Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
Based upon the description of what you're trying to model and your goal (close to representative of the real life scenario), you may be using the wrong tool. EnergyPlus can't simulate the air movement inside large volumes in the way that would be very accurate, but it there are possibly some ways to alleviate the problems. If you know how the air moves within the theater volume, either from observation or from more detailed simulation (computational fluid dynamics), then it is possible to set up a model that mimics that (with ZoneMixing, AirflowNetwork, or maybe the RoomAir model) but it is difficult to get EnergyPlus to compute those air movements for you. AirflowNetwork implements a pressure network that computes bulk airflows given proper inputs, but those inputs would very difficult to obtain for this case and would require either measurement or more detailed simulation. ZoneMixing allows the specifications of the flow, but I'm not sure where you would get that information without either measurement or more detailed simulation (unless you are less concerned about the details).
If you just want to make sure that the air in the theater is pretty well mixed, then ZoneMixing will do that for you (but you'll need to figure out the flow rates). For more details results than that would allow, you'll need a more detailed tool than EnergyPlus.
| | 2 | No.2 Revision |
Based upon the description of what you're trying to model and your goal (close to representative of the real life scenario), you may be using the wrong tool. EnergyPlus can't simulate the air movement inside large volumes in the way that would be very accurate, but it there are possibly some ways to alleviate the problems. If you know how the air moves within the theater volume, either from observation or from more detailed simulation (computational fluid dynamics), then it is possible to set up a model that mimics that (with ZoneMixing, AirflowNetwork, or maybe the RoomAir model) but it is difficult to get EnergyPlus to compute those air movements for you. AirflowNetwork implements a pressure network that computes bulk airflows given proper inputs, but those inputs would very difficult to obtain for this case and would require either measurement or more detailed simulation. ZoneMixing allows the specifications of the flow, but I'm not sure where you would get that information without either measurement or more detailed simulation (unless you are less concerned about the details).
If you just want to make sure that the air in the theater is pretty well mixed, then ZoneMixing will do that for you (but you'll need to figure out the flow rates). For more details detailed results than that would allow, you'll need a more detailed tool than EnergyPlus.
UPDATE
If you have done the CFD, then you should be able to post-process those results to get the total flows across the surfaces and some estimate of the pressures involved. This can be used to develop an AirflowNetwork that will approximate the movement of air for the conditions in your CFD simulation. If it works and produces the same flow pattern that the CFD does then that is reasonable and would allow for some variation of the conditions and still produce acceptable results. However, that's going to be a lot more work than than using ZoneMixing and/or ZoneCrossMixing and probably not really all that much better. For those all that's needed will be the flows from the CFD. Setting the flows from thermal comfort requirements is not a good idea, so I advise strongly against that. Use the flows from the CFD, otherwise you're just creating a set of well-mixed zones that could be treated as one zone.
As to whether this is all reasonable or a good strategy or not, that depends on how comfortable you are with the limitations. For larger volumes, gradients are just important and there's not much that can be done about it. If you can get results that make sense, then it is a defensible strategy as long as it is acceptable that you are mimicking the internal flow patterns instead of predicting them.
