The best recipe for kitchen ventilation
Commercial kitchen-ventilation systems can create significant problems for neighbours and the environment — especially if the type of use changes but not the ventilation. Kevin Bristow of Trion considers this issue — and others.
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.
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. They act in line with best practice guidance published by DEFRA in January 2005.
In new-build situations, this partnership generally works. 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 environmental health officer to respond to nuisance complaints and resolve the problem.
There is 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 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.
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| A key element of kitchen ventilation is removing odours using carbon filters such as Trion’s T-Carb. |
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.
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 products, such as Trion’s T-Carb, feature a number of carbon-filter cells with special-grade activated carbon to ensure no odour can escape. Equipment featuring disposable G4 particle pre-filters also gives 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 the carbon filter, modern electronic air cleaners use electrostatic precipitation (ESP) technology, which is perfectly suited to commercial kitchens. 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 µm, then pass into a strong electrical field within the air cleaner’s ionising section, where the particulates receive an electrical charge. Charged particles then pass into the collector plate cell, which is made up of a series of equally spaced parallel plates. Alternate plates are 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 on their own. A reduced dwell-time requirement in the unit translates to more efficient performance; up to 95% particulates smaller than 1 µm can be removed at an air velocity of 3 m/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 is 50 W. There will also be fewer issues with noise attenuation.
Using an ESP 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 carbon filters and electronic air cleaners are also modular in design, so they can cope straightforwardly with changes of use. 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.
Kevin Bristow is sales director with Trion.
