tekmar 362 Mixing Control Installation User Manual

Page 10

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tensile stress

View

NOTE: When operating in the Snow Melting mode, the

Reset Ratio / Characterized Heating Curve DIP switch has no effect on the

operation of the contro

SLAB PROTECTION (

∆

T MAX)

Boiler Sensor on the Return or No Boiler Sensor

(

NON

DEDICATED

HEAT

SOURCE

)

If the snow melting system is one of several loads on a boiler or boiler plant, the amount of
heat available to the system can potentially damage the snow melting slab. The 362 controls
a mixing device that is installed between the snow melting slab and the boiler(s). The control
limits the rate at which heat can be applied to the slab through the

∆

T MAX setting. The

∆T

is the temperature difference between the slab supply temperature and the slab return
temperature. By limiting this temperature difference, the rate at which heat is applied to the
slab can be controlled and thermal stresses in the slab can be minimized. When the control
is operating at the

∆

T MAX, the

Maximum pointer can be seen when viewing the MIX

∆T item

in the View menu. This mode of operation only works when the Boil SENS item is set to RET
or NONE.

Boiler Sensor on the Supply

(

DEDICATED

HEAT

SOURCE

)

If the snow melting system consists of a snow melting slab and a dedicated boiler, a mixing
device is installed between the snow melting slab and the boiler to protect the boiler from
low operating temperatures. In a dedicated snow melting system with a properly sized
boiler, it is not necessary for the control to provide

∆T protection of the snow melting slab;

Since the boiler output is matched to the slab requirements, it is not possible to heat the slab
too rapidly and cause thermal stresses that will result in damage to the slab. Therefore, the
∆T MAX item in the Adjust menu and the MIX ∆T item in the View menu are not available.
When operating a dedicated snow melting system, the 362 is designed to operate the boiler
as efficiently as possible. This mode of operation only works when the Boil SENS item is
set to SUP.

VISCOSITY COMPENSATION (EXCEEDING

∆

T MAX)

At low temperatures, the glycol solutions used in snow melting systems become very viscous and difficult to pump. In order to overcome
this condition during a cold start of a snow melting system, the 362 is allowed to exceed the

∆

T MAX setting for a period of time in order

to warm the glycol solution. This allows the control to compensate for the high viscosity of the glycol solution and is used when the supply
temperature is below 30˚F (-1˚C). When the control exceeds the

∆

T MAX setting, the

Maximum pointer will flash when viewing the MIX

∆

item in the

View menu.

RAMPING OF THE

∆

When the control starts applying heat to the slab, the supply temperature to the snow melting system is ramped up over a period of time
until it reaches the maximum allowed

∆T. This function does not occur when the boiler sensor is on the supply.

OPERATING STATUS (SNOWMELT)

While in the Snow Melting mode (Mode 2), an additional item is available in the

View menu called SNOWMELT. This item displays the

current operating status of the snow melting system.

• STRT The word STRT is displayed after the snow melting system has been enabled. It is

displayed until the slab reaches the melting temperature. If the slab is at the melting
temperature, STRT is displayed for five seconds after the snow melting system has
started operation. This is to verify that the control has entered into the
snow melting mode.

• STOP The word STOP is displayed for five seconds after the snow melting system has

stopped operation. The word STOP is also displayed if either a Remote Start/Stop
Module 039 or Remote Display Module 040 stops the snow melting system and an
external demand is still present.

• IDLE The word IDLE is displayed as long as the control is operating the slab at the idling temperature.

• EXT The word EXT is displayed when the RUN TIME has reached 0:00 and the control still has an external demand for melting. In

this situation, the control continues melting until the snow melting demand is removed or the control is stopped.

• 0:00 to 17:00 hr While the slab is up to temperature, and the control is melting, the remaining RUN TIME is displayed.

• INF If an infinite RUN TIME is selected and the control is melting, INF is displayed.

• WWSD When the control is in a Warm Weather Shut Down, WWSD is displayed.

• CWCO When the control is in a Cold Weather Cut Off, CWCO is displayed