At-A-Glance
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NA7.5.11 Fault Detection and Diagnostics (FDD) for Packaged Direct-Expansion (DX) Units Acceptance |
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Use Document NRCA-MCH-12-A |
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Purpose of the Test |
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The purpose of this test is to verify proper fault detection and reporting for automated fault detection and diagnostics systems for packaged DX units. Automated FDD systems ensure proper equipment operation by identifying and diagnosing common equipment problems such as temperature sensor faults, low airflow or faulty economizer operation. FDD systems help to maintain equipment efficiency closer to rated conditions over the life of the equipment. |
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Instrumentation |
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The system test for refrigerant charge requires a calibrated refrigerant gauge with an accuracy of plus or minus 3 percent. |
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Test Conditions |
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Packaged unit and thermostat installation along with programming must be complete. |
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HVAC system must be installed and ready for operation, including completion of all start-up procedures, per manufacturer’s recommendations. |
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Prior to FDD verification, test the system operating modes. When the system includes a field-installed air economizer, test the economizer per NRCA-MCH-02-A. |
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Estimated Time to Complete |
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Construction inspection: 0.5 hour |
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Functional testing: 1 to 2 hours |
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FDD systems have the capability to report alarms to a remote server; accessible via a Web interface. It may be helpful to have two people conducting the test – one to perform testing on the unit and a second to verify reporting of the alarm to the remote interface. |
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Acceptance Criteria |
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The FDD system is able to detect a disconnected outside air temperature sensor and report the fault. |
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The FDD system is able to detect excess outside air and report the fault. The FDD system is able to detect a stuck outdoor air economizer damper and report the fault. The saturated discharge and saturated suction temperatures must be measured within 5°F of a calibrated refrigerant gauge.
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Potential Problems and Cautions |
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Compared to the pressure sensors, the temperature sensors can have a longer response time to reach a steady-state condition. Therefore, the FDD algorithms may have trouble working properly during transitional states – for example, when the fan or compressor first turns on. The tester should be aware of the potential for false alarms. |
A. Test Application
Newly Constructed and Additions/Alterations: Applies to any FDD system installed on a packaged direct expansion (DX) unit.
B. Construction Inspection
Prior to functional testing, verify and document the following:
•Verify that the installed FDD has been certified to the Energy Commission and is listed on the Energy Commission’s website (http://www.energy.ca.gov/title24/equipment_cert/).
C. Functional Testing
For each HVAC unit to be tested do the following:
1. Test for Air Temperature Sensor Failure/Fault
Step 1: Verify the FDD system indicates normal operation.
Step 2: Disconnect outside air temperature sensor from unit controller. Verify and document the following:
•FDD system reports a fault.
Step 3: Connect outside air temperature sensor to unit controller. Verify and document the following:
•FDD system indicates normal operation.
2. Test for Excessive Outside Air
Step 1: Coordinate this test with NA7.5.1 Outdoor Air
•After passing the tests described in NA7.5.1 Outdoor Air, verify FDD system indicates normal operation.
3. Test for Economizer Operation
Step 1: Interfere with normal unit operation to generate an Air Economizer Control failure by immobilizing the outdoor air economizer damper according to manufacturer’s instructions.
•After Air Economizer Controls fails, verify FDD system reports a fault.
Step 2: Successfully complete and pass tests described in NA7.5.4 Air Economizer Controls
•Verify FDD system reports normal operation.