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DEFINITIONS
Warns of possible exposure to risk which can cause personal injury or property
WARNING
damage if ignored.
Attention is required to avoid wrong control operation or restricted access to some
ALERT
settings.
WWC
Warm Weather Cutoff. See "Warm Weather Cutoff (WWC)" on page 26.
ISP
Idle Set Point. See "Idle Set Point (ISP)" on page 26.
CWC
Cold Weather Cutoff. See "Cold Weather Cutoff (CWC)" on page 28.
(Slab ΔT)
The Slab Delta T is the difference in temperature between the Slab Supply temperature
and the Slab Return temperature.
SMC OPERATION MODES
The Snowmelt Control (SMC) is designed to operate a radiant slab Hydronic heating system to prevent snow
and ice accumulation on sidewalks, driveways, and other areas where buildup is undesirable. It does this
using the provided Slab Sensor. This is the Heat-Timer preferred operation mode.
In Slab Sensor Type mode, the slab sensor base and its conduit must be installed before the slab installation.
However, in some sites where the concrete slab is old and cannot be altered, the SMC can operate based
on the Outdoor Sensor using the Outdoor Sensor Type mode. This method does not provide any moisture
detection and requires the purchase of the optional Outdoor Sensor (HT# 904220-00).
SLAB SENSOR OPERATION OVERVIEW
The SMC uses the Slab Sensor in two steps. First, the SMC continuously monitors the slab temperature
and detects moisture. When the SMC starts the Idle mode, it will try to maintain the slab temperature above
freezing. Second, when it detects moisture and the temperature suggests possible ice or snow accumulation,
the SMC activates the heating system to evaporate the moisture by raising the supply temperature.
The Slab Sensor provides the slab temperature and moisture information necessary to run the slab heating
system. This Brass sensor is designed to become an integral part of the slab. Therefore, it is specifically
engineered to support extreme heat and cold temperatures and to withstand pressure and impact, such
as might occur when a car drives over it. Despite its sturdy structure, the sensor is very accurate. Its
temperature accuracy is within one degree and its moisture sensitivity is adjustable to sense even traces
of precipitation. The Slab Sensor does not allow any snow or ice accumulation. It does this using a built-in
heater that operates below freezing temperatures.
A snowmelt system generally includes a heating plant and a slab pump to move the water/anti-freeze solution
through the slab's radiant piping. Whenever the Slab Sensor reads a temperature below the adjustable
WWC, the SMC enables the Idle mode. In Idle mode the SMC maintains the slab temperature above freezing
(at the ISP). It does this by pulsing the Slab Pump (15 seconds for every Antifreeze period) when the slab
temperature is above the ISP. See "Antifreeze" on page 30. When the slab temperature drops below the ISP,
the SMC activates the heating plant Slab and System Pumps to maintain the slab at the ISP temperature.
This gives the slab a head start on melting should precipitation occur.
Once the slab heating system is activated, the amount of energy entering the slab is determined by the
difference between the temperature of the fluid going to the slab (the Slab Supply temperature) and the
temperature of the fluid returning from the slab (the Slab Return temperature). The difference between these
two is called the Slab ΔT. The Slab ΔT is different for each slab composition based on the slab design. The
higher the Slab ΔT, the more energy is being input to the slab. If the Slab ΔT is set larger than its design ΔT
(Max ΔT), the slab itself may be damaged. The SMC provides a maximum Slab ΔT adjustment. This setting
protects the slab during the initial warm-up periods. See "Maximum Delta Temperature (Max ∆T)" on page 29.
4
ALERT
SMC Installation and Operation Manual
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