Ask a Modeler: What is the Biggest Misconception Designers Have About Energy Modeling?

What is the biggest misconception designers have about energy modeling?
-First-time Modeler
Dear First-time,
Energy modeling provides us an insight about the importance of design decisions on total energy consumption. On one hand, I’ve seen architects who are eagerly waiting for the energy modeling results as they are tweaking the envelope and making it more energy efficient. They believe that a change in the envelope can noticeably change the total energy consumption. On the other hand, I’ve talked to my colleagues in engineering companies who are brushing off the notion that the envelope design significantly impacts energy consumption. So why does this rift exist between the architects and engineers?
Let’s discuss the elephant in the room: a misconception about the importance of envelope design on the total energy consumption. In other words, does the envelope design matter regarding total energy consumption? The answer is it depends on four “whats.”
  • What are you comparing to?
  • What is the function of the building?
  • What is the general building mass?
  • And what is the climate? 
It depends on what we are comparing our envelope decision to. As we are designing more and more efficient envelopes with better U-values, and as the baseline and the local building code become more efficient and stringent, the impact of envelope design on the total energy consumption is getting diminished. 
In addition, the energy consumption of a building is defined by what the function of the building is. In some projects the internal load of the building largely contributes to the total energy consumption which pushes the envelope loads to the side, such as in data centers. 
Moreover, the general shape of the building can determine whether the envelope decision matters regarding total energy consumption. The general shape of the building is defined by the surface to volume ratio: how tall or how flat the building is. If you design a multi-story office building, then the surface to volume ratio is low. This indicates that the envelope decision in a multi-story office building is not a significant role player compared to a one-story office building. 
And finally, the climate can diminish or highlight the importance of the envelope design. If you design for mild climate zones similar to California, then the internal loads probably play a more significant role than the envelope loads when it comes to the total energy consumption.   
Per the discussed four “whats,” one may conclude that for some projects the envelope design is not an important player regarding total energy consumption. While this is true, we should not dismiss the significance of architects’ decisions about the envelope design. Keeping the holistic view, total energy consumption is just one design criterion. Peak energy, visual and thermal comfort are other design criteria that will always be impacted by the envelope decisions regardless of the discussed four points. The envelope design as a part of a multi-faced design problem impacts different design criteria which can be studied by building simulation tools.

Sara Motamedi, PhD
Senior Building Performance Analyst, Interface Engineering

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