Slant/Fin SF-10 Operation And Instruction Manual page 6

MODE 6
(External Target Temperature Input and DHW Operation -
Primary / Secondary Piping)
Mode 6 is designed for an external input signal and domestic hot water
(DHW) with primary / secondary piping. The external input signal can
be provided from a BMS, an EMS, or a tekmar tN4 System Control. The
external input signal creates an internal demand and changes the
boiler target according to a linear scale. The control operates the boiler
burner to maintain the boiler target at the boiler supply sensor. Refer to
section D for a description of external target temperature operation.
Once a DHW demand is present, the control operates the boiler burn-
er to maintain the DHW target at the boiler supply sensor. If both a heat
demand and a DHW demand are present at the same time, the control
targets the higher of the two requirements. Refer to section F for a
description of indirect domestic hot water operation.
MODE 7
(External Direct Drive Operation)
Mode 7 is designed for an external input signal to directly control the
firing rate of the burner with either parallel or primary / secondary pip-
ing. The DHW demand input is disabled. Refer to section E for a
description of external target temperature operation.
BOILER DIFFERENTIAL (DIFF)
A heat source must be operated with a differential in order to reduce short cycling. The boiler differential is divided around
the boiler target temperature. The first stage contact will close once the water temperature at the operating sensor is 1/2
of the differential setting below the boiler target temperature, and will open once the water temperature at the operating
sensor is 1/2 of the differential setting above the boiler target temperature.
Manual Differential
The differential can be manually set using the DIFF setting in the
Adjust menu.
Auto Differential
If the Auto Differential is selected, the control automatically deter-
mines the best differential as the load changes, thereby improving
efficiency. During light loads, the differential is increased to allow
longer on and off times to reduce the potential for short cycling.
During large loads, the differential is narrowed thereby improving
comfort in heating spaces by reducing temperature swing.
6 Model SF-10 Control Instructions Manual
External
0 - 10 V (dc)
Control
Temperature Target
DHW Tank
External 0 - 10 V (dc)
Control Direct Drive
Boiler
Supply
Sensor
165°F
(74°C)
160°F
Desired temperature
(71°C)
155°F
(68°C)
Boiler On
Time
Off
On
Differential
Time
BTC
Boiler
Outlet
Sensor
Boiler
Supply
Sensor
Boiler Inlet Sensor
2PDA 2PDA
BTC BTC
Boiler Boiler
Outlet Outlet
Sensor Sensor
Boiler Boiler
Inlet Inlet
Sensor Sensor
Differential
10°F (6°C)
Boiler On