Cascade - Lochinvar FTxl 400 Installation & Operation Manual

11
Operating information
Low water cutoff protection
1. The SMART SYSTEM control module uses temperature
sensing of both supply and return areas of the heat
exchanger. If the fl ow rate is too low or the outlet
temperature too high, the control module modulates and
shuts the boiler down. This ensures boiler shutdown in
the event of low water or low fl ow conditions.
2. In addition, an electronic low water cutoff control is
provided.
Outdoor reset operation, if used
Target temperature with outdoor reset
This feature improves the system's effi ciency as the outdoor
temperature warms up.
See the FTXL Service Manual to change the settings.
Reset curve
The reset curves look at outdoor air temperature and adjust
the set points.

Cascade

When multiple boilers are installed, they can be wired
together in a cascade sequence. A maximum of eight boilers
can be controlled from a single control. In this application
one boiler would be designated as the Leader control and all
others would be designated as Member controls. Member
1 can be confi gured to take over control of the Cascade
should the Leader stop communicating with the Members.
The Leader control can be programmed to use Lead/Lag or
Effi ciency Optimization control methods.
Once the Leader boiler receives a call for heat from a room
thermostat, BMS, Modbus, or BACnet the control will
determine what the set point will be. If outdoor air reset is
desired, connect the outdoor air sensor to the terminals on
the Low Voltage Connection Board on the Leader boiler. The
set point will be calculated based on the programmed reset
curve parameters. See the FTXL Service Manual to program
the reset curve. If outdoor air reset is not desired, do not
connect the outdoor air sensor. A fi xed temperature set point
can be programmed into the control. See page 61 of this
manual to program the set point.
If the water temperature at the system supply sensor is less
than the set point + the turn-off offset - the off-on differential,
then the control will initiate a call for heat on the Cascade
(see the FTXL Service Manual for an explanation of the offset
and differential). The Leader will energize the lead boiler on
the Cascade. For a new startup this will be the Leader boiler.
66
Installation & Operation Manual
Sequence of the cascade
To equalize the run time of all boilers on the Cascade, the fi ring
sequence will automatically be changed at set intervals.
For the fi rst 24 hours, the sequence will be changed once every
hour. The switching on/off sequence will be as follows:
TIME
Start
1 hour
2 hours
After the fi rst 24 hours, the sequence will change every night
at 2:00 a.m. If a boiler locks out or is used to heat an indirect
DHW tank, it will automatically be given the lowest priority
until 2:00 a.m.
DHW, Night Setback, and Ramp Delay operation with
cascade
For normal mode DHW operation any boiler(s) in the Cascade
can be selected to provide heat for a DHW call. Select a boiler to
be designated as the DHW boiler. Connect the DHW thermostat
or sensor to the terminals on the Low Voltage Connection
Board marked for the corresponding device. When the boiler
receives a DHW call, the Leader control will take that boiler
out of the Cascade sequence. If another boiler is available, the
Leader will start it up to take its place.
The DHW boiler will adjust its set point to the programmed
DHW boiler set point and will adjust its fi ring rate to maintain
this. Once the DHW call has been satisfi ed, the Leader control
will place that boiler back into the Cascade sequence.
Switching of the boiler between DHW operation and SH
operation when there is a call for both does not occur in Cascade
Mode.
When DHW is programmed for Zone Mode, connect the DHW
thermostat or tank sensor to the Leader boiler. When a DHW
call is received, the Leader will modulate the entire Cascade to
bring the system supply temperature up to the DHW boiler set
point (if higher).
Night Setback operation of the boilers within the Cascade is
available. Programming of the Night Setback will be done
through the Leader boiler. Refer to the FTXL Service manual for
information regarding Night Setback.
Ramp Delay operation of the boilers as described in the FTXL
Service Manual is available when the boilers are part of a
Cascade system.
SWITCHING ON SEQUENCE
L-M1-M2-M3-M4-M5-M6-M7
M1-M2-M3-M4-M5-M6-M7-L
M2-M3-M4-M5-M6-M7-L-M1