Illustration 3.2: The fixed speed compressor(s) is staged/destaged if the actual feedback enters one of the zones outside the neutral zone
for more than the delay time set for this zone. If the actual feedback enters the ++zone or - -zone the compressor(s) is staged/destaged
at the time the first delay timer runs out. The ++zone delay should therefore always be set shorter than the + zone delay to make it active.
25-20 25-20 Neutral Zone [unit]
Range:
Function:
4.00*
[0-9999.99]
Set the neutral zone (NZ) to accommodate normal system pressure fluctuations. In pack control
systems, to avoid frequent switching of fixed speed compressors, the desired system pressure is
typically kept within a zone rather than at a constant level.
The NZ is programmed in the same unit as selected in par. 20-12
Reference/Feedback Unit
.. It
places a zone above and below the set-point in which staging and destaging will not occur. For
example, if the set-point is - 20
˚
C and the NZ is set to 4
˚
C, a suction pressure equivalent to a
temperature between - 24
˚
C and - 16
˚
C is tolerated. No staging or destaging will occur within this
zone.
25-21 +Zone [unit]
Range:
Function:
3.00*
[0-9999.99]
When a large and quick change in the system demand occurs, the system pressure rapidly changes
and a quicker staging or destaging of a fixed speed compressor becomes necessary to match the
requirement. The +Zone defines the range where the + zone delay is active.
Setting the +Zone too close to zero could defeat the purpose with frequent staging at momentary
pressure changes. Setting the +Zone too high might lead to an unacceptably high or low pressure
in the system while the +Zone Delay timer (par. 25-24) is running. The +Zone value can be opti-
mized with increased familiarity with the system. See ++Zone Delay, par. 25-26.
To avoid unintended staging during the commissioning phase and fine tuning of the controller,
initially set the +Zone to a large value beyond any expected pressure peak. This implicitly disables
the override function for pressure peaks. When the fine tuning is complete, the +Zone should be
set to the desired value. An initial value of 3
˚
C is suggested.
25-22 -Zone [unit]
Range:
Function:
3.00*
[0-9999.99]
When a large and quick change in the system demand occurs, the system pressure rapidly changes
and a quicker staging or destaging of a fixed speed compressor becomes necessary to match the
requirement. The -Zone defines the range where the - zone delay is active.
Setting the -Zone too close to zero could defeat the purpose with frequent staging at momentary
pressure changes. Setting the -Zone too high might lead to an unacceptably high or low pressure
in the system while the -Zone Delay timer (par. 25-25) is running. The -Zone value can be optimized
with increased familiarity with the system. See --Zone Delay, par. 25-27.
To avoid unintended staging during the commissioning phase and fine tuning of the controller,
initially set the -Zone to a large value beyond any expected pressure drop. This implicitly disables
ADAP-KOOL
®
Drive Programming Guide
3 Parameter Description
MG.11.N1.02 - VLT
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is a registered Danfoss trademark
203
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