Watts tekmar 294 - System Operation - Staging Types; Boiler Target and Min;Max Settings; Staging Type Selection; PID Staging Parameters

IOM-T-294 2205 © 2022 tekmar
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The Smart Boiler Control 294 is able to operate up to four boil-
ers and can be expanded up to a maximum of sixteen boilers
through the use of Smart Boiler Expansion 294EXP.
Boiler Target Temperature
The boiler target temperature is determined by the type of call
received. If there are multiple heat calls, the boiler target is
adjusted to the highest call. If the control does not presently
have a requirement for heat, “---” is displayed on the home
screen.
Boiler Minimum
The Boiler Minimum is the lowest temperature that the control
is allowed to use as a boiler target temperature. During mild
conditions, if the control receives a call that is below the boiler
minimum setting, the boiler target temperature is adjusted to
the boiler minimum setting.
Notice:
The Boiler Minimum is only applied when at least one of the
boilers is configured to part of the non-condensing boiler
group. Set the Boiler Minimum setting to the boiler manufac-
turer’s recommended temperature.
Boiler Maximum
The Boiler Maximum is the highest temperature that the control
is allowed to use as a boiler target temperature. If a heat call is
higher than the boiler maximum, the boiler maximum is adjusted
down to the boiler maximum setting. Set the boiler maximum
setting below the boiler operator or aquastat temperature.
Notice:
The boiler operator, or aquastat, remains in the burner circuit
and acts as a upper limit on the boiler temperature. The boil-
er aquastat temperature setting must be adjusted above the
294’s boiler maximum setting in order to prevent short cycling
of the burner.
Staging Type
The control supports two staging operations:
• Proportional-Integral-Derivative (PID)
• Proportional
PID is recommend for central heating and combined central
heating with domestic hot water applications. Proportional
staging is recommended for volume domestic hot water heat-
ing and applications that require rapid response to heating
loads.
PID Staging
PID staging makes use of the following parameters to deter-
mine when the next boiler is turned on:
• PID Boiler Differential
• PID Stage Delay
PID Boiler Differential
Both on/off and modulating boilers are operated with a differ-
ential. For modulating boilers, the differential no longer applies
once operating the boiler above low fire.
The differential operates by turning on the boiler when the
boiler supply water temperature is ½ of the differential below
the boiler target temperature. As the boiler supply water tem-
perature reaches ½ of the differential above the boiler target
temperature, the boiler is shut off.
Manual Differential
Differential = 10°F (6°C)
Target + 1/2 Differential
Target – 1/2 Differential
Target
165°F (74°C)
160°F (71°C)
155°F (68°C)
Boiler
On
Boiler
On
Automatic Differential
The automatic differential operation monitors previous boiler
on and off cycles and automatically adjusts the differential to
minimize boiler short cycling. In light load conditions the boiler
differential is increased; while in high load conditions the boiler
differential is decreased.
Off
Differential
Time
Heating Load
On
PID Stage Delay
The Stage Delay is the minimum time delay between the firing
of each boiler or boiler stage. After this delay has expired the
control can fire the next boiler or boiler stage if it is required.
This setting can be adjusted manually or set to an automatic
setting. When the automatic setting is used, the control
determines the stage delay based on the boiler mass setting
with low mass having a short delay and high mass having long
delays.
Proportional Staging
Proportional staging makes use of the following parameters
to determine when the next boiler is turned on. All conditions
must be met to turn on the next available boiler.
• Interstage Differential
• Interstage On Delay
• Interstage Off Delay
• Minimum Stage Run Time
• Minimum Stage Off Time
System Operation