tekmar 654 Snow Melting Control Installation - Manual (Page 33)

33 of 44 © 2013 654_D - 06/13
Application Modes
Pulse Width Modulation Operation
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
Protect Slab setting in the System menu to On. The control
measures and limits the temperature differential between
the supply water and the slab.
tensile stresses
The snow melting control can operate either an electric or
a hydronic snow melting system. A hydronic system can be
further categorized as either boiler, mixing or pulse width
modulation zone operation, as well as, whether the boiler
plant is dedicated or non-dedicated for the snow melting
system. A dedicated boiler only provides heat from the snow
melting system. A non-dedicated boiler provides heat for
the snow melting system in addtion to the space heating
and / or domestic hot water system. The control requires that one of the following Application Modes is selected in
the System menu:
PWM Pulse Width Modulation
BOIL Boiler Operation
MIX Mixing Operation
ELEC Electrical Operation
090 Tandem Snow / Ice Detection using an
090 or 094
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Electric Operation
The control operates the heat relay on a 20 minute pulse
width modulation 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 and
Storm operation are 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 in
order to reduce operating costs.
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 pulse width
modulation 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 and
Storm operation are 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
in order 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 continu-
ous 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, Idle or Storm temperature setting. The control can
operate a boiler in one of six different methods: modulating
boiler, 1 stage, EMS1, EMS2, control and enable. The Boiler Target is shown in the View menu. Settings for the boiler
operation are located in the Boiler menu.
Important 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 200°F (93.5°C) in order to prevent
short cycling of the burner.