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CFD analisys of a glazed atrium

 
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matrix



Posts: 13
PostPosted: Tue Oct 18, 2011 7:19 am    Post subject: CFD analisys of a glazed atrium Reply with quote
Hi,
I have some questions about a CFD internal simulation concerning a glazed atrium without mechanical/natural ventilation (neither open windows nor supply diffusor).
First I made an E+ simulation of the atrium during a tipical summer week. Then I imported the resulting temperatures of the walls and windows as CFD boundary conditions. In the hottest hour, the walls/windows temperatures are about 55 °C while the floor one is about 73 °C. Is it possible that the floor has such a high temperature in comparasion with walls/windows temperature?
Then I started the CFD simulation, that converged in about 5000 iterations.
During the postprocessing, I saw that the temperature contours had smaller values of temperature in proximity of the boundaries, in contrast to the imported ones (30-40 °C instead of 55 °C). The floor temperature is even smaller than the windows/walls ones, while the imported boundary floor temperature was higher.
How is it possible? Is it possible that this is due to a heat transfer to the outside? The imported boundary temperature shouldn't already have to take into account external conditions?
Thanks
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Steve Potter



Posts: 614
Location: newcastle
PostPosted: Fri Oct 21, 2011 9:06 am    Post subject: Reply with quote
Hi,

Quote:
Is it possible that the floor has such a high temperature in comparasion with walls/windows temperature?


Yes, this is possible. If you have opted for the Full Exterior option for Solar Distribution, EnergyPlus assumes that all beam solar radiation is received by the floor and so in an atrium, the calculated floor temperature could be significantly higher than the wall temperatures.

Quote:
I saw that the temperature contours had smaller values of temperature in proximity of the boundaries, in contrast to the imported ones (30-40 °C instead of 55 °C).


Bear in mind that the imported temperatures are the temperatures of the room surfaces and not the temperatures of the adjacent air. The principal mechanism of heat transfer in the layer adjacent to a wall can be conduction and because air is a poor conductor, the temperature drop across this layer can be very significant.

Quote:
The floor temperature is even smaller than the windows/walls ones, while the imported boundary floor temperature was higher.


The rate of heat transfer from upward facing horizontal room surfaces is normally significantly less than that from vertical surfaces.

Hope this is of help.

Regards,

Steve
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