Service Manual

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Sequence of Operation
Snow Melting Overview
A snow melting system can offer a safe, convenient, and cost
effective way of removing snow and ice from the snow melting
slab and similar surfaces. Safety is increased by activating
the snow melting system as soon as the snow falls rather
than waiting for mechanical snow removal after snow has
accumulated. This eliminates slip hazards and reduces the
risk of injury by mechanized snow melting equipment, thereby
reducing potential liability costs. The elimination of snow plow
equipment and corrosive salts also reduces damage to the
slab surface and to the environment. When controlled correctly,
snow melting systems can be cost competitive compared to
mechanical snow removal.
The snow melting control can operate in one of four
different ways:
Melt Heats the slab to melt snow or ice
Idle Pre-heats the slab just below freezing to shorten the
time required to melt snow
Storm Temporarily pre-heats the slab just below freezing to
shorten the time required to melt snow
Off Snow melting system is off
The display shows the control operation in the home screen.
Melt Operation
The snow melting system operates the heating equipment
to heat the slab from a cold start or from the idle or storm
temperature to reach the melt temperature setting to melt
snow or ice. Melt operation can be triggered automatically
using a snow/ice sensor, manually by pressing the Melt button
on the display, or through the BACnet or Modbus protocol.
The melt temperature setting affects calculated targets such
as the slab target, boiler target and mix target.
Melt – Automatic Start and Stop
Automatic start and stop operation requires the installation of
a Snow/Ice Sensor 090 (65' or 20 m cable) or 094 (208' or 63
m cable). The sensor is installed in-slab level with the melting
surface. The control continually monitors the sensor for the
presence of moisture and slab temperature conditions in which
snow or ice may be present. When moisture is detected, the
control shows “Sensor 1 Water Status Wet” in the Slab Status
menu. When the sensor is dry the control shows “Sensor Water
Status Dry”. The control includes a Sensitivity setting in the
Setpoints menu that allows the installer to adjust the amount
of moisture required to start and stop the melting operation. In
areas with low amounts of dust and/or air pollution, the sensitivity
may need to be increased. The default sensitivity setting is
Auto. This setting allows the control to automatically determine
the best suitable sensitivity setting for the installation.
Push STOP button
090 or 094 and slab dry and
Add Melt time elapses
or
Idle
Off
WWSD
BACnet or Modbus Stop Request
090 or 094 detects water
Exits
CW
CO
Melt
Suspended
Enters
CWCO
Auto
Melt
When moisture is detected and the slab and outdoor tempera-
tures are at or below freezing, the control will automatically
start the snow melting system. As the snow or ice melts and
the slab dries off, the sensor also dries off at the same time.
When the sensor is dry, the snow melt system automatically
shuts off. If there are low spots on the slab surface that dry
off slower than the sensor, additional melting run time can be
included by adjusting the Additional Melt Time setting in the
Setpoints menu.
If the snow melting system is manually stopped, the snow/ice
sensor must fully dry before it is able to detect a new snow fall
and automatically start the snow melting system.
Snow/Ice Sensor
090 or 094
The slab temperature must reach the slab target in order for the
system to shut off automatically. The capacity of the heat source
must be sized to ensure melting as low as the cold weather cut
off. In addition, the heat source maximum temperature setting
must be set to provide the full capacity of the heating appliance.
For example, boiler aquastats should be set to 180°F (82°C).
Failure to meet these requirements may result in the snow melting
system not automatically shutting off when the slab is dry.