Service Manual

39 of 48 © 2015 680_D - 10/15
BAS
680
Snow Melt
Zone 1
Snow Melt
Zone 2
680
Dividing a system into a number of snow melting zones and
prioritizing the zone operation reduces the size requirements
of the hydronic heating plant or the amperage of the electri-
cal service panel. This results in lower initial capital cost of
the snow melting system. The tradeoff is that some snow
melt zones may not be able to melt as soon as the snow
fall begins and the user must tolerate snow accumulation
on the slab.
Prioritization of the snow melting zones can be accomplished
using the BAS system. If two or more snow melting zones
start automatically, the lower priority zone can be shut off
using the Melt/Stop Request parameter in the BACnet or
Modbus communication protocol. When the highest priority
has finished melting, the BAS system can provide a Melt
Request to manually start melting the zone. The zone will
continue to operate until the snow/ice sensor is dry or the
time has elapsed on the manual melt run timer.
Warm Weather Shut Down
Cold Weather Cut Off
During warm weather, the slab is warm enough to naturally
melt snow or ice. The control has a Warm Weather Shut Down
(WWSD) setting in the Setpoints menu that prevents the control
from entering Melt, Idle or Storm operation in order to conserve
energy. The control shows, "System is Off – Warm Weather
Shut Down" on the display when WWSD is in effect.
Automatic (Auto)
The control enters WWSD when both the slab temperature
and the outdoor temperature exceed the Melting Setpoint
temperature setting by more than 2°F (1°C).
Manual WWSD
The control 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 control 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. An
example of this are installations using paving bricks on top
of sand and concrete layers.
Maintaining the melting or idling setpoint temperature 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 control
turns the snow melting system off when the outdoor air
temperature drops below the Cold Weather Cut Off (CWCO)
temperature and the slab is below freezing. This is a safety
and energy saving measure. The control shows, "System is
Off – Cold Weather Cut Off" on the display when CWCO is
in effect. When the temperature reaches the CWCO setting
in an actively melting system with an 090 or 094, melting is
suspended until the outdoor temperature rises above the
CWCO setting at which time melting is resumed. If an 090
or 094 is not installed, melting is stopped when CWCO is in
effect and melting does not resume when the temperature
rises above the CWCO setting.
Snow Melt Zones and Priority
Slab Protection
In a hydronic snow melting system, the boiler or heating
plant capacity may be much larger than the load of the snow
melting zones. This can result in large temperature differentials
between the supply water temperature and the slab creating
large tensile stresses on the slab. Concrete is weak to tensile
forces and when repeatedly exposed to tensile loads the
concrete may crack. This may be prevented by selecting
the Slab Protection setting in the System Setup menu to On.
The control measures and limits the temperature differential
between the supply water and the slab.
tensile stresses