Section B1
General
Section B2
Installer
Section B3
Advanced
BOILER DEMAND
A boiler demand is required in order for the 256 to provide heat to the heating system. A
boiler demand is generated by connecting terminal
T
(7) to terminal
C-
(9) through a switching
device. Once the switching device closes, the
Boiler Demand
pointer is displayed in the
LCD. The 256 calculates a BOIL TARGET supply temperature based on the outdoor air
temperature and settings.
BOILER OPERATION
When the 256 determines that boiler operation is required, the
Boiler
contact terminals (5 and 6) close. While the
Boiler
contact is
closed, the burner segment in the LCD is displayed.
CHARACTERIZED HEATING CURVE
The 256 varies the supply water temperature based on the outdoor air temperature. The control takes into account the type of terminal
unit that the system is using. Since different types of terminal units transfer heat to a space using different proportions of radiation,
convection and conduction, the supply water temperature must be controlled differently. Once the control is told what type of terminal
unit is used, the control varies the supply water temperature according to the type of terminal unit. This improves the control of the
air temperature in the building.
BOILER TARGET TEMPERATURE (BOIL TARGET)
The BOIL TARGET temperature is determined from the
Characterized Heating Curve
settings and the outdoor air temperature. The
control displays the temperature that it is currently trying to maintain as the boiler supply temperature. 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. At no time does the
control operate the boiler above 248°F (120°C).
OUTDOOR DESIGN (OUTDR DSGN
)
The OUTDR DSGN is the outdoor air temperature that is the typical
coldest temperature of the year where the building is located. This
temperature is used when doing the heat loss calculations for the
building. If a cold outdoor design temperature is selected, the boiler
supply temperature rises gradually as the outdoor temperature drops.
If a warm outdoor design temperature is selected, the boiler supply
temperature rises rapidly as the outdoor temperature drops.
Section B: Boiler Reset
Section B1: General
Section B2: Installer
© 2019 tekmar 256_D - 09/19
5 of 20
C-
T
Power
R+
7
8
9
Boiler demand switches
24 V (ac)