Question-and-Answer Resource for the Building Energy Modeling Community
Get started with the Help page
Ask Your Question

Energy Pro / Native CBECCs / Open Studio / IES - Is there a difference?

asked 2017-04-03 19:00:03 -0500

_sleepyowl gravatar image

updated 2017-04-04 10:52:06 -0500

Hi all,

I've been playing with 3 of the 4 mentioned above (Epro, CBECCs, IES) and was interested in getting opinions from others who have used these tools.

I've run a simple 5 story office building and the results were fairly across the 3. Now of course they all rely on the CBECC engine for title 24 compliance, so this should be expected. However, I was curious if there is ever a reason to prefer one tool over the other, other than having the capability to model 3D geometry in open studio / IES.

Is there a dramatic benefit to using open studio? I've heard of people doing interesting things that involves running python scripts on open studio's energy plus outputs (or I may be getting this mixed up), but I don't really have an understanding of the reason or need to do so when energy pro or IES gets the same result.

Personally, I like IES more, although I'm worried about their ability to keep up with CBECC's updates. We normally do LEED modeling in IES and it would be great to have it as our one stop shop for loads, Title 24, and LEED.

Would be interested to here other people's thoughts regarding these different tools.

Thanks everyone!

edit retag flag offensive close merge delete

5 Answers

Sort by ยป oldest newest most voted

answered 2017-04-04 08:39:50 -0500

Not an answer to your primary question, but CBECC-Com has the OpenStudio SDK (not the graphical part) and EnergyPlus inside it. So in some sense you are using OpenStudio and EnergyPlus for this particular calculation whichever interface you use. Given that, it seems--for this application at least--the choice is a matter of preference. If you are already using IES-VE and like it ...

In other matters, the OpenStudio scripting facility you've heard about is called Measures. It's a generic facility that has access to the OpenStudio API and can be used to transform and query models, query and process simulation results, and implement general workflow automation. The name Measures comes from the fact that initial uses were implementation of transformations that correspond to ECMs (Energy Conservation Measures). Measures are written in Ruby, not Python. Close enough. If ever there was a reason for you to switch to OpenStudio, Measures would be it. But, again, it sounds like your current setup is working for you.

edit flag offensive delete link more


Thanks @_AmirRoth_!

Measures sounds very useful. I spoke too soon in regards to IES as I just found what I think is a bug in the construction of T24 assemblies... However, the geometry may still be useful, as we've already modeled the geometry for LEED.

Would a workflow like this

  • Create 3D geometry in IES
  • Export generated XML file to CBECCs
  • Open CBECCs file in OpenStudio (Is CBECCs -> OpenStudio Possible?)
  • Run measures script to transform model (say constructions, etc.)
_sleepyowl gravatar image_sleepyowl ( 2017-04-05 14:03:33 -0500 )edit

Ok - so I just typed an answer and now need to completely start over after some testing. Initial response was: 'no, once the model is exported from OS -> SDDXML to CBECCcom its mostly a one-way trip. The model can be opened in OS for review, but changes probably wont get exported back to CBECCcom properly. revised: 'Mostly the same as above, except that - yes - it can be reopened, and re-exported, but there are some nasty/funny looking errors that would need to be addressed. Mainly on the HVAC side. Now, it might be possible to make some geometry revisions; and then recopy/paste in the ....

dradair gravatar imagedradair ( 2017-06-14 09:25:38 -0500 )edit

...HVAC systems from the CBECCcom file (provided zone names & such don't change)....but this is definitely not a workflow that is advertised (or advisable). is possible, but seems ill-advised without some significant caution. Also note: this requires the model to have run at lease once. The OS files (and E+ files) aren't not created until the project is run. So that could also be a barrier if looking to try/test something like this out.

dradair gravatar imagedradair ( 2017-06-14 09:27:40 -0500 )edit

answered 2017-04-06 18:50:03 -0500

yungahhh gravatar image

I think the answer to which is the best program to use always wind down to three things: 1) preferences and 2) what you are trying to achieve and 3) given the budget and the human resources (familiarity).

I'm replying to your question in the context of doing LEED and T24 only. Other type of analysis (parametric, box modelling, component modelling)... that's another day of discussion on its own. Ranking in term of my personal preference, it would be: (hate to love) CBECC-COM, Epro, Open Studio, IES.

IES VE generating results are not as straight forward, several clicks vs one click for OS or EPro, so that's one of the con I don't like about it. I like using IES VE for geometry as well, so we usually just export to CBECC-com to clean up the things that are buggy with IES-T24 module.

But overall, to build T24 and LEED model altogether using this software or that.... it's probably:

  • Fastest/cheapest pathway:
    • IES geometry w/ dxf -> EnergyPro for LEED and T24 for basic buildings w/ traditional system
  • Detailed Analysis System :
    • IES geometry w/ dxf -> T24 using CBECC-com to clean up the scrap IES geometry w/ dxf
    • IES for LEED to model nat vent, more complex system, claim more savings because there's more capability, better documentation, etc.

I haven't have a reason to use OS over IES-VE other than refrigeration system, eventually need to go down to the IDF editor for E+. But I imagine OS would be more useful at the city-level modeling since there's linkage with 3D warehouse , but there's the sad disconnect from Google Earth. >:( OS is also better if you replicate similar model over and over again. IES Run time can be tedious if you have to click 3 runs to get results. I'm quite fond of the OS measures as well, but have not explore better how it can be better utilized to fasten the LEED / T24 purposes quite yet beside probably QC purposes. Otherwise, most software have the template idea. IES-VE ASHRAE 62.1 interface to integrate with the ApacheHVAC is pretty awesome. The Table for the Zone (the excel-looking one) is also pretty awesome for internal QC. Those features are hard for OS to win over for day to day modeling.

As a reviewer, Open Studio / E+ standard results are pretty easy to review, which is nice. Since that's all you get sometimes, and not the model itself. Have not received IES model to review via incentive program so I can't say much here, but from submitting IES-results reports and what not, it's a little harder to put together into a review-friendly template without doing that Excel magic.

So eh, preferences.

edit flag offensive delete link more


Curious why you need to use the IDF editor in OS workflows. EMS?

ljbrackney gravatar imageljbrackney ( 2017-04-06 21:20:48 -0500 )edit

@ljbrackney sorry for the late reply, but yes, for EMS and linking the refrigeration system with the HVAC

yungahhh gravatar imageyungahhh ( 2017-09-26 16:34:59 -0500 )edit

answered 2017-06-14 09:17:38 -0500

I am going to buck the trend and state when I am doing a Title 24 model I use CBECCcom as the modeling tool of choice. Workflow is typically geometry in OpenStudio -> Export SDDXML to CBECCcom.

I've use IES and Epro as well. Both had significant, though different, issues in my experience. For IES the HVAC systems must be either built twice (if needing to use Apache engine) or only in the CBECCcom portion if only needed for CA T24. EnergyPro I found elements to be lost in translation from EPro to CBECCcom simulation - building orientation being one. EPro is also only a 2D element, so geometry can take a while. Epro uses 'absolute' wall reference system, which is fine, as long as the user knows this. But I commonly find that the north arrow on plans magically changes on some projects...hummm....anyways, the above are reasons I've got almost exclusively to CBECCcom. We do have a few uses who use Epro, but its based on their experience with it.

A major plus is that with CBECCcom we can work on the 'back side' in NotePad++/text to create/replicate many of the systems. If I have 10 AHUs, I can build one in CBECCcom then replicate this on the text side(w/ renaming) very quickly. Same for luminaries or other lighting systems. I've also been able to use RegEx to help make changes to big model files as well. The other nice thing is that within CBECCcom you can select to have it save all of files used in simulation (ex: E+ files) then go look at these to see what was actually simulated. This is especially true for the Baseline building. This may be an option in IES or Epro, unknown, but it has been a huge plus for native CBECCcom.

The workflow above of OS-> SDDXML -> CBECCcom also allows the use of some measures OA measure to help with things. Namely the creation of thermal zones, renaming zones/envelope elements. OS also has access to the CAT24 approved constructions, so this is also nice if a visual 3D reference to assign constructions on a project with multiple constructions is wanted/needed. I haven't taken the time to build a CA T24 construction/construction set in OS, but I'd bet it'd be super useful and awesome. Note: I am not an expert OS scripting super guru. The scripts above are some that come pre-packaged with OS.

Since all 3 run an EnergyPlus simulation, I wouldn't imagine there to be a huge difference in simulation time. Probably some difference in 'translation time', but I haven't studied this.

At the end of the day, the 'right' software is the one you feel comfortable with and fits a workflow that makes sense.

edit flag offensive delete link more

answered 2017-06-05 01:18:52 -0500

bbrannon4 gravatar image

Assuming you are just talking about Title 24 compliance (the title wasn't clear):

I'd generally agree with the above. They are (or should be) all identical in terms of results and modeling capabilities, so there is no reason there. I tend to use IES for LEED models and other things, so the benefit there is that you already have geometry and glazing, and are familiar with the editor. IES also adds a couple useful tabular editing views to the CBECC-Com model which can save time. As you correctly point out, there will always be a slight lag in IES updating to the most recent version of CBECC-Com, and for that reason I always finish my models in the native CBECC-Com app. I would guess if someone has a workflow in OpenStudio that they are comfortable with, that the same rationale would apply to continuing to use it.

edit flag offensive delete link more

answered 2017-11-20 13:47:48 -0500

IESVE is definitely my favorite.

For code compliance modeling and LEED modeling, IESVE does a really good job.

For Title 24 modeling, I use IESVE to develop the geometry and then transfer it to CBECC-COM to do the remaining(generate .XML file and then open it in CBECC). The Title 24 module in IESVE is a pain in the ass, but using ModelIT to develop geometry is definitely better than in SketchUp.

edit flag offensive delete link more

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer


Question Tools


Asked: 2017-04-03 19:00:03 -0500

Seen: 530 times

Last updated: Jun 14 '17