AUTOFLAME Mk8 MM, Техническое руководство, Страница: 86 / 98

5 Intelligent Boiler Sequencing
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MM Application Possibilities
For example, if the change up threshold in parameter 87 is set at 90%, then if the last firing MM in the
sequence is above 90% firing rate, then upon the elapse of the next scan time, the next lag MM will
be brought online. If at the next scan time, the firing rates of the last two online lag MM are 30% and
40% respectively, and the change down threshold in parameter 86 is set at 80%, then the last lag MM
will go into standby, warming or off depending on how the sequencing mode is set.
If a lag burner fails to start when requested, the scan time will be decreased by the offset set in
parameter 1, until it is automatically ignored from the sequencing communication loop. If a lag burner
fails to modulate after being requested to contribute to the load requirement, then that MM will be
ignored from the sequencing communication loop after a time delay set in parameter 5.
After a power recycle, the number of MMs which are initially set on when the MMs start up again, is
set in parameter 3.
5.3.2 Two Port Valve Operation
In hot water sequencing, when there is no demand for all of the lag boilers to be on, the system will
close the two port valves on the lag boilers that do not need to be on. This will stop the hot water
circulating in the system from passing through the boiler and the heat being wasted. It is possible to
use Terminal 78 which is a switched neutral to control the two port valve. This works by switching to
neutral once the burner has stopped firing but if the temperature of the boiler ever gets above the
required set point then Terminal 78 will switch back even if the boiler is not firing.
• When the two port valve is closed on an OFF lag boiler, if at any time, the residual heat in that
boiler is above the required setpoint, the valve is opened immediately and the heat is let
through the system. The two port valve then stays open.
•
When the lead boiler recognises that it needs a lag boiler to come online after the sequence
scan time, the lag boiler will then run its relay tests. This will open the two port valve
immediately and it will then stay open.
For the two port valve to close, the lag boiler must be in standby mode, and the actual setpoint must
be on or below the required setpoint; it must be in this condition for at least one minute.
Terminal 78 on the MM is a switched neutral connection for controlling a two port valve that would
normally be installed in the boilers return pipe connection to the common return header. This facility
ensures that boilers that are switched ‘offline’ do not contribute return temperature water to the flow
header thereby diluting the flow temperature to the building.