SETUP & OPERATON HeatNet Control V3
Page 18
Figure 10 Boiler System Response 2
(1) MB/MW 500, (3) MB/MW 1250, 60% Mod-
Max
To correct this would require the MB/MW 500 to set the
MOD-MAX to roughly 90% (Boiler System Response 3: not
as efficient as it could be when using CB/CW Fusion
boilers) in order to have a linear BTU transfer when the
MB/MW 1250 is added (fired).
Figure 11 Boiler System Response 3
(1) MB/MW 500, (3) MB/MW 1250, 90% Mod-
Max
An MB/MW 500 running with a MB/MW 1250 may not be
an optimal choice unless (2) MB/MW 500s are used in the
Priority 1 set or (3) MB/MW 500s and one is allowed to be
taken offline.
A system employing this redundancy where (1) is allowed
to be taken offline is listed in the MIXED BOILER SYSTEM
chart. This system uses (3) MB/MW 500s and (3) MB/MW
1500s. Two of the MB/MW 500s are treated as one when
adding the min inputs of the Priority 1 set.
Figure 12 Boiler System Response 4
(2) MB/MW 500s, (3) MB/MW 2000s
The Boiler System Response 4 graph illustrates another
system where 80% is used as the MOD-MAX clamp. With
this example, when using all non-condensing boilers, the
system can maximize the use of the smaller boilers before
calling the larger ones.
In summary, the system should be tuned using the boiler
selection charts and the MOD-MAX value. Since selecting
the Priority 1 boiler is integral to the fault tolerance of the
system, it is important to note any discontinuities in BTUs if
a Priority 1 boiler fails when multiple Priority 1 boilers are
used.
Mixed System Type 2:
Condensing / Non-Condensing
This mixed system may also have mixed boilers with
differing sizes as outlined in the Mixed System Type 1:
High System Turndown section. In the following examples
condensing high mass boilers will be used with non-
condensing low mass boilers. The reason for creating a
mixed system is primarily to control the system cost.
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