Install Instructions

72
11 Operating information
Cascade
When multiple Noble Fire Tubes are installed, they can be
wired together in a Cascade sequence. A maximum of eight
(8) 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. The Leader control can be programmed to use Lead/
Lag or Efficiency Optimization control methods. Noble Fire
Tubes can only control Space Heating demands in Cascade. A
Noble Fire Tube in a Cascade must have its own DHW circuit,
as DHW will be controlled individually.
Once the Leader receives a call for heat from a room
thermostat, 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 of the Leader. If the water
temperature at the system supply sensor is less than the set
point – 10°F, then the control will initiate a call for heat on
the Cascade.
When a Noble Fire Tube in a Cascade receives a DHW call
for heat, it will be taken out of the Cascade to satisfy its own
DHW demand. Once its DHW demand has ended, it will be
put back into the Cascade.
To equalize the run time of all boilers on the Cascade, the
firing sequence will automatically be changed at set intervals.
Installation & Service Manual
The control monitors the temperature difference between the
inlet and the outlet sensor. If this difference exceeds 55°F the
control will reduce the maximum fan speed. If the temperature
difference exceeds 60°F the control will shut the unit down. The
unit will restart automatically once the temperature difference
has dropped below 55°F and the minimum off time has expired.
Protection features
Outlet temperature, flue temperature, and
temperature rise limiting
The outlet temperature is monitored by the boiler outlet
temperature sensor. When the outlet temperature exceeds
185°F, the unit will reduce the maximum fan speed. If the
outlet water temperature exceeds 195°F the control will shut
the unit down until it cools off.
The control module monitors the flue temperature by a
sensor located in the flue exhaust. If the flue temperature
exceeds 215°F the control will reduce the maximum fan
speed. If the flue temperature exceeds 240°F the control will
shut the unit down. The unit will restart automatically once
the flue temperature drops 25°F and the minimum off time
has expired.
The control module monitors the change in the temperature
after the burner fires to ensure that the flue sensor is properly
installed. In the event that the control module does not detect
the required change in the temperature, modulation will be
limited to 50% or less. Once the required flue temperature
change is observed, the boiler will be allowed to modulate
above 50% on the next call for heat or after the ● (RESET)
button is pressed.
NOTICE
When system return temperatures
are maintained below the dew point,
condensation will form on the inside of the
boiler jacket causing some internal sheet
metal components to rust.
FIRE TUBE
™
Neither this feature, the boiler control module, nor the use of
glycol, eliminates the possibility of freezing. The installation
must still use recognized design, installation, and maintenance
practice to prevent freeze potential for the boiler and system.
The Freeze Protection feature will not work if the appliance
does not have power, is locked out, is in shutdown mode, had a
component failure, or is otherwise prevented from firing.
The following integral feature of the boiler control module
provides some protection for the boiler only -- not for the
system.
The boiler control module provides a freeze protection feature
with the following attributes:
• Below an inlet temperature of 45°F, the boiler pump
operates constantly.
• Below an inlet temperature of 37°F, the burner fires.
• Boiler and pumps turn off if boiler water inlet
temperature rises above 45°F.