There’s no better way to build momentum early for a successful project.

I  was taught from the very beginning of my engineering career to always start with a system flow diagram. The phrase, “A picture is worth a 1,000 words,” doesn’t do justice to the true value of a system flow diagram. However, I am routinely reminded of how many design engineers I interact with don’t start with a flow diagram when designing a job, troubleshooting a problematic system, or commissioning a system. Had the designer started with a flow diagram and wrote their own sequence of operation at the very start of schematic design phase documentation, so many of the systems that fail to achieve client satisfaction and/or result in contractor “requests for information” followed by changeorder proposals to make things right could have been avoided.

This got me to thinking that maybe there should be mandatory design engineering steps, the likes of which I introduced (with help from Amanda Parolise) in a book titled, Handbook On Process, Project, Profits – A Practitioner’s Guide To The Building Industry.  It’s an online, chapter-by-chapter writing venture at a time when the industry is at an interesting crossroads between continuing down the 20th-century technology road or making a course correction to the 21st-century process of HVAC engineering. Our online publication is also at a similar crossroads, as we have reached an editorial roadblock with chapter 2-3 titled, “Construction Document-GMP.”


We believe that in this phase of the engineering design process, we need to rethink what needs to be produced once the design development phase of the work is completed. Namely, the following steps should occur to follow the correct course and realize the most efficient design engineering method:

  • From the owner’s owner’s project requirements(OPR), draft the HVAC basis-of-design.
  • Budget estimate HVAC loads (sq ft/ton, Btuh/cu ft, cfm/sq ft, etc.).
  • Proceed next to the 2008 ASHRAE Handbook – Systems and Equipment, Chapter 1.“HVAC System Analysis & Selection Process.”
  • With the optimum system(s) selected, create a system flow diagram per system (central system, chilled water system, etc.).
  • With system flow diagrams completed, write the ATC/FPT sequence similar to the “Back2Basics” series.
  • Using the same system flow diagrams, produce the following:
  • Insert estimated airflow along with associated static pressures, and attach the optimum fan selection and motor hp (these documents can be used and updated by the balancing contractor near the end of the construction work).
  • Insert estimated water flow along with associated pressure drops, and attach the optimum pump selection and motor hp (these documents can be used and updated by the balancing contractor near the end of the construction work).
  • Overlay the electrical data including motor hp, power wiring, interlock wiring, smoke detection, etc. (information needed by the electrical engineer in parallel with the HVAC design).
  • Overlay the alarms and safeties (if not already included in the ATC/FPT checklist narrative above).
  • Overlay the plumbing data including city water makeup, backflow preventor, floor drain needs, gas, etc., (information needed by the plumbing engineer in parallel with the HVAC design).
  • Overlay the equipment and distribution estimated weights (e.g., piping shall be 30 lb/ft), housekeeping pad, and concrete inertia pad requirements, etc., (information needed by the structural engineer in parallel with the HVAC design).

What's The Difference?

What have we got so far with these system flow diagrams? We have the HVAC systems sketched out along with estimated block loads, system loads, ATC/FPT sequence and commissioning narratives, and estimated air and water balance per system with associated pressure losses and associated motor hp. We also have estimated and coordinated electrical data, plumbing data, and structural data to allow the other design engineers to keep pace with the HVAC design.

Now, without even beginning to show any HVAC system layouts/distribution on floor plan drawings, we have provided our client and her facility staff with most of what they need to know about how to operate and maintain the HVAC system(s). The information is also valuable training data for the future operators of these systems.

Based on all this information, I’m sure an experienced construction estimator can provide a relatively accurate project cost. At the same time, based on my design-build experience, a design-builder could certainly provide a single-source bid to complete the HVAC work and, using the same approach to the other trades, could come up with a total D-B project bid. Not a bad start to a job when you begin with system flow diagrams that the design engineer, builder, and the facility manager can use and you’re still in the schematic phase of the project!  ES

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