
IOM-T-294
2205
© 2022 tekmar
33
When powered on and in automatic mode, the control remains in standby until it receives a heating call from one of the following
inputs:
• Central heating call
• Domestic hot water call
• Setpoint call
• tekmarNet call
Once a call is received, the control displays a boiler target and the control starts the boiler firing sequence . The heating calls are
visible on the System Inputs screen on the control .
Sequence of Operation
Heating Calls
Central Heating Operation
A central heating call is created when a contact closure or 24
V (ac) signal is applied across the Heat Call terminals .
Central heating calls use outdoor temperature reset to calcu-
late the boiler target . This weather responsive feature reduces
energy consumption by up to 30% compared to operating the
boilers at a fixed setpoint . The boiler target is calculated using
the following factors:
• Room temperature occupied (default: 70
°
F, 21 .0
°
C) or
unoccupied (default: 65
°
F, 18 .5
°
C)
• Outdoor air temperature
• Outdoor start temperature (default: 70
°
F, 21 .0
°
C)
• Boiler start temperature (default: 70
°
F, 21 .0
°
C)
• Outdoor design temperature (default: 10
°
F, -12 .0
°
C)
• Boiler design temperature (default: 180
°
F, 82 .0
°
C)
As the outdoor air temperature gets colder, the boiler target is
automatically ramped up to match the additional heat loss of
the building using a heating curve .
Heating Curve
Terminal
Unit
Boiler
Design
Boiler
Start
Outdoor
Design
Decreasing Outdoor Temperatures
Increasing W
ater T
emperatures
Room Occupied and Unoccupied
Increasing the Room Temperature setting shifts the heating
curve upwards; therefore calculating higher boiler target tem-
peratures . Likewise, decreasing the Room Temperature set-
ting shifts the heating curve downwards; therefore calculating
lower boiler target temperatures . When using a programmable
schedule, the Room Temperature Unoccupied reduces energy
use by automatically lowering the heating curve and lowering
the boiler target temperatures .
Outdoor Start
This setting determines the outdoor air temperature starting
point of the heating curve .
Boiler Start
This setting determines the boiler temperature starting point of
the heating curve .
Outdoor Design
This setting determines the outdoor air temperature at which
the highest boiler water temperature is required . This is typi-
cally set to the coldest outdoor air temperature for your local
region .
Boiler Design
This setting determines the highest boiler temperature required
to heat the building based upon the Heating Terminal Unit
type .
Heating Terminal Unit
The Heating Terminal Unit changes the shape of the character-
ized heating curve to better match the heat transfer properties
of that specific terminal unit .
Radiant Floor
A hydronic radiant floor is embedded in either a concrete pour
or stapled up in the floor joist . This heating system has a large
thermal mass and is slow acting .