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 1/2 of the differential below
the boiler target temperature . As the boiler supply water tem-
perature reaches 1/2 of the differential above the boiler target
temperature, the boiler is shut off .
Manual Differential
Differential = 10°F (6°C)
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