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A large portion of kitchen ventilation planning is dedicated to properly exhausting cooking effluent. Appliance layout and energy input are evaluated, hoods are located and specified, ductwork size and routing are determined, and exhaust fans are specified to remove the proper volume of air. Unfortunately, much less time is usually dedicated to planning how the exhausted volume of air will be replaced, although an air balance schedule is commonly used to indicate the source of the makeup air (MUA).
Overlooking MUA delivery system details can have a negative impact on the performance of an otherwise well-designed kitchen. Cross drafts and high air velocities due to improper introduction of MUA can result in failure of the hood to capture and contain effluent from the appliances. This effluent spillage may include convective heat, products of combustion (carbon dioxide, water and potentially carbon monoxide), and products from the cooking process, such as grease vapor and particles, odors, water vapor, and various hydrocarbon gases.
Overall commercial kitchen ventilation issues include indoor air quality, fire prevention, safety, employee comfort and equipment first costs, energy operating costs and maintenance costs. This article presents strategies that can minimize the impact that makeup air introduction has on hood performance.
To address these MUA issues, a two-year research project was sponsored by a state government energy agency1 and large utility. Subsequent testing for several manufacturers augmented this public research initiative. This research project focused on how the introduction of makeup air affects the capture and containment (C&C) performance of commercial food service ventilation equipment. The investigation included combinations of hoods, appliances, cooking conditions, MUA strategies and other factors.
Three hood types were tested: wall-mounted canopy, island-mounted canopy, and proximity (backshelf). Charbroilers and griddles, representing heavy-duty and medium-duty appliances respectively, were tested during idle and representative cooking conditions.
The six MUA strategies included: displacement ventilation (base case), ceiling diffuser, front face diffuser, air curtain diffuser, backwall supply, and short-circuit supply (Figure 1). Certain features of the hoods and local makeup air devices were modified to represent designs and configurations found in commercial kitchen installations, but not necessarily the best or worst designs or configurations.
To determine which MUA strategy offered the most effective operation while providing full capture and containment (C&C), the research team tested...