Restaurant Vent Hood - Commercial Kitchen Ventilation Education

KITCHEN VENTILATION 102

Ventilation is the single most important factor in the design, construction, and operation of a commercial kitchen.

An exhaust hood is an air intake device connected to a fan that removes smoke, cooking vapors, grease, steam, heat, and odors that are made by cooking and ware washing equipment.

There are several different types of vent hood systems on the market, the most popular being the Type I Canopy hood. A canopy hood is basically a hood that is hung from the ceiling and covers all of the cooking equipment under it. None of the equipment can extend outside of the hood and there should be a minimum of 6" clearances to spare on each end of the hood. Canopy hoods used for cooking equipment will also have a "compensating hood", or fresh-air make-up hood around the perimeter of the canopy hood to bring fresh outside air back in to replace the exhaust air going out. Therefore, there are two integrated components to a kitchen ventilator hood - exhaust air and make-up air.

A kitchen ventilation system also works interdependently with the buildings HVAC system to produce a properly balanced flow of air to the building. A very slight negative air pressure is preferred in a commercial kitchen in order to keep the heat and odors of a kitchen from migrating back into the dining area or other parts of the building.

There are many factors involved in determining the size and type of kitchen vent hood required . A lot depends on the type and amount of cooking equipment that will be going under the hood. #1 the equipment must physically fit under the hood and have at least 6" overhang left on each end, not extend out in front of the hood, and be matched to the proper size fans (air flow requirements) for the particular equipment.

There are four classes of cooking appliances that require different cfm or air flow requirements. These are referred to as light duty, medium duty, heavy duty, and extra heavy duty. By this we mean the heavier duty equipment expends more heat, smoke and grease and hence requires a higher volume of air flow to remove more smoke and heat. Just a few examples are as follows:

• light duty - ovens, kettles, and other non-grease producing appliances
• medium duty - fryers, grills, griddles
• heavy duty - electric broilers and char broilers
• extra heave duty - gas char broilers, woks, mesquite burning broilers

Ducting is another major component to a ventilation hood. The ducting must be installed in compliance with local and national building and fire codes. Ducting should have the shortest and most direct path to exiting the building. It is also important that all duct sizing be properly calculated according to the amount of air flow and velocities required for proper performance of the hood while keeping the balance of air in the building at a proper level as talked about previously. Exhaust fan ducts must be welded water tight and wrapped with approved fire wrap insulation. Bends and elbows in the ducting should be kept to a minimum so as to allow for better air movement. Horizontal runs should have a slight slope downward (approximately 1/4" per foot) back toward the hood so that grease and water vapor can run back to the grease catcher or water drain.

A certified fire control system will also need to be installed in all commercial kitchen ventilation hoods that have cooking equipment under them.

Visit our website at: www.JeansRestaurantSupply.com

Contact Jean's Restaurant Supply if you have any questions about commercial kitchen vent hoods. 1-866-618-4999

COMMERCIAL VENT HOODS - AIR BALANCE

                                                         Restaurant Vent Hood - Air Balance

 Call us @ 1-866-618-4999 if you have any questions about commercial restaurant hoods or air balance in a kitchen. www.jeansrestaurantsupply.com

Below is from an actual service call:

I was dispatched out to do an air balance on a new vent hood at a new restaurant. The contractor bought the new vent hood from us but he had the installation done by someone else. Upon arrival we unpacked our electronic micro manometer instrument (which measures air flow in cfm's) and set it up to take our air flow readings. Readings are taken at each filter of the exhaust and at numerous locations across the make-up air to measure cfm's of each fan and measure the balance across the length of the hood. Several measurements are taken at each location and averaged together to get a more accurate average. Once the final figures are all put together we can analyze the air flow to see if both the exhaust air and the make-up air is actually balanced and flowing as it should.

After finding the results of the air balance test we can determine if the unit is functioning as it should or if any adjustments need to be done to either the exhaust fan or the make-up air fan. Each fan can be sped up or slowed down if needed to make any required adjustments in the balance of the air flow if need be.

To slow a motor down and decrease air flow to the commercial vent hood you need to decrease the size of the variable motor pulley and then make a readjustment to the belt. To speed up a motor and increase air flow you need to increase the size of the variable motor pulley and then readjust the belt tension. When you increase the size of the pulley you are increasing the speed of the motor and you must check amperage draw of the motor to be sure you don't speed the motor to a point to where its amperage draw is more than the listed motor amp draw rating that is listed on its nameplate.

You can also increase or decrease speed by adjusting the pulley on the blower wheel, however, the opposite rule applies to adjusting the blower wheel. Instead of increasing pulley size to increase speed, it would actually decrease speed if you increase pulley size don the blower wheel pulley. So you see, increase motor pulley size, increase speed, increase blower wheel pulley size, decrease speed of rotation.

Instances where some of the smaller fans use direct drive motors the speed cannot be changed unless it has a variable speed control mounted on it as many of the direct drive fans have. Then you simply turn the control up or down to increase or decrease speed.

Once the motor speeds have been altered a new air balance test would need to be performed to analyze the results and see if the hood has been properly balanced.

If you have questions about vent hoods or air balance on restaurant vent hoods please visit us online at: Jean's Restaurant Supply or give us a call at 1-866-618-4999

Commercial Vent Hoods - Jean's Restaurant Supply

                                                         Restaurant Vent Hood - Air Balance

 Call us @ 1-866-618-4999 if you have any questions about commercial restaurant hoods or air balance in a kitchen. www.jeansrestaurantsupply.com

Below is from an actual service call:

I was dispatched out to do an air balance on a new vent hood at a new restaurant. The contractor bought the new vent hood from us but he did the installation. Upon arrival we unpacked our electronic micro manometer instrument (which measures air flow in cfm's) and set it up to take our air flow readings. Readings are taken at each filter of the exhaust and at numerous locations across the make-up air to measure cfm's of each fan and measure the balance across the hood. Several measurements are taken at each location and averaged together to get a more accurate average. Once the final figures are all put together we can analyze the air flow to see if both the exhaust air and the make-up air is actually balanced and flowing as it should.

After finding the results of the air balance test we can determine if the unit is functioning as it should or if any adjustments need to be done to either the exhaust fan or the make-up air fan. Each fan can be sped up or slowed down if needed to make any required adjustments in the balance of the air flow if need be.

To slow a motor down and decrease air flow to the commercial vent hood you need to decrease the size of the variable motor pulley and then make a readjustment to the belt. To speed up a motor and increase air flow you need to increase the size of the variable motor pulley and then readjust the belt tension. When you increase the size of the pulley you are increasing the speed of the motor and you must check amperage draw of the motor to be sure you don't speed the motor to a point to where its amperage draw is more than the listed motor amp draw rating that is listed on its nameplate.

You can also increase or decrease speed by adjusting the pulley on the blower wheel, however, the opposite rule applies to adjusting the blower wheel. Instead of increasing

pulley size to increase speed, it would actually decrease speed if you increase pulley size don the blower wheel pulley. So you see, increase motor pulley size, increase speed, increase blower wheel pulley size, increase speed.

Instances where some of the smaller fans use direct drive motors the speed cannot be changed unless it has a variable speed control mounted on it. Then you simply turn the control up or down to increase or decrease speed.

Once the motor speeds have been altered a new air balance test would need to be performed to analyze the results and see if the hood has been properly balanced.

If you have questions about vent hoods or air balance on restaurant vent hoods please visit us online Jean's Restaurant Supply or give us a call at 1-866-618-4999