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Size does matter

Phil Johnson (below) explains why ADCAS is once again highlighting the benefits of sticking to standard sizes for circular ductwork
Size does matter
CHOICE is a fine thing, within reason. Since the Latham Report, the UK construction industry has been tasked with avoiding unnecessary cost by using standard sizes for components wherever possible.

The standards - and a reasonable range of choice - exist. Committees of industry professionals throughout Europe have laboured long and hard to formulate optimum size ranges for virtually every building component - including ductwork.

A few years ago, ADCAS campaigned alongside other industry bodies including CIBSE, BSRIA, HEVAC and HVCA to rationalise the standard sizes of circular ductwork.

Now, with the publication of BS/EN 1506:2007, which incorporates those standards, the time is right to remind specifiers how they can avoid waste, excess cost and project delays by sticking to the comprehensive range of approved duct sizes that is available.

There are reports that some system designers are reverting to non-standard sizes such as 224mm and 280mm, which were declared non-standard back in 2001. The old 180mm and 224mm sizes are also still being requested for dust and fume removal systems.

All of these sizes - along with 600mm ducts - were supposed to be phased out, so the new ADCAS campaign will be targeted at winning hearts and minds by tactfully reminding the industry, of this fact and of the problems non-standard sizing can cause.

Those problems are potentially major ones, because ductwork impacts on so many aspects of the building services system.

Ductwork systems are not supplied as an off-the-shelf product. Considerable investment has to be made in machinery and skilled workers to design, manufacture and install a good system that meets complicated technical and environmental specifications. Demanding non-standard diameter ducts can throw a sizeable spanner into some delicate machinery.

Nor are the problems limited to the ductwork manufacturers alone. There is a distinct domino effect. Makers of air terminal devices, for example, are also affected by having to provide grilles and diffusers and plenum boxes to match non-standard sizes.

Cutting the number of standard duct sizes reduces the number of ancillary components from volume control and fire dampers to VAV boxes and attenuators.

Reducing the range of ductwork and components as required by the standard makes it possible for manufacturers to offer a good selection of standard products at competitive prices - and for prompt delivery.

In short, rationalisation reduces the chance of confusion and error and minimises cost without any prejudice to system performance.

ADCAS plans to talk to designers, consultants and clients to highlight these issues.

It will even be speaking to the software houses that provide design programmes for building services. If they can build in simple alarms to flag up non-standard sizing, the problem could be stopped before it starts.

It believes that the new ADCAS initiative is very much in the spirit of the Egan and Latham recommendations. And surely that is a choice for the better.

Phil Johnson chairs the ADCAS/HEVAC working group on spiral duct standardisation
1 February 2008


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