Section 4
VARIABLE SPEED DRIVE
26
SYSTEM SETUP WITH ONE VSD COMPRESSOR AND OTHER FIXED-SPEED
COMPRESSORS
Target system pressure at discharge of compressors: 100 psi
VSD Compressor COM # 1 Fixed-Speed Compressor/s COM # 2/+
VSD Setpoint 101.5
Load Setpoint 100 96
Unload Setpoint 106 102
Lowest Pressure 90 90
Since a fixed-speed L compressor's pressure regulator doesn't begin to throttle until 101-
102 psi, it should have no effect, thereby causing the machine to operate Load/Unload with
or without the Full Load solenoid valve.
The net result would have the VSD always running and be able to modulate; the fixed-speed
machines would come on and go off as necessary but operate Load/Unload.
II. SYSTEM SETUP WITH ONLY VSD COMPRESSORS
Configure all compressors by Sequence Hours. Enable the Max. Speed Input function. All
but one of the compressors will be full-loaded, thus limiting the pressure to the rated value
of the machines. If the compressors are L machines, set the program points as listed below:
Target system pressure at discharge of compressors: 95 psi
* VSD Setpoint 98.5
Load Setpoint 95
* Unload Setpoint 102
* Lowest Pressure 90
* Recover Time 10 sec.
(See Section 6)
* Parameters that may require adjustment based on system capacity and application.
Unload Setpoint should NEVER be more than 2 psi above package rating (See explanation
on Page 3).
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