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The
O
MNI
T
HERM
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.
Log In
Settings
Parameter
User
Installer
OEM
Min
Max
Default
Unit
Base Load
X
X
40
100
65
%
Drop Load
X
X
20
100
20
%
Min On Time
X
X
30
600
60
Seconds
Min Off Time
X
X
30
600
30
Seconds
Table 17. Parameter Settings
1
2
30%
1
2
1
2
65%
30%
30%
1
2
1
2
100%
100%
65%
65%
1
2
1
2
20%
20%
20%
1
2
1
2
20%
Lead/Lag - 2 Boilers
Decreasing demand:
As the demand decreases, once the requested
firing rate reaches the
Drop Load Value
, the second boiler turns off.
Boilers
Boilers
Demand Satisfied:
When the heat demand is satisfied or the
temperature is at the set point + off hysteresis, the final boiler will turn
off.
Boilers
Boilers
Approaching max demand:
Once both boilers reach 65%, both units
are allowed to increase firing rate (same at both boilers) up to
maximum firing rate.
Boilers
Boilers
Boilers
Boilers
Boilers
Increased demand:
Once the first boiler reaches the
Base Load Value
(65%) firing rate, the second boiler ignites. After ignition, both units
modulate to half of the cascade firing rate, then gradually increase the
firing rate together, up to the
Base Load Value
.
Low demand:
The first boiler in sequence ignites and gradually
increases firing rate to satify the heat demand.
Low demand:
The first boiler in sequence ignites and
gradually increases firing rate to satify the heat demand.
Increased demand:
Once the first boiler reaches the Base
Load Value (65%) firing rate, the second boiler ignites. After
ignition, both units modulate to half of the cascade firing rate,
then gradually increase the firing rate together, up to the Base
Load Value.
Approaching max demand:
Once both boilers reach
65%, both units are allowed to increase firing rate (same at
both boilers) up to maximum firing rate.
Decreasing demand:
As the demand decreases, once
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 off.
Figure 31. Lead / Lag, 2 Boilers
C O N F I G U R AT I O N
