20
RSM-DEV1 Technical Guide
SEQUENCE OF OPERATIONS
Envelope Protection
Envelope Protection
Compressor manufacturer specifications require the compressor
to operate within its given operating envelope to maintain the life
and longevity of the compressor. Some envelopes also have areas
within that limit the minimum/maximum operating speeds. Min/
max speeds may also be limited based on the requirements of the
unit’s total capacity. Prism 2 interface allows the ability to see real
time envelope plotting while the compressor is running.
The minimum operating speed reference is read from the VFD and
can change depending on where the compressor is operating within
its envelope.
The VFD compressor is set to 67% at any stage event. Therefore,
whenever a staging event occurs, the VFD compressor position is
reset to the middle point of the modulation range. This allows the
compressor enough modulation time before making another staging
event to try to avoid cycling between staging events.
Figures 5-8, this page,
are examples of compressor envelopes.
Figure 6: Copeland ZPV0662E Envelope
Figure 7: Copeland ZPV0962E Envelope
Figure 4: Danfoss VZH028, VZH035, VZH044 Envelope
Figure 5: Danfoss VZH052 and VZH065 Envelope
