Watts tekmar 294 - Sequence of Operation - Heating Calls; Heating Call Types; Central Heating Operation

IOM-T-294 2205 © 2022 tekmar
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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 Water Temperatures
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.