ATC:  automatic temperature control sequence of operation
FPT:  functional performance test narrative to demonstrate the system performance to the commissioning engineer and/or building owner

No sooner had the July edition of the "Tomorrow’s Engineer" column titled “Combining the ATC with the FPT” hit the main Engineered Systems website than I received around 30 requests for more information on the concept I have been able to implement within our firm.

With years of design, commissioning, and troubleshooting experience, I have formed an opinion that the industry standard ATC sequence of operation format is inadequate for helping produce a correctly engineered HVAC system. The problem with these narratives begins with the ATC industry and carry on to the design community followed by the construction process. In the end, the building operator has inadequate documents to troubleshoot and/or continuously operate the systems efficiently over the lives of the systems. 

Since the July column highlights my approach and the August "Tomorrow’s Engineer" continues on with the concept, let’s address the participants' issues, concerns, and solutions as follows.

The ATC Industry

Issue:  To its credit, the ATC industry has done a great job of providing control technology to the design engineers in the form of ATC specifications, CAD system flow diagrams, and standard sequence of operation over the past 40 years.

Concern:  It is not unusual for design engineers to draw upon these specifications, flow diagrams, and sequences of operation on a regular basis without sitting down and assessing them so that the design engineer is truly knowledgeable of the criteria and how this ATC performance will affect a given HVAC design. As a result -- and commissioning services constantly prove this out -- the design engineers in many ways abdicated their design responsibility to the ATC contractor in the construction phase, because they did not truly understand the full and interactive scope of work being specified.

Solution:  Take back ownership of the ATC sequence of operation. I never let a designer engineer a project if he cannot write the sequence of operation from scratch in sync with creation of a system flow diagram.  I also require him to do the sequence in the schematic phase of the job, and not late in the construction document phase of the job (as is frequently done). It doesn’t matter in schematic phase whether a 100% outdoor air unit is 9,550 CFM or 11,300 CFM. The sequence of operation will be the same.

The Design Engineer

Issue:  The July column talks about the 25 devices and 10 modes of operation resulting in 250 “reactions." The standard sequence of operation does not address all the control devices that will eventually end up in the shop drawing ATC submittal. At the same time, the ATC programmer who will write the program sequence also doesn’t have all the components in front of her when she reads the standard ATC sequence.

Concern:  Without the complete list of control components and equipment, the design engineer is at a disadvantage regarding how the system will be started up, how it will be commissioned, and how one or more of these “missing components” could influence how the system will truly function.

Solution:  If an engineer will sit down in front of her computer and begin to develop a system flow diagram in parallel with writing the ATC sequence of operation, she will inherently insert components (i.e., the 25 devices noted in the July column) as she drafts the narrative (i.e., the 10 modes of operation noted in the July column).

Once the design engineer has mastered this approach, why not change the method of documentation to create a series of sequence overviews (refer to the AHU sample ATC-FPT file, page 2 of 5 based on our Commissioning 1-2-3TM process) and an inventory of the components as shown in this file? The designer now has an ATC-FPT document. At this point in the design, the engineer can either insert the draft into the contract specification or insert the flow diagram and the ATC-FPT onto a contract drawing (refer to the H1.02 HVAC Flow Diagram and FPT Mode 2). The end product is far more complete, and the itemized Action-Reaction format of the FPT is inherently formatted for the ATC contractor’s programmer to understand when writing the various modes of operation.

A side benefit of these system flow diagrams is the ability to also document the air and/or water balancing data onto the contract documents (refer to H1.06 HVAC TAB Flow Diagram) during the design phase, providing the design engineer with the opportunity to assess how the system will be balanced in sync with the commissioning of the system during construction. Refer to TAB Specification posts in this Sustainable & Attainable series.

The Builders

Issues: Not enough construction administration is provided by the design engineer during the construction phase. As a result, much of the responsibility for coordination of equipment, components, ATC sequences and electrical system interaction (e.g., smoke control/fire alarm system) falls on the shoulders of the contractor and those subcontractors associated with the project (e.g., HVAC, ATC, and TAB).

Concern:  The design engineering community has always relied heavily on the builder to transform construction documents into a working system, but this process doesn’t assure that the working system will be functioning efficiently or as intended. If the ATC sequence is not clearly understood and documented in the design phase, incompleteness of design can occur in the construction phase.

Solution: If the ATC sequence was packaged with the commissioning FPT in the design phase, there will be less chance of error on the part of the builder as it pertains to pulling all the pieces together so that the system can be started up, tested, adjusted, balanced and then demonstrated to the commissioning engineer and/or building operator. This process also prevents the designer from relying on the builder to finalize the design intent during the construction phase.

The Building Operator

Issue: All too often, the building operator does not arrive on the project until well after the systems have been designed, and sometimes even after equipment has been started up on the job site. Getting up to speed with the design intent and the complexity of the ATC sequence of operation, as well with as the air and water balancing, can compound an already dysfunctional transfer of information from design to construction to owner occupancy.

Concern: Whether a building operator is on site or not at the time of system demonstration, transfer of useful and complete operating data is inherently missed because the ATC sequence of operation and the commissioning FPT narrative are two different documents. In addition, with the distribution of ATC documentation spread between the project ATC contractor and various other ATC contractors (e.g., chiller, boiler, and air-handling unit manufacturers with self-contained ATC documents), the building operator will need to compile several sequence files to have the complete system narrative.

Solution: By combining the ATC with the FPT in the design phase and maintaining system-by-system updates in the construction phase, the building operator will have one document to reference. In addition, the ATC/FPT with system flow diagram can be laminated and posted in the vicinity of the associated equipment for quick reference at any time. The same can be done with the TAB flow diagram, if the design engineer were to place the air and/or water balancing data onto the contract documents in the design phase and the building were to update design-to-actual in the construction phase.


Time management is a critical part of combining the ATC sequence of operation with the FPT narrative. Somewhere along the line in the design phase, construction phase, or building operation of the facility, the documentation of the complete system/performance is needed. It’s needed because the system is required to achieve design intent. It’s needed to understand the system performance and, if necessary, trouble-shoot the system. It is needed to continuously improve the system relative to operation and energy conservation.

The final ATC/FPT documents are single point of reference and can achieve all of these needs. To do so, the process should start in the design phase by the design engineer and progress from there.

(Related material: February 2006 "Tomorrow's Engineer" column titled "More On Jump-Starting The TAB Process.")