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

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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.

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.

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.

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.