When is the best time to functionally test new systems? Some of the common answers to that question are:

  1. Do not test until a system is complete and ready for testing.
  2. Do not test one system until the systems on which that system relies have been successfully tested.
  3. Test as soon as both one and two have been achieved in order to stay off the project schedule’s critical path.

Part of the challenge is defining “systems,” assuming, by definition, that there is a one-to-one relationship between a system and its functional performance test (FPT). For example, does an “air handling system” include the air handler, return fan, all terminal units served by that air handler, and all smoke/fire dampers and other fire alarm devices? If that is the “system,” it will be very late in the project when all of those elements and supporting subsystems (fire alarm, chilled water, heating hot water, steam, etc.) are complete and ready for testing.

If each air handler, each terminal unit, and each fire/smoke damper are defined as a system with associated AHU FPTs, terminal unit FPTs, and fire/smoke damper FPTs, then there is more flexibility on the timing of the individual system tests. However, breaking systems up into smaller elements could lead to imperfect or at least inefficient testing of the integration of those elements.

On the other hand, there are efficiencies associated with testing some systems earlier than later. For example, confirming smoke/fire damper operation is more efficient if it is performed after the lay-in ceiling grid is installed but before the tiles are in place. It is much easier to access the dampers for visual observation of proper damper operation without needing to find the right ceiling tile (which could involve moving and climbing a ladder two to three times if labeling is not complete yet), lifting the tile out of the way, and then replacing it.

The same could be suggested for testing above-ceiling terminal units such as VAV boxes. However, VAV boxes would not be ready for testing that early because balancing is a prerequisite to functional testing, and ceilings typically must be in place for air balancing to be performed. 

At first blush, it seems like it would be best to wait until all systems are complete and ready for testing before any testing is performed. This theoretically allows for the most efficient and effective testing of individual systems and their interactions with each other. However, it is a bad time to find performance problems that need to be corrected. The further into the construction process, the more costly and time consuming corrective actions are likely to be.

In addition, most of the installing contractors are no longer fully engaged (because the installation is complete) and it is harder to rally appropriate resources to correct problems in a coordinated and timely fashion. Combine this with the fact that today’s construction projects all have a tight timeframe (“time is money”) and there is no room for a standalone “testing phase.” Waiting until after construction to start testing is almost never a viable strategy.

Finally, the normal electrical power system is invariably the first system to be tested in a new construction project. This is because it is a common prerequisite system that needs to be tested and operational well before testing all other commissioned systems. In addition, many of the electrical power tests cannot reasonably be performed after energization of the building.

In summary, there is no single “right” time to perform functional performance tests. Commissioning scheduling needs to be customized for each project and its unique collection of systems to achieve a balance of efficiency, effectiveness, and coordination with the contractor’s installation and start-up sequencing.