Ensuring that air filtration equipment is fit for purpose is essential in kitchen ventilation applications, but contractors and their clients also need to consider installation and maintenance issues. Kevin Bristow explains
The tasks of advising, approving and policing exhaust ventilation from catering outlets are shared by the local planning authority in partnership with environmental health officers. They act in line with best practice guidance published by the Government in January 2005.

There are a number of filtration techniques available, including carbon filters, electrostatic precipitation (ESP) and UV-C technology.

Traditionally, activated carbon filters have been used as a primary method of fume and odour control in catering applications. But, on its own, carbon filtration is not the best solution. The performance of carbon filters often leads to secondary issues. For example, they demand regular maintenance every four to six months and equally regular replacement with new filter cartridges. When using filter cartridges in this way, costs can quickly mount up and, if the need for replacement is ignored, then air cleaning performance will inevitably be compromised. Should maintenance slip, carbon filters can have an adverse effect on back pressure and fan operation within the system, leading to noise and further inefficiencies.

Combination approach works best
Our view, shared in the best practice guidance, is that a combination approach to filtration works best in the vast majority of projects. Typically, this combination solution will involve the use of an electronic air cleaner ahead of an activated carbon filtration system to provide the most efficient removal of fumes, odour, grease and other particulates.

This arrangement ensures high efficiency odour removal from extracted air once grease, fat and other particles have already been eliminated by the electronic air cleaner. The latest filter units feature up to 14 carbon filter cells with special grade activated carbon to ensure no odour can escape.

Such equipment also includes disposable G4 particle pre-filters to give extra protection to the carbon cells from any particle contamination. Using the correct carbon filter cell construction will allow the use of a greater weight of activated carbon providing a higher performance rate, longer dwell times and greater filtration efficiency.

Sitting in front of these carbon filter units, modern electronic air cleaners use electrostatic precipitation (ESP) technology which is perfectly suited to commercial kitchen extract projects. At the heart of this approach is a high efficiency collector cell.

Contaminated air is first drawn through the unit's washable metal mesh pre-filter, which traps larger airborne particles. Remaining particles, some as small as 0.01 microns, then pass into a strong electrical field within the air cleaner's ionising section, where the particulate receives an electrical charge. Charged particles then pass into the collector plate cell, which is made up of a series of equally spaced, parallel plates. Each alternate plate is charged with the same polarity as the particles, which repel, while the interleaving plates are grounded to attract and collect the particulate.

This type of electronic filtration can remove contaminants more efficiently from the air than traditional media filters on their own. A reduced dwell time requirement in the unit translates to more efficient performance - up to 98 per cent sub-micron particulate can be removed at an air velocity of 3m/s.

This performance, in turn, will have an impact on the design, sizing and energy efficiency of the entire system.

Smaller extract fans used
Less power is needed because smaller extract fans can be used with smaller motors. In fact, the typical power consumption of an electronic air cleaner of this type equates to 50 Watts, which is equivalent to a domestic light bulb. At the same time, there will be fewer issues with sound attenuation.

Using an ESP type air cleaner in front of carbon in this way will also significantly reduce the cost of consumables required. ESPs themselves are quick and easy to maintain in comparison. New innovations in the sector has seen the introduction of air cleaners that feature an automatic wash option facility to allow removal of contaminants in situ, saving time and hassle. Once washing is complete, the system activates the exhaust fan to pull air across the cells and dry them before automatically switching on the power supply.

The latest carbon filters and electronic air cleaners on the market are also modular in design, so they can cope straightforwardly with change of use situations. This versatility allows contractors to combine collector cells with stainless steel spiked ionisers, according to the size and demand of individual applications.

Practical experience and know-how of the issues around commercial kitchen extract ventilation counts for a great deal when searching for the right solution to nuisance problems. It is also important that contractors partner with organisations whose equipment is manufactured and tested to the required CE (Machinery Directive 2006/42/EG), ISO9001 and ASHRAE standards.

For example, build tolerances and manufacturing repeatability are critical in creating the right spacing within an electronic air cleaner's collector cell. Anything short of precision in manufacture will result in inadequate performance in the field and continued complaints, and the risk of premises closure for your clients.

The author is sales director at Trion