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.

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