SETUP & OPERATION
HeatNet Control V3 3.x
Page 24
Figure 12
Boiler System Response 2
(1) KN6, (1) KN20, 60% Mod-Max
To correct this would require the KN6 to set the MOD-
MAX to roughly 90% (Boiler System Response 3: not as
efficient as it could be) in order to have a linear BTU
transfer when the KN20 is added (fired).
Figure 13
Boiler System Response 3
(1) KN6, (1) KN20, 90% Mod-Max
A KN6 running with a KN20 may not be an optimal choice
unless (2) KN6’s are always functional and used in the
Priority 1 set or (3) KN6s 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. The example system uses (3) KN2s and (3)
KN10s. Two of the KN2s are treated as one when adding
the min inputs of the Priority 1 set.
Figure 14
Boiler System Response 4
(2) KN2s, (3) KN6s
The above Boiler System Response 4 graph illustrates
another system where 80% is used as the MOD-MAX
clamp.
In summary, the system should be tuned using the boiler
selection charts and the MOD-MAX value so that boilers
are brought on and fired in their respective efficiency curve
while maintaining continuity in BTUs. 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.
For the examples, the RBI FIII-Series water heaters will be
used. These boilers are non-Condensing, fully modulating,
low mass, and HeatNet compatible. Also, consider the
SMITH-Series 28 with the HeatNet option in Priority 2 set.
Figure 15
Mixed Boiler System
System
MMBTU
Effective
Turndown
MOD
MAX
Priority 1
KN 5:1
Priority 2
MB/MW 3:1
3.45
28:01:00
62%
KN6, KN6
FIII 750,
750, 750
4.2
35:01:00
76%
KN6, KN6
FIII 1000,
1000, 1000
2.3
29:01:00
62%
KN4, KN4
FIII 500,
500, 500