C0240111-04-05-GB
s e t p o i n t
s e t p o i n t
+
b a n d a p r o p o r z i o n a l e
s t a r t 1 ° c o m p r e s s o r e
t [ m i n ]
T i n [ ° C ]
A 1
m i n
m a x
A 2
s t a r t 2 ° c o m p r e s s o r e
m a x
m i n
C o m p r . 1
C o m p r . 2
A
B
P a s s [ K w ]
P a s s [ K w ]
S e t p o i n t
+
p r o p o r t i o n a l b a n d
s t a r t c o m p r e s s o r 2 °
s t a r t c o m p r e s s o r 1 °
Figure 5.8:
adjustment for a two-compressor unit
x
CONTINUOUS ADJUSTMENT METHOD FOR SCREW COMPRESSORS (modulating
adjustment)
In screw compressors, modulating adjustment requires Quick mind outlet adjustment.
Modulating adjustment is only available on “Bitzer” screw compressors.
set point
t [min]
Tout [°C]
ZN
B
(incremento)
C
(decremento)
Figure 5.9:
adjustment for screw compressors
Reference is made to
figure 5.9
.
The setpoint remains within a dead area.
If the temperature also remains within
this zone, no change is made to the
number of active compressors or their
load percentages (position of modulating
chamber).
When the temperature rises above zone B
following a change in the system load, the
compressors are activated in order to
return the temperature to the dead area.
Inside zone B, compressor power is
modulated to return the temperature to
the dead area (DA).
(increase)
(decrease)
When the temperature falls below zone C following a change in the system load, the compressors are
either deactivated in order to return the temperature to the dead area.
Inside zone C, compressor power is modulated to return the temperature to the dead area (DA).
The amplitude of the dead area depends on the dynamic characteristics of the system and, in particular,
on the amount of water it contains and the load. The self-adapting algorithm is able to “measure” system
dynamics and calculate the minimum dead area in order to respect compressor activation times and the
maximum number of start-ups per hour.
5.2.2 ) RECOVERY
The “user menu” can be used to set certain “recovery” parameters, such as the “recovery adjustment
band” and the “recovery setpoint”.
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