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Commissioning: Controls Design Timing

There’s a right stage for every delivery method, but it may be sooner than you think.

One of the longest running challenges in commissioning is related to timely control system design. In particular, it has been a consistent struggle to obtain detailed, project-specific control sequences early enough in a project to avoid confusion, costly changeorders, and/or inadequate systems documentation. Avoidance of these sorts of problems is supposed to be one of the benefits of commissioning. When is early enough?

Early enough depends on the project delivery method, of which there seem to be an increasing diversity as owners, developers, designers, and contractors attempt to find the best way to design and build new facilities. The following are three of today’s more common project delivery methods and my opinion regarding when control sequences need to be defined for each.

Design-Bid-Build

For the traditional design-bid-build process, it is best to have the design engineer’s control sequences defined and ready for review and coordination no later than about 75% construction documents in the design phase. This is not a first pass at control sequences. It is not the generic sequences from the design engineer’s master control specification. This is the designer’s comprehensive and fully customized description of how the project’s unique systems are to be operated.

This is the level of design that the commissioning professional can meaningfully review. It is a waste of everyone’s time to have the commissioning professional review design documents which are not yet customized for the project. Yet, that is what we see as late as the bid package addenda on some traditional projects.

Design-Build

Design-build projects have a tendency to put off detailed control system design until the mechanical system design is complete and even under construction. This may be because the controls contractor typically prepares the controls design, and the mechanical contractor does not engage the controls contractor until as late as practical.

The controls contractor/designer needs to be involved with the mechanical system designer throughout the design process. It is not a linear process of designing the systems and then letting someone else figure out how to control it; mechanical design and controls design must be integrated to be successful.

Therefore, the controls contractor’s design should be completed simultaneously with the mechanical contractor’s design. It should be presented in a typical controls submittal format of schematic diagrams, control panel wiring, valve and damper schedules, and written sequences of operation. This is not necessarily more work for the controls contractor, but rather the same work performed earlier in the project. This allows the commissioning design review to be performed on a full system design prior to the ordering of equipment/components and the beginning of construction.

Guaranteed Maximum Price

There are an increasing number of projects where the contractors are selected and put under contract before the design engineers have completed their design work. This often happens after design development or around 50% construction documents. There is a lot of value in having the contractors on the team prior to completion of final construction documents in order to provide input regarding constructability, costs/benefits of various options, etc. The contractors “bid” a guaranteed maximum price (GMP) based on the design documents completed to date and their experience and expectations regarding how the details will eventually be worked out in the final documents.

In this situation, one of the most important things to have completed prior to negotiating a GMP is the sequences of operation. There are too many ways of controlling mechanical systems for any contractor to successfully guess at what is expected for a particular project. When competing for a job, the contractors will naturally assume a minimal control system design in order to keep their costs competitive with other contractors who are also making unsubstantiated assumptions

The value to the entire project team of having the design engineers provide customized control sequences and points lists prior to the GMP being negotiated cannot be overestimated. The alternative is to expect costly changeorders once the design engineers complete their design and share it with the contractors who are already under contract.

Summary

One of the keys to design phase commissioning is helping to make sure that all of the required dynamic systems operations are understood, clearly defined, and coordinated before a price is set and a contract is signed. This needs to be defined in detail in order to have apples-to-apples bids from contractors who will have little or no room to come back for changeorders later. It is imperative for building owners’ project managers to define expected controls design deliverables when procuring design engineering services and enforce those requirements throughout the project

 

Commissioning: Getting It Right

Engineered Systems, January, 2010

by
Rebecca Ellis, PE, LEED AP, CCP, CxA
President
Questions & Solutions Engineering
1079 Falls Curve
Chaska, MN  55318
rteesmag@QSEng.com