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Multiple fan arrangement offers an array of benefits

Using multiple fans has advanced air handler technology. Joe Wieckoswki explains the technology and outlines its benefits
One of the most innovative developments in air handling technology is the replacement of the single or dual fans found in conventional air handlers with a modular array of small diameter fans housed in individual cubes.

Each array can be designed to match the performance specification and so enables a reduction in footprint and significant improvements in reliability, energy efficiency, noise levels and operating costs.

The use of fan arrays was pioneered in the USA by Huntair, Inc and is known as 'Fanwall technology' (FWT). The basic concept of a fan array has since been emulated by other manufacturers.

FWT is now manufactured in the UK by the Eaton-Williams Group, which launched it in 2011. FWT is an integrated system using fans, motors, cabinetry, controls, and accessories. These components have been successfully combined to provide the benefits of redundancy, quiet and vibration-free operation, optimised energy efficiency from design minimum to maximum flow, and low cost.

Although it is relatively easy to design an air handler using an array of fans the key differentiator between FWT and other fan array systems is the direct drive fan itself, the use of system optimisation controls, Huntair's Coplaner Silencer and the FBD backdraft damper that has a revolutionary blade profile that laminarises incoming air and improves airflow characteristics.

FWT fans have been designed specifically for FWT applications, achieving the highest efficiency ratings in their size range and equal efficiencies to much larger fans used for the same purpose. The resulting net efficiency advantage of FWT fans when used in a cube environment must be overcome by alternative fan array systems that use off-the-shelf fans from commercial fan manufacturers.

Optimisation controls enable individual fan/motor combinations to be selected for peak motor efficiency and lower power for most applications and an integral part of the optimisation controls is the FBD backdraft damper.

Disabling a fan or fans in a fan array system requires a means to prevent backflow of air through the idle cube. Traditional dampers are not designed for fan array applications and can result in unwanted airflow and static pressure losses whilst adding to acoustic and leakage concerns.

The FBD backdraft damper used in a Fanwall system has a revolutionary blade profile that can actually improve air flow characteristics. The vertical blades of the damper open as airflow commences and closes when the fan is idle. This is achieved without the use of mechanical means or added weights. The damper has a smaller footprint than the industry standard versions and designed with a bell mouth opening. Tests have shown this to have near zero effect with reduced acoustic impact.

The FBD backdraft also has a low leakage rate and sealed ball bearings ensure little or no maintenance.

The Coplanar Silencer can provide up to an 18db reduction in fan sound power levels without adding any length to the system for sound attenuation devices, and without reducing fan efficiency.

Preventing turbulence
The silencer comprises a sound absorbing enclosure built around the four sides of each of the fans in the array and the technology ensures no turbulence and lower frequency rumble which is typical in conventional fan systems.

Fan arrays offer greater flexibility in unit sizing. Designers are able to incorporate lower profile units where height and width restrictions are involved. Less floor space is also required as fan sections are shortened in length by 50 per cent or more and the inlet and discharge plenum length is reduced for supply and return fans. Lower capital costs are involved as a result of reduced airway section lengths and individual fan section modules can easily be installed.

Components in a fan array system are typically significantly smaller, more lightweight and easier to access than the same components for conventional fan systems and as the same fan cartridge can be used for multiple units, replacement costs are reduced. When repair or replacement is required for a component in an array system, it can typically be accomplished by one or two engineers on site.

One of the most pressing issues facing the industry is the number of old installed AHUs in need of replacement or refurbishment and are often difficult to access. A fan array based solution is ideal for retrofit applications as they are modular in design and can fit through standard doorways, tight hall way access points and can be transported in standard lifts.

Yeovil theatre is a typical example and was one of the first installations in the UK. When it underwent a major upgrade of facilities, improved comfort cooling was a major part of the design specifications to replace its aged air conditioning system.

The owners, South Somerset District Council had a number of requirements for the theatre which restricted the solution specified. Low noise levels, energy efficiency and minimal vibration were key priorities but also included restrictions on power supply as a significant wattage was taken up by the stage lights.

The plant room was constructed in an external extension directly above the stage with limited access and restricted headroom presented logistical issues that also dictated the layout and connections of the ductwork.

To avoid a lengthy shut down and any loss of revenue a modular approach was specified. New ductwork was routed outside the plant room then taken back into the auditorium through the space deck frame and a modular build air handling system using fan arrays was built on site to overcome the space and access constraints.

An array approach met all the requirements including low noise levels which were 12dBa or lower and the energy savings achieved were far greater than if conventional air handlers had been used.

For the new museum under construction for the Mary Rose in Portsmouth, the overriding benefit of using array technology was that it offered a fast build and unrivalled flexibility. Thanks to the modular design the units could be built and installed on site in one of the most inaccessible areas - the dry dock beneath the ship's hull, where space was restricted and access was limited to the use of a small opening adjacent to the hull and the use of ladders for onsite contractors.

Keeping the Mary Rose dry
Three air handling systems using fan arrays were supplied to site in modules and built in situ where they will be run 24/7 to provide continuous air drying of the Mary Rose to ensure its continued preservation.

A fan array approach came to the rescue when the RNLI's (Royal National Lifeboat Institute) Inshore Lifeboat Centre had a need for provide energy efficient comfort cooling whilst fulfilling the charity's requirements for reliability, built-in redundancy and low noise levels.

Space constraints favoured the modular approach and a smaller footprint. The centre's exposed coastal location and rigid specifications also presented a number of unique challenges. But two identical air handler units using array technology were delivered in three sections with a base footprint of 4970mm and a total weight unit of 2510kg and assembled on site. The units were installed side by side to form 6w x 3h units supplying 19.5 cu m/s inside the centre, with an array of four fans in each unit.

// The author is general sales manager of Colman Moducel //
14 May 2013

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