LAARS Mascot LX MLXC 175 MBH - Install and Operating Manual - Manual (Page 40)

LAARS Heating Systems Page 36
8.8 High Limit
The control uses a dual thermistor sensor to monitor
the Mascot LX's maximum temperature. The high
limit sensor is installed in the outlet water. A dual
thermistor sensor is used, so that the two temperatures
can be monitored and compared to confirm accuracy.
The control will automatically reduce the firing of the
Mascot LX to prevent the high limit from tripping. The
high limit setpoint is not adjustable.
8.9 Stack Temperature
The stack temperature is a dual thermistor sensor
and is limit rated. The control compares each of the
temperature readings to determine accuracy. The stack
sensor is used as a limiting feature to avoid excessive
temperatures in the venting.
8.10 Domestic Hot Water Temperature
The domestic hot water temperature sensor is used to
control the DHW temperature. The DHW setpoint can
be adjusted through the Base / Home state and the User
Mode. On LX ‘C’ or Combi models, the DHW sensor
is pre-installed in the DHW exchanger. On LX ‘H’ or
Heat models the DHW can be can be controlled by an
aquastat or optional DHW sensor installed in an indirect
tank.
SECTION 9.
OPERATION Modes
To access the setup parameters for configuring different
Operation Modes, the installer level password most be
used according to section 8.4.
9.1 Hydronic Heating Demand
When using the Mascot LX for hydronic heating a
call for heat must be supplied to the "T-T or Interlock"
terminals. Once the call is supplied the control energizes
the boiler pump, the system pump relay, shifts the 3-way
valve position and begins the ignition process. The
ignition process consists of a prepurge, trial for ignition,
and run period. The prepurge period starts once the fan
RPM reaches a preset level. The trial for ignition period
follows. The trial for ignition period lasts 4 seconds
during which the direct spark ignition system and gas
valve are energized. At the end of the trial for ignition
period the flame signal is compared with the preset flame
threshold value. If the flame signal is higher than the
flame threshold the Mascot LX enters "run". If the flame
signal is below the threshold the Mascot LX returns to
prepurge and starts the ignition process over. In "run"
the Mascot LX monitors the flame signal, call for heat,
safeties, and water temperatures and modulates as
needed between 100% and 20% of rate to satisfy the call
for heat.
9.2 Hydronic Heating with Outdoor Reset
Outdoor reset varies the control setpoint based on the
outdoor temperature. The reset function works as shown
in Figure 25. When the outdoor air temperature reaches
P61 "high outdoor temperature setpoint” the control
point setting is adjusted to P62 “low boiler temperature
setpoint”. When the outdoor air temperature reaches P63
“low outdoor temperature setpoint” the control setpoint
is adjusted to P64 “high boiler temperature”.
9.3 Hydronic Heating Using External
Modulation Control (BMS)
The Mascot LX can accept a 0-10 VDC input to
integrate with a building management system or external
modulating control. Utilizing Installer Parameters P31
“BMS Voltage at minimum” and P32 ”BMS voltage
at maximum” the installer can set the minimum and
maximum input voltages. By default this input is
enabled but can be disabled using Installer Parameter
P30 “0-10v Input Enable / Disable”.
The Mascot LX can use an external 0-10VDC signal to
control its fan speed (modulation rate), or to control its