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Dividing a snow melting system into a num-
ber of snow melting zones reduces the size
requirements of the hydronic heating plant or the
amperage of the electrical service panel . This
results in lower initial capital cost of the snow
melting system . In applications where a BAS
operates a snow melting system with multiple
zones, each zone requires a 681 with a Snow/Ice
Sensor to detect snow or ice . Each 681 continu-
ously monitors one Snow/Ice Sensor 090 or one
Snow Sensor 095 . Zones that require additional
sensors due to the size of the melting area, multi-
ple 681 can be installed to cover the entire area .
Snow Melting System with Multiple Zones
During warm weather, the slab is warm enough
to naturally melt snow or ice . The 681 has a
Warm Weather Shut Down (WWSD) setting in the
Setpoints menu that prevents the Interface from
entering “Snow Detected: True” in order to con-
serve energy . The 681 shows, “Snow Detected:
False – Warm Weather Shut Down” on the dis-
play when WWSD is in effect, and communicates
to the BAS to turn off the snow melting system .
Automatic (Auto)
The 681 enters WWSD when both the slab tem-
perature and the outdoor temperature exceed
the Melting Setpoint temperature setting by more
than 2°F (1°C) .
WWSD setpoint
The 681 enters WWSD when the outdoor air
temperature exceeds the WWSD setting by 1°F
(0 .5°C) and when the slab temperature exceeds
34°F (1°C) .
The 681 exits WWSD when the outdoor air
temperature falls 1°F (0 .5°C) below the WWSD
setting or if the slab temperature falls below 34°F
(1°C) . This allows the Melting Setpoint setting
to be set higher than the WWSD . This is useful
when high slab temperatures are required to melt
the snow or ice .
Maintaining the snow melting system running
during extremely cold temperatures is not only
expensive but may be impossible if the heat
loss of the slab exceeds the input capacity of
the heating plant or electric cable . The 681 has
a Cold Weather Cut Off (CWCO) setting in the
Setpoints menu that prevents the Interface from
entering “Snow Detected: True” in order to
conserve energy .
The 681 shows “Snow Detected: False” - Cold
Weather Cut Off on the display when CWCO is in
effect, and communicates with the BAS to turn or
maintain the snow melting system off .
The 681 enters in CWCO when the outdoor air
temperature drops below the CWCO temperature
setpoint . This is a safety and energy
saving measure .
The 681 exits the CWCO when the outdoor air
temperature rises above the CWCO temperature
setpoint at which time melting may be resumed .
Warm Weather Shut Down
Cold Weather Cut Off
The slab target is calculated based on the out-
door temperature and the melting setting . The
slab temperature must reach the slab target
and the sensor must be dry for the 681 displays
“Snow Detected False” .
Slab Target
