WHAT ARE COMMERCIAL KITCHEN EXHAUST SYSTEMS?

Commercial kitchen exhaust systems create a better environment for the occupants in the kitchen by efficiently removing contaminated air from the immediate cooking area and replacing it with clean, comfortable air.

Here’s how it works. A commercial kitchen exhaust system is made up of several components that complete a commercial kitchen exhaust unit. Common components are typically the hood canopy, ductwork, and fan unit.

The hood canopy commonly referred to as “the hood,” is the most visible part of the kitchen exhaust system.  The hood plays an integral role in the effectiveness and efficiency of the system. It’s design, size, construction, maintenance, and cleanliness are essential characteristics for optimum productivity and safety.

The hood canopy  is designed to collect and trap cooking vapors and residues and functions as the primary point of collection for effluent. Effluent is created by cooking equipment and defined as clouds of smoke, heat, grease laden vapors, gas, odors, fumes and steam. It is generally known as all the “bad elements” in the kitchen that require removal by the exhaust system.

The hood canopy is the first component of the ventilation system to capture the harmful effluent. As the process continues, polluted air flows through the system components including filters, or grease extraction devices, which help restrict air and create velocity. Then it travels through ductwork that aids in containing and directing air to the fan unit. Polluted air may then travel through a pollution control device (if required by the AHJ), and finally through a fan unit, which creates air draft and air velocity. The exhaust air is then expelled or dismissed out of the system into the atmosphere.

A hood canopy is a device designed to direct and capture grease -laden vapors and exhaust gases created from cooking appliances.

Let’s begin our discussion by defining some terms we will use throughout this module.

*All above-noted definitions are referenced from NFPA 96 2017 

WHAT ARE THE PARTS OF THE HOOD CANOPY?

While different hood designs may have some unique features, most exhaust hood canopies are built for grease application and share four common features; filters, grease drip pan, trough, and plenum.

Filter – a removable device of a kitchen exhaust system designed to capture grease and direct it to a safe collection point.

Grease Drip Pan – the safe collection point usually at the end of the grease trough.

Trough – Commonly referred to as the bottom filter rail or filter guide, the trough is a long, narrow, gutter-like structure designed to capture 
grease and oil.

Plenum –A plenum is the area behind the filters where air flow is collected and moves through the exhaust system by a change in pressure.

LEARN ABOUT HOOD TYPES

There are two categories or types of hoods:

• Type I Hood – Type I Hoods are required above grease-producing cooking equipment and built to specifications and standards that provide adequate fire protection and safety for operation. Type I Hoods also require filters to be mounted on a 45-degree angle, include grease troughs and a collection point for grease no larger than 1 gallon. A Type 1 Hood must be continuously welded, liquid-tight and grease tight.
  
• Type II Hood – Type II Hoods CANNOT be used over equipment producing grease-laden vapors, and are specifically designed to remove steam, odors, heat and dishwasher vapors only.  Type II hoods may or may not require filters or fire protection. Type II Hood canopies do not have the same construction requirements as Type I Hood canopies.
  

LEARN ABOUT HOOD DESIGNS

Hoods designs are categorized as AIR or WATER Hoods. Air hoods move air through a grease removal device or filter. Water hoods incorporate a series of baffles that cause changes in airflow direction, allowing the grease to drop out of the air stream and depositing in the wash plenum. The accumulated grease is removed by a wash system using hot water and detergent to clean during a set wash schedule, usually when the system is shut off.

DID YOU KNOW?Kitchen exhaust air hoods have two basic designs:

1. Back Shelf, or Low Proximity Hood
2. Canopy Style Hood

BACK SHELF HOODS

• The distinct characteristics of a back shelf (or low proximity hood) is that it does not hang over the front of the cooking equipment. This type of hood is in close “proximity” to the cooking equipment surfaces.

• Back Shelf Hoods have close clearances between cooking surfaces and filters.

• Back Shelf Hoods are used in instances where a regular canopy style hood cannot be used or would not fit.

• Back Shelf Hoods require less exhaust, or airflow than a regular canopy, which makes them ideal for fryer and griddle type cooking and appliances that are relatively low-profile. Back shelf hoods are not recommended for open-flame char-broiling.

• A back shelf hood canopy does not extend very far over the cooking equipment. This hood relies on its close “proximity” to the cooking equipment to be effective.

CANOPY HOODS

The distinguishing factor of a canopy hood is that the canopy hangs over the cooking equipment with enough extension to collect the plume of effluent and exhaust it out of the system. The overhang of the canopy is typically at least 6” past the cooking surfaces. The overhang can be more than 6″ for appliances that emit larger plumes of effluent.

Canopy hoods require larger volumes of air and can, therefore, exhaust any cooking equipment.

DID YOU KNOW?Canopy Hoods can have different styles. The styles are determined by installation characteristics and include wall-mounted canopy hood, single-island canopy hood, double-island canopy hood, and eyebrow canopy hood.

HOOD CANOPY DESIGN STYLES

Wall-Mounted Canopy – Wall-Mounted Canopies are a very common style of a hood canopy installed against a wall. The wall helps to develop the plume of effluent so that airflow can be very efficient and functional.

Single-Island Canopy – A Single-Island Canopy is a common design, installed as an island in the middle of a kitchen. Airflow balance and correct canopy size over commercial cooking equipment are critical on this type of canopy for proper exhausting due to the lack of the wall.

Double-island Canopy – Seen mostly, but not exclusively, in institutional type cooking applications, a Double-island Canopy is designed for installations with a double line of cooking equipment gathered in one area with a 360° radius. These canopies are installed when a large amount of diverse cooking equipment is used in a commercial kitchen.

Eyebrow Canopy – This unique style of hood canopy is used mostly in bakery-oven, smoker and dish-wash applications in a kitchen. It can be identified by the hood canopy which usually hangs directly over a specific piece of equipment and is designed to capture effluent when the equipment doors open.

WATER WASH HOOD TECHNOLOGY

Water Wash Hoods are designed to remove up to 95% of grease particulate from the air stream without the use of filters. Grease particulate is extracted by centrifugal force from the air stream through a series of baffles. As the high-velocity air stream is forced to make a series of turns, the droplets of grease are forced out and deposited on to the baffles. The accumulated grease is then removed daily during the wash cycle with hot water (140°F minimum) and detergent. The collected grease is washed away by utilizing a series of nozzles.

DID YOU KNOW?Modern technology has developed water wash hoods to clean themselves in place. Wash cycles can be set to wash away the accumulated daily grease from the filters internal baffles while the hood is in operation or while cooking occurs. The wash cycle can occur several times a day depending on the cook-load or volume of grease produced. The hood plenum is washed each time the fan shuts down.

DEMAND VENTILATION CONTROL (DVC)

With the increased demand for energy conservation and efficiencies in the operation of commercial kitchens, manufacturers are producing hood exhaust systems to adjust fan speeds depending on cook-loads. Demand controlled kitchen ventilation in commercial kitchens involves controlling the exhaust and make-up air volume of exhaust hoods based on the actual demand. When equipment is idle or little ventilation is required, the fan motors slow down to significantly reduce energy use. With the use of temperature sensing devices or measuring thermal currents, hoods can adjust air volumes with motorized dampers in the outlet collars of each hood.

Some hood systems incorporate auto start and shut down features that allow selected hoods to remain idle while other hoods operate at 100% capacity within the same system. These hoods operate along with the building supply air and automated building controls. Canopy lighting can also be turned on or off during idle periods for further efficiency and cost savings.

As kitchen exhaust cleaning professionals, great care should be taken during the cleaning and maintenance process to protect any canopy sensors and other components that could get wet or damaged.  Make sure that you follow manufacturer’s guidelines and proper precautions with these components.

VENTILATION CEILING TECHNOLOGY

Ventilated Ceiling Technology (VCT), is a relatively new concept in commercial kitchen exhaust systems. A Ventilated Ceiling System configuration includes a series of modular exhaust pod(s) installed in a grid. The system can be custom configured to suit a variety of commercial cooking operations and accommodate the addition of integrated lighting and supply air diffusers. With VCT the entire kitchen can become a cooking space without the limitation of hood canopies.

In a VCT environment, the entire ceiling acts as the ventilation system for supply and exhaust air. The benefits of VCT include a clean and sanitary appearance, highly efficient operations, low noise, low humidity, and a visibly pleasing work area for the occupants.

REVIEW

To be efficient and effective, a kitchen exhaust ventilation system needs to remove contaminated air and bring fresh, clean air into the kitchen area. This “circle of air” is vital to the comfort of the employees and the productivity of the kitchen operation.

Hood canopies, whether Type I (grease) of type II (no grease), are an integral part of the kitchen exhaust ventilation system. It captures all the harmful elements that are byproducts of the cooking process and helps to filter and remove them from the airflow.

Hood canopies come in different types, designs, and styles such as:

• Water-wash Hoods – Designed to run a wash cycle washing grease residue away
• Air Hoods – Designed as either Back-Shelf or Canopy Style Hoods (Wall-Mount, Single Island, or Double-Island, and Eyebrow Canopies)

Different hood types, designs, and styles of hood canopies help restaurant owners and facilities managers meet the specific requirements of a commercial kitchen and the exact kind of cooking being done.

As technology advances into every aspect of our world, ventilation control is no exception, and as a kitchen exhaust cleaning professional, you will encounter these components in our field experience.  Things such as Water-Wash Systems, UV Technology, Demand Ventilation Control, and Ventilation Ceiling Technology are becoming more and more prevalent in kitchen designs and operations.

You are now ready to take the quiz on Hood Canopies. You must score 100% to move on. Should you need to review the material again, you can do so by starting the module over. Good luck