"In order to provide the best possible outcome for our new building project, my concern is that the commissioning work be focused in the most valuable areas. How do I determine whether we should perform fully detailed tests on a sample of systems or test all systems at a reduced rigor?"
At the core of this question was an owner with a fixed commissioning budget and an admirable desire to spend that money as wisely as possible. The query demonstrated a sophisticated understanding of the wide variety and levels of rigor that can be applied to the term "test" and the cost implications thereof. Very detailed test procedures not only consume more time during field execution but also take more effort to develop prior to testing. All of this comes down to time and money.
Test Each System TypeI strongly recommend sampling each system type with a high level of rigor, instead of testing 100% of all systems at a lower level of rigor. The value of commissioning comes in the level of detail that is applied to the systems being commissioned.
Testing to verify only some of the operational features of a system will be an incomplete check and will fail to achieve some of the major benefits of commissioning for the owner.
First, the owner will not be comfortable that the systems are reliable through all modes of operation. I have recently heard of a "commissioning provider" who simply watched a system operate in whatever state it was in for 30 to 40 minutes one afternoon at the completion of construction. That provider may have been able to say, for example, that the air-handling system performed as specified in occupied, economizer, non-emergency mode operation. The owner did not learn whether the system would function as intended in non-economizer, unoccupied, warmup, freeze, or fire modes.
Another benefit that would be lost is the input of a third-party team member, not only identifying issues that require resolution, but also helping to arbitrate responsibility and expedite correction prior to project closeout. If all modes of operation are not tested during the commissioning process, it leaves problems with other modes to be found by the owner's O&M personnel sometime after the designers and contractors have moved on to other priorities. The delays, fingerpointing, and eternal lack of resolution associated with this scenario are the major problems owners are looking to greatly diminish through a commissioning program.
In addition, if the untested modes of operation are the "non-normal" modes such as freeze conditions, system shutdown, loss of power, fire alarm, and other safety-related strategies, the risks associated with finding deficiencies during a real emergency could be far greater than the cost of the most rigorous commissioning process.
Quality Over QuantityTherefore, performing a thorough test procedure on a random sample of systems is a more valuable approach to commissioning on a budget. Quality wins over quantity. What will happen if, amongst the systems sampled, there are multiple and/or consistent deficiencies in operation? Will the owner's project manager look those facts in the eye and deny that additional testing (over and above the initial random sample) is necessary? I don't believe so.
Faced with well-documented failed test results, the owner will need to address the likelihood that those failures would also occur on the untested systems. All of a sudden, there will be interest and, possibly, funding available to extend the testing as deemed necessary to confirm that all systems perform as specified. If nothing else, the owner's O&M division will either offer the money to extend the construction-phase commissioning or will plan on executing the additional test procedures on their own after being handed the systems to operate. They know all too well that the cost and effectiveness of haphazardly discovering problems and having to address them alone over the first one to two years can make their lives and the lives of the building occupants miserable.
Of course, as with all things, early planning is the key to success. The owner can avoid taking on the risk of failed sample testing by thinking through his approach to commissioning and putting the onus on the installation contractors to pass the functional tests the first time. This means writing an enforceable commissioning specification that clearly details the testing rigor, acceptance criteria, and the consequences of test failures. Many owners are choosing to have the contractors pick up the tab for additional testing required due to failures of the initial specified random samples. ES