To deliver consistency for their customers and drive speed, most large pizza chains utilize conveyor ovens to cook their pizzas and other menu items. These ovens are typically configured with one, two or three ‘decks’ and utilize impinger technology to rapidly cook pizzas. In addition to high velocity fans, the ovens consume a lot of energy to cook the pizzas – around 110,000 Btuh per deck. If not properly captured, this heat can have significant negative impacts on the health, safety and comfort of the team members working in the kitchen. Choosing the right exhaust hood for your pizza oven can mitigate these impacts and save money too.
In many cases the restaurant owner gives little thought to their pizza oven exhaust hood and simply purchases a standard canopy hood. These hoods are typically lower cost, flexible and can capture the heat and grease from various cooking appliances. Although canopy hoods can work, they may not be the best solution for conveyor ovens.
It’s been proven that hoods perform best when they are as close as possible to the heat source. For a three-deck conveyor oven, the bottom deck is located 17” above the floor. We all know how heat expands as it rises, so you can imagine how the heat from the bottom deck will expand as it rises the 63” toward the canopy hood. In order to ensure it captures this heat plume, the canopy hood must have a large overhang beyond each end of the conveyor. Often these hoods are undersized and the heat escapes, resulting in a hot kitchen and discoloration of the ceiling tiles. Also, even when sized properly, canopy hoods require a very high flow rate to capture the heat from a conveyor oven. This high flow rate adds another form of discomfort in the kitchen – noise.
Close-proximity exhaust hoods
An alternative to the canopy is a close-proximity exhaust hood specifically designed for use on conveyor ovens. In addition to its unique shape, the key feature of the close-proximity exhaust hood is that it’s mounted only a half inch above the oven. Being this close to the heat source enables this hood to operate at much lower airflow than a canopy hood. In addition to more readily capturing the heat from the oven, reducing the flow saves energy and provides a quieter kitchen too.
To quantify the difference between the two hood types, a 2-deck oven was evaluated in two separate tests, one with a canopy hood and one with a close-proximity exhaust hood. The ASTM F1704 test protocol was followed which is used to measure the amount of airflow required to capture the heat from cooking appliances. With the oven operating with only the top deck, the canopy hood required 1,300 cfm to capture the heat. Under the same conditions, the close-proximity exhaust hood only required 750 cfm, a 42% reduction.
While a flow rate reduction is interesting, the real question is how it translates into energy savings. The comparative flow rates were input into an energy model that factored in four different climate zones across the U.S. For a 2-deck oven, the model predicted that reducing the flow rate would save an average of $1,311 per year. Because lower exhaust means that less outdoor air is required to replace the exhaust air, most of the savings comes from the reduced cooling and heating of this outdoor air. Therefore, the savings were of course greater in climates with extreme hot or cold temperatures. Although conveyor ovens are well insulated, they still emit radiant heat to the kitchen that must be taken care of by the air conditioning system. Having a hood that captures at a lower flow rate allows this air conditioning to be focused solely on the radiant heat rather than the convective heat escaping from the oven or cooling the large amount of outdoor air.
The model was also run to predict the energy savings from varying the exhaust based upon the number of decks in operation, typically referred to as Demand Controlled Ventilation (DCV). DCV systems are often required when the exhaust is above 5,000 cfm and they can provide a solid business case. The model predicted an incremental 15% airflow reduction from DCV and total incremental savings of $233 per year.
Specifying the proper conveyor oven to deliver hot, tasty pizzas quickly is a big decision. Taking the time to pair it with an efficient close-proximity hood will provide a better environment for the kitchen team and generate energy savings for years to come.
Director of Chain Development, Halton Group
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