NA7.10.4 Compressor Variable Speed Controls

Use Form NRCA-PRC-07-A

Purpose of the Test

The test ensures that the applicable compressors control compressor speed in response to the refrigeration load, per §120.6(a)5B.

Instrumentation

None

Test Conditions

To perform the test, it will be necessary to override the normal operation of the controls. The control system for the compressor must be complete, including:

•      Variable speed drive on all applicable screw compressors.

•      Controls to control the compressor motor speed.

Document the initial control settings before executing system overrides or manipulation of the setpoints. The compressor control system must be returned to normal operation at the end of the test.

Estimated Time to Complete

Construction inspection: 1 hour (for one compressor)

Functional testing: 2  hour (for one compressor)

Acceptance Criteria

•      Compressor speed decreases with decrease in load, and the slide valve (or other unloading means) are held at 100% capacity until the compressor speed reaches the minimum allowable setpoint.

•      With an increase in load, the compressor slide valve (or other unloading means) should load to 100% capacity, and then the compressor speed should start in increase.

Potential Issues and Cautions

Coordinate test procedures with the refrigeration or controls contractor, or the facility supervisor since they may be needed to assist with the manipulation of the control system.