Difference between Commissioning, Acceptance Testing and Functional Testing

Prime Technology
3 min readJul 6, 2024

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I’ve learned from my experiences as an acceptance tester and a commissioning provider that not everyone is aware of the distinctions. Stakeholders should be aware of their differences in order to ensure that construction proceeds without hiccups and that expectations are met.

Commissioning is not a functional testing event but a systematic procedure

Functional testing is not what commissioning is. It is a methodical procedure. Functional testing, post-occupancy/off-season testing, OPR/BOD/Design reviews, and other assessments are all included in commissioning.

Functional testing: What is it?

Testing for functionality is an event. Functional testing is tailored to the architecture and verifies that the system operates as intended by the owner and in accordance with the design.

Functional testing differs from acceptance testing

A canned test called acceptance testing just verifies that the system complies with the code. The commissioning authority is not in a position to approve the system. Their responsibility is to record the function testing and recommend to the owner that the system be accepted.

Contrasting Testing Methods: an instance

The occupancy sensors for this project were supposed to be integrated with the VAV boxes and to turn off the ventilation and lights after 30 minutes, according to the plan. But because the general contractor (GC) failed to coordinate the work of the mechanical and electrical contractors, they were set to cut off after 20 minutes and the VAV box integration was never completed.

There have been other instances where the general contractor and their subcontractors failed to coordinate the project. We frequently witness this problem. Depending on the kind of testing the outcomes vary.

Because the occupancy sensors turned off before the code-allowed maximum period had passed, the acceptance test result was PASS. Since integration with the VAV boxes is not part of the acceptance test and was not mandated by the code, there is no testing for it.

Since the sensors cut off at 20, not 30, minutes, they did not wait for the design-required setting to elapse, making the functional testing an FAIL. Since they weren’t integrated with the VAV boxes, it’s also a failure.

The benefits of functional testing

In such cases, the Owner may rehire the contractor to correct the issue — but only if they recognize the significance of the design and how it affects performance. If functional testing isn’t done, the owner won’t know about the integration problem and won’t get the savings from occupancy-based demand control ventilation.

In this instance, the problems were identified and resolved prior to the owner taking possession thanks to our work as the commissioning provider.

Despite the modest nomenclature changes between these names, their differences could have important implications. By ensuring that your systems function both as-designed and to code, knowing the difference can help you avoid expensive operational problems later on. Check out how we can help or read more about commissioning here if you need help with commissioning, acceptability testing, or functional testing and would like to know more about us.

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