March 2016

Measure Twice, Cut Once

I forget the name of my 7th grade wood-shop teacher, but I remember his words: "measure twice, cut once". I’m guessing you’ve heard that too.

I’d like to propose an alternative: model twice, build once. Or better yet,

Model (at least) twice, build once (getting it right the first time and avoiding expensive change orders and retrofits and maybe even figuring out ways to reduce the total construction cost while saving energy at the same time).

That’s catchy, right?

Those who know me might see this as a self-serving statement. I’m an energy modeling person. The more modeling, the better (for me). Okay, guilty.

But this idea applies to many types of modeling: lighting modeling, daylight modeling, airflow modeling, acoustical modeling, 3D modeling for coordination and clash detection, and many more that I’m forgetting at the moment. We have some great tools available, and they are getting better and better every year.

But let’s get back to the (self-serving) topic of energy modeling…

How many times is enough? Here you go:

  1. Concept design. Before the first sketch on a cocktail napkin (because after that point it’s too late), perform a really quick energy modeling exercise to compare some alternatives for the basic building form and their impact on energy performance. Set an energy performance target. Very high bang-for-buck factor.
  2. Schematic design. Here’s where the really important modeling happens because important design decisions are happening. It’s now or never. Explore strategies to minimize HVAC loads.
  3. Design development. Lots of details to evaluate here. Which glass type? Does that newfangled chiller make sense? How about that insulation made out of recycled ductilators (ask the old farts…)?
  4. Construction documents. (Note that this is where we often start energy modeling; so sad). Project over budget? Some value engineering going on? Use energy modeling to show there are implications to eliminating roof insulation.
  5. Construction. Substitutions threatening to get you down? Use your model to show that gas lamps are not equal to high performance LEDs.
  6. Verification. The building has been occupied for a year. Compare the utility bills to the energy model results to see if actual performance meets expectations. (If not, don’t blame the model. Tear the building down and try again. Or perhaps investigate reasons for the discrepancy and find some savings opportunities).

Okay, maybe not every step is necessary for every project. But many, especially the early modeling steps, will make sense on any project.

At this point I hear you saying, “If this energy modeling stuff is so important, then why doesn’t ASHRAE have a standard for it? There’s a standard everything else.”

Well, it’s true we don’t have a standard today, but that oversight may soon be remedied. ASHRAE 209P Simulation Aided Design for Buildings Except Low-Rise Residential Buildings has been under development for several years and will soon be going out for public review. So keep on the lookout. This proposed standard sets requirements for the use of energy simulation in the design of new commercial buildings. As currently written, Standard 209 requires at least two modeling “cycles”, and one must occur before the end of schematic design.  

So there you go… model (at least) twice. ASHRAE says so.

-Erik Kolderup
ASHRAE Golden Gate President, 2015-2016

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