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Application Modes
Pulse Width Modulation Zone Operation
The snow melting control can operate either an electric or
a hydronic snow melting system. A hydronic system can be
categorized as boiler, mixing, boiler and mixing, or pulse
width modulation zone operation. A dedicated boiler only
provides heat for the snow melting system. A shared boiler
provides heat for the snow melting system in addition to the
space heating and/or a domestic hot water system. These
choices affect which Application Mode is selected in the
System Setup menu:
• PWM Zone
Pulse Width Modulation Zone Operation
• Boiler
Boiler Operation
• Mixing
Mixing Operation
• Mix
Boiler and Mixing Operation
• Electric
Electrical Operation
Electric Operation
The Application Mode should be set to Electric when operating
an electric heating cable. The control operates the heat relay
on a 20-minute pulse width modulation cycle. The heat relay
in turn activates a line voltage electrical contactor to energize
the electrical cable heater installed in the slab. The relay on
time is determined by the calculated slab target and by the
measured slab temperature reading. As the slab temperature
reaches the slab target, the on-time per cycle of the relay is
reduced to prevent the slab temperature from overshooting.
If no slab sensor is installed the relay remains on 100% of the
time until the Melt operation has completed. Idle and Storm
operation are not available when a slab sensor is not installed.
The electric operation requires the installation of an outdoor
sensor. A slab sensor is highly recommended in order to
reduce operating costs.
Relay operation:
• Heat relay — cycles on and off using Pulse Width Modulation
• System pump — not used
• Primary pump — not used
• Boiler stage 1 — not used
• Boiler stage 2 — not used
The Application Mode should be set to Pulse Width Modulation
(PWM) Zone when the snow melting system is warmed from
a heat source that is shared with other loads in a building.
The control operates the system pump to operate continuously
during melt, idle and storm operation. The boiler stage 1 relay
operates on a 20-minute pulse width modulation cycle. The relay
on time is determined by the calculated slab target and by the
measured slab temperature reading. As the slab temperature
reaches the slab target, the on time per cycle of the relay is
reduced to prevent the slab temperature from overshooting.
If no slab sensor is installed the heat relay remains on 100%
of the time until the Melt operation has completed. Idle and
Storm operation are not available when a slab sensor is not
installed. The PWM Zone operation requires the installation
of an outdoor sensor. A slab sensor is highly recommended
in order to reduce operating costs.
Relay operation:
• System pump — operates continuously during melting,
idling or storm
• Heat relay — cycles on/off using Pulse Width Modulation to
control the slab temperature
• Boiler stage 1 — cycles on/off using Pulse Width Modulation
to control the slab temperature
• Boiler stage 2 — not used