HBX CPU-1000 HVAC Controller
Version 1.38
Page 22
MODULATION TYPE: PROGRESSIVE
Progressive modulation is a complex algorithm for
very precise control over modulating devices. HBX
Controls has optimized the process to work effectively
for multiple modulating boilers. This modulation
algorithm is a combination of series and parallel
modulation with additional benefits.
Underlying theory causes the first boiler to modulate
from the start percent (designated by the installer
within the modulating options in of the Control) to
80% modulation. If the load still requires more heat
then boiler 1 decreases to 40%, and boiler 2 increases
from 0% to 40% (maintaining 80% output with 2
modulating boilers now on). As the load increases both
modulating boiler 1 and modulating boiler 2 will
increase to 80%. If there is still a higher load
requirement, both boiler 1 and boiler 2 will decrease to
55% and modulating boiler 3 will
increase from 0% to 55%. All 3 modulating
boilers now take on approximately the same load as
the 2 modulating boilers at 80%. This process will
continue on until all boilers set up in the system are
firing. When all the modulating boilers are firing and a
load is still required, all 3 boilers will modulate to
100% simultaneously.
As load decreases the modulating boilers will
simultaneously modulate down to the start percent.
The lag boiler will shut down and remaining
modulating boilers will increase their modulating to
split the remaining load in percent. At this point to
help with boiler cycling the Control will allow the PID
calculation to increase. This will hold the lead boiler in
the minimum fire position for longer allowing the
modulating boiler to cycle less. As a result; system
maintenance and system wear due to boiler cycling is
decreased.
BTU Output
Modulating Staging Types - Progressive
0%
100%
50%
25%
75%
Time Progression
B 2B 1 B 3 B 2B 1 B 3 B 2B 1 B 3 B 2B 1 B 3 B 2B 1 B 3 B 2B 1 B 3 B 2B 1 B 3
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