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eight boilers reach the Base Load
Value , all units are allowed to increase
firing rate (same at all boilers) up to
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maximum firing rate.
Decreasing demand: As the demand
decreases, once the requested firing
rate reaches the Drop Load Value , the
eighth boiler turns off.
Continued decreasing demand: As
the demand decreases, once the
requested firing rate reaches the Drop
Load Value , the seventh boiler turns
off. This pattern continues as demand
continues to decrease until there is a
single boiler firing.
Demand Satisfied: When the heat
demand is satisfied or the temperature
reaches the set point + off hysteresis,
the final boiler will turn off.
Figure 38. Lead / Lag, Demand Decrease, 4 to 8 Boilers
1
2
C O N F I G U R A T I O N
100%
100%
100%
1
2
20%
20%
20%
1
2
23%
23%
23%
1
2
20%
20%
20%
1
2
23%
23%
23%
1
2
39%
1
2
20%
1
2
Lead/Lag - 4 up to 8 boilers
3
4
5
6
LAARS Heating Systems
100%
100%
100%
3
4
5
6
20%
20%
20%
3
4
5
6
23%
23%
23%
3
4
5
6
20%
20%
20%
3
4
5
6
23%
23%
23%
3
4
5
6
3
4
5
6
3
4
5
6
7
8
100%
100%
7
8
20%
20%
7
8
23%
7
8
20%
7
8
7
8
7
8
7
8
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