operate until the low stage thermostat is
satisfied, at which time both the main and pilot valves close
100%.
c. Electronic Modulation Units: The unit continues to
operate in this manner until the thermostat is satisfied or
the BMS heat enable contact opens. Power is then cut to
both the main and pilot valves, closing them 100% and
stopping gas flow to the main and pilot burners.
8. If the unit was not provided with a time delay relay, the blower
stops immediately. If the unit was provided with a time delay
relay, the blower stops after 30 to 45 seconds.
Multiple Furnace Controls
Staged Control (Digit 12=1 or 2):
For control of multiple staged units, each furnace would be
individually controlled. Refer to the section for Single Furnace
Controls, Staged Control (Digit 12=1 or 2).
Electronic Modulating Control (Digit 12=4):
Electronic modulation control of multiple furnaces with model
nomenclature Digit 12=4 is not available. Refer to the section
below for Electronic Modulating Control (Digit 12 = 5 and 6).
Electronic Modulating Control (Digit 12=7, or 8):
For control of multiple electronic modulation units for BMS
control, each furnace would be individually controlled. Refer to
the section for Single Furnace Controls, Electronic Modulation
Control (Digit 12=7 or 8).
Electronic Modulating Control (Digit 12=5 and 6):
These units are the same as Electronic Modulating Gas Controls
– Single Furnace (Digit 12=4) except the Master unit (Digit
12=5) features a modulating amplifier capable of driving multiple
modulating gas valves for systems with a Master and up to three
Slave units (Digit 12=6). Slave units do not have a modulating
amplifier. The units would be controlled by one of the following:
• Modulating room thermostat
• Modulating duct thermostat with remote temperature set point
adjuster
The sequence of operation for Electronic Modulating Gas
Controls - Master/Slave is the same as Electronic Modulating
Gas Controls - Single Furnace. The modulating amplifier sends
an equal voltage signal to all of the modulating gas valves so
that they modulate at the same percentage, between 40% and
100% full fire.

Variable Air Movement Applications

When the air mover supplied by others can provide variable air
movement (i.e. variable frequency drive units), the allowable
minimum CFM of the duct furnace can be 66% of the minimum
listed CFM in Table 18.1 if the unit is applied as follows:
1. The unit is provided with 2-stage or electronic modulating gas
controls (See Model Identification).
2. The unit is provided with a discharge air controller.
3. The system does not include a room thermostat.
The 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.
AIR 5-593.9
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