tekmar 420 Boiler Reset Module - Manual (Page 14)

© 2007 D 420 - 08/07 14 of 24
Boiler Characterized Heating Curve
Terminal Unit
Boiler
Design
Boiler
Indoor
Outdoor
Design
Decreasing Outdoor Temperatures
Increasing W
a
ter T
e
mperatures
Boiler Temperature Control Section C
Warm Weather Shut Down (WWSD)
The Warm Weather Shut Down is the outdoor temperature
at which hydronic heating is no longer required. The boiler
operates only when a Domestic Hot Water (DHW) Demand
or a Setpoint Demand is present.
The WWSD setting is found in the Adjust menu.
Boiler Terminal Unit Defaults
When a terminal unit is selected for boiler zones, the
control loads default values for the boiler design, boiler
maximum supply, and boiler minimum supply temperatures.
The factory defaults can be changed to better match the
installed system. Locate the Boiler Terminal Unit setting
in the Adjust menu.
Terminal Unit BOIL DSGN BOIL MAX BOIL MIN
High Mass Radiant (1) 120°F (49°C) 140°F (60°C) OFF
Low Mass Radiant (2) 140°F (60°C) 160°F (71°C) OFF
Fancoil (3) 190°F (88°C) 210°F (99°C) 140°F (60°C)
Fin-Tube Convector (4) 180°F (82°C) 200°F (93°C) 140°F (60°C)
Radiator (5) 160°F (71°C) 180°F (82°C) 140°F (60°C)
Baseboard (6) 150°F (76°C) 170°F (77°C) 140°F (60°C)
Boiler Indoor Design
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.
• • Locate the Boiler Indoor Design setting in the Adjust
menu.
Boiler Design Temperature
The boiler design supply temperature is the boiler water
temperature required to heat the zones on the typical
coldest day of the year.
• • Locate the Boiler Design setting in the Adjust menu.
The 420 is able to operate a single, hot water, on-off or
modulating boiler as a heat source. For proper operation of
the boiler, the 420 must be the only control that determines
when the boiler is to fire.
*Important note:
The boiler operator, also known as
an aquastat, remains in the burner circuit and acts as a
secondary upper limit on the boiler temperature. The boiler
operator temperature setting must be adjusted above the
420’s Boiler Maximum setting in order to prevent short
cycling of the boiler burner.
Boiler Target Temperature
The boiler target temperature is determined by connected
tN4 devices or by a DHW or Setpoint demand received by
the control. The tN4 devices determine the highest water
temperature required and then, requests 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 Minimum
The boiler minimum is the lowest temperature that the
control is allowed to use as a boiler target temperature.
During mild conditions, if the control calculates a boiler
target temperature that is below the Boiler Minimum setting,
the boiler target temperature is adjusted to at least the
Boiler Minimum setting. During this condition, if the boiler is
operating, the minimum segment is turned on in the display
when viewing either the boiler supply temperature or the
boiler target temperature. Set the Boiler Minimum setting
to the boiler manufacturer’s recommended temperature.
• • Locate the Boiler Minimum setting in the Adjust menu.
Boil MIN + 1/2 Boiler Differential
Boil MIN
Boil MIN – 1/2 Boiler Differential
MIN segment on
Boil Water Te
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Boil Water Te
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