Kitchen Exhaust Fail

Kitchen exhaust is always a point of contention.  Where to locate it and how much to exhaust can be a challenge to determine.  Luckily there is code out there to assist the engineer in determining this.  Unfortunately a lot of engineers don’t know this or do not follow it.

In this particular Kitchen Catastrophe Evolve Mechanical Solutions has been retained to fix a mistake another engineer made.  The exhaust termination is above a patio with downward facing blades.  The problem is the exhaust is smelled by the patrons below and thus no one wishes to sit there, causing a loss of revenue to the restaurant.  Click here: Kitchen Exhaust Fail to see a video of a test done on the system.  You’ll see not only does the exhaust blow onto the patrons it gets drawn into the building due to negative pressure.

The solution:

In NFPA-96 the Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations states:

7.8.3(4) The exhaust flow directed perpendicularly outward from the wall face or upward.

Click here to see copy of NFPA-96 7.8.3(4)

In Vancouver the engineer must complete the K2 – Kitchen Ventilation Details Checklist.  On this list it requests the engineer to confirm:

Item#3 e)  For a wall termination, the exhaust flow is directed upward or perpendicularly outward from the wall face. [7.8.3.(4)]

Click here to see copy of K2 Item #3 e)

The above two codes that are fundamental to kitchen design, if followed by the engineer, would be enough to avoid this problem.  So to fix the issue we changed the blades from downward facing to upward thus pushing the exhaust up and away from the patio.

However we weren’t done there, as I mentioned before there was negative pressure in the building.  What this means is that the kitchen is exhausting much more air than it’s bringing in.  The amount of air you need to bring in (make-up air) should be between 80-96% of the kitchen exhaust rate. This kitchen was around 40% thus creating drafts, outside doors were difficult to open, cold spots felt around doors and windows and of course when you blow down kitchen exhaust over a door you get smoke and smells in the dining area.

Luckily the make-up air fan had enough capacity to bring in the air to meet our demands.  So all we needed to do was to adjust the pulley ratio and change the motor to a higher horse power.