heat-timer SMC Installation & Operation Manuals page 6

• Set the following SMC System Startup settings:
○ Sensor Type
○ Control Mode
• Suggested starting point for SMC Operating settings:
○ WWC
○ CWC
○ ISP
○ Maximum Delta T
○ Maximum Slab Supply =
○ Minimum Boiler Return
○ Season
OUTDOOR SENSOR OPERATION OVERVIEW
The Snowmelt Control (SMC) is designed to control under slab
heating systems to prevent accumulations of ice or snow. Heat-
Timer recommends that the Slab Sensor be utilized, but the SMC
can be used with an Outdoor Sensor instead in situations where
a Slab Sensor installation is difficult. In the Outdoor Sensor
Type mode, the SMC monitors three temperatures, the outside
temperature, the temperature of the fluid going to the slab (Slab
Supply temperature), and the temperature of the fluid returning
from the slab (Slab return temperature).
The slab must be kept above freezing whenever there could be
frozen precipitation. As a result, any ice or snow that falls on the
slab will melt immediately. If precipitation is allowed to accumulate
before heating the slab, an effect called bridging can occur. The
snow or ice directly in contact with the slab will melt. But, the
snow above will act as an insulator, reflecting the heat back into
the slab. The slab itself will have no ice touching its surface, but
the remaining accumulation will melt very slowly. To prevent this,
the SMC activates the slab heating system whenever the outside
temperature falls below the adjustable WWC setting.
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) and the
temperature of the fluid returning from the slab (the Slab Return).
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= Slab. See "Sensor Type" on page 22.
= Select "Motorized Valve" if the slab loop is using a 2-way steam motorized
valve (and a heat-exchanger) or a 3-way hydronic mixing motorized valve.
= Select "Boiler" if the slab loop is heated directly by a modulating boiler.
= Select "Ext. Interface" if the SMC is connected to a Heat-Timer multi-boiler
control (Multi-MOD Platinum, Mini-MOD, SQ-Elite, etc..). Then set the
EMS 4 and 20mA set points to match the boiler control 4-20mA set points.
See "Control Mode" on page 22.
= 38°F. See "Warm Weather Cutoff (WWC)" on page 26.
= 10°F or as per engineers criteria. See "Cold Weather Cutoff (CWC)" on
page 28.
= 34°F or as per engineers criteria. See "Idle Set Point (ISP)" on page 26.
= As per engineers criteria. See "Maximum Delta Temperature (Max ∆T)" on
page 29.
As per slab design engineer. See "Maximum Slab Supply" on page 29.
= As per boiler manufacturer specifications. See "Minimum Boiler
Return" on page 29.
= Winter. See "Season" on page 26.
Heat-Timer recommends installing a high-limit control to shutdown the
heating system in case of excessive high slab supply temperatures.
WARNING
38°F
10°F
SMC Installation and Operation Manual
No Moisture
Detection Available
Slab Target = Off
Boiler = Off
Valve = Close
Slab Pump = Off
System Pump = Off
Warm Weather
Cutoff (WWC)
Slab Return Target = On
Boiler = On
Valve = Modulating
Slab Pump = On
System Pump = On
Cold Weather
Cutoff (CWC)
Slab Target = Off
Boiler = Off
Valve = Close
Slab Pump = Pulse
System Pump = Off