On energy analysis and BIM

While at the Building Science program at USC, an exciting thing that I discovered (apart from Revit itself!) was the integration of energy analysis functions within Revit in early 2007. IES, a well known building performance analysis tool, had incorporated some analysis functions within Revit MEP. The analysis itself was pretty basic - heating and cooling loads; but just its very inclusion meant that Revit was more than just a modeling/database tool. In fact, it was moving in the direction that Revit, as a Building Information Model, was supposed to….performing its role as a truly informative tool. Thanks to this feature(albeit a basic one), architects could take design decisions pertaining to energy efficiency earlier in the design, as opposed to relegating the task to MEP engineers after the design was done..(which simply doesn’t make sense!...what’s the point of analyzing a building for efficiency after the design has been frozen???)

In addition, IES also came out with a toolkit…essentially, you could export your Revit model into the toolkit and it was roll out some calculations for you…thermal loads as well as lighting loads. It also came with a neat little feature that estimated whether your building would qualify for LEED v2.2 Cr8: Daylight and Views.

Pretty exciting developments...except for some gaps. For example, Revit MEP comes with a drop down menu containing a list of walls, windows, roofs and floors that you could use for your analysis model.Revit takes values for the parameters associated with these components from their counterparts in IES, called the Apache Construction database. Unfortunately, what that means is that your analytical model, (apart from the actual geometry of the building) has very little to do with the building model itself...in other words, if you modeled a 6" timber frame wall, but selected, lets say, an 8" heavy weight concrete block, from the list, the program took the concrete block.

During a small experiment at SC, I discovered a slight discrepancy in the analysis results while testing a BIM model.I modeled a building, changed the thickness of the building fabric, kept the internal spatial volume the same and found that changing the thickness resulted in a different thermal load . This was pretty amazing, since this seemed to indicate that the wall thickness, at the very least, was being carried over for analysis!....till Mr Harriman at IES pointed out that the discrepancy was happening due to the increased external surface area(and therefore increased heat transfer etc)

For all the obvious gaps, I still think that have analysis embedded in your BIM model is a pretty neat idea and the industry certainly seems to be going in that direction....