FloAire INDIRECT FIRED BENT TUBE MODULE - Manual (Page 25)

25
FVFAB and High Fire Start
The FVFAB translates the 0-10 VDC or 0-20 mA signal from a stat or BAS control to the modulating
furnace(s). The signal is linearized such that input voltage is directly proportional to amount of gas being
delivered to the modulating valve(s). If that signal is greater than a high voltage threshold for a certain
interval it will relay 24 V to the FSC on the next furnace. This will repeat if the heat capacity is still not
enough and more stages will be turned on. If the call for heat is lower than a low voltage threshold for a
certain period of time the FVFAB will cut power to the last stage that turned on, starting the post purge
sequence and repeat the process for subsequent stages if needed. On furnaces that have two modulating
burners the linearized signal is sent to one of these burners depending on the need for heat while the
furnace not receiving the modulating signal is locked into high fire, low fire or off.
In order to ensure proper light-off in all conditions, every unit’s FVFAB contains software that forces the
modulating furnace(s) to light at high fire when that furnace’s main gas valve is first opened. There is a
built in timer that allows it to send a constant 10Vdc signal to the modulating gas valve(s) and power-vent
blower speed controller(s) and force the furnace(s) into high fire for a period of 17 seconds after the initial
spark is sent by the FSC. After this forced high-fire light-off period has expired, the modulating furnace’s
power-vent blower and modulating gas valve will receive a modulating signal from the FVFAB as
mentioned above.
Re-Circulating Control Options
Manual Positioning Control (Potentiometer)
The dampers can be controlled at a remote location by a manual potentiometer to any position from 20%
to 100% fresh air. This will allow manually setting the dampers to match the building ventilation
requirements. It will take an extra 3 control wires at the remote location. On a power failure, or if the unit is
turned off, the return air damper will close by spring return.
Two Position Control
The dampers can be controlled by a two position switch (a field supplied switching device) to open the
fresh air to 100%. On opening of the circuit, power failure, or if the unit is shutoff, the return air damper
will close by spring return.