LAARS Mascot ll LMC - Users Manual - Manual (Page 7)

User’s Manual - Mascot II Boilers and Water Heaters Page 7
3.8 Lead Lag / Cascading
Lead Lag/Cascading allows multiple boilers
to be connected together and controlled from
one common sensor input. Up to 8 boilers can be
connected together in a single system. To setup Lead/
Lag or cascading operation there are several settings
in the “setup” menu structure that must be adjusted
for the specific installation, each is covered in the
following sections.
3.8.1 Lead Lag Setpoint
The lead lag setpoint is set from the “user”
menu using the “LL” variable. This is the temperature
the boiler is attempting to maintain at the system
sensor. This setting doesn’t control the boiler
outlet temperature, so the water temperature at the
boiler outlet may be much hotter than the system
temperature setpoint. Adjust the LL setpoint to the
desired operating temperature of the system.
3.8.2 Lead Lag Master/Slave Selection
In the SETUP menu structure, the “LL” menu
allows the lead lag system to be turned on and the
boiler to be configured as a master or slave control.
In each lead lag system there can only be one master
control, so proper selection is important to avoid
operating issues. To set the boiler to lead lag “master”
operation the LL menu should be set to “LDR”. To set
the boiler to slave, “SLA” should be selected.
3.8.3 Lead Lag Address
The Lead Lag address must be set for each boiler
connected to the lead lag system. Each boiler must
have a unique address selected for the system to work
properly. Typically, the lead or master boiler should be
set to address one and the remaining boilers should be
set to values 2–8 depending upon how many boilers
are installed in the system.
3.8.4 Lead Lag Hysteresis
The lead lag system uses a hysteresis value set
in the setup menu, called, “HS”. The hysteresis and
setpoint values control the on and off points of the
boiler. If the lead lag setpoint is adjusted to 120°F
with a hysteresis value of 5°F the boiler will turn off
when the water temperature reaches 125°F and will
turn back on when the water temperature reaches
115°F. Set the hysteresis values to match the boiler to
the system operating characteristics. Setting this value
correctly will help reduce the chance of short cycling.
3.8.5 Lead Lag Base Load Setting
The lead lag system uses a base load setting that
is set through the “setup” menu called “bL”. The base
load setting identifies the firing rate that the operating
boiler must achieve before the next boiler in the
system is allowed to operate. The default setting is
50% to avoid short cycling and operating the boilers at
higher, less efficient, firing rates.