The type of cooking influences the amount of particulate pollution (smoke and grease) and also the level of odour produced. Typically a char grill operation has a lot of smoke and grease and an Indian restaurant a lot of odour.

With a char grilling operation Purified Air would always recommend a double pass unit because:

Char grill cooking provides a high particulate by volume in the extract air. Typically a cubic metre of air could contain 1,000,000 visible smoke particles. On the basis that these are filtered with a system at an efficiency of 95% the result will leave 50,000 visible smoke particles per cubic metre of air. If a second electrostatic precipitator is installed in a double pass arrangement then the remaining 50,000 particles are reduced to 2,500, thus providing a separation efficiency of 99.9975%.

These issues are accentuated when the system becomes dirty in between maintenance visits. As the dirt builds up on the plates and insulators the efficiency of the system can fall as low as 75% separation. This means, based on the example above, a breakthrough of around 250,000 visible particles. In a double pass system serviced at the correct intervals the second pass unit nearly always works to the optimum efficiency, this provides that the 250,000 visible particles are reduced to just 12,500, an overall separation efficiency of 99.9875%.

Where the extract will discharge is important as it may impact on the level of odour control ie high, medium or low where high would be discharging directly below a residential window or less than 10 metres from a neighbouring property.

The answer to these questions enables Purified Air to select the correct type of equipment with the main criteria being air volume. Where possible Purified Air work on 80% of maximum design particularly where the type of cooking and risk factor falls into the high category.

a) Particulate Control - almost always this is dealt with by using Electrostatic Precipitators.

b) Odour Control - this can be dealt with using; ON 100, UV-C or Carbon / Mixed Media Filters.

Carbon / Mixed Media filters come in many sizes but the standard we promote is the 594 x 594 x 597 cube. This will handle an air volume of: 1.06 M3/Sec with a dwell time of 0.1 seconds, to achieve greater dwell times or cover larger air volumes you simply increase the quantity. E.g. to achieve 0.4 seconds dwell time at 1.06 M3/Sec you would need to apply 4 No filters in series or parallel.