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2012 274_D
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Outdoor Design Setting in Adjust Menu
The outdoor design temperature is typically the coldest
outdoor air temperature of the year. This temperature is
used when doing the heat loss calculations for the building
and is used to size the heating system equipment. If a cold
outdoor design temperature is selected, the supply water
temperature rises gradually as the outdoor temperature
drops. If a warm outdoor design temperature is selected,
the supply water temperature rises rapidly as the outdoor
temperature drops.
Boiler Indoor Setting in Adjust Menu
The boiler indoor design temperature is the indoor
temperature the heating designer chose while calculating the
heat loss for the boiler water heated zones. This temperature
is typically 70°F (21.0°C). This setting establishes the
beginning of the boiler characterized heating curve.
Boiler Design Setting in Adjust Menu
The boiler design supply temperature is the boiler water
temperature required to heat the zones at the outdoor design
temperature, or on the typical coldest day of the year.
(Default automatically changes based on terminal unit
setting)
Warm Weather Shut Down (WWSD) Setting in Adjust
Menu
Warm Weather Shut Down disables the heating system when
the outdoor air temperature rises above this programmable
setting. When the control enters into WWSD, the LCD will
indicate this in the status field. WWSD is only available
when the DIP switch = Demands. The boilers will operate
when a Domestic Hot Water (DHW) demand or a Setpoint
Demand is present.
Boiler Operation
Section C
The 274 is able to operate up to four on/off boilers as a heat
source. For proper operation of the boilers, the 274 must be
the only control that determines when a boiler is to fire.
*Important note:
The boiler operator, or aquastat, remains
in the burner circuit and acts as a secondary upper limit
on the boiler temperature. The boiler aquastat temperature
setting must be adjusted above the 274’s boiler maximum
setting in order to prevent short cycling of the burner.
Mode
The 274 control is capable of staging single stage, two
stage, three stage and four stage on/off heat sources. As
well, in certain modes of operation, the control is capable
of controlling the individual boiler pumps. The control has 6
modes of operation based on the type of staging and pump
operation that is desired. The following describes the modes
of operation.
Mode 1:
4 Single stage boilers and primary pump.
Mode 2:
2 Single stage boilers with individual boiler
pumps and primary pump.
Mode 3:
2 Two stage boilers and a primary pump.
Mode 4:
1 Two stage boiler and individual pump.
Mode 5:
1 Three stage boiler and individual pump.
Mode 6:
1 Four stage boiler and primary pump.
Relay 1
Relay 2
Relay3
Relay 4
Mode 1
Boiler 1
Boiler 2
Boiler 3
Boiler 4
Mode 2
Boiler 1
Boiler 1
Pump
Boiler 2
Boiler 2
Pump
Mode 3
Boiler 1
Stage 1
Boiler 1
Stage 2
Boiler 2
Stage 1
Boiler 2
Stage 2
Mode 4
Boiler 1
Stage 1
Boiler 1
Stage 2
Boiler 1
Pump
not used
Mode 5
Boiler 1
Stage 1
Boiler 1
Stage 2
Boiler 1
Stage 3
Boiler 1
Pump
Mode 6
Boiler 1
Stage 1
Boiler 1
Stage 2
Boiler 1
Stage 3
Boiler 1
Stage 4
Boiler Target Temperature
The boiler target temperature is determined by connected tN4
devices or by a Boiler, DHW or Setpoint demand received
by the control. An Energy Management System (EMS) can
also give a boiler target. The tN4 devices determine the
highest water temperature required and then request this
temperature on the tN4 boiler bus. The temperature request
creates a Boiler Demand and this is indicated on the display.
A DHW demand and a Setpoint demand have temperature
settings to which the boilers are operated to meet and are
able to override the tN4 bus temperature if required. The
control displays the temperature that it is currently trying to
maintain as the boiler supply temperature in the View menu.
If the control does not presently have a requirement for heat,
it does not show a boiler target temperature. Instead, “– – –”
is displayed in the LCD.
Boiler
Pumps
Supply
Sensor
Return
Sensor
Primary
Pump
Boiler
Pumps
Supply
Sensor
Return
Sensor
Primary
Pump