Air movement & ventilation Distribution
Fan-maker Fläkt Woods says it is important to have high-quality components throughout the air system.
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Iain Robertson, joint managing director of Lindab, is more concerned about the component that lies behind them – the ductwork. Ductwork is out of sight and therefore, more often
than not, out of mind. However, Robertson believes that taking it for granted can also leave the client seriously out of pocket. The drive for energy savings has resulted in lower
pressure drops within many air movement systems. Although generally regarded as a positive trend, this has significant implications for the quality of the ductwork in terms of its leakage class (‘C’ being the best and ‘A’ the worst). A properly sealed ductwork system will save energy
Air terminal
devices affect people’s perception of the installation as a whole because they are all that people feel, hear and potentially
see – Craig MacFadyen
56
CIBSE Journal May 2010
because it does not have to overcome leakage losses and the fan does not have to work so hard to deliver the correct amount of air. So, it would seem to make sense to specify Class C
ductwork rather than Classes A or B. However, this is not always the case, says Robertson: ‘Most jobs specify Class B ductwork but, by going to Class C, there is a 15 per cent saving in the amount of energy you need to get the same amount of air down the ducting.’ Robertson says he is puzzled about why Class C is
not specified more often, especially, he says, because ‘there is a slight price difference [between Class B and Class C ductwork], but it is not significant’. Like ductwork, ATD selection is not always down to
the consultant; contractors can also have a big influence on their specification. Says MacFadyen: ‘Consultants almost always want the best for their clients; all too often contractors want
the best for themselves, which you can understand because they are there to make money, as everyone else is; but it is important to ensure that what goes in is going to create a comfortable indoor environment.’ He believes that creating a building with a
comfortable environment is the responsibility of everybody in the entire supply chain. For Thomas, this chain can get exceptionally
complex. He explains: ‘The architect starts designing his building and by the time we get to our equipment we have one hand and, in many cases, both hands, tied behind our back.’ Thomas sees consultants as the go-between
between the ATD manufacturer (‘since we are perceived to be the design authority because we know the products’) and the architect (’whose vision is often aesthetically driven’). But, he concludes: ‘By the time the manufacturers
get involved, the overall scheme of the building is pretty much mapped out so we are trying to bend something to fit and the consultant’s role as the go- between means he is trying to get the elbow room for a workable compromise.’
Systems
Some manufacturers argue that too many specifiers choose the cheapest ATDs available – these are sold as off-the-shelf products and are usually simply filling a hole in the ceiling where the ducting terminates. But grilles, louvres and diffusers work best when they are integrated into the air movement design, using a systems engineering approach.
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Fläkt Woods
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