[Bldg-sim] Links between CFD or MZ and thermal simulations for simulating air and temperature distributions in atria

Paul Carey paul at zed-uk.com
Fri May 29 07:49:12 PDT 2009


Hi Frederik,

 

DesignBuilder CFD would allow you to come up with an EnergyPlus multizone
air flow linked thermal simulation coupled with a steady state CFD solution.
This has recently been released and is a cost-effective way of linking the
2.  If you used DesignBuilder to develop the energy model/Steady State CFD
solution carried out and then use their model export options to give you the
model upon which to then import it into a more complex transient CFD tool
should it be necessary.  To some extent you could argue whether or not you
need the transient analysis as the dynamic simulations should give you the
temporal solution for the airflow and then you could look at what happens
for say peak or mean flow conditions perhaps.  But I’d suggest that it might
well be worth it from what you are describing as even a well set up thermal
multizone model would do most of what you describe, but the thermal
stratification issues are going to be a sticking point for most simulation
tools, both Dynamic or CFD to some extent.

 

If you really wanted to see the time effects of the Solar Gain on airflows,
etc, there are many CFD tools available that would be able to do this,
obviously all the major CFD engines would do this comfortably (Airpak from
Ansys Fluent most easily I suspect with its integrated solar gain modelling
tool) but they are going to be quite expensive and there is quite a learning
curve to some of them.

 

Alternatively, you could use something like PyroSim, which is a good front
end for NIST that would probably be suitable.  NIST does transient analysis
and is used commonly for smoke/fire analysis.  It uses LES turbulence models
from memory and so would be likely to be more accurate for the sort of
stratified flows you’d get in an Atria as well.  You could then set
transient boundaries based on files of data exported by the dynamic engine.
Might take a bit of work, but it should work.

 

Regards

Paul

 

 




Dr Paul Carey

 

Director

Low Carbon Energy Assessor

 

Zero Energy Design Ltd

10A Portland Place

2-22 Mottram Road

Stalybridge

SK15 3AD

 


T:  0161 3386200

F:  0161 3031281

M: 0789 4098012

E:  paul at zed-uk.com

W:  www.zed-uk.com

 


 



 

 

 

 

 

 

 


 



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From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Frederik
Vildbrad Winther (FRW)
Sent: 29 May 2009 13:17
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Links between CFD or MZ and thermal simulations for
simulating air and temperature distributions in atria

 

Hi, 

I am currently starting up on simulating a relatively large atrium in
Denmark (app. 55°N) with a glazed roof (sloped towards the sun - clever),
open balconies with working areas connected to the atrium, as well as a
smaller atrium with smaller openings connecting the two atria together with
each other. The main focus in the simulation is first of all the air
velocity and temperature distribution in the occupied zone and on the
balconies - describing the thermal comfort as well as draft rate. The next
focus is on integrating the smaller atria as a heat exchanger in winter time
as well as analyzing if this can be used for cooling in summer time,
transporting the air from outside to the biggest atrium, via the smaller
atrium with little heating of the air. The calculations I want to perform in
CFD also regards simulations of the solar gain in the biggest atrium.
However simulating radiation in CFD simulations require more computing power
for bigger rooms with a lot of surfaces. Any advice on simulating solar gain
in CFD? How can this dynamic gain be simulated in CFD? Another cool thing in
this atrium would be the heat recovery of the extracted air in the top part
of the atrium.

Simulating this in a thermal simulation software requires a lot of luck to
obtain the correct (and true) result in the first couple of simulations.
However I am thinking of integrating the results from a CFD calculation into
the thermal simulation. I am thinking of doing this as an iterative process,
integrating the results from CFD when needed in the thermal simulations.
This will probably result in at least 4 different simulations over a whole
year, giving detailed results (temperature gradient, flow between zones,
convective heat-transfer coefficients etc.) which can be used in the thermal
simulation for these 4 periods over a year. As mentioned above simulating
radiation in CFD is tough, I am thinking of leaving this calculation in the
thermal simulation.

Another simpler setup would be the integration of a multi-zone calculation
in the thermal simulation giving a more coarse result of the main flow route
in the atrium and mixing between balconies and the atrium. However these
results could potentially give the same detailed results I am looking for.

Finally has any one worked on an uncertainty analysis of these coupling
methods illustrating first of all the uncertainty in the results as well as
the sensitivity in the input parameters?

Has anyone done something like this before and what tools were used? I have
been given free hands with regards to choice of software so any feedback on
this subject will be useful. I'm really looking forward to hear from you :-)

Kind regards 

 

Frederik Vildbrad Winther (FRW)
M.Sc., Indoor Environments 
Indoor Climate and HVAC 

Rambøll Danmark A/S 
Teknikerbyen 31 
DK-2830 Virum 
 <http://www.ramboll.dk> http://www.ramboll.dk

Direct 4598 6254
 <mailto:frw at ramboll.dk> mailto:frw at ramboll.dk 
__________________________________________________ 
Knowledge taking people further--- 

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