Installation / Operation Instruction Manual

Table Of Contents
Page 70
is limited to 20% minimum (instead of the allowable minimum ring rate of 5%). In addition, if the Drop Load Value is higher
than the minimum ring rate of the unit, the unit will turn o󰀨 at the Drop Load Value and not the minimum ring rate of the unit.
NOTE: The single exception to a unit turning o󰀨 at the Drop Load Value in a cascade conguration is when there is only one
unit running, where the single unit acts as a standalone boiler/heater.
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 rst boiler in sequence ignites and
gradually increases ring rate to satify the heat demand.
Increased demand: Once the rst boiler reaches the Base
Load Value (65%) ring rate, the second boiler ignites. After
ignition, both units modulate to half of the cascade ring rate,
then gradually increase the ring rate together, up to the Base
Load Value.
Approaching max demand: Once both boilers reach
65%, both units are allowed to increase ring rate (same at
both boilers) up to maximum ring rate.
Decreasing demand: As the demand decreases, once
the requested ring rate reaches the Drop Load Value, the
second boiler turns o󰀨.
DemandSatised: When the heat demand is satised or
the temperature is at the set point + o󰀨 hysteresis, the nal
boiler will turn o󰀨.
Table 21. Parameter Settings
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 O󰀨 Time X X 30 600 30 Seconds
About Cascading (Lead / Lag) -continued
Figure 37. Lead / Lag, 2 Boilers