Single-zone snow melt control installation and operation manual | 29
Single stage on/off boiler (1STG)
The control turns the heat relay on or off
to fire the boiler in order to maintain the
Boiler Target temperature. The boiler supply
temperature operates on a differential that is
half above and half below the boiler target.
The status of the boiler is shown by the Boil
Relay item in the View menu.
Modulating boiler (MOD)
The control can operate a single hot-water
modulating boiler using the Mod output and
the Heat contact. The control operates the
boiler by first switching the heat contact to
allow the modulating boiler to go through
the ignition sequence (the heat contact may
not be required on all modulating boilers).
A 0-10 VDC or 4-20 mA analog signal is
then used to modulate the boiler firing rate
starting at 50% (5 VDC or 12 mA signal)
for 30 seconds. After the 30-second delay
has elapsed, the control will then allow the
boiler to modulate down to the Minimum
Modulation setting and hold it there for the
Modulation Delay time setting.
After the modulation delay has elapsed,
the control uses PID logic to change the
boiler firing rate signal in order to satisfy the
boiler target temperature. When the firing
rate signal is reduced down to the minimum
modulating setting and the boiler supply
temperature exceeds the boiler target by half
the differential, the control will shut off the
boiler burner. The modulating signal output
is shown by the Boil Rate in the View menu.
The Modulation Delay setting is determined
by the boiler manufacturer. It is the amount
of time that the burner must operate before
the internal boiler control allows an external
signal to operate the burner.
The Motor Speed sets the rate at which the
modulating electrical signal can change. For
most modulating boilers with an ECM fan,
the motor speed can be set to 30 seconds.
For commercial boilers with a mod motor,
set the motor speed according to the time
required by the mod motor to travel from the
closed to the open position.
EMS1
The EMS1 signal is a method for the snow
melting control to send the boiler target
temperature to a compatible boiler control
(if used). The control provides a 0-10 VDC
signal proportional to the boiler target and
turns on the heat relay to operate the boiler
to maintain the Boiler Target temperature.
EMS2
The EMS2 signal is a method for the snow
melting control to send the boiler target
to a Viessmann boiler that supports the
OpenTherm temperature targeting. Typical
boilers include the Viessmann Vitodens
100-W and 200-W. The boiler may require
an OpenTherm Input Module 0-10V.
Contact Viessmann for details.
The control provides a 0-10 VDC signal
proportional to the boiler target and turns
on the heat relay to operate the boiler to
maintain the Boiler Target temperature.
EMS1 conversion table
0-10 VDC
Boiler target
0
– – – (Off)
1
50ºF (10ºC)
2
68ºF (20ºC)
3
86ºF (30ºC)
4
103ºF (39ºC)
5
121ºF (49ºC)
6
139ºF (59ºC)
7
157ºF (69ºC)
8
174ºF (79ºC)
9
192ºF (89ºC)
10
210ºF (99ºC)