Hi,

I was looking for recommendations for CFD tools to model airflow within and around buildings for purposes of ventilation design. It would be great if anyone could suggest the most appropriate tools for this and which of the two, Fluent and Flovent are more suitable.

Thanks, Shweta

A good way to judge what is a good CFD tool for the building and general environment is to find out which tool(s) are used by the premier civil engineering players. These outfits employ civil engineers to make the good, the bad and the ugly works churned out by architects stay up once built.

Also ask architects which "easy to use, low functionality, toys" they play with and then avoid those tools like the plague. Why, because to heat and ventilate a building properly requires a balance of heat and mass transfer, including buoyancy and radiation modelling. Cheap toys will not handle this lot properly.

So to your short list kindly add Star-CD from CD-adapco. CFX is another tool you could consider, but being cheaper than Fluent it is highly unlikely that the Ansys Empire will ever sell a cheap tool before an expensive, non discountable, lump like Fluent.

Regards

PS Will someone out there kildly send my congratulations to Fluent for employing Denis Feindt out of CD Nuremberg. Fluent has picked up a good one there.

"Also ask architects which "easy to use, low functionality, toys" they play with and then avoid those tools like the plague. Why, because to heat and ventilate a building properly requires a balance of heat and mass transfer, including buoyancy and radiation modelling. Cheap toys will not handle this lot properly."

Do you honestly think that this is true? You think that Flovent doesn't have radiation modelling? It does, it also has a solar loading capability to impose heat sources on sun apparent surfaces based on location, time of year and cloudiness. Funnily enough it also handles buoyancy, either using the Boussinesq assumption or via ideal gas. And you seem to be saying that it also does not obey conservation. Of course it does, rigidly.

Shweta, I would advise asking for references of existing customers from both vendors. If you have time take a trial of both (you can rely on their demo ability if you like but all you will get a feel of is how good the software can be made to work, not how well you will perform as you learn to use it).

In terms of Fluent vs. Flovent I know that Flovent does not handle radiation exchange to smoke laden air, it just does surface to surface exchange. Due to the lack of general purpose functionality though it is often said to be a more productive tool for doing routine HVAC simulations.

I would also advise you to be aware that there are many cfd experts who have built careers out of cfd expertise and look upon any tool that erodes the need for their expertise with scepticism... Be careful of their responses.

In my response I mentioned Star-CD, CFX and Fluent. I did not say anything regrading Flovent. This has not stopped you getting on your soap box and sounding off.

Nice to see the thought Police are up early. I do not work for any of the CFD vendors, but is the same true of you?

I know of one architect in the UK who was given his money back on a CFD code because in his first support case it was clear that he no understanding of Bernoulli's equation. Why does the flow pressure and velocity change when the wind goes round the corner of a building, oh dear.

I am aware that in some countries such as Germany, architects have an understanding of structural engineering. Not the same everywhere else.

Whenever I think of UK architecture I automatically think of "their finest hour," namely the Tricorn in Portsmouth.

Its necessary for architects everywhere as far as I know, to have a basic understanding of structural engineering. They have to have some basis for assuming their designs won't fall over. However, I suspect very few if any have much understanding of CFD or heat transfer. There are specialty firms of engineers that do this for both the interior and exteriors of buildings. These are the people that architects go to when they have need of these kinds of analyses. You should be looking to see what those people use for CFD codes and I expect you will probably find 1 of everything if you look hard enough.

a possible one: http://www.optiflow.fr/

I think a key feature ifor design is solar radiation. The Flow field itself around building does not influence much the design as the wind can come any direction. Heat transfer is important to know where to put the radiators.

Smoke dispersion also may be

What do you think?

Have a look at the web portals of the International Energy Agency and the DOE (Dept. of Energy), they have evaluated and tested many available codes.

Sorry are you saying that the flow field around a building doesn't matter? So I guess we can all make our buildings out of cardboard then as the wind loading clearly won't have any effect.....

I will huff and I will puff and I will blow your house down!

It does not influence the shape of the building as the wind direction is arbitrary.

of course it influences the shape of the building, maybe not directly, but the effect of the flow around the building must be considered. Pedestrian comfort, pollutant dispersal and how the building's shape affects buildings surrounding it are key considerations

TG,

Enough of the jokes. We can all find example of bad architecture everywhere. I guess what was known as the "piggories" in Liverpool has finally been torn down, but that was a social failure more than anything else.

My position on architects comes from my days at University when I shared a house with various others including a pair of architects. A total of six weeks tuition over four years was allocated to structural engineering. This may have changed, I left the UK permanently some years ago.

A more serious point that Shweta should consider is the link(s) if any between CFD codes designed for architects to use and the higher functionality codes on the market. There is a code from IES, which I believe can be linked to Star-CD so that these codes can swap modelling data. This means that if an architect needs a higher functionality code then the work they have done to date can be easily transferred. The architect would not have to start again from scratch.

I am also believe that Flowmerics approached CD-adapco for access to their advanced technology, but there was nothing in the deal for CD-adapco so this did not go ahead.

If you want to find engineers instead of architects who use software for climate control then look at the automotive, aerospace and train key players. These players also include include detailed a model for a human integrated into the solution.

Regards

PS Engineers don't always get it right. Look up Reading University library.

Read this report: http://epb1.lbl.gov/Publications/lbnl-42182.pdf

A wrote: "Read this report: http://epb1.lbl.gov/Publications/lbnl-42182.pdf" _____________________________________________

The report is about multizone modelling, a kind of sub-CFD that is exactly the reason that many building services companies are turning to CFD.

Legislation is forcing building designers to demonstrate that their buildings are sustainable (energy efficient). In the (so called) developed world buildings account for 40% of energy usage, but are only renewed at about 1% per year.

In order to have any impact on future energy usage, new buildings have to be extremely energy efficient. Multizone tools (and simple CFD tools) are good enough when you can design conservatively (wasting as much energy as you like in keeping an occupied environment cool enough / warm enough) but not when you are trying to shave every Watt off the energy bill. Multizone models such as COMIS are paticularly poor in tackling displacement ventilation systems, which are currently very fasionable in sustainable design.

To do bulding services simulation modelling properly you need to have a decent meshing engine (that doesn't approximate every building to a series of hexahedral blocks), a solver that can handle buoyancy (not just using the Boussinesq assumption), and good models for long and short wave radiation (ignore anyone who tells you that you don't need radiation modelling for thermal comfort). Customised thermal comfort post-procesing is also useful.

The big boys, such as Arup and Atkins, have been doing this for years, but they all use "big codes".

S.

Peter You do not buy a Jaguar then drive it to the super market and fill it with potatoes and other stuff, you can do that with a Honda or Toyota etc..... There are a lot of engineering applications requiring CFD analyses, but you do not need a highly priced complicated first tier programme such Fluent, Star-CD etc.. In the case of Buildings, the question to ask is what medium is going to be analyzed most of the time (Air) and what speeds might be involved (Subsonic flows) Then a good incompressible solver can do the job perfectly, airpak, etc..... are cheaper,easier to learn, and give results that most engineers can understand. Is there a need for a solver optimised for high speed moving mesh flows?

[Faraday]

The UrbaWind software is a less expensive software that gives good understanding of the wind flow in built environment. Although wind direction is arbitrary, yearly statistics can be done and UrbaWind integrates the local climatology.
The weak point for architects is that heat transfer is not calculated. But still good estimation of pedestrian comfort and wind pressure on facades for natural ventilation can be done quickly.

Best,
Faraday