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Why You Should Prioritize Your Customized Sequences of Operations

A Tale of Two Projects

By Rebecca T. Ellis, P.E.

This is a story about two new construction commissioning projects with similar challenges and as-yet unwritten endings.

The first project is one in which the commissioning professional was engaged before the schematic design phase, and the project is currently early in construction. The design engineers did not develop a detailed set of control sequences during the design phase. This was despite repeated requests from the commissioning professional for more information regarding the intended operation of the HVAC systems through multiple design review cycles.

The design engineers’ corporate standard for control system design was to provide a points list along with a brief description of what some (not even all) of the systems should do. For example:

The boiler system shall deliver hot water to all terminal units;
The heat recovery ventilator shall precondition the outside air;
The AHU shall maintain a set point building pressure; and
The unit heater shall maintain a set point space temperature.

They believed the controls contractor should be given latitude with respect to how the systems achieve these high-level performance goals. The project is currently awaiting the controls contractor’s submittal package.

“Controls contractors can be smart, creative, and experienced with a variety of HVAC equipment and system types; however, in a design-bid-build project, I do not believe it is their responsibility to figure out how to properly control the design engineers’ systems.”

The second project is one in which the commissioning professional was not engaged until the early construction phase. As such, there was no design phase review of the design engineer’s documents. As the commissioning professional became familiar with the design, it was clear that the specified control sequences, although reasonably detailed, did not match the equipment/systems shown on the drawings. The controls contractor’s submittal is expected any day now.

In both of these cases, the design engineers expect the controls contractor to develop a customized, meaningful, and commissionable control system. Controls contractors can be smart, creative, and experienced with a variety of HVAC equipment and system types; however, in a design-bid-build project, I do not believe it is their responsibility to figure out how to properly control the design engineers’ systems. Even if it were, who has the final say about what is “proper?”

The next chapter of this tale is the controls submittal review process. What is this going to look like? Two plausible possibilities are as follows.

1. The controls submittal reiterates exactly what is in the design engineers’ documents.

a. Project No. 1: This will not be helpful to the commissioning process (or to the long-term success of the project) because there will be no specifics regarding exactly how the inputs and outputs will be programmed. The commissioning professional will not be able to write meaningful, functional performance test procedures based on such vague descriptions.

b. Project No. 2: This will result in flat-out wrong sequences that do not correlate with the equipment and other installed system components.

2. The controls submittal includes the contractor’s proposed sequences of operation, i.e., likely the simplest and easiest to develop and program.

a. Project No. 1: The proposed sequences of operation may meet the design engineers’ high-level performance requirements but may do so very inefficiently.

b. Project No. 2: The proposed sequences may not reflect or properly integrate the equipment/systems shown on the drawings. If the design engineers couldn’t be bothered to develop customized sequences of operation, what are the chances the controls contractor will put in the effort to do so?

In either of these scenarios, on what basis can the design engineer (with input from the commissioning professional) ask for more detail, request different sequences, and/or reject the submittal? There is a strong possibility that the submittal review process will be contentious, drawn out, and end far from optimally for the owner.

These two examples help illustrate the importance of including reasonably detailed and customized sequences of operation in the bid documents. Systems are no longer only a collection of equipment, devices, and sensors connected by pipes, ducts, and wires. Systems are also defined by how those individual components communicate with and respond to each other.