Troubleshooting guide

MAGNUM VERSION 8 MANUAL REVISION 3.1
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This screen is an example of a variable capacity, screw, and compressor with EXV valves. Note the Type column
selection. The EXV data must be provided.
This information can be viewed and changed, with proper authorization, from MCS Connect. By double clicking on the
name field the following will be displayed.
7.7. Centrifugal Compressor Control
There are many differences, in both concept and function, between centrifugal compressors and other types. For
certain applications, centrifugal compressors have distinct advantages such as high energy efficiency, high volume of
airflow, and low maintenance due to the small number of moving parts. When combined with a Variable Frequency
Drive (VFD) it becomes simple and efficient to vary the speed of the compressor and operate at part load.
To provide control for this unique type of compressor MCS has developed a new type software specific to centrifugal
units: CENT V8. Much of the control logic is similar to that found in HVAC V8. A target value and control zone are
calculated, and then compressor capacity is modulated to keep the control sensor within that zone. Input sensors are
monitored constantly and preventative action is taken to protect the unit from any potentially unsafe or damaging
conditions. Different from other types of units though, both compressor speed and vane position must be taken into
consideration since both affect cooling capacity.
Centrifugal Related Terminology 7.7.1.
The following terms relate to the control of centrifugal compressors and how CENT V8 processes them.
7.7.1.1. Lift Pressure:
Lift pressure equals condenser pressure minus evaporator pressure. The lower the lift pressure is, the
more efficiently the system operates.
7.7.1.2. Surge and Surge Protection:
Surge is an unstable condition that occurs at low mass flows. Surges decrease compressor
performance and efficiency, and could even cause permanent equipment damage.
CENT V8 defines a single surge as a large decrease in compressor amps followed by a large
increase in the amps or a large decrease in lift pressure followed by large increase in lift pressure.