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

Ding Li dingli at ucla.edu
Thu Jun 4 08:57:26 PDT 2009


Good luck on your work. 

Ding




________________________________
From: Frederik Vildbrad Winther (FRW) <FRW at ramboll.dk>
To: Ding Li <dingli at ucla.edu>; bldg-sim at lists.onebuilding.org
Sent: Wednesday, June 3, 2009 11:57:08 PM
Subject: RE: [Bldg-sim] Links between CFD or MZ and thermal simulations for simulating air and temperature distributions in atria


Hi Ding,
 
I need to do a dynamic simulation, because the client wants to know how many hours during the year, his demands regarding indoor climate are met. However I won't do CFD calculations for a whole year, because of the computing time. It's simply not possible. This is why I need a dynamic simulation tool which can simulate varying temperature stratefication and different loads. Your advice on using E+ is therefore taken ito concideration as well as TRNSYS.
 
Both programs offer som output which can be imported into the CFD calculations in order to glance at the draft rate in the occupied zone. For the CFD calculations I will use your advice on using "Indoor zero equation" and see how it works, as well as minimizing the amount of objects in the model so that I can use the radiation module.
 
Thanks for your help and advice. Hope it works. :-)
 
 



________________________________
From: Ding Li [mailto:dingli at ucla.edu] 
Sent: 3. juni 2009 17:51
To: Frederik Vildbrad Winther (FRW); bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Links between CFD or MZ and thermal simulations for simulating air and temperature distributions in atria


Frederik,

You are thinking too much. IMO, you don't need to do dynamic simulation. You only need the worst case. If you want to do CFD simulation for a year, it's almost impossible.. It takes forever for the calculation to finish. The industry don't even calculate a year load to size the equipement, why do you need to? Unless you want to do energy analysis for the building for the whole year, you are not supposed to do that. 

If you want to do energy modeling for the building for a year and you want to include stratification effect, I know E+ and Trace have DV feature. Actually Trace just released this feature about a month ago since it produced unexpected result. You may try these two products.

As for the stratification, it's not very sensitive to your input. If you create the model correctly and the computation converges, the stratification is quite stable. 

About the radiation, you need to choose the appropriate model. The calculation time can be much longer if you have many objects in the model. It's easy to take several days for one CFD model to finish from my experience. 


Ding Li, PhD, P.E.
Capital Engineering Consultants Inc.
11020 Sun Center Drive, Suite 100
Rancho Cordova, CA  95670




________________________________
From: Frederik Vildbrad Winther (FRW) <FRW at ramboll.dk>
To: Ding Li <dingli at ucla.edu>; bldg-sim at lists.onebuilding.org
Sent: Tuesday, June 2, 2009 11:57:37 PM
Subject: RE: [Bldg-sim] Links between CFD or MZ and thermal simulations for simulating air and temperature distributions in atria


Hi Ding,
 
With regards to importing the boundary conditions from the dynamic (thermal) simulation, how do you take building mass into account. Some of the external conditions i absorbed by the floors and walls.. Can you get the CFD calculations to take this factor into account when using CFD? I haven't heard of this before. 
 
Also the CFD results are only a predicted airflow and are extremely sensitive to input parameters, and the flow is more or less steady state. Therefore the CFD can only be used to illustrate what could possibly happen, and to get an idea of the stratefication.. However as you mention with regards to stratefication, I need a dynamic simulation which can calculate stratefication relatively simple so that the stratefication would vary over time. E+ sounds like a possibility, but if it only can calculate stratefication when using displacement ventilation, then it becomes less attractive to use. Do you know of any other software which can calculate stratefication? The Danish program BSim has a fixed parameter for stratification so this program can not be used for calculation over a whole year unless the calculation is divided up into smaller parts, and the stratefication is changed manually, based on CFD calculations.
 
I agree with you that it is important to include radiation! However it takes longer to obtain convergance with this module "on". How do you manage to calculate large rooms with many surfaces, and still including radiation? Clustering of (many) computers?
 
 



________________________________
From: Ding Li [mailto:dingli at ucla.edu] 
Sent: 3. juni 2009 02:41
To: Frederik Vildbrad Winther (FRW); Paul Carey; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Links between CFD or MZ and thermal simulations for simulating air and temperature distributions in atria


I put my comments in blue below.


Ding Li, PhD, PE

Capital Engineering Consultants Inc.
11020 Sun Center Drive, Suite 100
Rancho Cordova, CA  95670
Tel:  916-851-3579
Fax: 916-631-4424




________________________________
From: Frederik Vildbrad Winther (FRW) <FRW at ramboll.dk>
To: Paul Carey <paul at zed-uk.com>; bldg-sim at lists.onebuilding.org
Sent: Tuesday, June 2, 2009 6:35:38 AM
Subject: Re: [Bldg-sim] Links between CFD or MZ and thermal simulations for simulating air and temperature distributions in atria


Hi Paul,
 
Thanks for your reply. I haven't heard about DesignBuilder CFD before and I have only heard and peaked to EnergyPlus. EnergyPlus seems OK for simulating multizones and thermal simulations. Do you know how it handles stratification? I am thinking of using thermal simulations, with a good link to a multizone program so that the 2 programs can predict the air movement as well as the stratification in the room. I am then thinking of doing 4 CFD studies and these simulations should have input from the thermal simulation. The output from the CFD simulations should then be compared to the results from the thermal simulation. The two calculations should therefor be reasonably comparable (in the end).
 
DesignBuilder just released v2. I'm not quite familiar with its CFD module, but I believe DB was mainly used with E+. If you want to achieve stratification, you have to use some CFD package. E+ has a DV module which may have stratification feature, but that's only for DV. 
 
I think that the use LES turbulence model for indoor climate analysis is rather hazardous because this turbulence model is mostly used for fire and smoke simulations. I have obtained good results for indoor climate using ke-turbulence model. Is my thought "out of date" on this point? Does ke-turbulence model also work for larger rooms? When can/should LES-turbulence model be used, apart from smoke/fire simulations? The problem is also getting a thermal simulation program, which can import the results from a CFD calculation. 
 
Using the transient calculations could prove very useful in showing the uncertainty in the CFD calculations. However, can I, when importing the boundary conditions from the thermal simulation to the CFD simulation, import the temperature stratefication as a start condition for the simulation? What is your experience on coupling thermal/multizone simulations with CFD calculations? Does it work? It could be very useful if the CFD calculation starts with the same boundary conditions and results from the thermal simulation, rather than starting from scratch every time a CFD analysis has to be performed.
 
I'm not sure the exact meaning of your "thermal simulation". If you refer to the mechanical load calculation software, eg. Trane trace or other heating/cooling software, the answer is yes. You can calculate the heat flux at the exterior wall/roof/floor and then import them into your CFD model. But you need to verify the CFD result carefully since the setpoint may be different from the result of your CFD modeling. This could cause some inaccurate result.
 
Do you know of any papers dealing with modeling of solar gain in CFD tools?

 

 



________________________________
From: Paul Carey [mailto:paul at zed-uk.com] 
Sent: 29. maj 2009 16:49
To: Frederik Vildbrad Winther (FRW); bldg-sim at lists.onebuilding..org
Subject: RE: [Bldg-sim] Links between CFD or MZ and thermal simulations for simulating air and temperature distributions in atria


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
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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

Direct 4598 6254
mailto:frw at ramboll.dk
__________________________________________________ 
Knowledge taking people further---
Med venlig hilsen
Frederik V. Winther
 
Civilingeniør, Indeklima og Energi
Ingeniør
Indeklima og Miljø
 
D +45 4598 6254
frw at ramboll.dk
________________________________________
 
Rambøll
Teknikerbyen 31
DK-2830 Virum
www.ramboll.dk


Med venlig hilsen
Frederik V. Winther
 
Civilingeniør, Indeklima og Energi
Ingeniør
Indeklima og Miljø
 
D +45 4598 6254
frw at ramboll..dk
________________________________________
 
Rambøll
Teknikerbyen 31
DK-2830 Virum
www.ramboll.dk


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/

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


      
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