How’s that for a sexy image! I know I’m likely to have just sent most of you running for a site with better graphics – CLICK (it’s safe, I promise). But if you can muster and stick with me, I am pretty sure it will be worth it.
The Dialog Box
We all know that energy modeling is far more about the data than the geometry. So in this post we will explore the data that Revit uses when creating a conceptual energy analysis. The tough part of writing about this is the tangential way things are linked into this dialog box. Although tangents can be fun at times. That reminds me of a story. This one time, at band camp… Oh, sorry. There I go, off on a tangent. I will try to stay focused. Maybe more coffee will help. I like coffee. That reminds me of a story…
Okay, let’s get into it. We are going to take this dialog box one section at a time. First thing to mention is a not very obvious connection. This Energy Settings dialog is the same dialog you get by going to Manage tab>Project Information>Energy Settings. That is one thing I think the factory did well with CEA. They didn’t create new dialogs, they just exposed and enhanced existing ones.
In this first section of the dialog, you have three options to set: your building type, the ground level and your projects location.
The Building Types gives some 33 building types to choose from. Each building type is associated with a set of assumptions about its operation and use. For example, the Hospital or Healthcare building type assumes certain values for sensible heat gain, light load density, operating schedule, infiltration flow, etc., that are different from an Exercise Center. The actual values at this stage of the project are not really what’s important. Since this tool is best for comparing various designs, choosing a building type and sticking with it is the most important.
The ground level seems simple enough, right? What level of your model defines the ground level around your building. Important to note here is that Revit will make assumptions about the Conceptual Constructions of components that occur below your ground plane. In other words, it will treat those elements as being under ground and will analyze them accordingly.
The Location setting is another example of how the factory smartly decided NOT to make a new dialog box. Clicking the little nugget here takes you to the same place as if you had click Location from the Manage tab. Be sure to pick a weather station location that makes sense for your project. It might be the one physically closest, but not always. Watch out for microclimate elements like bodies of water, hills or valleys around your site and pick a weather station that most closely represents the same kind of geography.
Last note on the Common settings section: These settings affect both the Conceptual Energy Analysis results as well as analysis in Revit MEP (using heating and cooling loads) and exporting a gbXML of a more developed model.
Detailed Model Settings
This is gonna be a quickie. Nothing in this section of the dialog box affects the Conceptual Energy Analysis. These settings do affect analysis in Revit MEP (using heating and cooling loads) and exporting a gbXML of a more developed model. Also, check out the difference in the Detailed Model section between Revit Architecture (above) and Revit MEP (below).
This should illustrate to you that there is more information available to put into a gbXML from Revit MEP than from Revit Architecture. But that is a discussion for a different post.
This is where the magic happens! This is the control center for the Conceptual Energy Analysis tool. It is so simple, yet so complex! Ah, irony. Don’t you love it? It all starts with a simple check box. The Create Energy Model check box makes the rest of this section come alive (literally). Until you check the box, you can’t edit the parameter values. So we check the box. If we do nothing else and just click OK, Revit chugs away and generates zones and analytical surfaces based on the default values preset for the parameters in this section. I would call this a baseline model, at least in terms of the CEA. So what happens when we click OK? This is what I’ve observed. Follow along with the description in the image above.
- Revit divided each level into 5 zones:
- A Core zone Offset 12’ back from the exterior face of the overall mass.
- Revit created four Perimeter Zones, equal in area, around the Core zone.
- Revit assigned Conceptual Constructions to the zones and surfaces. (we’ll discuss this in more detail later)
- Revit created rectangular glazing on the exterior surfaces of each zone comprising of 40% of that surface.
- Revit also set the sill height of this glazing to 2’-6”.
- Revit did not apply a 2’ deep shading device over each glazing area as the checkbox was unchecked.
- Likewise, Revit did not make skylights on the top surface of the mass as the Target Percentage Skylights was set to 0%.
These are the defaults settings if you do nothing to the parameter values after checking the Create Energy Model checkbox. Of course, if you so choose, you can manipulate these till your hearts content. If you don’t want to generate a core zone, set the offset to 0’. If you don’t want to divide the perimeter, uncheck the checkbox. Etcetera, etcetera, etcetera.
One final note. These setting, do not affect analysis in Revit MEP (using heating and cooling loads) or exporting a gbXML of a more developed model. They only affect the Conceptual Energy Analysis.
Energy Model - Building Services
The last section of the Energy Settings dialog is small but important. Only three parameters here: Building Operating Schedule, HVAC System and Outdoor Air Information. The values you see in the image directly above are the defaults.
The Default value for Building Operating Schedule means that the operating schedule is being taken from the Building Type setting in the Common section. This parameter allows you to override the default by choosing from a list of operating schedules such as 24/7, 24/6, 12/7, Year-Round School, etc. This provides further flexibility in your energy calculations.
HVAC System allows you to choose from among different system configurations. Personally, I don’t know enough about HVAC systems to be able to pick a good one, so I would need to ask an engineer. What is displayed in the image above is the default system.
Outdoor Air Information is interesting. By default it is blank (as shown below). You can actually make multiple selections here. Revit will choose which one to use in analysis depending on which produces the largest outdoor air volume. The person count is set by the Building Type you picked; the area is found in the model and the air changes per hour is
based on the operating schedule set - either by the Building Type or the override set in the Building Operating Schedule [CORRECTION] the number of times in one hour that the total volume of air in the building is replaced with outdoor air.
And again, like the Energy Model section, these setting do not affect analysis in Revit MEP (using heating and cooling loads) or exporting a gbXML of a more developed model. They only affect the Conceptual Energy Analysis.
All the data that you could ever want about the settings is available in the help menu. More graphs and charts than you could dream of. If you need to know exactly what the percent occupied assumption is for a 12/6 operating schedule on a Thursday at 6pm, you can find that. (It’s 40%). Check out the Reference section of the help menu…you'll find it.
Next time, we’ll talk about custom zoning and glazing tools.
Wow that was long. I’m exhausted. I think I was able to stay on track…all that coffee paid off. I like coffee. That reminds me of a story…