Functional Test Failure and the Contractor's "Adjust the Test" Request
A 200,000 sq ft distribution center has a new variable-air-volume system with 24 terminal boxes and two rooftop units. During functional performance testing, one rooftop unit fails to maintain static pressure setpoint when 18 of 24 boxes are at minimum flow. The contractor proposes to change the test by running only 12 boxes at minimum, arguing that the design condition is unrealistic. The design engineer's sequence of operations calls for static pressure reset based on box demand, and the test was written directly from that sequence. The owner's facility manager says the building will rarely run at that condition. The contractor also offers to "tweak the PID" during the test and re-run it immediately. The CxA has one day of testing left in the schedule.
1. Should the CxA accept the modified test condition? Explain the reasoning.
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The CxA should not accept the reduced box count as a substitute for the specified test. The test was derived from the design sequence of operations, which requires the static pressure reset to function across the range of box demand. Testing only 12 boxes at minimum would not exercise the control logic the owner paid for and would leave the failure mode undiagnosed.
The owner's statement that the condition is rare is relevant to priority, not to whether the system must function. A system that cannot maintain control at a legitimate operating point is a deficiency, even if infrequent, because the failure may indicate a sensor location, sizing, or control-tuning problem that will also affect more common conditions. The CxA should explain that the purpose of the test is to reveal whether the sequence works, and the observed failure is exactly the kind of finding the test exists to catch.
The CxA may agree to add a second, less extreme test point as supplementary evidence, but the original test condition should remain part of acceptance.
2. How should the CxA handle the contractor's offer to tune the PID and immediately re-run?
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The CxA should allow tuning only under controlled conditions. A quick tune-and-retest during the test window risks masking the root cause and produces no record of what changed. The CxA should require the contractor to document the as-found settings, the proposed change, and the rationale, then re-run the full test, not just the failing point. The CxA should also verify that the static pressure sensor is correctly located and calibrated before accepting any tuning as the fix, because tuning around a bad sensor is not a repair.
If the schedule cannot accommodate a proper retest, the CxA should record the test as failed, document the deficiency, and issue a retest requirement with a defined acceptance criterion. Signing a conditional pass without evidence would undermine the commissioning record and the owner's warranty position.