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Types

Commercial kitchen heating, ventilating, and air conditioning systems are similar to standard building designs except for make-up air systems and hoods. Make-up air systems include wall registers, ceiling diffusers, and slotted ceiling panels. Kitchen hoods are designed for specific cooking situations and are divided into two broad categories: Type I and Type II.

Type I hoods are used for the collection and removal of grease and smoke. They always include filters or baffles for grease removal and are normally required over fryers, ranges, griddles, broilers, ovens, and steam jacketed kettles.

Type II hoods are general-duty hoods for the collection and removal of steam and water vapors, heat, and odors where grease is not present. Therefore, these units may not have grease filters or baffles. They are typically used over dishwashers, steam tables, and similar equipment. However, they may also be specified for use over other equipment when allowed by local codes and authorities. Always check with a design professional for these rulings.

Ventilation Study

As part of a larger study to identify optimal designs for commercial kitchen appliances, researchers tested one electric griddle and one gas griddle in operation with two hood types: an exhaust-only, wall-mounted canopy hood and a custom-engineered backshelf hood.

These tests revealed the following:

  • The cooking capture and containment (C&C) flow rate under a canopy hood for the electric griddle is 241 scfm/lf, 13% lower than for the gas griddle, 40% lower than the 400 scfm/lf building code value, and 7% lower than the 260 scfm/lf Underwriters Laboratories (UL) listing.
  • The cooking C&C flow rate under a custom-engineered backshelf hood for the electric griddle is 100 scfm/lf, 9% lower than for the gas griddle, 67% lower than the 304 scfm/lf building code value, and 26% lower than the 136 scfm/lf UL listing.
  • The idle C&C flow rate under a canopy hood was 26% and 32% less, respectively, than the cooking C&C flow rate for gas and electric griddles, and was 0.5% and 22% less, respectively, under the backshelf hood.
  • At the cooking C&C flow rate, the electric and gas griddles required about 60% lower flow under the backshelf hood than under the canopy hood. These results indicate that custom-engineered backshelf hoods can operate with exhaust flows about 65% below code values, and that electric griddles with both hood types require about 10% less exhaust than gas units. Designers should apply site-specific data when evaluating equipment options.

Background

To help electric utilities and the food service industry minimize commercial kitchen exhaust hood operating costs, EPRI is undertaking a series of tests to determine the exhaust requirement for a wide range of food service equipment and ventilation hoods. The exhaust requirement is the air flow needed to capture and contain cooking products and heat. Findings compare actual exhaust requirements with building code and UL levels. The ventilation tests described here examined electric and gas griddles operating under a wall-mounted canopy hood and under a custom-engineered backshelf hood using American Society for Testing of Materials (ASTM) standard method production conditions.

Test Equipment & Conditions

Both griddles measured 28 in by 3 ft. The electric griddle was rated at 17.1 kW and the gas griddle at 90,000 Btu/h.

The canopy hood, an exhaust-only, wall-mounted type, was 5-ft wide by 4-ft deep and UL listed at 260 scfm/lf for cooking operation. The backshelf hood, a custom-engineered, exhaust-only type, was 3.4- ft wide by 3.5-ft deep by 5-ft high and was UL listed at 136 scfm/lf for cooking operation. Both hoods had three nominal 20-in by 20-in standard baffle filters.

For each test, researchers positioned the griddle under the hood in accordance with ASTM F1275-95 and performed the tests using ASTM F1704-96. The temperature of the griddle was set to a calibrated 375°F.

The project team evaluated C&C with visualization techniques aided by a smoke generator. They ran each test a minimum of three times in a consecutive series to attain statistical certainty as prescribed in ASTM F1704-96.

Results

Figure 1 shows C&C flow rates for electric and gas griddles operating under both canopy and custom backshelf hoods, as well as flow requirements under two specification options. Operating under a canopy hood, the electric griddle’s measured cooking C&C flow rate is 241 scfm/lf, 40% lower than the rate required by building codes and 7% lower than that listed by UL. The idle C&C flow rate is 165 scfm/lf, 32% lower than the cooking rate. The gas griddle’s measured cooking C&C flow rate is 276 scfm/lf, 31% lower than the rate required by building codes and 6% higher than that listed by UL. The idle C&C flow rate is 203 scfm/lf, 27% lower than the cooking rate.

Operating under a custom-engineered backshelf hood, the electric griddle’s measured cooking C&C flow rate is 100 scfm/lf, 67% lower than the rate required by building codes and 26% lower than that listed by UL. The idle C&C flow rate is 78 scfm/lf, 22% lower than the cooking rate.

The gas griddle’s measured cooking C&C flow rate is 110 scfm/lf, 64% lower than the rate required by building codes and 19% lower than that listed by UL. The idle C&C flow rate is 109 scfm/lf, 0.5% lower than the cooking rate.

References

  • Commercial Kitchen Ventilation Performance Report, Electric Griddle Under Canopy Hood, EPRI TR-106493-V4, July 1996.
  • Commercial Kitchen Ventilation Performance Report, Gas Griddle Under Canopy Hood, EPRI TR-106493- V3, July 1996.
  • Commercial Kitchen Ventilation Performance Report, Electric Griddle Under Custom Engineered Backshelf Hood, EPRI TR-106493-V6, July 1996.
  • Commercial Kitchen Ventilation Performance Report, Gas Griddle Under Custom Engineered Backshelf Hood, EPRI TR-106493- V5, July 1996.
  • Too Much Hot Air: Reexamining Commercial Kitchen Ventilation Systems, EPRI TB-105709, October 1995.
  • Minimum Energy Ventilation for Fast Food Restaurant Kitchens, EPRI TR-106671, July 1996.
  • Standard Test Method for Performance of Commercial Kitchen Ventilation Systems, ASTM F1704-96.
  • Standard Test Method for the Performance of Griddles, ASTM F1275-95.