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Re: [EnergyPlus_Support] Re: Thermal Chimney modelling method



 Dear Aymeric,

 Based on my experience, the natural venilation caused by the thermal
chimney does not always peak at noon. I observed many cases peaking in
the afternoon (1 ~ 3pm) when the solar radiation ramps up.

 In "forced ventilation is proportional to room temperature", the room
temperature means the thermal chimney zone temp, not the office space,
right?

 Regards,

 Kwang


> 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:
>>
>>
>>
>> Hello.
>>
>>
>>
>> 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+.
>>
>>
>>
>> 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).
>>
>> Pedro.
>>
>> 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,
>>
>>
>>
>> I am struggeling to know whether or not I did simulate properly a solar
>> chimney. It is in Jerusalem climate.
>>
>> 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.
>>
>>
>>
>> Although it seems to work logically, it doesn't match experimental
>> results. Basically it seems it doesn't enhance enough the natural
>> ventilation...
>>
>>
>>
>> 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?
>>
>>
>>
>> Plus, an additional problem I can't explain is that I get some massflow
>> through ceilings although I do not activate infiltration calculations...
>>
>>
>>
>> If anyone has experience modelling thermal chimney, I would be happy to
>> know more about that!
>>
>>
>>
>> Thanks a million
>>
>> Aymeric
>>
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>> _________________________________________________________________
>> Hotmail: Trusted email with Microsoft's powerful SPAM protection.
>> http://clk.atdmt.com/GBL/go/210850552/direct/01/
>>
>
>
>




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