Ingersoll Rand X8I Mode D'emploi page 14

When the compressed air system storage is relatively
small compared to the system demand, and fluctuations
are large and quick, the tolerance band setting should
be increased to maintain energy efficient operation and
avoid a situation in which multiple compressors are
loaded just to be unloaded moments later.
When the compressed air system is relatively large
compared to system demand and fluctuations are
smaller and slower, the tolerance band can be reduced to
improve pressure control and maintain energy efficient
operation.
The factory default setting for tolerance is 3.0 PSI (0.2Bar).
This setting is user adjustable.
DAMPING
Any time the pressure is within the Tolerance band the
Anti-Cycling algorithm is active, sampling the rate of
pressure change and calculating when to load or unload
the next compressor. The damping (DA) setting is a user
adjustable setpoint that determines how quickly the
controller samples and recalculates, effectively speeding
up or slowing down the reaction time.
The X8I's factory default DA setting of "1" is adequate for
the majority of compressed air systems but may need
to be adjusted in the following circumstances involving
aggressive and disproportionate system pressure
changes:
• Inadequate air storage
• High pressure differential across the air
treatment equipment
• Incorrectly sized piping
• Slow or delayed compressor response
In these circumstances, the X8I may overreact and
attempt to load additional compressors that may not
be necessary if the system was given time to allow the
system pressure to stabilize after the initial compressor
is given time to load. If the tolerance has already been
increased and the X8I is still overreacting, then increasing
the damping factor is the next step.
Damping is adjustable and is scaled from 0.1 to 10 with
a factory default of 1. A factor of 0.1 is a reaction time
10 times faster than the default and a factor of 10 is a
reaction time 10 times slower than the default.
NOTE: There are many variables that go into deter-
mining the stability and control of the system pres-
sure, only some of which are able to be controlled by
the X8I. System storage, air compressor capacity, and
air demand all need to be analyzed by experienced
professionals to determine the best installation for
your system. Tolerance (TO) and damping (DA) can be
used for minor tuning of the system.
SYSTEM VOLUME
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Assorted Receiver Tanks
System volume defines how fast system pressure will rise
or fall in reaction to either increased/decreased demand
or increased/decreased supply. The larger the system
volume, the slower the pressure changes in relation to
increased/decreased demand or supply. Adequate system
volume enables effective pressure control and avoids
system over-pressurization in response to abrupt pressure
fluctuations. Adequate system volume is created by
correctly sizing and utilizing air receivers.
The most accurate way to determine the size of air
receivers or the additional volume required would
be to measure the size and duration of the largest
demand event that occurs in the system, then size the
volume large enough to ride through the event with
an acceptable decrease in system pressure. Sizing the
volume for the worst event will ensure system stability
and effective control over all other normal operating
conditions.
If measurement is not available, then estimating the
largest event is a reasonable alternative. For example,
assume that the largest demand event could be equal to
the loss of the largest operating air compressor. System
volume would be sized to allow time for a back-up
compressor to be started and loaded with an acceptable
decrease in pressure.
The following formula determines the recommended
minimum storage volume for a compressed air system:
V — "Volume of Required Storage" (Gal, Ft3, m3, L)
T — "Time to Start Back-up Compressor" (Minutes)
C — "Lost Capacity of Compressed Air" (CFM, m3/min)
Pa — "Atmospheric pressure" (PSIa, BAR)
ΔP — "Allowable Pressure Drop" (PSI, BAR)
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