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Page 74
8.D.4 Cascading (Lead / Lag) -continued
Log In
Parameter
User
Installer
Base Load
X
Drop Load
X
Min On Time
X
Min Off Time
X
Table 20. Parameter Settings
is limited to 20% minimum (instead of the allowable minimum firing rate of 5%). In addition, if the Drop Load Value is higher
than the minimum firing rate of the unit, the unit will turn off at the Drop Load Value and not the minimum firing rate of the unit.
NOTE: The single exception to a unit turning off at the Drop Load Value in a cascade configuration is when there is only one
unit running, where the single unit acts as a standalone boiler/heater.
Low demand: The first boiler in sequence ignites and gradually
Low demand: The first boiler in sequence ignites and
increases firing rate to satify the heat demand.
gradually increases firing rate to satify the heat demand.
Increased demand: Once the first boiler reaches the Base Load Value
Increased demand: Once the first boiler reaches the Base
(65%) firing rate, the second boiler ignites. After ignition, both units
Load Value (65%) firing rate, the second boiler ignites. After
modulate to half of the cascade firing rate, then gradually increase the
ignition, both units modulate to half of the cascade firing rate,
firing rate together, up to the Base Load Value .
then gradually increase the firing rate together, up to the Base
Load Value.
Approaching max demand: Once both boilers reach 65%, both units
Approaching max demand: Once both boilers reach
are allowed to increase firing rate (same at both boilers) up to
65%, both units are allowed to increase firing rate (same at
maximum firing rate.
both boilers) up to maximum firing rate.
Decreasing demand: As the demand decreases, once the requested
Decreasing demand: As the demand decreases, once
firing rate reaches the Drop Load Value , the second boiler turns off.
the requested firing rate reaches the Drop Load Value, the
second boiler turns off.
Demand Satisfied: When the heat demand is satisfied or the
temperature is at the set point + off hysteresis, the final boiler will turn
DemandSatisfied: When the heat demand is satisfied or
off.
the temperature is at the set point + off hysteresis, the final
boiler will turn off.
Figure 43.
Lead / Lag, 2 Boilers
C O N F I G U R A T I O N
Settings
OEM
Min
Max
Default Unit
X
40
100
65
X
20
100
20
X
30
600
60
X
30
600
30
Lead/Lag - 2 Boilers
%
%
Seconds
Seconds
Boilers
1
2
30%
Boilers
1
2
65%
Boilers
1
2
65%
65%
Boilers
1
2
20%
20%
Boilers
1
2
20%
Boilers
1
2
30%
30%
Boilers
1
2
100%
100%
Boilers
1
2
20%
Boilers
1
2
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