In the past year, our group has been bypassing the traditional sequence of operation narratives for a combined sequence-FPT format. It does a lot for the design and startup process by thinking through not only how the system will operate, but also how each component within the system will function under each sequence scenario.

In addition, it eliminates the building owner asking the design engineer, "Didn't I buy that the functional performance narrative when I hired you to create the sequence of operation?" Our process combines the sequence with the FPT, and I require that it be done in the schematic phase of the job and not the construction document phase of the job. Why do we do this?


First, it forces the engineer to think through the system concept early in the job so that he clearly understands the design. All too often, engineers wait until midway through the construction document phase of the job before they get into the details of system performance. The perception by these experienced professionals is that they know what they are doing so it isn't essential to document it so soon into the job. I wonder how many HVAC contractors and ATC contractors would agree with this perception?

For the less experienced designer, why do they start so late in the job to begin to write the sequence of operation? Is it because they are following their mentor's process and maybe haven't realized how important this part of the design is to the success of the job? For our group, this isn't an option. Starting early in the design with the establishment of the system flow diagram and the associated sequence of operation/FPT is required; this way, the engineer doesn't leave out an important piece of the equipment (such as a heating coil or final filter) because he didn't clearly understand the basis of design and/or industry standards for certain applications.

By getting this individual to enhance his writing of the sequence similar to how a commissioning engineer would write it, the narrative becomes far more detailed and helps the designer to understand not only the system operation but also how each component in the control sequence reacts based on the specific mode of operation.


You don't agree? Take one of your ATC submittals and review the three or four paragraphs of sequence and then count up how many devices are shown in the ATC flow diagram. There may be 25 devices (e.g., temperature transmitters, flow switch, dampers). Adding up the potential number of sequences that this system can function through (off, on-warm up, on-normal heating, on-maximum heating, etc.), there can be eight to 12 different modes of operation.

Now, multiply the 25 devices and, say, 10 sequences of operation. This will equate to 250 reactions by the devices over the full range of system function. With a sequence/FPT, you will create a 10-column, 25-reaction-per-column checklist vs. the very limited three to four ATC paragraphs of sequence. Big difference in the information provided, don't you think?

I believe all sequences should be written as an FPT because the designer will inherently think through the commissioning process as she writes the ATC sequence.

For our group - where we are always involved with the startup, TAB, and commissioning of the systems we design - the results are essential to project success, and the designer will become a better practitioner/engineer over time. In this process, the designer methodically thinks through how the system is going to start and operate based on the design and outdoor temperatures, and how to confirm the 250 action-reactions. Another benefit of this process is that it is better to be wrong on paper early in the design than to be troubleshooting a system problem when it is 0°F or 90° outdoors.

So why don't others think this way? I see it as a culture change that even the ATC contractors struggle with. Like their design engineer counterparts, they are used to producing these less detailed, information-deficient sequences of operation. We have seen ATC contractors take our sequence/FPT (250 action-reaction/10 modes of operation format) and dummy it back down to three or four paragraphs of narrative. So much for technological advancement, but we are persistent as we combine the ATC with the FPT for more responsible documents. If you would like to see an example of the format, e-mail me and I will send you a copy of a sequence/FPT.