Nuisance odours, grease, fat and other contaminants are routinely exhausted from commercial kitchens into the environment without proper concern for the correct application of the filtration systems that should be used to prevent them. Kevin Bristow suggests a way to tackle the problem.
Commercial kitchen ventilation systems can create significant problems for neighbours and the environment. Complaints arising from unwanted cooking smells are especially common in densely populated urban environments, where people are living close to or above fast food outlets, pubs and restaurants. Grease, fat and other cooking residues are less obvious, but can be equally unpleasant in the urban environment.

Let's face it, none of us would actually like to see the pavement or our parked car caked in the leftovers exhausted from the fish and chip shop's ventilation stack, but that can be the result.We should not have to put up with it.

The task of advising, approving and policing exhaust ventilation from catering outlets is shared by the local planning authority in partnership with environmental health officers (EHOs). They act in line with best practice guidance published by DEFRA in January 2005.

Generally, in new build situations, this partnership works effectively to recommend solutions before they arise. However, when an outlet changes cooking type - such as moving from a coffee shop to a kebab house - the result will be a higher level of odour, grease and other emissions. In such circumstances, it is quite common for the existing planning permission not to include an odour control requirement, or one that is insufficient to handle the change of use. The onus then falls on the EHO to respond to nuisance complaints and resolve the problem.

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 proper regular maintenance every four to six months and equally regular replacement with new filter cartridges, the cost of which acts as a deterrent to the maintenance, which is essential if filtration efficiencies are to be maintained. Should maintenance slip, carbon filters can have an adverse effect on back pressure and fan operation within the system, leading to noise and inefficiencies.

Our view, shared in the best practice guidance, is that a combination approach to filtration works best in most projects. Typically, this involves 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.

The electrostatic precipitation (ESP) technology in electronic air cleaners 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 quickly from the air than traditional carbon filters. A reduced dwell time requirement in the unit translates to more efficient performance - up to 95 per cent submicron 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.

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.

As an example, we have recently completed an installation at a fish and chip shop in Worthing called Chips Inc. The shop's location presented a problem for installing the kitchen extract system. The building is a terraced row of shops with privately owned flats housed above. Due to this, we could not house a flue system above the eaves at high level as would typically happen in a standard take away ventilation setup. So, to reduce any problem with emissions, an electrostatic unit is installed in front of backup carbon filters, allowing extraction of clean air at low level.

Air is extracted from the frying range, passes through the Trion unit and the activated carbon filters before being exhausted to outside. The Trion can handle an air volume of 4,420 cu m/h and features two aluminium ioniser/collector cells with stainless steel spiked ionisers.

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 have 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 electronic air cleaners are modular in design, so they can cope 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 kitchen hygiene 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, 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.

• Kevin Bristow is sales director of Trion