tekmar 667 Snow Detector & Melting Control User Manual

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Section B: Snow Melting

SLAB PROTECTION (

∆T MAX)

The control can limit the rate at which heat is applied to the zone through the

∆T MAX

setting. The

∆T (delta T) is the temperature difference between the snow melting supply

temperature and the snow melting return temperature. By limiting this temperature dif-
ference, the rate at which heat is ap p lied to the zone 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

∆T item in the View menu. The control

provides slab protection differently based on boiler sensor placement.

Section B1

General

Snow Melting

Section B1: General Snow Melting

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 667 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 mixing return temperature is below 30°F (-1°C). When the control exceeds the

∆T MAX setting, the Maximum pointer

will flash when viewing the

∆T item in the View menu.

SOFT START

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 target mixed supply temperature. This feature helps reduce thermal stresses in the slab.

Note: This operation only occurs if the Boil SENS item is set to RET or NONE.

RUNNING TIME (RUN TIME)

The running time is the length of time that the system operates once it has reached its slab target temperature. During the time that
the system is approaching its slab target temperature, the RUN TIME does not decrease. Once the system reaches its slab target
temperature, the RUN TIME begins counting down. When the RUN TIME reaches 0:00 as displayed in the STATUS item in the View
menu, the system has finished melting.

Note: The running time is only applicable when a manual melting enable signal starts the snow melting system. Refer to
Section D1 for a description of a manual melting enable.

WARM WEATHER SHUT DOWN (WWSD)

There is a warm weather shut down for the system. When both the slab temperature of the system and the outdoor tempera-
ture exceed the system’s melting temperature by more than 2°F (1°C), the system enters into WWSD. In WWSD, the system is
shut down in order to conserve energy. While the system is in WWSD, the word WWSD is displayed in the STATUS item in the
View menu. The 667 turns on the WWSD pointer in the display.

COLD WEATHER CUT OFF (CWCO)

Maintaining the system at either the melting or idling temperature during extremely cold temperatures can be expensive or impossi-
ble. The control turns the snow melting system off when the outdoor air temperature drops below the Cold Weather Cut Off (CWCO)
temperature. While the control is in CWCO, the word CWCO is displayed in the STATUS item in the View menu. The heater in the
sensor is kept on during CWCO until the control detects moisture. If water is detected, the heater is turned off but the control retains
the moisture detected information. When the outdoor temperature rises above the CWCO temperature, the control exits CWCO and
if the Snow / Ice Sensor 090 detected moisture during CWCO, the control initiates melting mode. If the control has been started prior
to the CWCO, it resumes the melting mode once the outdoor air temperature rises above the CWCO temperature.

tensile stresses