At-A-Glance
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NA7.10.2 Evaporator Fan Motor Controls |
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Use Document NRCA-PRC-04-A |
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Purpose of the Test |
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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. |
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Instrumentation |
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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. |
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Test Conditions |
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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. |
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Document the value of the initial control parameters before starting the test. |
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Estimated Time to Complete |
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Construction inspection: 0.5 hours (for each evaporator) |
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Functional testing: 1 hour (for each evaporator) |
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Acceptance Criteria |
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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 dead band range. |
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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 dead band range until fans go to minimum speed. |
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Potential Issues and Cautions |
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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. |
A. Test Application
Newly Constructed Buildings: Applies to functional testing and verification of evaporator motor fan motor variable speed controls.
B. Construction Inspection
The field technician should check the following:
•All temperature and sensors have been calibrated and read accurately.
•All sensors are mounted in a location away from direct evaporator discharge air draft.
•All evaporator motors are operational and rotate in the correct direction.
•Fan speed control is operational and connected to evaporator fan motors.
•All speed controls are in “auto” mode.
•Records showing calibration was performed, what offsets or control system calibration values were used, and documentation of the instrumentation used for calibration.
C. Functional Testing
Step 1: Measure the current space temperature and program this temperature as the test temperature into the control system. Allow 5 minutes for system to normalize.
Verify whether the evaporator fans are controlled based on the space temperature. This step brings the temperature setpoint for the evaporator within range to the current conditions of the space.
Step 2: Using the control system, lower the test temperature setpoint in 1 degree increments below any control dead band range.
Verify:
•Evaporator fan controls modulate to increase fan motor speed, by observing control system readout or variable speed drive readout values.
•Evaporator fan motor speed increases in response to controls, by observation of fan speed or sound level.
Step 3: Using the control system, raise the test temperature setpoint in 1 degree increments above any control dead band range until fans go to minimum speed.
Verify:
•Evaporator fan controls modulate to decrease fan motor speed, by observing control system readout or variable frequency drive readout values.
•Evaporator fan motor speed decreases in response to controls, by observation of fan speed or sound level.
Document:
•Record the minimum fan motor control speed and how it was determined.
Note: Control system parameters may utilize percent of full speed, frequency (Hz), or sometimes RPM. Variable Frequency Drive (VFD) readouts may also provide these values, and may not read the same as the control system. The control system programmer may be needed to explain readout values.
Step 4: Restore the control system to correct control setpoints.
Confirm that the control system is restored back to initial space temperature setpoint.