ATH KN-10, Control Manual

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SETUP & OPERATION HeatNet Control V3 2.x
When boiler types are the same, the system turndown is
limited to the boiler‟s min input and fault tolerance is
always present. When the system has mixed boiler types,
consideration needs to be taken on what types can be mixed
properly to achieve a high system turndown and provide
some fault tolerance.
Fault tolerance allows for one boiler in the Priority 1 system
to fail and any boiler(s) in the Priority 2 system to fail and
still provide near linear (continuity) BTU response when
adding boilers. This is illustrated in the following examples
using the Boiler System Response graphs.
The KN Mixed Boiler System (examples) is advantageous
in providing low BTU input for light loads and high BTUs
for heavy loads. The effective system turndown minimizes
short cycling when light loads are present by assigning
smaller boilers to Priority 1, running them first, and then
stopping them last.
In order to achieve the high effective
turndown, smaller boilers are required
(plumbing considerations need to be
considered here due to differing flow/volume
characteristics through the large and small
boilers).
Example Systems:
Figure 4 Non-Mixed Boiler System
System
MMBTU
Effective
Turndown
MOD
MAX
MB/MW 4:1
10.0 25:1 70%
KN20, KN20,
KN20, KN20, KN20
5.0 25:1 70%
KN10, KN10,
KN10, KN10, KN10
3.0 25:1 70%
500, 500, 500, 500,
500
With the traditional Non-Mixed boiler system, the effective
turndown increases by the turndown ratio for every boiler
added. The min fire rate is equal to the minimum BTUs that
can be delivered to the system.
Number of boilers * Turndown Ratio = Effective System
Turndown: 5 * 5:1 = 25:1.
Figure 5 Mixed Boiler System
System
MMBTU
Effective
Turndown
MOD
MAX
Priority 1
5:1
Priority 2
4:1
4.2 35:1 60% KN6, KN6
KN10, KN10,
KN10
3.8 42:1 70% KN4, KN4
KN10, KN10,
KN10
2.2 55:1 81% KN2, KN2
KN6, KN6,
KN6
3.6 90:1 72%
KN2, KN2,
KN2
KN10, KN10,
KN10
With the mixed boiler system, a lower minimum fire
rate/BTU can be delivered to the system by using small
boilers with larger boilers. This works in much the same
way as base loading.
Figure 6 KN Boiler Btu Chart (MBH)
KN2 KN4 KN6 KN10 KN20 KN30
Max Input 200M 400M 600M 1MM 2MM 3MM
Min Input
5:1
40M 80M 120M 200M 400M 600M
Mod Max
80%
160M 320M 480M 800M 1.6MM 2.4MM
Mod Max
70%
140M 280M 420M 700M 1.4MM 2.1MM
Mod Max
60%
120M 240M 360M 600M 1.2MM 1.8MM
Mod Max
50%
100M 200M 300M 500M 1MM 1.5MM
When selecting the Priority 1 boiler(s) for a high effective
system turndown, the BTU Min Input is selected first. (See:
KN Fusion & Boiler Btu Chart ). Next, the MOD-MAX
value of this Priority 1 boiler needs to be greater than : Mod
MAX % =
(Priority 1 „s Min Input + Priority 2 „s Min Input)
Max Input of the Priority 1 boiler
The reason for this is keep the continuity of BTUs linear
without a BTU bump (discontinuity) when boilers are added
or shed. This is illustrated in the
Boiler System Response 2
graph.
If redundancy is not required, the min inputs of the
Priority 1 boilers may be summed to lower the Mod Max %
value so smaller Priority 1 boilers can be used. The sum of
the min inputs would then need to be divided by the sum of
the Max Input of the Priority 1 boilers. The effect of this
would create a higher turndown. See:
EXCEPTION NOTES:
Mod MAX % =
( ((Priority 1 Min) * (#Priority 1‟s)) + Priority 2 Min)
Max Input of Priority 1 boiler * (#Priority 1‟s)
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