I know that EnergyPlus models some things in more detail than eQuest, and that eQuest runs much faster than EnergyPlus. What are the best applications for each platform? Why use EnergyPlus if I can get a much faster result with eQuest?
There is a separate thread that addresses the differences in simulation speed between DOE-2 and EnergyPlus. Some of that information--including the speed difference itself--is relevant here. If you need results very quickly, you should probably use DOE-2!
More to the point of the question, there is a simulation capability gap between DOE-2 and EnergyPlus. EnergyPlus does a more realistic job modeling radiant effects, and unmet loads, and novel systems, and controls, and some other things too. If these effects are important in your design then you probably want to use EnergyPlus or something similarly capable. If they are not important, then it doesn't matter which you use and you should probably use the one you are more familiar and productive with. Or DOE-2 if simulation speed is very important to you.
How do you know whether "EnergyPlus capabilities" are important in your design? That is the rub. I believe California is developing some design-feature specific guidance on tool use (e.g., if you are modeling natural ventilation please use engine A or B, otherwise use A, B, C or D) although I don't have a reference for that (I will try to find it and then edit the response). The ASHRAE 140 tests can be used in a similar fashion although they are not very accessible for this purpose. We certainly need to develop better guidance in this area.
re: 'some other things too'. and 'the rub'... If someone can provide a more comprehensive list of things that make the difference between EnergyPlus and Equest, I'll nominate that as the answer. The answers thus far do provide good insight into the question, and they are much appreciated. I'm hoping to get to a more definite/complete/final list of reasons or areas where one engine outperforms the other. I.e. for novel systems, must use energyplus, for a basic building, equest will do fine.
@RyanStochastic. If you are looking for a citable peer-reviewed comparison, there is "Constrasting the Capabilities" by Crawley et al. (http://sbi.dk/download/bsim/contrastingthecapabilitiesofbuildingenergyperformancesimulationprograms_v1.0.pdf). That work is nearly ten years old and revisiting/refreshing it is a good idea. Either way, it doesn't directly address accuracy of modeling features, only their presence. DOE is currently ramping up efforts to add measured data tests to ASHRAE 140 to answer some of the accuracy questions, but those will take time.
@RyanStochastic. Continuing in a separate comment to circumvent the Twitter-esque character limit. The best comparative assessment of both coverage and accuracy you may be able to get right now is a crowd-sourced experiential/anecdotal discussion on specific topics. Fortunately, you're on the right platform for that!
One of the reasons quoted during the recent Energy Modeling Conference was that VRF systems could not be simulated using eQuest. There are a number of other high performance building modeling features (too many to list here) available in EnergyPlus. Another comment I hear often is that there is limited technical support and on-going development/maintenance.
I've heard that the developers for eQUEST have been working on VRF for over 3 years, and that it should show up in the next release of DOE-2.3, which is now out in BETA. I've also heard that there's more development currently going on with eQUEST than at any previous time. It is true that the developers do not provide technical support, since it's freeware, but there is the eQUEST-users bulletin board where users can help each other. I have often noticed that people make disparaging comments on eQUEST/DOE-2 with limited or partial knowledge.
People also make disparaging comments about EnergyPlus with limited or partial knowledge.
@Krishnan, re: "(too many to list here)" - that sort of list, a list of the can's can'ts, and pro's con's of the two platforms would make a great answer to this question.
Do eQuest and EnergyPlus leap-frog each other with each update so a comparison of specific capabilities is not universal to all the versions? Do both programs intend to cover the same market?
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