Using data trend logs to supplement in-field functional performance testing (FPT) has always been an option in the commissioning process, particularly for HVAC systems controlled by DDC systems. As DDC system trending capabilities and computer hardware storage capacities have improved substantially over the past few years, I propose that trend logs be given a more prominent place in the commissioning toolbox.
A well-defined set of graphical trend logs can be quickly analyzed to ascertain if controlled devices are performing as specified and/or if there are any rogue points that need attention. The best trend graphs have points deliberately grouped together to provide the commissioning professional with a visual snapshot of a system’s operation and the interaction between related parameters. For example, the discharge air temperature, the heating and cooling control signals, and the discharge air temperature setpoint would be on the same graph.
In an ideal world, trend logs would be run for at least one week as part of the pre-functional check-out process. The trends would be submitted to the commissioning professional for review and comment and any anomalies would be corrected and trends re-run for another week prior to on-site FPT. This would catch many (but not all) system deficiencies before the contractors, owner, and commissioning professional committed time and other resources to the intense FPT process on site.
WHY NOT?
This detailed pre-test trending program is not currently a common practice for new construction commissioning for a number of reasons. The top reasons include: