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Electric operation
The control operates the heat relay on
a 20-minute PWM cycle. The heat relay,
in turn, activates a line voltage electrical
contactor to energize the electrical cable
heater installed in the slab. The heat 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
heat 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 operation
is 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 to reduce
operating costs.
Pulse width modulation
operation
The Application Mode should be set to
Pulse Width Modulation (PWM) when the
boiler or heat source is non-dedicated to
the snow melting system and there is no
mixing system. The snow melting system
is considered to be a zone together with
space heating and the domestic hot water
system. The control operates the heat
relay on a 20-minute PWM cycle. The
heat relay, in turn, activates the hydronic
heating system zone pump or zone valve.
The heat 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 heat 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 operation is not available when a slab
sensor is not installed.
The hydronic PWM operation requires the
installation of an outdoor sensor and a
supply sensor. The supply sensor is
installed on the glycol antifreeze system
supply pipe and allows the control to
provide slab protection and as well as
supply zone priority. A slab sensor is highly
recommended to reduce operating costs.
Boiler operation
The Application Mode should be set to
Boil when the snow melting system has a
dedicated boiler or heat source. The boiler
is piped primary-secondary to the snow
melting loop, 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 or Idle
temperature setting. The control can
operate a boiler in one of four different
methods: single stage, modulating boiler,
EMS1 or EMS2. The Boiler Target is shown
in the View menu. Settings for the boiler
operation are located in the Boiler menu.
Note:
The boiler operator, or aquastat,
remains in the burner circuit and acts
as a secondary upper limit on the
boiler temperature. The boiler aquastat
temperature setting must be adjusted
above 200ºF (93.5ºC) in order to
prevent short cycling of the burner.
