Ovens in Commercial Food Service Operations

END-USE BRIEFING Summary A Quick Tutorial on an Important Energy End Use An oven can be simply described as a fully enclosed, insulated chamber used to heat food. There are many variations of this basic concept in the commercial Ovens in kitchen, but each type of commercial oven cooks by controlling the temperature and/or humidity of the oven cavity. Commercial The oven’s versatility makes it useful in Food Service many types of food service operation. Efficiencies vary between the different Operations types of ovens and fuel sources. Stan- dard-efficiency gas ovens are typically 30 to 40 percent energy efficient; high- efficiency gas ovens between 40 and 50 percent. Electric efficiencies run between 50 and 80 percent. This end-use briefing offers a quick tutorial on the common types of ovens in commercial food service operations. It covers the following topics: · Definitions of key terms, such as standard and convection. Summary .............................................1 · Description of common oven Definitions of Key Terms ...................2 types and their operational characteristics. Conceptual Overview .........................3 Common Oven Types and · Description of new oven tech- Categorization.....................................3 nologies and their operational characteristics. New Oven Technologies ....................7 · Typical applications of each type Typical Customer Applications.........8 of oven. What to Look for in the Field.............8 · Key field observations to help as- Tips for Efficient Operation And sess operational efficiency and energy Maintenance........................................8 conservation opportunities. References to More Information........9 Copyright © May 1997, Pacific Gas and Electric Company, all rights reserved. Revised 12/10/1999 · References to other documents that induced in the oven cavity by fans or provide detailed information on the top- blowers. ics in this briefing. · Indirect Fired: Describes gas ovens which route the combustion products Definitions of Key Terms around the bottom, sides and top of the oven without entering the cooking cavity. The oven cavity walls of indirect · Air Impingement: Jets of air are di- fired ovens become hot and heat is rected onto the food product using a transferred to the food by either con- ported manifold. vection or forced convection. · Atmospheric Burner: A burner · Idle Energy Rate: The rate at which which jets gas and air through a hole an empty oven uses energy to maintain (“burner port”) at which point it mixes its cavity temperature at the thermostat and is ignited. This “Bunsen” type set point (e.g., 350ºF). burner shows a blue flame when prop- erly adjusted. · Infrared Burner: A burner made of porous ceramic plates or metal screens. · Conduction: A cooking process in Combustion of premixed air and gas which heat is transferred to the food via takes place on the burner surface, direct contact with a heated medium which can reach 1800ºF. The high sur- (e.g., ceramic hearthstone, firebrick or face temperatures cause the material to composite hearth.) emit radiant heat. Up to 50 percent of the energy in the gas can be converted · Convection: A cooking process in to radiant heat. which currents of hot air transfer heat to the surface of the food. Convection ov- · Natural Convection: Convection ens use fan(s) to circulate hot air in the created in the oven cavity due to the oven cavity. natural movement of hot air heated by burners, elements or heated cavity walls · Cooking Energy Efficiency: The (i.e., without the use of fans or blowers). ratio of the quantity of energy absorbed by the specified food to the quantity of · Oven Capacity: Maximum amount energy input to the oven during a cook- of food that can be cooked at one time ing energy efficiency test, expressed as (e.g., 6 12”-diameter pizzas, 40 pies, a percent. 20 to 40 sheet pans). · Direct Fired: Describes gas ovens · Oven Cavity: The cooking zone, which route the combustion products chamber or compartment in an oven. from the burners through the cooking cavity, transferring heat directly to the · Radiant heat: Hot surfaces emit ra- food from the hot gases. diant heat. In ovens, the heat radiated by burners, elements or the heated cav- · Forced Convection: Convection ity walls moves towards the food. PG&E Energy Efficiency Information© “Ovens in Food Service Facilities” Page 2 · Rated Input: (Also “Nameplate In- convection ovens are divided into sub put”) The maximum rate of energy con- categories (rack, combination, con- sumption for an appliance. veyor, rotisserie, etc.). The matrix in Table 1 presents the characteristics of each sub category, along with common Conceptual Overview use and customer application. Standard Commercial ovens are available for use with gas, electricity or liquid propane Standard ovens use natural convection and come in many sizes. (hot air currents) and radiant heat to cook food products. These ovens can An oven heats food by surrounding it be used for nearly all types of food with hot air. Heat is transferred to the preparation. Because they do not use food via convection, conduction, radia- blowers or fans to move air inside the tion and steam, either singularly or in oven cavity, standard ovens are used combination. In standard ovens the for precision-baking sensitive pastry burners or elements heat the air inside products such as meringues, cream the cavity causing natural convection puffs and pastry shells. Standard ovens currents which transfer heat to the sur- are the least expensive to purchase, but face of the food. What the industry calls they are not as fast-cooking or flexible a “convection” oven employs motorized as forced convection ovens. fans or blowers to create forced convection currents in the cavity; this cooks Standard ovens usually have simple the food faster while maintaining uni- controls, limited to a thermostat and a form heating. selector that allows the oven to bake or broil. Modulating thermostats, which Heat may be transferred to a oven ei- adjust the burner incrementally, are ther indirectly or directly. In indirect-fired most common. ovens, the hot combustion products of the gas heat the bottom, sides and top Range Oven of the oven without entering the cooking cavity. In direct gas-fired ovens the hot The most common standard oven is the combustion products are directed range oven. Range ovens are part of through the cooking cavity rather than the base of a rangetop, and are the fa- around the cavity. Heat is transferred miliar type of oven seen in most resi- directly from the hot gases to the food. dential applications. Gas range ovens are heated with at- Common Oven Types and mospheric gas burners located directly Categorization below the oven cavity. The flue gases are routed around and/or through the cavity. In electric ovens the elements Ovens fall into two common categories: are placed in the top and bottom of the standard (or natural convection) and oven cavity, where they add both radi- forced convection. Standard and forced PG&E Energy Efficiency Information© “Ovens in Food Service Facilities” Page 3 ant and convective heat; they also may fired. Manufacturers differ in how they be placed underneath the oven cavity. route the flue gases and how they mix them with cavity air. Gas burners may Deck Oven be protected from air currents by an ar- rangement of baffles, and the flue gases These ovens have a flat, wide cavity. directed around or through the cavity. The floor of the cavity is referred to as a Alternatively, the flames and flue gases deck, and it is usually possible to place may be directed into tubes that act as pans or the food product itself directly heat exchangers and vent into the flue. on the deck surface. These ovens are usually freestanding, and may consist of Forced convection ovens come in full- one to four stacked compartments. size or half-size capacities, depending on whether they are dimensioned to ac- Compartment size and construction cept standard full-size 18 x 26 x 1” or vary. Manufacturers list deck ovens by half-size 18 x 13 x 1” sheet pans. Full- intended use. Baking and roasting com- size ovens have large interior cavities partments may be combined into one capable of handling up to six full-size oven with multiple cavities; the baking pans. Half-size models accommodate compartments are about half the height up to five half-size pans. Countertop of roasting compartments (7” vs. 15”). and range type convection ovens are Specialized deck ovens for baking pizza also available, as are high-capacity roll- may have modified decks and/or damp- in or rack ovens. The convection princi- ers to adjust temperature. ple has also been applied to conveyor and rotisserie ovens. Deck ovens also can be used to cook a wide variety of other foods; the limiting In general, convection ovens offer more factor is the height or thickness of the control over cooking than standard ov- food product. ens. Convection ovens generally use accurate electronic sensors and ther- Convection mostats. Many gas models feature electronic ignition and controls. Also, Convection ovens force air through a most of the newer gas and electric motorized fan (or blower) which blows models have programmable cooking heated air throughout the oven’s cavity. computers. Some ovens allow the user The speed of the fan affects cook time to control cooking by regulating fan and uniformity, as does the pattern of speed as well as temperature, humidity airflow through the interior. Gas con- and cooking time. vection ovens are available with single or multiple burners. Burners are usually Rack Oven located at the bottom of the oven cavity, or between the cavity and the insulated Rack ovens are tall stainless steel oven wall. Until recently, most gas con- boxes.

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