Everyone likes the word ‘custom’. It is on of those words that has increased the value of countless, otherwise mundane items. It makes the item feel special, unique and individually tailored. And anyone can us it. See what happens when it is added to everyday words. Custom Shoes, Custom Car, Custom Paper, Custom Design (one of architect’s favorites). But does it work in Revit. Do you get the same feeling when you read: Custom Energy Model? Yeah, me neither. So we don’t feel the same about a Custom Energy Model as we might a custom suit, but let’s try it on and see how it fits (see what I did there).
Customizing the Energy Model
There are three basic ways to customize your energy model in Revit. The first way is through geometry by creating custom zones and fenestration. The second way is through the analysis properties of individual surfaces and zones. Finally, the third way is to adjust the graphical appearance of each individual zone or surface. Although this last one sounds good in theory, it does not work well. You can check out my previous post “Hey Doc, it hurts when I do this…”. In addition to this issue, I discovered that if you change the graphical appearance of an analytical surface to anything other than By Construction, you cannot get the graphical appearance back to By Construction. Oh sure, it says in the parameter value “By Construction” but the actual graphical appearance in the modeling window is still whatever the last material was. I have another support request into Autodesk for this.
Geometry for Custom Zones
But let’s re-focus and talk about what does work. It is actually quite cool to be able to use the auto-magical zone tool. In talking to a few engineers and energy modelers, the zoning that is produced by the CEA tool is much more realistic than what is required for a Revit gbXML export. Five zones per level is more like what the engineers want to work with, instead of a zone for every room in the building. But sometimes the way the zones work out is funky, so sometimes it is better to create your zones more deliberately. It is really quite simple. You just need to think about creating a mass for each zone you want. The best way to do this is to create your overall mass building shape. Then for every place you want a zone, you create another mass and subtract it from the overall mass using the Solid-Cut-Solid tool.
Once you finish your mass, go to the Energy Settings and check the Create Energy Model checkbox. Be sure to set your Core Offset to 0’ and uncheck Divide Perimeter Zones. Now click OK and check out the zones in your model. You will have one zone per mass per floor that the mass intersects. You can see this by selecting various zones and using Hide/Isolate to expose them as shown below.
Talking to your energy modelers or engineers when doing this will really go a long ways towards getting a better model for analysis that they will not have to fiddle with as much.
Geometry for Custom Fenestration
The next major way to affect your energy model through geometry is by doing custom glazing. It is really nice to use the Target Percentage Glazing parameter in the Energy Settings dialog to set your glazing automatically for you. And I think that at the conceptual stage this is probably the best thing to do, but you can make your own glazing layout using some new drawing features in the Conceptual Massing environment.
These new options appear when editing a mass in the options bar when you start the draw command (either line or rectangle) and check 3D Snapping (as shown). They allow you to draw on the surface of your mass. Now, in order for the CEA to know that these are windows you’re drawing and not just lines on the surface of your mass, you must have “Make surface from closed loops” and “Sketch on Surface” checked. So, what do these three options do? David Light has a very good blog entry on their function here. But suffice to say they allow you to draw glazing on the surface of your mass. Like so (showing mass surfaces)…
As you play around with this you will get the feel for it. It can be very useful. But it can also be a little frustrating to try to draw something regular on an irregular surface. But give it a try.
It is important to point out that you can combine the custom glazing with the Target Percentage Glazing parameter. However the results are very weird.
This is what it looks like when I go into the Energy Settings dialog and set the Target Percentage Glazing to 50%. The little windows that run up the sides of the large custom glazing areas are what Revit added. As you can obviously see, the glazed area is far more than 50% of the wall area as set in the target parameter. What this means is that Revit does not take into account the custom glazing in the target percentage calculation. In fact, it is very difficult to see how the math is being done. So when using both % glazing and custom glazing, Revit sees the custom glazing shape and adjusts the automatic glazing around it but does not take the custom glazing into account when looking at the target percentage glazing. Target percentage glazing is only calculated by the automatic glazing feature.
Wow! So that was a lot longer than I thought it would be. I will pick up with the other way to customize - through the adjusting of analysis properties of individual surfaces and zones – with the next post. For now, I will leave you with one of my all time favorite quotes. I don’t know who said it but for sure they were smarter than me.
“Heavy emphasis on the “how-to” guarantees the loss of the critical “why”.