Outdoor Reset Operation - Slant/Fin EM-10 Operation Manual

Outdoor Reset Operation

When either mode 4 or 5 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. As a result, the boiler target changes
proportional to the outdoor temperature. 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) pins.
Once voltage is applied, the control turns on the Dem 1
segment in the display. If the control is not in warm weather
shut down (WWSD), the control calculates a boiler target
based on the reset ratio and outdoor air temperature. The
pump and the boiler stages are operated to maintain the
boiler target at the boiler outlet sensor (Mode 4), or the
boiler supply sensor (Mode 5).
If the control is in WWSD, the WWSD segment is shown
in the display and the boiler target in the View menu of the
display remains "---" (no target).
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 B oil MIN
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.
WWS D
EM-10-40 Operation and Instruction Manual
B oil MAX
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.
Reset Ratio
B oil DS GN Boil DSGN
B oil S TAR T Boil START
OUTDR DSGN OUTDR DS GN
OUTDR S TAR T OUTDR START
Decreasing Outdoor Air Temperature
Warm Weather Shut Down (WWSD)
When the outdoor air temperature rises above the WWSD
setting, the control enters WWSD and turns on the WWSD
segment in the display. Once the outdoor air temperature
falls below the WWSD setting, the control exits WWSD.
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 the heat
demand. The control continues to respond to setpoint
demands.
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