PEERLESS PUREFIRE PFW-199, Installation, Operation & Maintenance Manual

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• With all the boilers operating, the system will
modulate the gas input to each of the boilers
to follow the system load. The control uses the
Stop Delay Time and the Stop Boiler
Differential values to determine when to drop
a boiler from the sequence.
If the tank temperature exceeds the Tank
Se the Stop Boiler Differential for
longer than the Stop Delay Time, it will stop
one of the boilers.
• The control uses the Tank Se the
Offset Temperature as set in the User menu to
provide a Boiler Supply Setpoint. It will then
offset this setpoint up or down to meet the
tank temperature. The Calculated Setpoint
Max Offset Up (Figure 8.58) and Calculated
Setpoint Max Offset Down (Figure 8.59) are
used to limit this offset. Increasing either of
these parameters may cause the system to
react more quickly, but may result in frequent
cycling. It may be necessary to reduce the Max
Offset Up to prevent a lockout on boiler limit.
Table 8.13 shows the range of values for these
parameters.
• The control also uses the Next Boiler Stop
Rate to determine when to shed a boiler from
the cascade system. Figure 8.60 and Table
8.14 show the screen and the range of values.
• The Cascade Rotation Interval (Figure 8.61)
will change the frequency at which the control
will change the lead boiler in the system.
• Table 8.15 shows how the Rotation Interval
affects the boiler rotation sequence.
Figure 8.56: Cascade Stop Delay Time
C A S C A D E ▲
S t o p D e l a y T i m e :
1 m i n ▼
Figure 8.57: Cascade Stop Boiler Differential
Parameter Minimum Default Maximum
Stop Delay Time 1 minute 1 minute 15 minutes
Stop Boiler Differential 1°F 18°F 45°F
Table 8.12: Start Delay Time Range
Figure 8.58: Calculated Setpoint Max Offset Up
C A S C A D E ▲
C a l c u l a t e d S e t p o i n t
M a x o f f s e t u p :
1 8 ° F ▼
Figure 8.59: Calculated Setpoint Max Offset Down
C A S C A D E ▲
C a l c u l a t e d S e t p o i n t
M a x o f f s e t d o w n :
9 ° F ▼
Parameter Minimum Default Maximum
Calculated Setpoint
Max Offset Up
0°F 18°F 36°F
Calculated Setpoint
Max Offset Down
0°F 9°F 36°F
Table 8.13: Calculated Setpoint Max Offset
Up/Down
Figure 8.60: Next Boiler Stop Rate
C A S C A D E ▲
N e x t B o i l e r
S t o p r a t e :
9 % ▼
Parameter Minimum Default Maximum
Next Boiler Stop Rate 5% 9% 40%
Table 8.14: Next Boiler Stop Rate
Figure 8.61: Rotation Interval
C A S C A D E ▲
R o t a t i o n I n t e r v a l
5 D a y s ▼
Days of
Operation
1 Day 3 Days 5 days
1 1-2-3-4 1-2-3-4 1-2-3-4
2 2-3-4-1 1-2-3-4 1-2-3-4
3 3-4-1-2 1-2-3-4 1-2-3-4
4 4-1-2-3 2-3-4-1 1-2-3-4
5 1-2-3-4 2-3-4-1 1-2-3-4
6 2-3-4-1 2-3-4-1 2-3-4-1
7 3-4-1-2 3-4-1-2 2-3-4-1
8 4-1-2-3 3-4-1-2 2-3-4-1
9 1-2-3-4 3-4-1-2 2-3-4-1
10 2-3-4-1 4-1-2-3 2-3-4-1
11 3-4-1-2 4-1-2-3 3-4-1-2
12 4-1-2-3 4-1-2-3 3-4-1-2
Table 8.15: Rotation Interval (4 Boilers)
BOILER CONTROL: INTERNAL WIRING & OPERATION