HBX CPU-1000 HVAC Controller
Version 1.38
Page 20
MODULATION TYPE: SERIES
The Series method of modulating boilers is based on a
simple but effective algorithm. Underlying theory
causes boiler 1 to fire when there is a load; modulating
from the start percent (designated by the installer
within the modulating options of the Control) to
100%. If the heat demand has not been satisfied at
this point boiler 2 will then begin to modulate from
the start percent to 100% (if required). This process
will continue for each installed modulating boiler in the
system to a maximum of five.
The process of modulating the boilers off works the
same. When the last boiler in the system drops to the
start percent it will then shut off that
boiler. If the load continues to decrease then the
Control will modulate down the second last boiler set
up in the system. This will continue on until the lead
boiler has dropped to the start percent. At this point
the Control will allow the PID calculation to increase
helping with boiler cycling. This will hold the lead
boiler in the minimum fire (or start percent) position
for longer, allowing the boiler to cycle less. As a result;
system maintenance and system wear due to boiler
cycling is decreased.
BTU Output
Boiler 1 Boiler 2 Boiler 3
Modulating Staging Types - Series
0%
100%
50%
25%
75%
Time Progression
Boiler 1 Boiler 2 Boiler 3 Boiler 1 Boiler 2 Boiler 3 Boiler 1 Boiler 2 Boiler 3
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