When asked to put a price to a service offering, we want to know what we're pricing. Nowadays as technology marches ever onward, we are faced with the myriad of terminology in the AEC industry when it comes to "Energy Modeling". Maybe we as modelers haven't been good enough at translating the efforts going on behind the scenes with all these calculations. Regardless...

This term isn't good enough anymore.

As codes and other requirements drive our industry closer towards net-zero, Energy Modeling will continue to be essential for high-performance projects.

So, we still need an Energy Model
But... are we talking about an 8-hour massing study, a 50-hour parametric analysis, a 20-hour daylight and shading study, or a 100-hour LEED compliance model? Do we need work-sessions with the Architect, Lighting Designer, Interior Designer and Mechanical Engineer together? What kinds of input do we need from the Owner?

ASHRAE defines a building energy model as, "a computer model that provides information on the energy-using systems in a building (e.g., HVAC, lighting, occupancy, plug loads, building envelope). The model serves as the input data for a specific computer building energy simulation program, along with weather data. When run, the computer program will simulate the energy use and demand in the described building for a time interval specified in the simulation model. Depending on the kind of simulation program and how it is set up to run, various kinds of output may be produced".

Does that clear it up? No?
As I oftentimes do when faced with something worth explaining, here's a written summary for my reference [and your enjoyment].

Types of Models

The world that we live in now is full of data.

In the AEC world, we're not unique in that regard. The way that we gather and leverage that data is constantly evolving, as are software options we use to process it (note: this is not a post about software).

If it weren't enough, the types of modeling summarized below oftentimes go by other names as well. These phases can also blend and evolve into one-another, but they all come with varying degrees of effort.

The outputs we want are driven by the project goals. The inputs we choose to use and how many steps of analysis we want to look at all drive the time investment. And every project is different. So, without further ado, here are some different types of Energy Models we could end up with...

Parametric Model

Usually undertaken at conceptual or schematic design level, this study could analyze any number of variables, such as: massing, window-wall-ratio, shading, daylight, insulation, thermal comfort, and more. Results are comparative, not necessarily predictive.

These models need to be simple, they need to be nimble, and they need to be completed quickly in order to feed results back to the design team for quick decision-making.

This type of modeling is performed at multiple points throughout the design phase of a project to determine energy use and affirm design decisions. They are more of a time effort, and more specific, but can still use general assumptions for occupancy, scheduling, and the like.

Compliance Model

Ideally this model doesn't start until the project is around 90% construction documents. Due to the nature of accuracy required in a compliance model, any significant design change will have ripple effects. Not to mention the amount of detail needed for inputs is quite tedious... occupancy schedules, plug loads, internal and external lighting, elevators, data center equipment, kitchen equipment, HVAC sequence of operations, utility rate structure, etc. Everything needs to be translated to data. Then input into software. This is the 'Proposed' model.

And then, a completely separate Baseline model needs to be created to compare the Proposed to (and calculate savings from).

Compliance models are used for LEED documentation, energy code compliance under the Performance Path, and 179D commercial tax deduction.

Calibrated Model

Once the building is built, the Energy Modeling fun doesn't have to stop there! A calibrated model is built (or fine-tuned from the Compliance Model) to mimic the actual performance - and weather - of a post-occupancy project.

This type of model can help find new areas of savings that weren't previously identified, be used as a tool for future retro-commissioning efforts, or verify 'as-designed' high performance project goals.

As engineers we always want to be precise AND accurate. These two concepts don't necessarily always go hand in hand without input and effort of multiple individuals on the design team.

Not to mention that energy models, not matter how good, ultimately are oftentimes trying to predict the future. Abnormal weather, occupancy changes, set-point modifications, and the like can wreak havoc on even the best predictions.

This work cannot be done in a vacuum.

Doing the best job communicating the information we have at any given moment is like hitting a moving target. And when it comes to Energy Modeling, regardless of the type, staying light on one's feet and adapting to change is proving the be the most important skill of all.

Written by Sarah Gudeman