Why should this be the case? One would have thought that engineers at all levels would be eager to get to grips with the latest software packages that can predict the performance of various aspects of their buildings. The answer is confidence; or lack thereof. It would be unfair to lumber the built environment sector alone with the hang up of scepticism about new ideas, but this is one of its biggest problems. Before the industry will place its confidence in the images and data tables that software packages produce, potential users want to see that these programmes have worked, and have been working for a considerable length of time in the market before they trust that the solutions produced are reliable.
Computational fluid dynamics (cfd) is one such area where people have been unwilling to commit to it for various reasons. They have been unsure whether they can justify spending money on software they don't think they really need, or even don't fully understand. Cost of the software has also been a prohibitive factor in the past. Steve McCormick of Fluent UK says: "I think cost has kept cfd out of the market. People found it hard trying to justify spending money on it, especially when they were unsure how to get the best out of it."
Software developers are at the stage now where they can see that the old cynicisms surrounding software for cfd are beginning to fade: "I think a lot of the scepticism is dying away about cfd now," says McCormick. "People are becoming more open to it, although they are still not totally sure how to use it. The problems were that people didn't think they needed a tool like cfd, but now they realise that it can answer questions that no other software can."
User friendly
The focus for developers has been to build software that ordinary engineers can get to grips with in no time at all, as Alan Jones of Environmental Design System says: "Our objective is to get this software into the hands of more and more engineers." That sounds like a pretty obvious statement from a vendor, but it also means that the tool has to be as user friendly as possible if it is to be adopted by the majority of engineers and not just those specialising in fluids.
This is the route that new packages are taking. The purpose of software like EDSL's new Tas Ambiens 3D cfd and Fluent's Airpac, is to take as many of the difficult decisions involved in cfd modelling away from the engineer, leaving them to simply draw their space, set their boundary conditions and run the model. The most time consuming part of cfd modelling is the construction of the mesh, which is how the area being examined is divided into sub-volumes.
The holy grail for developers has been to come up with a package that takes the responsibility for generating the mesh away from the engineer and does it automatically. Both Fluent and EDSL claim to have achieved this.
McCormick says: "Solution turnover time is a big factor, and the new software allows users to build the geometry of the building very quickly and stops them from being weighed down by all the detail involved in building the mesh." Jones agrees that speed is a priority for reaching an accurate solution. "Your average engineer hasn't got the time to set up a hugely complex model. CFD is such a detailed piece of analytical software, that if you used it to answer a simple question like, "how hot is this atrium going to get?", it would be like attacking a cliff face with a toothpick."
Ease of use then, is crucial for the uptake of such packages, and this is where the new generation software has its biggest advantage over older tools. Most developers began with a general purpose package that could be used to model not only buildings, but spanned most of the industries that required air flow simulation. EDSL's product development director Ian Highton says: "Most packages you get are for the complete market. It's the same product whether you're in aerospace or buildings. The user then has to be technically competent enough to turn off the right areas and to make the right decisions about the way you should model the flows in one particular situation."
This raises the issue of accuracy once again, and the fact that successful use depends on the person driving the model. "With these generic packages," says Highton, "it comes down to how much faith you have in the individual using it. You can give two people the same package and the same problem, and just the way they mesh it will give you a different answer."
There is also a need for customers to be educated about what different software can do for them. The level of detail required to build a cfd model is far greater than that required to perform a building simulation. This is where developers need to show their clients the easiest way to find the answers they are looking for. Jones explains: "People come to us and ask us to do cfd simulations on naturally ventilated offices. We show them what our building simulation tool can do, and it's then that they realise that they've just caught onto this cfd label and that that's what they thought was meant by modelling. In fact, the building simulation software can do 90% of what they wanted even in the most complex of spaces."
Software developers and engineering consultants alike want to educate their clients. The building simulation sets parameters and boundary conditions such as surface temperature and wind direction. These then drive the cfd software. The point is that often there is no need to use cfd because it's too detailed and isn't necessary.
"If you take a meeting room as an example, and it is going to use chilled beams, we are confident that it's going to work, but you need to convince the client. That's where cfd comes in," says Jones. The facility that cfd packages provide, is that they can communicate effectively the principles and the operation of a space clearly to the non-technical person.
Accessibility of the results from these packages is an important part of their appeal. The engineer is only the first person who is going to need to be able to understand and evaluate what has been modelled. It then needs to be communicated clearly to clients and other project team members. McCormick says: "The images and results that the software produces have got to look good. It's not just engineers looking at them so they have got to be available in a number of formats for a wide range of eyes."
Highton agrees that if the client has asked a simple question, then it is essential to show them a simple representation of the answer. "If a client has an open plan office building with a central atrium and wants to know how hot it's going to get, you can show him a 2D slice. He can see that where the red bits are at the top of the atrium its hot and the blue bits are where his workers are going to be sitting and he's happy."
As well as acting as a good communication tool, the detailed analysis cfd can offer is what sets it apart. For situations where jet nozzles are being used for instance, the evaluation is quite complex, as Jones explains: "If jet nozzles were being used in an art gallery for example, you need to find out how far they will throw air out, how it will disperse, and how it will affect the micro climate around the exhibits and the people in the space. This is where cfd is not just a demonstration tool, but is also helping you develop the design. You can change the nozzle type, the velocity, and the flow rate."
Information supplied by manufacturers enables the user to set up the cfd simulation conditions specific to the product's characteristics. This can all be taken and put into the building to see how it interacts with the air.
It is this kind of detail that should enable users to have confidence in their results. The software now available is capable of helping them reach accurate solutions in as little time as possible, and adding value to the building for the client. These kind of advantages should be acceptable to everyone.
Source
Building Sustainable Design
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