NA7.10.2 Evaporator Fan Motor Controls

Use Form NRCA-PRC-04-A

Purpose of the Test

This test ensures that the evaporator fans modulate their speed in response to either the space temperature or humidity, as required per §120.6(a)3B.

Note that control strategies using humidity are very uncommon and accordingly only methods based on temperature will be described below.  If humidity is included in the control logic, the design engineer should be involved in designing the test method.

Instrumentation

Performance of this test will require measuring the temperature of the space served by the evaporators under test. The instrumentation needed to perform the task may include, but is not limited to a temperature calibrated to +/- 0.7°F between -30°F and 200°F.

Test Conditions

The test will be performed by varying the control parameters used by the evaporator fan motor control system.  Therefore, the evaporator fan control system must be installed and operating, including completion of all start-up procedures per manufacturer’s or designer’s recommendations, to perform the test.

The test should not be performed if the evaporator is in defrost, if a scheduled defrost is eminent, or if the evaporator was recently in defrost. 

Document the value of the initial control parameters before starting the test.

Estimated Time to Complete

Construction inspection: 0.5 hours (for each evaporator)

Functional testing: 1 hour (for each evaporator)

Acceptance Criteria

•      Evaporator fan controls modulate to increase fan speed, and evaporator fan speed increases in response to controls, when the test temperature setpoint is lowered in 1 degree increments below any control deadband range.

•      Evaporator fan controls modulate to decrease fan speed, and evaporator fan speed decreases in response to controls, when the test temperature setpoint is raised in 1 degree increments below any control deadband range until fans go to minimum speed.

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.  Fan speeds change slowly in normal operation, so the test requires adequate time to allow response.