CAD systems offer a mixed bag of tricks for building designers

Computer-aided design (CAD) tools for buildings are now fundamental aspects of the construction process. So accurate has the technology become, that developers, architects and consultants can now call on a range of relevant software which can reveal a building's impact on shadow and daylight, wind flow and energy use. Solar radiation programmes are even available for those with an eye for more efficient building design.

This has undoubtedly made the design process more effective, with architects and designers able to understand the minutiae of building orientation, wind strength and so forth before any major commitment is made. This allows, therefore, for alterations to concepts and improved energy efficiency, which could prove costly further down the line.

"Tools are now powerful enough that as we look to alter our design conceptually in a very iterative way, we can change these models and have a true feedback loop between the changes in design form and how that would impact overall energy consumption," says Roger Frechette, director of building services, Skidmore, Owings & Merrill (SOM).

Frechette highlights a number of core design tools that have been developed recently, which lend themselves to this area of construction. Ecotect is a complete building design and environmental analysis tool which covers the broad range of simulation and analysis functions required to understand how a building design will operate and form. This was used on SOM's Pearl Tower - which is being built in the Guangzhou province of China - to look at the impact of solar radiation and where best to install PV panels.

Equest also allows users to perform analysis of a building's energy use. Computational Flow Dynamics (CFD) is a well-known tool in today's market and Virtual Environment assists designers in establishing a building's impact on shadow and daylight. "This enables us to precisely predict the amount of energy consumed by the building," he adds. Such tools have assisted SOM in ensuring that the 300m Pearl Tower optimises air flow for wind generation. Using CFD, a combination of sharp edges and a rounded top has aided the pressure differentials between the front and back of the building. "Form needs to aid and contribute to the building," says Frechette. Through this studied analysis, SOM has managed to convert wind velocity - which approached the building at 3m/s - to 9m/s through openings in the building. "Because of the doubling of wind velocity in the opening, this forms an increase of 800% in power potential," adds Frechette.

But while there are undeniably advantages in establishing these parameters on a computer, the accessibility and apparent competency of such programmes has caused concerns among some within the construction industry. Specifically, it has raised further questions regarding the value and worth of such measurements. Despite significant advances in technology, this should not mean proper, physical testing should be overlooked. Doing so could result in buildings whose structures will not meet required levels of structural strength, especially with regard to meteorological conditions specific to the region.

According to Paul Freathy, managing director of wind consultant RWDI, caution should be shown when using software such as CFD, especially when measuring wind loads on buildings in the Middle East. He cites the ease of use and apparent sophistication of CFD as setting a dangerous precedent - as people assume the figures for wind loads are more accurate than they actually are. "I think it has the potential to become an issue," he said. "What we are finding in the Middle East, is that CFD is being used by some outfits to look at wind environments. It has a place, but the problem with CFD is that the graphics are so brilliant that there is a danger people will believe everything they are looking at."

Despite possessing some benefits for smaller scale analysis, Freathy says that such technology has no place when it comes to testing wind speed or behaviour, and will not be suitable for at least a decade. "My word of warning is that the technology has not developed as far as some people would claim and the accuracy of the numbers, even at this stage is suspect. It isn't far off being used for environmental issues, such as micro climate, but my guess is that it will be a good 10 years before it is useful for structural design."