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Building Energy Simulations – More is NOT Better

By October 19, 2015November 7th, 2021Energy Rant

Do you recognize the city shown?  It is Chicago.  How many twin buildings do you see?  Ok.  Consider downtown in your city.  How many twin buildings are there?  Ok.

Why are they all different?  I would guess because if, say Donald Trump is going to build a $500-$1000 per square foot tower in the middle of all this, he wants an icon.  Wouldn’t you?  Besides, you’re not going to stop an architect from making it so anyway.  They want every building design to be a trophy for their wall.  Why not?

Even schools, office buildings, college and university buildings, hospitals, and government buildings are one-of-a kind.

Looking under the hoods of these buildings, as we have with thousands of buildings, including dozens in Chicago, we find that the guts are just as unique as the skin.  Conclusion: commercial buildings, other than some corporate box stores and franchises, are as unique as people, and that is no exaggeration.

Every new construction and especially, especially, especially, substantial retrofit project involving HVAC – everything from heating and cooling sources (boilers, chillers, furnaces, heat pumps) to water, air, and ventilation (fresh air) distribution must be considered in its unique circumstance; or the entity paying the energy bills is going to be wasting a lot of money, probably both on first cost and for sure in operating costs for the next thirty years.

This post is brought to you by a recent ad I saw for a building simulator that handles hundreds of commercial building retrofit projects a year, each with hundreds of measures per project.


Simulators are ok for comparing HVAC system options in new buildings, where nothing exists and you have to assume that buildings perform per code design and controls requirements.

In retrofit situations, if a custom replacement (they are all custom because buildings are as unique as people) of a major component or system is in play, a surface building simulation is a disservice.  It’s leaving most of the real savings on the table. We’re not buying refrigerators.


Let’s take a look at reality[1], considering new construction.  The figure was ginned up by me based on 20 years of experience looking at actual building performance, energy consumption, and how screwed up buildings are in reality; not operating in Lake Woebegone fantasy land.

The black diamonds represent energy consumption relative to energy code, where 100% is the fictitious code-compliant building.  The bar charts represent theoretical savings, blown savings, and net savings for a new building.  For orientation, negative is good, as it represents reduced energy consumption.

  • Theoretical Savings is what a building simulator will tell you.
  • Blown Savings are what happen once the meters are spinning and the building is operating for real.
  • The net savings (Actual Performance) is where the building actually performs. In this case, it was projected to be 40% better than code but is actually 21% worse than theoretical code.
  • High Performance Building is where buildings can operate when the system type/design and controls align for performance.

Energy codes allow unlimited (as unique as people) design latitude.  Nothing in an energy code says, “This is a bad application for system types A, D, E, H, and M.”  And believe me there are dozens more code compliant choices that are bad.  The “Sound Design” shown in the plot represents avoiding these dirty dozens.

A True Tale

Then we have software/controls, which are as unique as people in commercial buildings.  True story: a number of years ago we did a retro-commissioning project on a new YMCA.  The controls were screwed up.  In collaboration with the controls contractor, we fixed that with estimated savings of 30%.  The savings weren’t being realized, at all.

Investigation.  The “facility manager” had, for unknown reasons, undone everything we did.  (Computers are good things for seeing who did what, when).  Recently (years later), the account manager realized this facility’s energy consumption had suddenly soared.

Investigation.  The customer had installed a new control system – no idea why, and the controls contractor “forgot” to implement an unoccupied cycle.  Meanwhile, we checked energy records prior to the misbegotten controls replacement and the building was performing exactly as we predicted; post-retro-commissioning.  Thirty percent savings! – blown to bits AFTER wasting probably $50,000 on a new control system.

The above story is on the high end of wild, but absolutely true.  The punchline is, these kinds of things happen all the time.

What’s more, as we build a portfolio of retro-commissioning projects for a new program, we specifically seek NEW buildings, whether they went through a new construction program or not.  These are treasure troves of cost-effective opportunity because all the parts and capabilities are there.  It’s like teaching a person to become an outstanding golfer or skier.  Starting at age 3 or 4 will be much more successful than starting with a broken down, flawed and rickety machine like me.  I could be improved a lot but I don’t have potential like the three or four year old.

Nothing in the next fifty years will change the fact that commercial buildings are unique; and that fixing them to perform in the neighborhood of optimum requires custom approaches, not canned widget comparisons by the hundreds.

[1] Based on experience with hundreds of buildings.

Jeff Ihnen

Author Jeff Ihnen

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Join the discussion One Comment

  • Patrick O'Donnell says:

    So true, so true. Nice work at painting the picture of this reality that is often understated or not well-understood!

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