System Neurology of a Kitchen Ventilation System

Ok, I’ll admit, I made up the fancy title to pique the interest of the engineering crowd.  It has a nice bio-medical ring to it.  However, I thought it was somewhat appropriate, given that this article will be discussing the connections and control sequences for commercial kitchen ventilation (CKV) systems.

Several components make up a commercial kitchen ventilation CKV system.  There are hoods, the exhaust fan, the make-up air fan, fire suppression system, and often a demand control system.  Occasionally, you’ll find a pollution control unit substituting for the exhaust fan.  Add in the fact that the make-up air can have limitations on turndown (the amount of make up air that can be reduced,) and it makes things interesting when looking at how to connect it all and make it work properly.  One primary concern is “what controls everything?”. 

For simplicity, these will break down into two main categories.  The first is when there is a demand control system present.  The demand control systems determine when cooking occurs, when there is not cooking, and when we can reduce the exhaust cfm because there isn’t cooking, but there is heat.  These systems often turn the fans on and off automatically, depending on the status of the cooking equipment.    As such, these systems really need to be “in control” of the operation to ensure the IMC 507.1.1 interlocks with cooking appliances and properly directing the exhaust and make-up air volumes to maintain space balance.  Once you have a demand control system involved, expect that system to orchestrate the operations.

The second category would be, you guessed it, anything without a demand control system.  This arrangement is more straightforward.  When there is no demand control involved, the hood system needs to be wired together for an on-off operation that is simple and elegant.  The hoods can have switches on them to activate a contactor/overload or VFD for the exhaust fan, while simultaneously engaging the make up air.  In order to ensure the make up air is “off” upon fire conditions, the make up air can be wired through the fire suppression system to shut off make up air during a fire condition.  Turning off the make up air when the fire suppression discharges is a code requirement. The hood can still contain sensors for an interlock with the appliances. It turns on the exhaust fan automatically using two-position thermostatic switches – where they are seen by the fan like another “fan switch” to turn the system on upon encountering enough heat. 

What about the fire suppression system? Isn’t that important?  Why yes, it is!  View the fire suppression system as the guardian angel of the commercial kitchen system.  It doesn’t do anything most of the time until it’s activated by a manual pull station or a fusible link in the hood melts (due to an appliance or duct fire).  Once the fire system is activated, it takes over control of the ventilation system.  Typically, this means it wants the exhaust fan “on” the make-up air fan “off” and stays this way until things have stabilized and someone can come in to reset it. 

With a demand control system varying airflow, it’s important to have all the pieces of the puzzle tied together.  For instance, the main controller for the demand control system would need to tie to the fire suppression so it knows when to command the fans if there is a fire.  Additionally, if there is a pollution control unit or hoods that require wash-down, it has to be coordinated so that the fan doesn’t run during these events.  With PCU’s, often there is a “dry out” period, which the system needs to command the fan “on” for. It’s possible that the make up air unit cannot turn down below a certain speed, due to the limitations of its heating section or cooling section.  Those variables need to be plugged into the demand control system. 

The nice thing for the commercial kitchen designer and engineers is that the demand control systems can do much more than just kitchen airflow adjustments.  These systems have become advanced enough to handle other tasks or help with other ventilation goals within the space.  An example would be a large dining space that can be used for a meeting space when food isn’t being served.  If more ventilation air is brought into the space, there may be a general exhaust fan to maintain pressure in the space.  That general exhaust fan can be removed, and the hoods, with their fans, can be commanded “on” by the BMS to do that work.  Perhaps there is CO2 monitoring required.  These systems can be connected to handle that.  Even more far-fetched items, like monitoring the temperature of a walk-in cooler – or even whether the door to the cooler is open or closed – can be handled by the more advanced systems.

You can see that the demand control system needs to be the component in control of the commercial kitchen system.  It will integrate smoothly with all the other components, as long as it’s designed from the outset.  This is why it is recommended that if the demand control system is not in the mechanical package, where those integrations happen commonly, ensure there is language in the design for coordination between foodservice and the mechanical engineer. The coordination will save a lot of headaches during installation.  Even more importantly, it’s recommended to utilize components from the same manufacturer with all parts of the system so they can seamlessly work together.  As an example, PCU’s and demand control systems from different manufacturers provide for challenging wiring solutions to allow each of them to know what the other is trying to do.  Finally, some simple wiring and components can provide a system that works adequately for an on-off operation when there isn’t a demand control system. 

Published by:
Chris Lowell
Regional Sales Manager, Halton Company
Follow Chris Lowell on LinkedIn

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Our recommended next article would be: Demand Control Ventilation Systems for Commercial Kitchens, how do they differ, how are they the same?

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