In modern industrial kitchens, ever more stringent regulations and more sophisticated managers have led to a demand for high-quality, low-maintenance ventilation solutions. This is no surprise, as people now know that hygiene, safety and comfort depend on adequate ventilation. Not only are grease and heat removed by extractors, but carbon monoxide produced by gas heating equipment and steam from boiling and washing equipment must also be removed from the working environment. Ventilation supplies clean and cool air for workers and to provide sufficient air for complete gas combustion. Extraction hoods that are placed as close to combustion sources as possible will remove gases effectively and prevent residues of fat and grease (that can present a fire hazard or make work more difficult) from building up. The heavy load placed on ventilation fans in industrial fans means that they must be robust, efficient and user-friendly.

Goals of Kitchen Ventilation

The ventilation system must fulfil the following goals:

• Removing fumes from cooking as close to the source as possible.
• Improving comfort by exchanging hot kitchen air for cool outside air, thus reducing the risk of health problems and high staff turnover. The airflow volume rating of ventilation fans need to be high enough to ensure that there are no dead air zones in which stale, contaminant-laden air can accumulate. There are different rules of thumb for airflow volume that are used in the industry, often relating to the area of the stovetop.
• Controlling air movement such that it will not lead to discomfort.
• Keeping its own noise and vibration down to acceptable levels. Noisy operation often indicates an inefficiently operating, incorrectly sized or low quality fan, as well as being a nuisance.
• Being low-maintenance and easy to clean by avoiding residue build-up and inlet blockages that can reduce ventilation efficiency and lead to a fire hazard. This is crucial for kitchens, which must adhere to local health and safety regulations. Kitchen fans unfortunately tend to collect dust and dirt because they produce static electricity charges. Harmful mould can also grow on fans and in ducts.
• Ensure complete combustion of cooking gas and remove carbon monoxide.

System Design and Performance

Ventilation systems must be designed according to the kitchen workload, shape and layout; the cooking equipment that will be used; the number of kitchen staff; ease of maintenance and energy efficiency. In order to attain optimum exhaust operation, modern kitchens often make use of variable speed drive (VSD) fans. These may use hood thermostats or monitor appliance electricity use to assess the ventilation needs of a kitchen at a specific time. Since they generally run slower outside of peak times, effective air exchange can be maintained while cutting energy costs significantly.

It is important to keep in mind that a high quality fan is not enough to guarantee ventilation system performance. Dirty or poor dampers and inadequate ducting will cause pressure drops that reduce the capability of the fan to move large air volumes and results in less efficient operation. Indeed, any accessory will have an effect on fan efficiency. Fan, duct and vent placement are also important. The ideal situation involves designing the kitchen with the ventilation system in mind, considering all its components in relation to each other. Checking for blocked louvers and vents should be part of the maintenance of the ventilation system.

Fans and Make-up Air

The correct sizing of fans is critical to the total performance of the system. While undersized fans will not exchange enough air, considerable exhaust capacity can result in backdrafting, where gases from combustion appliances are drawn back into the ventilated space. Oversized fans are also more expensive to buy and operate. Where a need for excess exhaust capacity exists, a supply fan that can provide enough make-up air – that is, air that can replace exhausted air to maintain room pressure – can be installed. In some countries, this issue has given rise to legislation that requires the depressurisation of the kitchen when the exhaust fan is running to be measured and kept within strict limits. An additional incentive to balance the exhaust air with make-up air is that exhaust fan capacity and performance is reduced when the system lacks make-up air.

Usually, about 85% of the required make-up air needs to be introduced by mechanical ventilation. The remainder can be drawn naturally from the surrounding space. Vents may require fly screening to prevent insects and other pests from entering the kitchen.