Published on Sunday, 30 June 2013
Written by The Editors
Ventilation systems are among the most important design features of any kitchen. The performance of these systems directly impacts the working environment of the kitchen space and has a substantial impact on the operational cost of the kitchen.
Commercial kitchen ventilation systems remove cooking heat and effluent from commercial kitchens. Effective ventilation can assist greatly with controlling overall HVAC costs in any type of foodservice operation. Operators should work closely with a consultant to identify ways to capture as many efficiencies as possible.
These systems include hoods, fire supression systems, pollution control units, grease extraction, controls, exhaust and makeup air.
Stoves, ovens, grills, steam kettles and warewashers are examples of equipment that typically requires a hood.
The thermal plume of cooking equipment determines whether it is light, medium, heavy, or extra heavy duty as well as the amount of heat, smoke, grease, vapor, water and combustion products that will be created. This will determine the necessary exhaust rate.
Some processes, such as charbroiling and frying, create smoke and grease, which require a built-in fire suppression system. Other processes, like steaming and warewashing, produce heat and moisture and do not require built-in fire protection. Type I hoods are designed to contain smoke and grease. These systems are watertight and have built-in fire suppression systems utilizing either dry chemical or inert gas. Type II hoods, designed to expel heat and steam, are not sealed and don't require a fire suppression system.
There are different hood designs that have different capture areas geared for specific applications. For example, a single-island canopy hood requires more exhaust than a wall-mounted canopy hood, and a wall-mounted canopy hood requires more exhaust than a backshelf hood.
Operators should refer to local building and/or health codes for specific exhaust hood construction material requirements and exhaust rates based on appliance duty and hood length.
Air removed from the back of the house through an exhaust hood is required to be replaced with an equal volume of makeup air through any of the following: transfer air, displacement diffusers, ceiling diffusers with louvers, slot diffusers, ceiling diffusers with a perforated face or an integrated hood plenum.
Makeup air systems are available in either conventional or short cycle types, but most commercial kitchens use a combination of both. The short cycle systems utilize compensating hoods and air-curtain designs that draw makeup air directly from the outside and then discharge it back into the hood service area. Most conventional systems provide conditioned air from a dedicated system or through a central HVAC system.
- Grease filtration at the hood extracts grease particles from the airstream.
- When used with pollution control units that include charcoal media after the filters, these systems can remove cooking odors before discharging outside of the building.
- The appropriate exhaust rate is dependent on the menu of food products, type and use of cooking equipment under the hood, the hood design and how makeup air is dispelled in the kitchen.
- Assess the type of foodservice facility to determine the type and size ventilation system that is warranted.
- Demand control ventilation minimizes the amount of exhaust and supply required based on cooking loads to generate significant operating savings and a reduction in energy use.
- Decide what the priority is when purchasing the ventilation system: low cost, energy efficiency and/or aesthetic concerns.
- The comfort strategy should be considered to decide on tempered or untempered makeup air, heating and/or cooling for comfort. This is a critical design requirement and is dependent on climate conditions and local building and health jurisdictions.
- Specific national and local codes need to be followed.
- Factor in future plans for the operation to see if they will impact needs for ventilation equipment moving forward.
- Determine the type and shape of hood needs, since there are many options available. Some designs are more effective than others, depending on the foodservice equipment and overall design of the space. For example, open demonstration-type kitchens will have different needs than a fast food chain.
- Side-skirts can be very effective on the ends of hoods to make the capture of effluent more efficient.
- Consider the equipment arrangement under the hood to ensure operational efficiency. As an example, position higher Btu output items toward the center of the space beneath the hood.
- Work closely with HVAC engineers for the rest of the building to ensure air-handling systems are strategically placed so as not to interrupt the capture.
- Recognize that entrances from tempered space into non-tempered space can disrupt airflow and capture, which will impact the effectiveness of the ventilation system.
- Generally, the exhaust cost, or the cost to run the exhaust fans, equates to $2 per cubic foot per minute per foot of hood. This does not include the cost of makeup air.
Specifying Mistakes to Avoid
- Looking at only initial costs versus operational/life cycle costs, such as the quality of equipment, performance, demand control versus constant volume, etc. can result in spending more for a system in the long run.
- Not planning for possible future changes, such as fire suppression, future airflow and utilities, also will increase costs over the life of the ventilation system.
- Piecing a used system together typically results in significant costs that were not budgeted for, including exhaust and supply changes, fire suppression system modifications and finishing accessories considered part of a new package.
New & Notable Features
Newer features and options include demand control ventilation, pollution control units/grease extraction devices, 50 percent turndown of makeup air, self-cleaning hoods and electrically commutated motors (ECM) in exhaust ventilators.
Web-based technology improvements for resource management and facility optimization also are available.
When to Replace
- Heavy grease buildup: When this is not removed during professional maintenance, the ventilation system can be compromised and will need replacing sooner rather than later.
- Excessive airflows: Old design methods can produce excessive airflows in these systems that can increase HVAC costs. Ventilation systems that are outdated are best replaced to save money over the long term.
- Major cooking appliance/menu changes: If this is significant and requires the rework or total replacement of several components, a new system may be necessary.
- Remodel: If an existing facility is undergoing a remodel, it is possible that the ventilation system will need to be reworked or replaced.
- All maintenance is dependent on cooking operations, including type of cooking and hours of operation, in addition to local codes.
- Clean grease filters and the capture area daily or weekly depending on the application.
- Replace disposable makeup air filters monthly.
- Clean the hood and duct at least biannually or in accordance with National Fire Protection Association requirements.
- Clean and inspect the exhaust fan twice a year.
- Clean the makeup air unit's aluminum mesh filters at least two times a year and clear them whenever clogged.
- Although dependent on local code requirements, fire suppression inspections should normally take place twice a year.
- Annually replace the exhaust fan belt and makeup air belt.
- Control enclosures should be kept clean and free from any grease or dirt build-up.
- All fasteners should be checked for tightness each time maintenance checks are performed prior to restarting a unit.
- Control enclosure door panels should be securely closed after maintenance to prevent tampering or electrical shock.
- Temperature sensors in exhaust hood risers need to be cleaned monthly by wiping any grease or dust buildup from a probe with a clean cloth. A clean sensor ensures that the temperature switch will quickly respond to changes in exhaust air temperature.
- Demand control ventilation allows the system to operate only when necessary, saving energy and money.
- Pollution control units are more environmentally friendly, as they keep the air clean of pollutants.
- Components such as side panels, angles, flanges and deflectors can significantly improve both the capture and containment efficiency of a ventilation hood, which will help minimize the required exhaust flow.