The geometry of your building is the first piece of information required to process an accurate energy and daylight simulation. As such, it is very important that the geometry you are feeding into Sefaira is set up properly for analysis.
When it comes to building performance simulation, there is a common misconception that the more detailed the building, the more accurate the results. Not necessarily true. Here's a short Sefaira article and a not-so-short USGBC article that explains why.
From an architectural perspective, models are typically outfitted with every detail of the building’s design with the goal of producing realistic orthographics and renderings. There are some details in your building that will have little or no impact on the energy performance, and in fact, will increase run times and can be significant sources of error. It is best, therefore, to leave them out.
Keep it simple... An energy and daylight model only needs a few pieces of key geometry to represent the building's performance. Forget furniture, people, lights, etc., we can (and will) simulate all other information in the building without having to model its geometry.
You may be thinking: "Okay, got it -- we're looking for simplicity. So then what do I need to model?"
The first rule of performance modeling is, “always model the heat transfer surfaces first.” In a natural state (i.e. without the aid of a external work on the system), heat will generally transfer from hotter objects (or air) to colder objects (or air). Thus, any surface which separates environments of significantly different temperatures will have heat energy flowing through it.
So, which surfaces separate environments of significantly different temperatures?
The building envelope: any part of the building that separates the internal (conditioned) space from the outside air or ground should be modeled. This includes exterior walls, windows, curtain walls, doors, roofs, and the ground floor.
**Important Note: Sefaira models should be 'thin-surface' models, i.e. all the building elements should be built without thickness. For example, a 10' x 20' exterior wall with a .5' thickness will have 6 sides and a volume of 100ft^3 in an architectural or structural model. In an energy model, the only information we need to know is that there is 200 ft^2 of exterior wall that separates conditioned space from the outside. So, we would build a 10' x 20' single surface to represent that exterior wall. The video at the bottom shows how to do this for the entire building enclosure on an actual architectural model.
What about interior partitions and floors that separate two spaces with different cooling and heating setpoints?
In Sefaira web application, the interior walls are treated as ‘adiabatic’ in nature and will not have any heat transfer through them. However, it is important to still include key elements inside the building like floors and internal walls, since you can also use your Sefaira energy model to study daylighting. As noted above, make sure to model all your internal elements as thin surfaces.
In SketchUp, make sure to tag interior walls by right-clicking on the surface → Sefaira → tag as internal wall.
In Revit, interior walls need to be tagged with function type ‘interior’ in the type properties.
What other information should I know in order to conduct a successful Sefaira analysis.
- You should know how to set up your model.
- Obtain location where the project is going to be built. This information is necessary for Sefaira to pull in the proper weather file associated to the climate.
- Obtain sufficient building construction and space use information. i.e., do you have a baseline that this project is going to adhere to? What are some of the typical values that you will be using for envelope and space use parameters? Need help? You can obtain typical values here.
- Obtain information on the space use type. Is the building going to be predominantly an office building? Or a School? Etc.
From the standpoint of getting valuable results quickly that guide your early design decisions, there is really no need to spend hours on end adding detail to your energy model. Once the exterior shell, internal surfaces, and shading elements are properly tagged, the model is ready to be analyzed. Happy designing!