Kitchen hoods are one of the greatest opportunities in air diagnostics and balancing. Each system moves 5 to 10 times more air than a heating or cooling system serving an equal area. Balancing these systems provides a valuable service that delivers increased comfort and provides significant energy savings for our customers.
The reason opportunity is so grand for balancing kitchen exhaust systems is that very few of these systems are operating properly. The main problem we find is inadequate airflow.
Little or no makeup air
For a kitchen to be balanced, the amount of makeup air should equal the amount of air exhausted. Makeup air is a combination of the airflow from a makeup air system and from fresh air brought in through the air conditioning and heating equipment.
We frequently find systems where makeup air is only 50% of the exhaust air. This causes the exhaust fan to pull the makeup air it needs from wherever it can get it, usually through the front door every time it’s opened.
The easiest way to show this to your customer is to open the front door and release a small puff of smoke and watch as the smoke disappears into the restaurant.
Poorly performing exhaust fans
Kitchen exhaust fans work in a hostile environment. Many are not maintained or cleaned and deliver half the airflow they were designed to.
Unfortunately, like most air related matters in the HVAC industry, contractors assume that the kitchen systems work properly. Yet, season after season, restaurant and institutional customers suffer from serious comfort issues and excessive costs to run their systems resulting from low airflow. We will begin to do a better job servicing this equipment when we understand kitchen exhaust system performance and learn to capitalize on the opportunities before us.
It’s not uncommon for a kitchen system to move 10,000 CFM through a 1,000 sq. ft. kitchen. With this much air moving through a small space, opportunities are everywhere for diagnostic work and balancing.
Here’s what we find most often:
· Extreme discomfort, yet no one knows what to do or even whom to call. Too hot in the summer, too cold in the winter.
· High utility bills. But what's using all the electricity?
· High turnover in employees. They can’t stand the heat, so they find a more comfortable kitchen.
· Uncomfortable dining rooms. If the exhaust airflow is far greater than the makeup air, the hood steals the dining room’s conditioned air every time the front door is opened.
· Greasy kitchens. Insufficient exhaust or poor airflow patterns.
· Cold food. Many restaurants have a small window where the food is placed for the server. These are often between the dining room and the kitchens. If the makeup air is 3,000 CFM low, where’s the rest of the exhaust air going to come from? We have measured velocities over 1000 ft. per minute through food prep windows where plates of food are waiting to be served - even the heat lamps can’t overcome this cooling effect.
Our temperature recorders have tracked kitchen conditions at over 110F during operating hours. Not so good for the food quality and not too healthy for employees either.
By balancing these systems, we have cut some restaurant utility bills in half.
· Sometimes the front door of the restaurant is difficult to open because of a lack of makeup air.
· In the western U.S., many contractors use evaporative or swamp coolers to move the makeup air. Evaporative cooler airflow is based what is referred to as industry standard airflow. This is fan airflow at zero static pressure. When the unit is installed, actual airflow is often only 50% when the unit is attached to any ductwork. The result very low makeup airflow.
In recent years we have seen almost every major restaurant chain take extreme measures to reduce electrical expense and provide some sort of comfort to their cooks and chefs. They have tried compact split cooling units, chilled water systems with coils and fans, reduction of exhaust capacity, and monthly cleaning of exhaust systems. These are good attempts, but are not the one thing that is needed - a balanced kitchen system.
Next time you’re in a commercial kitchen with of one of your customers, strike up a conversation about their feelings about the performance of their kitchen exhaust systems and see if you can find a new opportunity to serve your customers and enhance your financial picture with balancing.
Rob Falke serves the industry as president of National Comfort Institute a training company with technical and business level membership organizations. If you're an HVAC contractor or technician interested In a free Kitchen Exhaust Balancing Procedure, contact Rob at [email protected] or call him at 800-633-7058. Go to NCI’s website at nationalcomfortinstitute.com for free information, articles and downloads.