The controller's reset mode adjusts the circulating
water temperature to maintain a steady and
comfortable indoor temperature. Indoor temperature
is compared with the preset operating range (set
point target), and if the temperature deviates (as
sensed by the room thermostat), the controller will
bring the temperature back to the set point limits.
For example, if the room temperature is 65°F and
the set point target range is 70°F-80°F, then the
controller will work to raise the room temperature
back to within that set point range. Since set point
regulates the target temperature based on the room
thermostat, an outdoor sensor is not required.
Figure 9 Controller compares set point target with
indoor temperature
To program the set point target range, set the:
Boiler Supply° – desired or fixed supply/outlet water temperature.
Maximum Supply° – the highest water temperature allowed to prevent overheating of the outlet
water temperature. Check that this temperature takes into account the construction and safety
requirements of each application (e.g., 140 °F/ 60°C maximum for in-slab radiant floor to avoid
thermal stress).
Supply Diff'l (differential) - Set the differential to prevent short cycling. The boiler will shut off
when the boiler supply water temperature minus half its differential falls below the boiler
Current Target°. The boiler will fire when the boiler supply water temperature plus its
differential rises above the boiler Current Target°. See Setting the supply differential in heating
modes on page 29.
Summer shutdown° - The cut-off temperature level that prevents further heating. Boiler ignores
a call for heat.
2.4 External Control
You can place the control of a load under an external electronic controller (such as a building
management or automation system). In external control mode, temperature management is controlled
by the building management system (BMS), consisting of one or more control panels wired to various
sensors and valves in a building. The BMS will determine the desired boiler set point for any given
building occupancy parameters.
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