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What software can integrally simulate CFD and energy?

asked 2018-01-13 08:51:52 -0500

Aryan Shahabian gravatar image

updated 2018-01-13 11:10:58 -0500

Dealing with energy calculations for high-rise buildings, I am looking for a computer program which takes into account the effect of wind on external surfaces temperature and therefore on the annual energy calculation. I would be grateful if you could let me know about (preferably free-) tools for such tasks.

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answered 2018-01-13 09:31:56 -0500

bbrannon4 gravatar image

Your text slightly disagrees with the title question, so I’ll try to answer both. Reagarding accounting for wind on external surfaces (via convective heat transfer) is taken into account by all major energy modeling software, such as EnergyPlus and IESVE, though there are different options I each to change the calculation methods used to do this. None of which are CFD because the assumption is that the wind matches the weather file and is uneffected by the surroundings. Of course this is an assumption but is often acceptable. Since you asked specifically about CFD integration - I’m it aware of any, and that would be a very long simulation. There are however ways to link different simulations. In the paid world, IESVE has the MicroFlo CFD module which can be used independently to understand internal or external airflow based on the same geometric model. To remain free and open source, you could do something similar with EnergyPlus and OpenFoam, though significantly more effort would be involved. Like I said though, I don’t think CFD is really needed for what you are after.

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@Aryan Shahabian I don't have any books or articles on hand, but in my experience this is usually a small percentage of the total thermal load, but is location dependent. When I've looked at it, the heat gain from conduction is pretty tiny in comparison to solar and internal gains. It would be a slightly higher percentage in winter in cold climates though. An easy sensitivity test might be to create two weather files, one with small (not 0) wind speeds, and the other with realistically large wind speeds to get reasonable bounds.

bbrannon4 gravatar image bbrannon4  ( 2018-01-13 19:32:15 -0500 )edit

And you're right, TMY files are poorly suited for detailed wind analysis. If it's proves to be important, it could be worth performing some external CFD work which could be used to alter the wind vectors of the TMY file to account for surrounding buildings and landscape. I'd suspect this is actually more important for external thermal comfort/natural ventilation purposes, and not so much for energy impact on buildings with typical HVAC systems.

bbrannon4 gravatar image bbrannon4  ( 2018-01-13 19:34:47 -0500 )edit

@bbrannon4 Thank you very much for your prompt and detailed reply. Do you have some rough estimation (or is there any book/article) about the effect of the surrounding buildings on the speed of wind and therefore on the temperature of facade and the annual heating/cooling energy demands of a tall building?

Aryan Shahabian gravatar image Aryan Shahabian  ( 2018-01-14 01:53:23 -0500 )edit

I mean is it marginal and negligible? i.e. Is it usually something in range of 1-2 percent or something like 5-10 percent roughly? If the effect is significant, one could argue that the weather data (usually from airports) are not a good source to rely on especially for energyplus simulations of highrise buildings within a pretty dense pattern of highrises. Please correct me if I'm wrong.

Aryan Shahabian gravatar image Aryan Shahabian  ( 2018-01-14 01:56:21 -0500 )edit

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Asked: 2018-01-13 08:51:52 -0500

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Last updated: Jan 13 '18