FEATURE HVAC
FABRIC DUCTWORK GIVES EVEN distribution with cost savings
Increased steel costs have made the fabric ductwork system more cost effective with regard to purchase price, simpler installation and reduced risk of condensation forming
A
rapid rise in worldwide steel prices has seen the cost of galvanised steel
ductwork dramatically increase. This has resulted in a trend toward greater use of fabric ductwork distribution systems. Traditional galvanised steel ductwork,
usually circular spiral wound, is the norm for most installations for heating, cooling and ventilation systems but for many applications there is a viable alternative. There are numerous installations in modern buildings where the distribution ductwork is exposed within the heated or air conditioned space. In these situations the fabric distribution duct provides even air distribution and aesthetics in addition to cost savings. The fabric distribution ductwork plenum
may be manufactured from a variety of materials to suit different applications and is inflated by the air pressure inside the duct. Modern fabric ductwork systems are far more sophisticated than simple air socks which diffuse air through the entire surface of the duct or polythene tube type ducts which have a simple row of holes down the length. These simple systems are useful for specific applications but lack the versatility and air distribution features of the modern fabric duct. Computer design technology now allows fabric duct systems to be individually created to match the proposed criteria of the individual application. They may be used for heating, air conditioning or ventilation with duct mounting heights between 2m and 15m.
Air discharge may be selected from specially designed perforations to promote high levels of air induction and subsequent air mixing. Unique to each application, distribution and location of the outlets depends on the air leaving temperature, mounting height and terminal velocity criteria to be achieved. For open plan areas air distribution would generally take place along the full length of the duct but for racked areas the ducts can be manufactured specifically for air discharge between the racks. The distribution outlets are designed to
induce large volumes of secondary air from around the duct into the discharge air stream. The combination of uniform air distribution down the full length of the duct plus the large volume of induced secondary air promotes substantial low velocity air movement within the building.
EVEN TEMPERATURE DISTRIBUTION This results in even temperature distribution with little or no discernable air movement at occupancy level. For ducts installed at high level the outlets can be designed to increase the amount of air induction to provide auto destratification, thereby eliminating excess roof space temperatures and reclaiming heat from lighting for example. While increased steel costs have made the fabric ductwork system more cost effective the savings are not confined to material. Site installation costs are reduced; the lightweight systems can be
18 DECEMBER 2014/JANUARY 2015 | FACTORY EQUIPMENT
As the system is self- balancing and does not require any grilles or terminals, balancing and commissioning is simplified
installed three or four times faster than traditional steel ductwork and since most installations are at high level and covered by the stringent Working at Heights legislation this is a significant advantage.
SIMPLIFIED BALANCING AND COMMISSIONING Furthermore, the induced air movement around the duct removes the risk of condensation forming on the ducts used for air conditioning applications so there is no requirement for insulation of the duct. As the system is self-balancing and does not require any grilles or terminals, balancing and commissioning is simplified. The fabric distribution duct is available in a wide range of colours to complement the building fabric without having to pay for painting and subsequent maintenance. “Over the past 12 months we have seen
a growth in applications of our Airmixing fabric ductwork distribution systems used in conjunction with our gas fired heating and ventilation units,” comments Joe Kiernan. “The Reznor AirMix distribution duct has become increasingly attractive and many more installers are now realising the benefits of lower installation costs and improved air distribution. “The system allows the installer to purchase the distribution duct and the heater from a single supplier.”
Reznor T: 01303 259141
www.reznor.co.uk
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