Air Supply System, Filtration Engineering Ltd, Air Filtration, Air Quality Control Systems, UK

The controls built into a modern air handling system should constantly monitor factors which affect the conditions within the manufacturing space. Some examples would be heating in winter to protect against freezing, cooling to maintain food production space temperature, and the differential pressure of the air filtration system.

The majority, if not all, air processing usually takes place within an air handling and filtration unit (AHFU), which delivers air to a ducted system under pressure, for use as environmental (room), direct food contact and other process air requirements.

An air handling unit will typically contain many of the following items, generally in the order listed when following the direction of air flow:

Some form of humidification control may also be required . The design and location of such equipment upstream of the final filters is critical to ensure successful long-term operation with good access for inspection and maintenance. Hygiene factors must be given careful attention when moisture may be present in the air supply system.

Important points to consider when designing an air handling and filtration unit include:

If the equipment is to be installed on a roof or adjacent ground level, care must be taken to ensure a well-ventilated outside (“fresh”) air inlet area, clear of factory exhaust and water treatment process.

For applications where there is no direct product contact, such as offices and store rooms, the final filtration can be located before the fan, which allows for a more compact and economical air supply system. The design specification may also be modified to give a wider use of standard equipment. Whatever design of air handling equipment is chosen, care must be taken to ensure good manufacturing practice with HACCP considerations.

The duct system from the air handling unit must be manufactured from a durable material in square or round form with a smooth interior finish. Stainless steel 304 grade can be specified for "high care / high risk" food process work; however, a good quality galvanised finish is generally acceptable. The duct system should be accessible for periodic inspection with access panels at regular intervals to suit duct design (DW144 standard). Where a high standard of air filtration has been specified and maintained, the internal duct surfaces will remain clean for many years of operation. Other materials such as 316 grade stainless steel may be required for some wet process return or exhaust air applications. A steam vapour exhaust is a good example.

Air leaving the air handling and filtration unit is under pressure and the duct system should be designed and built to avoid air loss (DW144 standard). Duct insulation to prevent condensation forming on cold surfaces may be required. It is good design practice to install a thermal barrier on ducts which are exposed to the elements and are located in ceiling voids. A high quality insulation outer surface is necessary for external ducts to prevent water or other contamination entering the insulation. Avoid the use of insulated ducts in the food process environment.

There are circumstances where a modified design of inlet duct is required, and an example is where an air handling unit is situated some distance from an outside air supply. In such cases the pre-filtration should be located as close to the inlet control screen as possible, thus preventing dust laden air entering the system. Inlet duct systems should be operated in a clean and dry condition offering the minimum of maintenance. The air inlet louvre screen should be located for easy access and periodic cleaning. Screens attached to the back of weather louvres are often difficult to inspect and clean. A blocked air inlet zone will affect the performance of the air supply and air quality control system

Wherever possible ducts should be installed outside of the food processing space, with adjustable ceiling diffusers fitted for efficient air delivery into the controlled room. A good quality diffuser can be set to avoid draughts when chilled air is delivered to the space. Careful attention is required when positioning extract ceiling / wall grilles, to ensure they are not situated above open food processing. Removable core type extract grilles will allow for cleaning outside of the controlled space. Extract air ductwork should receive particular attention with inspection access especially if the food manufacturing process is dry and particulate is released into the atmosphere under normal processing conditions. Extract from a cooking process will require careful attention to ensure that suitable and quick access for inspection and cleaning is available.

Sock or fabric air distribution systems are in common use, especially where a high air change rate is required. The advantages of lightweight construction and good air distribution should be considered carefully with each application, together with the requirement for a high standard of air filtration. Fabric duct and ceiling "D" shape systems act as a filter and can be expensive to clean, with more frequent maintenance if the air filtration is below F7 to BS EN779. The standard of air filtration should be up to "high care" requirement, and the control of the food process room conditions can be critical to the performance of fabric sock systems. Many food manufacturers have reverted to stainless steel diffusers to reduce maintenance costs and plant downtime.

A balance of supply and extract air volume is a critical consideration especially when cooking vessels and dust filter systems are in use. Allow extra air volume at the design stage to ensure air movement from the controlled space. To conserve energy it is advisable to consider a separate ambient air supply to compensate for high air volume extracts such an open cooking and oven exit zones. This dedicated air will not normally be chilled and thus a saving in energy can be realised. The supply air volume would be filtered to the required standard (minimum F7 BS EN779) and slightly less than the extract air volume. Localised input and extract air will not adversely affect the general room temperature; however, directional air movement in the working space must be considered.

There are numerous design features which will assist in reducing running costs and add to process efficiency, and we suggest you seek the services of a company with a track record in this type of work.

The Air Supply System from Filtration Engineering