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RE: [EnergyPlus_Support] Atria. One more thing
David,
There are basically two possible approaches when modelling tall spaces such
as atria using EnergyPlus/AIRNET (or any other simulation program coupled
with multi-zone airflow simulators):
1. Model the atrium as a single tall space or,
2. Model the atrium as a series of horizontal slices with air flow
connections between them.
Option 1, where the atrium is modelled as a single space is the best option
when using EnergyPlus/AIRNET because:
a) AIRNET openings are assumed to be LVO (Large Vertical Openings) and for
openings that are horizontal or near horizontal (LHO) no claims for accuracy
are made. If you had detailed information on the flow characteristics
through such fictitious openings (for example through CFD analysis or
measurements in a physical model) then it may be possible to calculate flow
coefficients and exponents to give approximate airflows and hence
temperature gradient through the space. As far as I know there is no
generally applicable data available on this. In any case this approach
would not model any strong downward airflow paths.
b) There is no reliable way to get solar radiation pass through multiple
horizontal slices in the general case.
c) EnergyPlus allows you to set up a dynamically varying temperature
gradients to improve the accuracy of simulations in tall spaces. This can be
accessed in DesignBuilder using the Temperature distribution data on the
HVAC tab. Be warned though that, in current versions, the EnergyPlus
temperature distribution model is not applied to airflow which occurs in the
AIRNET simulation so it is not possible for example to include the effect of
relatively warmer air being extracted from a vent at the top of an atrium.
In the simulation air would be extracted at the mean temperature. For more
information on air temperature distribution in DesignBuilder/EnergyPlus see:
www.designbuilder.co.uk/programhelp/index.htm#air_distribution.htm
So at the moment we have to live with some inaccuracy in EnergyPlus models
due to temperature gradients in tall spaces. Otherwise there is no problem.
DesignBuilder will soon include a CFD module which will calculate spatially
distributed temperatures within zones as a 'snapshot' but we have some way
away from dynamic CFD simulations!
In summary, there are inaccuracies involved with large horizontal openings
in AIRNET simulations (a and b above), but these may not be 'show stoppers',
especially if the openings are small. I would recommend trying it to see if
hourly temperature results in the various zones look believable.
Considering all the other inaccuracies involved in building energy
simulations you may find that the approximation involved with using
algorithms intended for LVO to model LHO may not cause serious problems.
I hope this helps,
Andy Tindale
DesignBuilder Software
-----Original Message-----
From: EnergyPlus_Support@xxxxxxxxxxxxxxx
[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]On Behalf Of David Barrera
Sent: lundi 22 janvier 2007 19:12
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: RE: [EnergyPlus_Support] Atria. One more thing
Thank you Mahabir. Just one more thing. The
restriction of AirflowNetwork model about
stratification is :
" For example, you should not try to divide a high
space, such as an atrium, into subzones separated by
artificial horizontal surfaces that have cracks or
openings with the expectation that AirflowNetwork will
give you a realistic temperature in each subzone
and/or a realistic air flow between subzones".
This is very clear. It means that it is NOT possible
to know the air temperature distribution along THE
ATRIUM SPACE, but what happen with the adyacent
zones,rooms around tha atrium in each floor of the
building. For example, if a take the Solar Chimney
example file of DBuilder, and make holes in ceilings
of ground and second floors, which defines kind of
atria, and run the simulation, should I expect
realistic results?
Thanks a lot.
-- Mahabir Bhandari <bhandari@xxxxxxxxxxxxxxxx> wrote:
> David,
>
> Yes, the atrium example in DesignBuilder is solving
> the parameters you
> mentioned for the whole building using E+ simulation
> engine. In fact it is a
> very good example of natural ventilation
> calculation, one of the powerful
> features of DesignBuilder, using Airflow Network
> model.
>
>
>
> BTW, DesignBuilder forum is not necessarily for the
> users with licensed
> version of the program.. Any registered (registered
> on the website) user can
> use this forum.
>
>
>
> Regards,
>
>
>
> Mahabir
>
> ____________________________________________________
>
> Mahabir Bhandari, Ph.D.
>
> LEEDR Accredited Professional
>
> DesignBuilder Software
>
> 18 Tanglewood Rd.
>
> Amherst, MA 01002
>
>
>
> Tel: (413) 256-4647
>
> Fax: (413) 256-4823
>
> cell: (413) 575-6825
>
> email: bhandari
> <BLOCKED::mailto:c@xxxxxxxxxxxxxxxxxxxxxxxxx>
> @designbuildersoftware.com
>
> web: <BLOCKED::http://www.fenestration.com/>
> http://www.designbuildersoftware.com
>
>
>
>
>
>
>
> _____
>
> From: David Barrera
> [mailto:davidabraham_b@xxxxxxxxx]
> Sent: Friday, January 19, 2007 2:32 PM
> To: Grupo EPlus
> Subject: [EnergyPlus_Support] Atria in E+ and
> DesignBuilder
>
>
>
> I hope there's someone who works with DesignBuilder
> so
> I can have an answer to my question. As you know,
> DBuilder adds E+ to run simulations of the areas
> graphically described with the interface of the
> program. In the example files, there's one of an
> atrium in a building. The question is: Is it solving
> for the parameters (temperature, humidity, etc) of
> the
> whole building? Actually I think so, because there's
> a
> unique group of graphics, I mean that clicking on
> the
> diferent zones of the building in the results
> analysis
> tab the graphics don't change.
> I hope someone can help me. The forum of DBuilder
> could be an option but it is only for those who have
> a
> licensed version of the program; I hope one of you
> has, because not me.
> Thanks a lot.
>
>
__________________________________________________________
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> Browse Top Cars by "Green Rating" at Yahoo! Autos'
> Green Center.
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>
>
>
>
> [Non-text portions of this message have been
> removed]
>
>
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