Redefining the production of air-handling units

AHU
The Airovision range of air-handling units is the outcome of a 3-year development programme by Carrier Holland Heating to address cost issues and deliver a higher-specification product.
Keeping up in a competitive market place demands periodic reviews of product ranges. We found out how Carrier Holland Heating enhanced its AHU offering and addressed costs.In just a few short months the factory of Carrier Holland Heating at Waalwijk in The Netherlands has been almost entirely reorganised to produce a new range of air-handling units that is described as ‘the most flexible range of air-handling units ever produced’. This factory has an output of 3000 AHUs a year with a value of over £33 million. With the existing design approaching 10 years old, the decision was taken three years ago to meet the challenge of market conditions head on and develop a product range that would be more economic to manufacture, require many fewer component parts and achieve a 50% reduction of inventory. At the same time the new range had to meet market demands for higher specifications and product quality. A 20% reduction in lead time has also been achieved. Main issues The design concept for the old ranges was innovative at its time, providing a high degree of customisation from 320 mm modules. There were two main issues. First, the increment in unit capacity for small airflows was too large. Secondly, there was a choice of five ranges, so it is easy to believe that of the 3000 units made in a year, no two were likely to be exactly the same. The new Airovision range replaces the five previous ranges. It is based on a module of 160 mm, so that the increase in air-flow steps is about 12% from one size to the next. The standard product range offers 120 sizes from 0.5 to 35 m3/s. Just as the factory has been reorganised, so has the supplier chain — in particular the supply of sheet metal for the casings and pentaposts for the framework. The steel for panels is just 0.8 mm thick and is galvanised and coated with high-build polyester. The same specification applies to the pentapost sections, which have 20 faces to achieve a very rigid structure and are welded down the inner corner for aesthetics. There is thus no longer any need for a paint shop; indeed, cut metal requires no further protection to exposed edges because the galvanising provides adequate protection for this thickness of steel. Reducing costs Reducing the choice of panel types to just one has made a major contribution to reducing costs. The double-skin insulated panels are 60 mm thick as standard and can be filled with glass-wool or rock-wool insulation. Intriguingly, the standard construction is cold-bridge-free to the TB2 thermal rating — without thermal breaks such as plastic insertions. The cost of achieving this performance has been reduced by 20%. At the same time, Class C air leakage can be achieved. The waste of steel is minimised by cutting as many parts as possible from one sheet — even though they may be for different orders. Scrap is just 6 to 8%. Lest anyone be concerned about the pressure capabilities of such thin metal, a 1.25 mm option is available for the UK market, but strength tests have proved that the standard design can withstand a fan pressure of 2500 Pa. Thermal performance The thermal performance is just one indication of how customers are getting more for less. Tony Millard, UK sales director for air-handling products, says, ‘Enhanced quality and performance is the direction Carrier has chosen. We’re doing this while still cutting costs by improving the manufacturing process and supply-chain management. Other manufacturers just seem to be cutting features in the face of market cost pressures.’ Inside these new AHUs is a totally smooth construction that R&D manager Rien van Benthem believes could meet hospital specifications. He explains, ‘Even though the drain tray is not removable, it can be cleaned. The eliminator box can be removed to totally expose the drain tray for steam cleaning.’ The fixed, but accessible, drain tray could be better suited to hospital environments than a removable one. There are no grooves and channels that would be needed with a removable drain tray, and hence no potential areas to harbour bacteria. Attention to detail in both manufacture and AHU performance abounds. For example, the fixing holes in the pentapost sections are punched, not drilled, to provide greater fixing depth for self-tapping screws. Screws that have been removed can be replaced more securely than if holes had been drilled. Since Airovision units can be supplied in flat-pack form, this is a valuable feature. Flat packs are assembled on site and then retested for air leakage. Filters The replacement of filters is achieved from the side of a unit. When several filters are used in a large unit, a simple clip links them so that the service engineer does not have to reach deep into the AHU or crawl into it. When bag filters are used, a special clip achievse F9 jointing quality between the filters and the stainless-steel channels. The inherent efficiency of Airovision units is not compromised by poor setting up of V-belt drives between motors and fans. They are tensioned to vibrate at a particular frequency, which achieves an efficiency of 97% initially, falling to 95%. Less precise methods of setting might achieve an initial efficiency of 80%, falling to 60%. This range of air-handling units has been designed to comply with EN 1886, which will be a British Standard by the end of this year. This standard includes the thermal performance and mechanical strength of the casing, air leakage, filter bypass leakage and acoustic insulation. The standard also specifies how testing should be carried out and includes an on-site procedure. Cost effective The overall impression of the Airovision range is one of identifying the needs of users, how they can best be met and applying the manufacturer’s design and production skills to meet those needs cost effectively — without compromising product quality. Holland Heating UK is at United Technologies, Guildford Road, Leatherhead KT22 9UT.
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