tekmar 667 Snow Detector & Melting Control Installation - Manual (Page 5)

5 of 32 © 2009 D 667 - 03/09
Section B1: General Snow Melting
SLAB PROTECTION (ΔT MAX)
The control can limit the rate at which heat is applied to the zone through the ΔT Max setting.
The ΔT (delta T) is the temperature difference between the snow melting supply temperature
and the snow melting return temperature. By limiting this temperature difference, the rate
at which heat is applied to the zone can be controlled and thermal stresses in the slab can
be minimized. When the control is operating at the ΔT MAX, the Maximum pointer can be
seen when viewing the ΔT item in the VIEW menu. The control provides slab protection
differently based on boiler sensor placement.
VISCOSITY COMPENSATION (EXCEEDING ΔT 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 ΔT 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 ΔT Max setting, the Maximum pointer
will flash when viewing the ΔT 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)
The control has a warm weather shut down that prevents the control from entering the Melt or Idle modes in order to conserve
energy. While in WWSD, the word WWSD is displayed in the Status item in the VIEW menu and the WWSD pointer is on the display.
The WWSD can be either set to Automatic or it can be set to a temperature.
Section B: Snow Melting
Section B1
General
Snow Melting
tensile stresses
Outdoor
Temperature
Slab
Temperature
MELT
IDLE
WWSD
CWCO
Control enters
Idle and waits
for Melt Enable
Automatic (Auto)
When the WWSD is set to AUTO, the WWSD occurs when the slab temperature and the
outdoor temperature exceed the Melting setting by 2°F (1°C). The control exits the WWSD
when the slab or outdoor temperature falls to the Melting setting temperature.
Adjustable WWSD
When the WWSD is set to a temperature, the WWSD occurs when the outdoor air
temperature exceeds the WWSD setting by 1°F (0.5°C) and when the slab temperature
exceeds 34°F (1°C). The control exits WWSD when the outdoor air temperature falls
1°F (0.5°C) below the WWSD setting or if the slab temperature falls below 34°F (1°C).
This allows the Melting Temperature setting to be set higher than the WWSD. This is useful
where high slab temperatures are required to melt the snow or ice. A good example of
this is installations using paving bricks on top of sand and concrete layers.