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# OpenStudio vs Design Builder

I’m trying to figure out if there are some advantages in using Design Builder over OpenStudio. For example, would Design Builder allow me to create some more complex HVAC systems (such as DOAS with radiant slabs, or central ground source heat pump, etc.) and export an IDF file including the detailed HVAC components?

Can you guys share your thoughts about advantages/disadvantages of Design Builder over OpenStudio? I’m asking this question because I need some reality check in terms of time I spend on my models and would greatly appreciate any suggestion.

I used OpenStudio for several projects, but found specifying HVAC parameters in Open Studio time consuming and difficult (a lot of errors). To avoid many errors in HVAC, I would just create geometry and assign attributes in OpenStudio, and create all HVAC systems directly in IDF file by using E+. The building size I typically have to model is 150,000 sf to 200,000 sf.

How many of HVAC components/ controls, in general, are you guys able to specify in Open Studio before switching to E+ ( idf) for this building size? Also, how much time roughly does it take for you to complete a model with standard systems ( e.g. VAV w/ boiler chiller) and a model with a more complex system ( e.g., radiant slabs with with DOAS w/ DCV providing ventilation air directly to the spaces)? Let’s assume that the building has 150,000 sq.ft and a simple rectangular shape.

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It helps to understand the intent of each software:

• DesignBuilder is built primarily as a Graphical User Interface (GUI) for EnergyPlus, though it does have some scripting capability.
• OpenStudio is built primarily as an Object-Oriented Application Program Interface (API) for EnergyPlus, though it does have a GUI.

If your goal is one-off models of single buildings, then DesignBuilder builder is an appropriate choice. It gives a friendlier feel to EnergyPlus objects which is nice for new modelers. There is a license fee.

If your goal is to do quick analysis on multiple buildings, and are comfortable with scripting, you will appreciate the utility of OpenStudio and the Building Component Library. The recent inclusion of the OpenStudio command-line-interface makes it a good choice for server-based applications. OpenStudio is free and opensource, which is why many 3rd-party developers use it. The Rhino/Grasshopper plugin Ladybug/Honeybee is particularly nice for thermal comfort analysis and recently CFD. There are still EnergyPlus objects, particularly HVAC systems, that are present in EnergyPlus but not yet OpenStudio.

I find most of the value in modeling is early-phase comparisons of massing, shading, envelope, or HVAC system options, which I can do very quickly with Grasshopper/Honeybee and OpenStudio measures.

Both DesignBuilder and OpenStudio are limited by the lack of controls detail in EnergyPlus, OpenStudio particularly so. I may do early modeling up through schematic or design development phases in Grasshopper/Honeybee/OpenStudio, and then import into IES if I know the controls are going to be really complicated (multiple timeclocks/setbacks, staged humidity controls, zonal and partial air-based system).

• You can model DOAS with radiant slabs or central ground source heat pump in either software. Be careful about modeling radiant slabs in EnergyPlus and consult the engineering reference guide. Setting up the controls correctly is tricky. You may need to do manual sizing.
• Time spent on models: geometry is a big time sink. If you are significantly faster building geometry in DesignBuilder or SketchUp/OpenStudio, that may be the best choice for you for speed.
• Once geometry is built, template objects and/or measures make it easy to get a model running in both softwares. I have OpenStudio measures to apply VAV+boiler+chiller and DOAS+radiant systems, which can run in < 5 minutes. If I have different HVAC systems, I have measures to specify which HVAC systems serve which zones, but need to input that as a .csv, so 20 min? The speed really comes in being able to build/tweak your own OpenStudio measures. You should never manually add and specify terminal unit sizing for a 50+ zone model unless you need to for a code/permit model.
• I'm not sure about DesignBuilder, but in OpenStudio a 150,000 sf rectangular building could be pretty quick. A simple 5-floor core and shell model with mostly defaults I could do in 15 min using measures. Needing to build geometry from floor diagrams and modeling shading adds another 1-5 hours depending on ...
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It would be better to leave cost out of this discussion. Cost isn't meaningless, but the real cost of modeling is modeler time, not the software. If software A costs 5,000 and B costs 0 but A is 2X more productive for what you do, you should go with software A every time. And twice on Sunday. The more useful part of this discussion is philosophy/orientation/workflow. Thanks.

( 2017-01-17 08:56:10 -0500 )edit

For clarity - on the 3rd bullet @mdahlhausen you note that you have a script that uses a .csv to assign zones to systems. This is in OpenStudio? Can you briefly walk thru how this process works (export / assign / modify script / import)??

( 2017-01-17 09:04:04 -0500 )edit

@mdahlhausen, thanks for sharing what you have found to be useful. Regarding geometry generation - do you prefer to do that in OS or in DB, and why? Regarding import to IES VE for complicated controls, are you importing via gbxml? And what are you preserving through the import process? Only geometry?

( 2017-01-17 11:03:31 -0500 )edit

@__AmirRoth__ I agree the cost doesn't matter for private sector consulting. This is more of concern for educational licenses (there is a big discount, but big discount != free, and dealing with educational administration around licenses can be annoying), teaching one-off "what is modeling" classes to architects, and incorporating components of a modeling software into 3rd-party applications.

( 2017-01-17 12:08:03 -0500 )edit

@dradair you can use the CSV class to read a CSV file into your measure. You just need to require 'csv' at the top. You can create a string argument that accepts the path to your csv file, and use, e.g., the foreach method to access the data in each row, and do whatever you want with it (e.g. create and assign sizes to HVAC by zone).

( 2017-01-17 12:26:07 -0500 )edit

Both softwares can be used for your purpose, but I would prefer Design Builder. It is less time consuming. In OpenStudio default settings are much more complex than design builder which is more user friendly. Plus OpenStudio model visualization is not possible. In Designbuilder majority settings are already set by default to help simulate multiple times and then make changes according to your needs. Chances of errors are less so it saves your time. As for HVAC system I would suggest using Simple HVAC first, after it completes without errors you can then add the detailed HVAC. To complete a model with standard systems (for building your size) can take me 7-10 days while detailed might take a more than 2 weeks (for complete detailed HVAC). But again it depends how much time you are spending on it. Hope this helps.

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Thanks for sharing your experience. From your response, it sounds like Design Builder is very similar to eQuest. With eQuest, simple HVAC is created in Wizard, and then more detailed input or additional HVAC systems are created in Detailed mode. I found that ability to visually see HVAC and respective zone is a huge time saver, especially when I have to go back to old models to make some quick changes. Can you share a few examples of the more complex HVAC when writings scripts in DB would be necessary? Thanks again!

( 2017-01-18 08:34:17 -0500 )edit

Yes I agree with you. Visit this site: https://designbuilder.co.uk/tutorials/ I am sure this will give you a clear idea of the detailed HVAC systems in Design Builder.

For transparency, I’ll caveat this post with the fact that I have a bias towards DesignBuilder and have limited knowledge of OS, however, I will only include factual information or what I have seen and/or been told by people using OS. You won’t find many DesignBuilder specific posts on this forum as the vast majority of our customers use our Helpdesk so don’t need to rely on forum assistance.

DesignBuilder is typically considered much faster and easier to learn and to use…how much faster will depend to some extent on your expertise in both tools. It was released over 10 years ago and has been subject to continual development to help improve modelling productivity as a GUI to EnergyPlus, Radiance and CFD. You don’t need to use script or to write measures to model in DB, although you can use our extended version of the EMS etc. to tailor simulations.

DesignBuilder includes Detailed HVAC templates for most complex HVAC systems so the basic system can be set up very quickly and then tailored to your requirements. You can set up the examples you list such as VAV w/boilers and chillers, chilled ceilings and heated floors with DOAS, and DB includes some very detailed ground source heat pump systems.

Ground loop heat exchanger tools such as GLHEPRO and GLD (which are not supplied by DesignBuilder or EnergyPlus) are able to carry out a more detailed and accurate sizing calculation taking into account specific borehole layouts and ground properties. These tools can export calculated G-function data in the form of IDF files which can be loaded automatically into DesignBuilder. If you search our online help you will find some information about modelling ground source heat pumps in DesignBuilder here: https://www.designbuilder.co.uk/helpv...

You can export the idf from DB if you want to but shouldn’t need to very often. Many DesignBuilder users aren’t familiar with working in EnergyPlus so we have included the majority of common EnergyPlus systems to minimise the need for idf export and manipulation. DesignBuilder is commercial software, but it typically has a fairly short payback period (due to productivity gains) and has the advantage of a comprehensive integrated Help system and dedicated Support Desk for customers.

If you want to find out more please contact DesignBuilder and we can answer any specific questions you have. If you'd prefer an unbiased/neutral perspective on the comparison then the guys at Big Ladder Software are well placed to highlight the strengths and weaknesses of each tool (approved trainers for EnergyPlus, OS and DesignBuilder) and may be willing to offer guidance relevant to your needs if you contact them.

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Dave, thanks for replying to my post. As soon as I can make some time in my schedule, I will download a free 30day trial of DesignBuilder. Would the 30day trial give me an access to Engineering Plus/Pro version that have Scripting included?

( 2017-01-18 08:59:15 -0500 )edit

Hi Anna, The DesignBuilder EMS extensions aren’t provided in the standard 30-day trial but if you want that functionality please contact/email the office and they'll make the necessary arrangements.

( 2017-01-18 10:16:27 -0500 )edit