Finned copper tube gas boilers & water heaters – Boiler Manual
23
BOILER/WATER HEATER OPERATION
Staging Operation
The Dominator boiler/water heater series is separated into on/off,
2-stage and 4-stage units depending on the model size. The 300 is
on/off only. The 400 through 900 models have two firing inputs. The
1050 through 2100 have four. Input staging is controlled from the
staging controller that signals the relay board to select the blower and
gas valve modes. Table 12 identifies the stages and firing modes
associated with the on/off (D300), 2-stage units (D400-D900), and
Table 13 identifies the stages and firing modes associated with the
4-stage units (D1050-D2100).
Table 12 Firing Modes (D400-D900) – D300 On/Off Only
Stage
Firing Mode
Off
Off
1
Low Fire
2
High Fire
Table 13 Firing Modes (D1050-D2100)
Stage
Left Firing Mode
Right Firing Mode
Off
Off
Off
1
Low Fire
Off
1
2
Low Fire
Low Fire
3
High Fire
Low Fire
4
High Fire
High Fire
1- The left main valve will operate at low fire, but left and right
blowers will be on and operating at low fire (low speed).
The outlet water temperature is automatically controlled by the
staging controller. It utilizes inputs from the inlet and outlet water
temperature sensors, plus optional tank and outside sensors, to stage
the boiler/water heater. The Dominator will stage up or down
progressively, but will not jump over a stage. Stage 1 will operate first,
last and whenever the boiler/water heater is in operation. Consult
the staging controller documentation for further information on
controller operation.
For the D1050-D2100, the air inlet plenum is divided into
left and right sides. A separate blower, main gas valve and manifold
are used for each side. However, the combustion chamber is
undivided. For best overall performance, gas and airflows should be
balanced so that when both sides are at low or high fire, stage 2 or 4,
the gas and airflows are equal.
Pressure Switch Settings
Differential pressure switches are provided in the Dominator to shut
down gas flow under a blocked flue or inlet condition. One high fire
pressure switch is used for the 300 and one low fire and one high fire
pressure switch are used for the 400 through 900 models. Two low
fire and two high fire pressure switches are used for the 1050 through
2100 models. The low fire pressure switches serve to shut down gas
flow if there is a blocked flue or inlet condition during low fire
operation. Similarly, the high fire switches will shut down gas flow if
there is a blocked flue or inlet condition during high fire operation.
The differential pressure is taken between the air plenum
and the pressure inside one of the main burners.
Pressure taps are provided in the control compartment for taking
the differential pressure readings, Figure 17. Table 14 lists the
differential pressure settings for all of the models.
Figure 17
Pressure Switch Tap(s)
Table 14 Differential Pressure Settings (All Units)
Model
Differential Pressure
Requirement at High Fire
(All Units)
Inches WC
mm WC
300-900
1.0 ± 0.1
20.3 ± 2.5
1050-2100
1.0 ± 0.1
25.4 ± 2.5
On the 4-stage units, the left low fire and high fire switches
will interrupt power to the control module under a blocked flue or
inlet condition. This will cause the pilot and left and right main gas
valves to close. The right switches will only shut down the right main
gas valve under a blocked flue or inlet condition. The relay board
automatically selects between pressure switches as the boiler/water
heater changes stages. Tables 15 and 16 identify how pressure switch
control changes during boiler/water heater staging. Tables 17 and 18
identify the control actions if a low air condition occurs at any stage.
For example, when operating at stage 2, the left and right low fire
pressure switches monitor the boiler/water heater, since the blowers
are operating at low speed. When the unit stages to stage 3 the left
blower will be switched to high speed and the relay board will switch
the circuit so that the left high fire switch monitors the differential
pressure for the left side. The right low fire pressure switch will
continue to control the right side until the unit stages to stage 4.
At that point, the right high fire pressure switch will automatically
take over monitoring duties for the right side. A low air condition
in either plenum will cause a red light to illuminate on the indicator
board.
