System Diagrams; Essential Design and Commissioning Tools

When I first started working in this industry (April 16, 1976), one of my first assignments, if not my first assignment was to make a system diagram for a renovation project that involved installing a new chilled-hot water system in an existing building to replace the existing hot water radiator heating system and provide air conditioning via chilled-hot fan coil units.  Chuck McClure, one of the principles in the company and the person who gave me the assignment suggested that a good starting point might be to review the drawings we had lying around and then left me to my own devices while he ran off to a meeting.

In paging through the documents, I was overjoyed to find that they already included a drawing labeled as a system diagram.  I don’t have access to those drawings, but the diagram I found looked similar to this diagram taken from the contract documents for the Pacific Energy Center, illustrating the ice  storage system.

Needless to say, I was pretty excited for Chuck to get back from his meeting so I could show him that I had completed my first assignment and was ready for the next step up my new-found career ladder.

When Chuck returned, I found out that I actually was not done.  For one thing, he wanted me to develop a diagram based on what was actually installed, not what the documents indicated should be installed.  In other words, he said I should use the drawings that were around to familiarize myself with the project, not as a substitute for going out in the field and finding out what was really there.

In addition, the diagram he wanted me to develop had some important characteristics that were not reflected in the diagram on the documents.  In rushing off to his appointment, he had not had time to fill me on on what those might be, but he sat down with me at that point and walked me through the details of what he was looking for and why it mattered.  The bottom line is he was looking for a diagram that looked more like this.

Despite what you might think at first glance, the drawing above and the one at the beginning of the post are of the same system.  But the drawing above is my version of the system diagram, based on the lessons Chuck taught me when I first started, along with lessons gleaned along the way from experience and other mentors.

As you can see, there are quite a few differences including the way the diagram is organized, the level of detail, and the amount of information conveyed. This first lesson from Chuck may have been one of the most important lessons of my career because the concepts he and others taught me with regard to creating system diagrams have become critical design and troubleshooting tools that I use just about every day.

This post is the first in a series of posts that will explore system diagrams and share the lessons I have learned regarding how to develop them and then use them to convey design concepts, troubleshoot operational problems, and document the details of a system for training and system manual purposes.

For those who would like to see the illustrations I will be using in more detail (including the illustrations above), I have created a public folder in my Google web albums account that you can access by following this link.


David Sellers
Senior Engineer – Facility Dynamics Engineering

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