BEM - the 1,000 foot view

This page attempts to boil down BEM into its key activities. If you are new to BEM, this is a good place to start. These concepts are expanded on throughout the Intro to BEM section, and even further with links to the many resources and tutorials on this wiki.

What are you doing when you create a model and run a simulation?

A high-level illustration of the steps associated with creating a model, running a simulation, and extracting results. (Source: IBPSA-USA BEM Workshop)

Identify a building design

Start by determining what you want to model. If it is very early in a design project, there may not be any design yet. At this stage, a BEM model may be a simple representation of a typical building shape or size for the given building type. As the design progresses, more detailed geometric representations will be available and can be represented more explicitly by the model. At the end of the design project (or for existing buildings that are already built), a very detailed model can be created that represents the building as it was designed and/or constructed.

In addition to the model geometry, you will need to determine appropriate inputs for the building's construction materials, its systems such as lighting and HVAC, the number of occupants, and their behavior (i.e., how they operate the building and its systems). As with the geometry, in the early stages many assumptions may need to be made and this information becomes more readily available and detailed as the design progresses.

Read more about different model types, and how BEM is used at different stages of design.

Describe building characteristics

Once you have determined what you wish to model, now you describe it within a building energy modeling software program. The format of this information will vary depending on the chosen software tool, but the concepts are consistent across many tools. Within the software, you provide inputs describing the building, its systems, and its operation.

Read much more about preparing model inputs.

Select weather data

Next, you choose annual hourly weather data for your building’s location to use in the simulation. There are options; this might be typical weather, weather for a specific year or even future-year weather.

Read more about weather data.

Run the software simulation

Then you push a button in your simulation software, which runs through a full year of calculations. It calculates energy consumed by lighting and other equipment. It calculates heating and cooling loads for the indoor spaces. And it calculates energy consumed by the HVAC system components. It will usually also calculate things like energy cost and carbon emissions.

Extract results

The final, most important step is extracting useful results to answer questions. This topic is a key focus of the Learn by Design Task section of this website which is geared around using BEM effectively to inform specific design tasks throughout a typical design project.

Repeat!

In many cases, we use building energy modeling as part of an iterative process. We learn something, and that raises new questions, and so we repeat.

Note: for those who work in SI units, please note that 1,000 feet = 304.8 meters