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Boiler Operation
The Application Mode should be set to Boiler when the snow
melting system has a dedicated boiler or heat source and there
is no mixing device. The boiler is piped primary-secondary
to the snow melting loop, thereby allowing the boiler to fire
on and off while allowing continuous flow through the snow
melting system loop. The control calculates a Boiler Target
based upon the Slab Target, which in turn is based upon the
measured outdoor temperature and the Melt, Idle or Storm
temperature setting. The boiler is fired to maintain the Boiler
Target at the Boiler Supply Sensor location. The control can
operate a boiler in one of four different methods: modulating
boiler, 1 stage, 2 stage and EMS. The Boiler Target is shown
in the System Status menu. Settings for the boiler operation
are located in the Boiler Setup menu.
1 Stage Boiler
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-----------------------------------
The control turns the boiler stage 1 relay on or off to fire the
boiler and maintain the Boiler Target temperature. The boiler
supply temperature operates on a differential that is half above
and half below the boiler target. The status of the boiler is
shown in the System Status menu.
2 Stage Boiler
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-----------------------------------
The control turns the boiler stage 1 and 2 relays on or off
to fire a single boiler in order to maintain the Boiler Target
temperature. The boiler supply temperature operates on a
differential that is half above and half below the boiler target.
The boiler staging is operated automatically using PID logic.
The status of the boiler stages 1 and 2 is shown in the System
Status menu.
Modulating Boiler
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The control can operate a single modulating boiler using
the modulating output and the boiler stage 1 contact. The
control operates the boiler by first switching the boiler stage 1
contact to allow the modulating boiler to go through the ignition
sequence. The boiler stage 1 contact may not be required
on all modulating boilers. A 0-10 V (dc) or 4-20 mA analog
signal is then used to modulate the boiler firing rate starting
at 50% (5 V (dc) or 12 mA signal) for 30 seconds. After the
30-second delay has elapsed, the control will then allow the
boiler to modulate down to the Boiler Minimum Modulation
setting and hold it there for the Boiler Modulation Delay time
setting. After the modulation delay has elapsed, the control
uses PID logic to change the boiler firing rate signal in order to
satisfy the boiler target temperature. When the firing rate signal
is reduced down to the minimum modulating setting and the
boiler supply temperature exceeds the boiler target by 1/2 of
the differential, the control will shut off the boiler burner. The
modulating signal output is shown by the Boiler Output in the
System Status menu.
The Boiler Modulation Delay setting is determined by the boiler
manufacturer. It is the amount of time that the burner must
operate before the internal boiler control allows an external
signal to operate the burner.
The Boiler Motor Speed sets the rate at which the modulating
electrical signal can change. For most modulating boilers with
an ECM fan, the boiler motor speed can be set to 30 seconds.
For commercial boilers with a mod motor, set the boiler motor
speed according to the time required by the mod motor to
travel from the closed to open position.
The boiler operator, or aquastat, remains in the burner
circuit and acts as a secondary upper limit on the boiler
temperature. It is recommended to set the boiler aquastat
temperature to at least 180°F (82.0°C) in order to prevent
short cycling of the burner.
EMS Voltage V (dc)
EMS
SIGNAL
MIN
10V(dc)
EMS
LOW
TEMP
EMS
HIGH
TEMP
Supply W
ater T
emperatur
e
EMS Current mA
EMS
SIGNAL
MIN
20mA
EMS
LOW
TEMP
EMS
HIGH
TEMP
Supply W
ater T
emperatur
e
EMS
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When the boiler is required to operate, the control's boiler
modulation output is adjusted to an appropriate analog signal
corresponding to the boiler target temperature and then turns
on the boiler stage 1 relay. The analog signal is proportional
to the boiler target in a linear line defined by the EMS Signal
Minimum, the EMS Low Temperature, and the EMS High
Temperature settings.
Relay operation:
System pump — operates continuously during melting,
idling or storm
Heat relay — not used
Boiler stage 1 — cycles on/off based on boiler target
Boiler stage 2 — cycles on/off based on boiler target
when using a two-stage boiler, otherwise off.
Mod Boiler — a signal ranges between 0-10 V (dc) or 4
-20 mA
