tekmar 275 Boiler Control - Manual (Page 8)

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Modulating Boilers Section D
The 275 can operate up to four modulating boilers. The
control also provides dry contacts for either burner ignition
or boiler pump. Selection is made through Boiler Relay
setting in the Adjust menu.
Once a boiler is required to operate, the control outputs
an analog signal corresponding to the Start Modulation
setting and then turns on the boiler relay. Once the Fire
Delay time has elapsed, the modulating output is adjusted
to the Minimum Modulation setting. The control then holds
the modulating output at Minimum Modulation until the
Minimum Modulation Delay time has elapsed. Proportional,
Integral and Derivative (PID) logic is used in order to satisfy
the boiler target temperature.
Modulation Mode Setting in Adjust Menu
The control includes a Modulation Mode setting that
selects either Sequential or Parallel Modulation. Sequential
modulation should be used on boilers that are more efficient
when operating at high fire. Parallel modulation should be
used on boilers that are more efficient when operating at
low fire.
Sequential Modulation
In sequential modulation, the first boiler is turned on and
is modulated to satisfy light loads. Once the first boiler
does not have enough capacity to satisfy the load, the first
boiler reduces its modulation to provide a smooth transition
when the second boiler fires at low fire. The first boiler
then modulates up to maximum modulation as the load
increases. Only then is the second boiler able to increase
its output as the load continues to increase. When the third
boiler is required, the second boiler reduces its modulation
to allow the third boiler to operate at low fire. As the load
continues to increase, the second boiler is modulated to
its maximum and then the third boiler is modulated. The
operation is reversed when shutting off the boilers.
100% 60% Off Off
Parallel Modulation
In parallel modulation, the first boiler turns on at low fire
and begins to increase its modulation. Once the first boiler’s
output is greater than the combined output of the first and
second boiler’s low fire, the first boiler is modulated down
to low fire and the second boiler is fired at low fire. The
two boilers now modulate together. Once the two boiler’s
combined output is greater than the combined output of
all three boilers operating at low fire, the first and second
boilers are modulated down to low fire, and all three boilers
are operated at low fire. The boilers are then modulated
as the load increases. The operation is reversed when
shutting off the boilers.
40% 40% 40% 40%
The 275 is restricted to sequential staging if:
1. 1 or more boilers are configured to be On/Off.
2. Condensing mode is selected.
3. The plant is configured for direct DHW.
Boiler Start Modulation Setting in Adjust Menu
(per boiler)
The Start Modulation setting is the lowest modulation
output required to obtain proper ignition. Whenever boiler
operation is required, the control outputs an analog signal
corresponding to the Start Modulation setting and closes
the boiler contact to turn on the burner. After the Fire Delay
has elapsed and the burner is ignited, the control modulates
the firing rate between the Minimum Modulation setting and
the Maximum Modulation setting.
Boiler Fire Delay Setting in Adjust Menu
(per boiler)
The Boiler Fire Delay sets the time it takes for the boiler to
generate flame from the time the boiler turns on.
Boiler Contact Closed
Time
Fire Delay
Burner On
Boiler Motor Speed Setting in Adjust Menu
(per boiler)
The Motor Speed is the amount of time the boiler requires
to go from 0% modulation to 100% modulation.
Gas valve actuating motors have a design time from
fully closed to fully opened which can be found in the
manufacturer’s manual. The Motor Speed should be set
to this time.
The Motor Speed setting for a Variable Frequency Drive
(VFD) is the amount of time required to go from a stopped
position to 100% fan speed. Since a VFD has a very quick
response rate, it may be necessary to increase the Motor
Speed setting in order to increase the stability of the boiler
modulation.
OR
Boiler % Modulation in View Menu
View the current % modulation of each boiler in the View
menu.