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670
tekmarNet
Snow Melt
Zone 1
Snow Melt
Zone 2
670
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
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 electrical
service panel. This results in lower initial capital cost of the
snow melting system. The trade off 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.
The snow melt system using Snow Melting Control 654 and
670 may have up to 12 snow melt zones. Zone 1 has the
highest priority and zone 12 has the lowest. The priority
setting in the tekmarNet
®
menu allows the installer to select
the level of zone priority for the entire snow melt system.
Changing the priority setting on one control will update on
all other snow melt controls at the same time. The zone
priority has 3 setting levels. There is some risk that lower
priority zones may ice up when they are shut off by the higher
priority zone. For example, if a high priority zone should finish
melting and allow a lower priority zone to start melting, and
then a new snow fall occurs, the high priority zone will shut
off the lower priority zones. This may potentially allow the
lower priority zones to ice over. The limitations of zoning and
using priority must be carefully considered and discussed
with the building owners and occupants when designing the
snow melting system.
Priority does not apply when the application mode is set to
Boiler. In this mode, the boiler is dedicated to a single snow
melting zone so priority is no longer applicable.
Slab Temperature Control
Controlling the slab temperature is critical to minimizing the
cost of snow melting. This requires that either a Snow/Ice
Sensor 090 or 094 or a Slab Sensor 072 or 073 is installed.
The Snow/Ice Sensor contains a built-in slab temperature
sensor. While the control can operate without a slab sensor
installed, operating costs are much higher.
The slab is operated using slab outdoor reset. As the outdoor
temperature gets colder, the heat loss of the slab increases.
In order to keep the slab surface at a constant temperature
while operating, the inner core of the slab must be heated
above the melt, idle or storm temperature setting. The amount
that the slab inner core temperature is above the melt, idle
or storm setting is proportional to the outdoor temperature.
Since the slab sensor is installed below the surface of the
slab, it is not measuring the true slab surface temperature but
rather the inner core temperature. The control automatically
compensates for this temperature difference. The Slab item in
the Status menu displays the actual measured temperature,
so it is normal to view slab temperatures that exceed the melt,
idle, or storm temperature settings.
Surface temperature = 35 F
Decreasing Air Temperature
Increasing Slab Core T
emperatur
e
Slab Surface Temperature is Constant
Slab Outdoor Reset
Slab Outdoor Reset
Core (sensor)
is warmer