“Smoke Gets In Your Eyes” is a lovely song by The Platters, but is not the ideal theme song for your patrons. Getting the steam, smoke and smells out of your restaurant kitchen is a priority, but how? A commercial kitchen exhaust fan is a different beast than a small home model.
In addition to considering airflow and safety systems, you need to think about several things in your workspace. Let our experts guide you before you invest in this vital piece of kitchen equipment. Read on to learn 6 things you should consider before making your big decision.
Which Commercial Kitchen Exhaust Fan Is Right for My Space?
A commercial kitchen exhaust fan is essential to operating your restaurant, bakery or catering kitchen. Most municipalities legally require them. All fans do the same basic thing, move air from inside your building to outside. However, your kitchen exhaust fan must move hot, dirty, greasy air through your hood system and vent it outside.
Consider these five things when choosing your commercial exhaust fan: placement, air flow rate, static pressure, energy efficiency and type of drive. Balancing your needs with cost is always a question, but your ventilation professional can help you with answers.
Where Do You Want the Fan to Be?
Where you place the fan is one of your first considerations. Most models of commercial fans are designed for one of three placements: inline (in the duct), on the wall, or on the roof. Where the fan is placed affects the housing, accessories and often the cost associated with installation.
Fan placement is often dictated by the space available or fire codes. Often, you must vent cooking odors away from occupied space. This can add costs if you must draw air upward several stories.
Fan placement also dictates other considerations like appearance, noise, and size.
How Much Air Do You Need to Move?
Simply put, the air volume flow rate is the measurement of air movement through your duct. It is expressed in cubic feet per minute (CFM). The type of cooking equipment you use and the amount of cooking you do changes your needs. For example, a large open flame grill used for meat roasting requires more ventilation than a pancake griddle. A high volume french fry line needs more air exchange than a convection oven.
The hood system you purchase will dictate the CFM needed. The National Fire Protection Association (NFPA) sets the standard for air removal volume. Most municipal codes meet or exceed these guidelines. Again, your ventilation professional can guide you.
In general, the minimum velocity (speed) through the duct is 500 feet per minute and the volume must be sufficient to capture and remove grease-laden cooking vapors. A lower volume is permissible during no-load conditions as long as it is sufficient to remove flue gases and residual vapors.
How Much Resistance in the System?
Static pressure is the resistance against the air traveling through the ventilation system. It is also known as friction loss or system air resistance. Static pressure relates to the balance of air intake and exhaust.
The unit of measurement is non-intuitive. It is measured in inches of water per linear foot of ductwork. The inches of water refer to an old-fashioned method of measuring pressure by comparing to an inch of water in a column. Online calculators now make this calculation much less tedious.
Static pressure must be optimized to prevent poor air distribution or energy waste. Balancing static pressure requires knowledge of all system components. This means making allowances for the duct material and texture, the length of the duct, system design and volume.
Selecting a proper commercial kitchen exhaust fan depends on getting the math right. CFM too low for your space results in poor performance and circulation. CFM too high and you are venting your expensive heated or air-conditioned air outside. Air resistance too high and you risk burning out your fan motor pushing air through grease filters and such.
How to Determine Energy Efficiency?
Fans generally give motor horsepower. Horsepower isn’t about the volume of air moved by the motor, although fans with a higher horsepower are likely to have a higher CFM. For a kitchen exhaust fan, it reflects the amount of power from the motor needed to move the blades at a certain speed.
Look at the CFM of a fan at the expected maximum air resistance (static pressure). Exhaust fans with a higher CFM need to be more energy efficient. Find the horsepower rating to give you the most energy efficient operation.
An underpowered motor will wear out too quickly and requires too frequent maintenance. An overpowered motor wastes energy.
What’s the Difference Between a Belt Drive and Direct Drive?
The amount of air you need to move largely determines this choice. Other considerations are the air temperature and static pressure. The major difference between belt drive and direct drive fans is whether the motor is in the air stream.
A belt and pulley system attached to the motor shaft drives a belt drive fan. In contrast, a direct drive fan has the fan blades or wheels connected directly to the shaft.
Obviously, a direct connection is more mechanically efficient. There is less vibration and there are fewer moving parts to maintain. Direct drive fans are compact and the power from the motor is transmitted directly to the fan blades.
Direct drive fans are less adaptable to changing condition, expose the motor to heated and dirty air and have a higher initial cost that belt drive fans. Belt drive fans are best for applications where the exhaust is more than 122F.
Belt drive exhaust fans use stronger and higher speed motors and can adjust to variable speeds. The motor operates outside the air stream. Maintenance of a belt drive system is more complex than a direct drive system.
So Which Fan Is Right for You?
Selecting the right commercial kitchen exhaust fan is part of your overall ventilation system. There are many calculations and considerations to get to the right answer. Our professionals are always ready to help you. Feel free to contact us with your questions.