Service Manual

© 2015 680_D - 10/15 40 of 48
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
• Boiler+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 boiler stage
1 relay on a 20-minute pulse width modulation cycle. The boiler
stage 1 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:
• System pump — not used
• Primary pump — not used
• Boiler pump — not used
• Boiler stage 1 — cycles on/off using Pulse Width Modulation
• Boiler stage 2 — not used
The Application Mode should be set to Pulse Width Modulation
(PWM) Zone when the boiler or heat source is shared with
the snow melting system and there is no mixing system. The
snow melting system is considered to be part of a zone that
includes space heating and domestic hot water.
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 melt, idle
or storm
• Primary pump — operates continuously during melt, idle
or storm
• Boiler pump — cycles on/off using Pulse Width Modulation
• Boiler stage 1 — cycles on/off using Pulse Width Modulation
• Boiler stage 2 — not used