The Process of Energy Modeling – Part I

By Paul Greenwalt, EIT

Wood Harbinger’s engineers have been blogging since 2013! This Throwback Thursday series features posts from back in the day that are just too good to stay at the back of the blog. Enjoy this one by Paul Greenwalt, originally published on November 14, 2013:

There seems to be a misconception about what energy modeling is that I would like to clear up.  Let me first tell you what energy modeling is NOT.  Energy modeling is not electrical panels “strutting their stuff” on the catwalk.  It is not glamorous.  Energy modeling is not a simple exercise and definitely not for the casual or inexperienced.  Now, you might be thinking,

“Well, that was exactly what I thought energy modeling was, especially the bit about the catwalk, so what is energy modeling then!?”  Since I aim to please, I will explain what an energy model is, how it is created, and then how it can benefit a project.

Defining Energy Modeling

Energy modeling is the process of developing a computer model based on a building design’s intended energy cost.  In other words, energy modeling is a way to compare a proposed building design to a reference building.  The reference building can be the building as it currently exists (pre-renovation) or a “baseline” building, which is usually a code minimum copy of the proposed design.  One of the two options is typically compulsory for your project, especially if the goal is LEED accreditation.   As owners, architects, designers and engineers, we want the model to be as accurate as possible; so keep in mind that either way the results are simply a comparative analysis.

Defining the Proposed Building Model

When defining the model we need to make the proposed building as realistic as possible. That would allow us to make the most accurate comparisons between the two buildings. We start with the bones of the building, inputting building geometry and applying construction types for the walls, floors, windows, and roof.  To create a realistic occupied environment, we add people, lighting, and miscellaneous loads to each space.  Next we “build” in the air systems that will serve the different areas in the building.  After the air systems have been added, we can build the cooling and heating plants that will serve the air systems.  Finally, we apply the actual energy costs from the rate schedules published by local utilities.

Defining the Baseline Building Model

What we use to compare our new or improved building with is critical.  If we build in 2013, it would seem to be unfair to compare it with a building built in 1953 since our new building would need little improvement to show substantial energy savings.  But if you are in fact renovating that 1953 building, then it is the appropriate comparison to make, since the (older) existing building is not required to meet current codes (although you’re about to renovate it) and is likely below current code requirements.  The simulation should use the exact same building geometry, schedules, and utility rates in both models.  This leaves the mechanical systems, lighting, and building construction for energy consumption comparison.

Uses for the Model

There are three primary uses for an energy model.  The first is for Energy Life Cycle Cost Analysis (ELCCA).  From a mechanical standpoint, an ELCCA compares multiple HVAC systems over a set time period (usually 20 -30 years).  This analysis includes the equipment cost, cost of maintenance, life of each piece of equipment, and annual energy cost.  The second reason for building an energy model would be for preconstruction recommendations.  A model can prove that the buildings orientation should be changed for optimum performance, that the insulation needs to be increased due to significant heat loss in the winter, or that the amount of South facing windows increases the solar heat gain of the building and the resulting cooling load in the summer.  The third use for an energy model is to prove that the whole building evaluation, relative to the prescriptive baseline case, shows a significant improvement in energy cost savings for LEED credits. Check out this blog post from energy-models.com for a great breakdown of LEED credits!

Whatever your need for energy modeling, it is a useful tool that can provide insight into potential cost savings before the project is issued for construction.  The important thing is to know what energy modeling is, how long it takes, and when it is useful to apply to a particular project.  So, when should you utilize energy modeling and what do you need to know before undertaking this exercise?  I will dive into the details in Part II of this energy modeling series next month!

Follow Paul on Twitter @PGreenwalt_WH

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    One Comment

    1. Jeff Yirak
      Posted November 14, 2013 at 2:33 pm | Permalink

      I’m a model, you know what I mean,
      and I do my little turn on the catwalk.
      Are we eventually going to get to that kind of modeling?

      On a more serious note, you “built” your proposed model in a single paragraph. Is it really that easy?

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