SETUP & OPERATION
HeatNet Control REV 1.38-1
Page 14
KN 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)
Example:
(2) KN6s, (2) 28A-W-5s
Redundancy:
(120 + 385)/600 = 84%
No Redundancy:
(120 * 2) + 385)/(600*2) =52%
EXCEPTION NOTES:
1.
Mixing more than two different size/type boilers
becomes more complex than the scope of this manual
and is not recommended.
2.
If using more than one Priority 1 boiler and the
calculated value is <
Priority 1Min * 2
Priority 1 Max Input
Use this result Plus note 3 vakue as the MOD MAX %.
3.
Always add a few % (3-5%) to the calculated MOD
MAX % value to allow a guard band (tolerance).
4.
If boilers are of different sizes, try to use larger priority
2 boilers.
5.
If the calculated Mod MAX % value is greater than
99%, the combination can not be used since short
cycling will occur.
Figure 6
Smith Boiler Btu Chart (MBH)
28A-W-5 28A-W-9 28A-W-14 28A-W-18
Max Input
1156
2232
3563
4629
Min Input
3:1
385
744
1187
1543
Mod Max
80%
925
1785
2850
3703
Mod Max
70%
809
1562
2494
3240
Mod Max
60%
693
1338
2137
2777
Mod Max
50%
578
1116
1781
2314
Figure 7
KN Boiler Btu Chart (MBH)
KN2
KN4 KN6 KN10 KN20
KN30
Max
Input
200
400
600
1000
2000
3000
Min Input
5:1
40
80
120
200
400
600
Mod Max
80%
160
320
480
800
1600
2400
Mod Max
70%
140
280
420
700
1400
2100
Mod Max
60%
120
240
360
600
1200
1800
Mod Max
50%
100
200
300
500
1000
1500
Once the Priority 1 and Priority 2 boilers are selected, they
can be multiplied in each priority set to achieve the desired
system design BTUs. If the # of boilers becomes a large
number, a Priority 1 boiler with a higher Min Input may
need to be selected.
While considering the MOD-MAX value, the lower the
MOD-MAX the greater the combustion efficiency since it
effectively limits the input rate. The
Typical Efficiency of
Non-Condensing Boilers
chart can help illustrate how the
MOD-MAX value can affect the efficiency by limiting the
input until all boilers have fired. Non-condensing boiler
efficiency is relatively flat compared with condensing as
illustrated in the
Typical Efficiency of Condensing Boiler
graph.