IOM-T-294
2205
© 2022 tekmar
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High
Select High mass for large commercial boilers . This provides
long pre and post purge times for the pumps, modulates the
boiler quickly, and operates the boiler staging with long inter-
stage delays .
Very High
Select V .High mass for large commercial boilers that are over-
shooting with the high mass setting .
Boiler Low and High Output
In order to accommodate different boiler capacities in the
same system, a low fire and high fire boiler output for each
boiler is available . This allows the control to properly operate
the boilers using either sequential or parallel modulation . Each
boiler typically has a rating plate that specifies the minimum
and maximum output . This information is also available in the
boiler manual .
The minimum and maximum boiler output is entered in units
of MBTU/hr . 1 MBTU / hr = 1,000 Btu per hour . The range is
from 10 to 9990 MBTU/hr .
Modulation Motor Speed
The Modulation Motor Speed is the amount of time the analog
modulating output signal to the boiler requires to go from 0%
to 100% modulation .
Boilers with an electronic blower fan are recommended to use
the factory default of 30 seconds .
Boilers with a modulating motor gas valve and linkage arms
should set the Modulating Motor Speed to the time required to
fully open the gas valve .
Start Modulation
The Start Modulation setting is the lowest modulation output
required to obtain proper ignition .
Minimum Modulation
The Minimum Modulation is the lowest signal the control can
send to modulate the boiler and operates the boiler at low fire .
• Refer to the boiler manufacturer’s literature to determine the
minimum output voltage V (dc) or current (mA) that the boiler
will successfully operate at .
For 0 to 10 V (dc):
Minimum Modulation =
Boiler’s Minimum Input Signal
x 100%
10 V (dc)
For 4 to 20 mA:
Minimum Modulation =
Boiler’s Minimum Input Signal - 4mA
x 100%
16 mA
Example:
A boiler requires a 1 .8 V (dc) signal to fire the boiler at low fire .
The boiler can be modulated to 10 V (dc) where it reaches
high fire .
Minimum Modulation =
1 .8 V x 100% = 18%
10 V
Control’s
Output
Signal
Range
Boiler’s
Input
Signal
Range
100%
10 V (dc)
10 V (dc)
0 V (dc)
Boiler’s
Minimum
Input
Signal
Minimum
Modulation
0%
1.8 V (dc)
18%
Maximum Modulation
The Maximum Modulation is the highest signal the control can
send to modulate the boiler .
For 0 to 10 V (dc):
Maximum Modulation =
Boiler’s Maximum Input Signal
x 100%
10 V (dc)
For 4 to 20 mA:
Maximum Modulation =
Boiler’s Maximum Input Signal - 4mA
x 100%
16 mA
Example:
A boiler’s input signal range is 0 to 9 V (dc) . The 294 control
has an output signal range of 0 to 10 V (dc) .
Maximum Modulation =
9 V
x 100% = 90%
10 V
Control’s
Output
Signal
Range
Boiler’s
Input
Signal
Range
100%
10 V (dc)
9 V (dc)
0 V (dc)
0 V (dc)
90%
Boiler’s
Maximum
Input
Signal
Maximum
Modulation
0%
Boiler Group
The control has two boiler groups: 1) Condensing; and 2)
Non-condensing . Select the boiler group based upon the con-
struction of the boiler . In general, most boilers with cast-iron
or copper-fin tube heat exchangers are non-condensing; while
boilers with stainless steel and aluminum heat exchangers are
condensing .
Post Purge
This setting sets the amount of time the control operates the
boiler pump or valve after the boiler is turned off . This purg-
es heat out of the boiler, reducing stand-by losses, and also
reduces “kettling” on low mass boilers . The amount of time
for the boiler pump post purge is adjustable between 0 to 20
minutes .
