Watts tekmar 294 - Boiler Operation - Output and Control; Boiler Output Range Settings; Modulation Speed and Start Settings; Boiler Group and Post Purge

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.