Mascot II Boilers and Water Heaters
Page 31
monitors the flame signal, call for heat, safeties, and
water temperatures. The boiler setpoint is used to limit
the maximum water temperature leaving the boiler only.
The modulation rate is controlled by a 4-20mA (0-
10Vdc using converter) signal supplied by an external
control. When setting up a system using an external
control care must be taken to set the external control
algorithms to prevent the boiler from short cycling or
"hunting " to prevent premature component failure.
NOTE:
A call for DHW will override external control.
9.4 Hydronic Heating Using Local Lead-
Lag/Cascading Feature
When using single or multiple Mascot II's in lead-
lag configuration, the system sensor is used to monitor
the demand and modulation rates of the operating
system (see
Section 7
for wiring instructions).
Let’s consider the following example:
Three Mascot II boilers (let’s call them “Lead”,
“Slave1” and “Slave2”) tied together via Modbus 1
connection, with appropriate RMT Address (1, 2, 3).
System sensor input is used to indicate common
secondary loop temperature.
System setpoint = 150°F
HS (hysteresis) = 10°F (default)
BL (base load) = 50% (default)
Anti-short-cycle = 5 minutes
Run sequence is initiated when system temperature
falls to 140°F (setpoint less hysteresis value). Lead
boiler will start. All firing rates will depend on several
application characteristics, including flow rate, system
load, water volume, etc. Boilers will start at a rate of
35%. If the load is such that Lead’s rate increases to
50%, “Slave1” will go through its startup sequence and
begin firing at 35%. At this point, both boilers (Lead
and Slave1) will continue to respond simultaneously to
the load/system characteristics, by modulating up or
down together, in relation to the relative system setpoint
and load characteristics.
Figure 24. Outdoor Reset Setpoint Temperatures.
Scenario 1: If the system loop temperature rises
quickly, and moves above setpoint, then the
boilers will simultaneously drop their firing rate. If
when reaching the point where both boilers drop
toward their minimum firing rate (20%), then the
first slave will drop out. Slave1 will remain
unavailable until its ASC timer has expired (5
minutes). If the load were to increase such to drive
all active boilers to 50% firing rate or more, during
the ASC time, Slave2 will begin its startup se-
quence and begin to fire at 35%, etc.
Scenario 2: If the system loop temperature continues to
drop (load increases), then the two boilers will
increase firing rate together. At 50%, Slave2 will
begin its firing sequence and be added to the
group.
All three boilers will continue to fire simultaneously at
equal input rates or…
1.
Modulation rate approaches minimum firing rate
(20%), in which case Slave2 will first drop out,
and then Slave1, accordingly.
2.
System temperature reaches 10°F (HS- hysteresis
value) above setpoint (e.g. 160°F), in which case
remaining boiler will shut off.
3.
Any of the boilers approach its high limit tempera-
ture the individual boiler will modulate back.
9.5 Warm Weather Shutdown
Warm weather shutdown overrides a central heat
call for heat when the outdoor air temperature is greater
than the warm weather shutdown setpoint. Warm
weather shutdown is always active whenever there is an
outdoor sensor attached to the control. To avoid warm
weather shutdown the warm weather shutdown
temperature should be increased as necessary. The
warm weather shutdown setpoint can be adjusted in
SETUP mode, using the SD menu.
9.6 Domestic Hot Water Demand
For Combi (LMC), DHW demand is triggered by a
flow switch 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.
For LMH, an optional indirect water heater can be
piped-in using Mascot's integral 3-way valve as a zone
valve. An aquastat in the indirect water heater
connected in place of the flow switch will signal
demand for DHW. The service person should note the
minor wiring differences on
Figure 22
.
Summary of Contents for Mascot II
Page 6: ...LAARS Heating Systems Page 6 Figure 2 Location of Components...
Page 27: ...Mascot II Boilers and Water Heaters Page 27 Figure 22 Wiring Diagram...
Page 42: ...LAARS Heating Systems Page 42 Figure 28 Panel Assembly Door Top...
Page 43: ...Mascot II Boilers and Water Heaters Page 43 Figure 29 Panel Assembly Door Middle...
Page 44: ...LAARS Heating Systems Page 44 Figure 30 Panel Assembly Door Bottom...
Page 45: ...Mascot II Boilers and Water Heaters Page 45 Figure 31 Base Jacket Assembly...
Page 46: ...LAARS Heating Systems Page 46 Figure 32 Heat Exchanger Cabinet Fan...
Page 47: ...Mascot II Boilers and Water Heaters Page 47 Figure 33 Heat Exchanger Burner Components...
Page 48: ...LAARS Heating Systems Page 48 Figure 34 Pump Assembly Components...
Page 49: ...Mascot II Boilers and Water Heaters Page 49 Figure 35 Plumbing Components...
Page 50: ...LAARS Heating Systems Page 50...
