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[EnergyPlus_Support] Re: Thermal Chimney modelling method
Hi Pedro,
Thanks a lot for your help. do you think the airflow network object is better or not as good as using Thermalchimney object?
Another thing, below is the comment of a university professor:
"in the case of solar chimney, air flow increases with solar radiation and temperature of the plate in the chimney. In such case, air flow velocities increase to maximum value at noon and decreases again in the afternoon. This means that forced ventilation is proportional to room temperature which increases to maximum at noon. For that, I strongly believe that there is some difference between the chimney we are using and that used by the simulation software"
I believe the guy is mistaking between the fact that the airflow is proportional to chinmney temperature and proportional to the temperature difference between chimney and outside... What do you think?
Thanks again!
Aymeric
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Pedro Peixeiro <pedro_peixeiro@...> wrote:
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> Hello.
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> My experience, I modelled a DSF using an independent zone for the
> middle cavity. It is important to model the natural ventilation using
> the AirFlow network objects to take advantage of a better simulation of
> the effects of pressure difference between inlet/outlet due to wind
> effect and temperature rise. Even so, it is very hard to simulate
> natural ventilation in these types of building elements, specially the air flow. My results
> were not entirely accurate, and I am still to do some more trials on
> E+.
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> One thing you can do to improve your results is 1. create independent zones for the inlet and outlet of the chimney so to introduce the right pressure coefficients of each one of these (experimentaly observed); 2. change the wind
> pressure coefficients of the outdoor surface side of the chimney so to aproximate your air flow results to the experimental
> data, and thus obtain a better funcionality. Unfortunately, #2 might be a
> bit laborous trial and error attempt. As far as the temperature gradient is concerned, you can divide your chimney into several vertical zones, or use the Room Air Models to try to find a good aproximation (note that the larger the gap depth and width is, the less accurate will be the air flow transition between vertical zones).
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> Pedro.
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> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> From: aymericnovel@...
> Date: Tue, 16 Mar 2010 10:26:57 +0000
> Subject: [EnergyPlus_Support] Thermal Chimney modelling method
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> Dear all,
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> I am struggeling to know whether or not I did simulate properly a solar chimney. It is in Jerusalem climate.
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> I first modelled a zone adjacent to the office I want to cool down. I positionned a low opening on the partition wall separating the two zones. This wall is of course composed by a structural part, here concrete, 2.5cm polyurethan board insulation and a black selective metal plate. The outer wall of the chimney is a glazed wall with an upper opening.
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> Although it seems to work logically, it doesn't match experimental results. Basically it seems it doesn't enhance enough the natural ventilation...
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> Using this method, I certainly don't take into account the temperature gradient within the thermal chimney, right? Is it more reliable to use the object Zone:ThermalChimney?
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> Plus, an additional problem I can't explain is that I get some massflow through ceilings although I do not activate infiltration calculations...
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> If anyone has experience modelling thermal chimney, I would be happy to know more about that!
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> Thanks a million
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> Aymeric
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> _________________________________________________________________
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