Slant/Fin SF-10 Operation And Instruction Manual page 9

Section C: Outdoor Reset Operation
When either mode 3 or 4 is selected, the control uses outdoor reset to control the water temperature while a heat demand
is present. Outdoor reset calculates the boiler target temperature based on the outdoor air temperature and reset ratio.
The reset ratio is determined from the Boiler Start, Boiler Design, Outdoor Start and Outdoor Design settings.
HEAT DEMAND (Dem 1)
A heat demand is required whenever heat is required in the system. A heat demand is generated when a voltage between
24 and 120 V (ac) is applied across the CD (common demand) and the Ht D (heat demand). Once voltage is applied, the
control turns on the Dem 1 segment in the display. If the control is in warm weather shut down (WWSD), the WWSD seg-
ment is shown in the display and the pump does not turn on and the burner remains off.
If the control is not in WWSD, it closes the pump contact, which starts the boiler pump and the control turns on the boil-
er pump segment in the display. If the operating sensor is 1/2 of the differential below the calculated BOIL TARGET, the
control then closes the Stage 1 contact. The boiler target temperature is determined using the reset ratio. If the operating
sensor reaches 1/2 of the differential above the BOIL TARGET setting, the boiler burner is shut off. The pump contact
remains closed until the heat demand is removed and Pump DLY setting expires.
RESET RATIO
The control uses the four following settings to determine the reset ratio:
Boiler Start (BOIL START)
The BOIL START temperature is the theoretical boiler supply water temperature that the heating system requires when the
outdoor air temperature equals the OUTDR START temperature setting. The BOIL START is typically set to the desired
building temperature.
Outdoor Start (OUTDR START)
The OUTDR START temperature is the outdoor air temperature at which the control provides the BOIL START water
temperature to the system. The OUTDR START is typically set to the desired building temperature.
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 completing heat loss calculations for the building.
Boiler Design (BOIL DSGN)
The BOIL DSGN temperature is the water temperature required to heat the boiler zones when the outdoor air is as cold
as the OUTDR DSGN temperature.
Warm Weather Shut Down (WWSD)
When the outdoor air temperature rises above the WWSD setting, the
control turns on the WWSD segment in the display. When the control is
in Warm Weather Shut Down, the Dem 1 segment is displayed if there
is a heat demand. However, the control does not operate the boiler to
satisfy this demand. The control continues to respond to DHW
demands.
BOIL DSGN BOIL DSGN
OUTDR OUTDR
BOIL BOIL
START START
OUTDR OUTDR
START START
Decreasing Outdoor Temperature
Model SF-10 Control Instructions Manual
DSGN DSGN
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