LAARS Mascot LX MLXC 175 MBH - Install and Operating Manual - Manual (Page 41)

Mascot LX Boilers and Water Heaters Page 37
outlet setpoint. The 0-10V signal may also be used to
create a heat demand eliminating the need to supply a
separate “TT call”.
9.3.a External Signal to Control Modulation.
Installer Parameter P25 “0-10V to Power (fan speed)”
– This is the default 0-10VDC configuration in which
the external signal directly corresponds to fan speed
or ‘boiler power’ In this mode, the call is initiated by
the 0-10v input based on Installer Parameters P33 “On
threshold voltage” and P34 “Off hysteresis voltage”.
The modulation power can also be scaled with P35
“BMS rate at minimum voltage” and P36 “BMS rate at
maximum voltage”.
9.3.b External Signal to Control Setpoint.
Installer Parameter P25 “0-10v BMS modulation
control” must be disabled – In this mode the 0-10VDC
input directly controls the boiler's outlet temperature.
Set the parameters using the Installer Parameters P37
“ BMS Temperature setpoint at minimum voltage” and
P38 “BMS temperature setpoint at maximum voltage”
9.3.c External Signal Initiates Heat Demand
In this mode P26 “0-10V BMS Thermostat Demand
Required” must be disabled to eliminate the need for
a separate “TT Call”. This allows a heat demand to be
created every time the 0-10V signal exceeds P33 “BMS
On Volts”. The heat demand will remain until the 0-10V
signal drops below P33 “BMS On Volts” – P34 “BMS
Demand Off Differential Voltage”
9.4 Warm Weather Shutdown
Warm weather shutdown overrides a central heat
call when the outdoor air temperature is greater than
the warm weather shutdown setpoint. Warm weather
shutdown is always active when there is an outdoor
sensor attached to the control. The warm weather
shutdown setpoint can be adjusted in Installer mode,
using P65 “CH outdoor Air Shutdown Temperature” and
P66 “CH Outdoor Air Shutdown Differential”.
9.5 Domestic Hot Water Demand
9.5.a Combi Boiler DHW
For Combi units (MLXC), DHW demand is triggered
by a flow sensor located near the DHW cold water inlet.
When water begins to flow (open faucet, shower, etc.),
the boiler will fire, based on the water temperature
requirements. It may cycle on and off under very low
flow rates. Minimum flow is 0.5 gpm.
9.5.b Boiler only DHW aquastat demand
For Boiler only units (MLXH), an indirect water heater
can be piped-in. An aquastat in the indirect water heater
connected to terminals 7 and 8 will signal demand for
DHW. In this demand mode the boiler will modulate on
the outlet water temperature sensor and use P51 “DHW
setpoint (S1 – Tank) as the setpoint.
9.5.c Boiler only DHW sensor demand
An optional DHW sensor (Laars PN E2337501) can
also be installed in an indirect water heater connected to
terminals 9 and 10 to initiate demand. In this mode the
tank sensor will control demand and modulation based
on the DHW setpoint. In the case of indirect heaters the
boiler will also modulate on the outlet water temperature
sensor and use P51 “DHW setpoint (S1 – Tank) as the
setpoint.
The service person should note the minor wiring
differences on Figure 22 .
9.6 Domestic Hot Water Priority
DHW priority is used to allow the CH call to be
interrupted when there is a DHW call. This allows
the boiler to use the full capacity to satisfy hot water
demands without interruptions. From the factory the
default settings give priority to DHW for 55 minutes
before switching to satisfy the CH demand. To adjust
navigate to installer parameter P50 “ DHW priority
over CH” and adjust the time as required.
At the end of the DHW priority period the
boiler will switch to CH priority to supply heat to the
building. The boiler remains in this state until P49,
“CH priority time over DHW” expires. To adjust
navigate to installer parameter P49 and adjust the time
as required.
Figure 25. Outdoor Reset Setpoint Temperatures.