Consulting-Specifying Engineer - September 2008 - (Page 15)

M/E Roundtable reduced velocity is adequate for capture and containment at the hood. Rivet: VFDs have been commonly used on fans, which are part of a variable volume kitchen system. These systems use temperature sensors and optic sensors to detect cooking activity under the hood, then send a signal to a processor that automatically adjusts the exhaust and supply rates. Variable volume systems’ typical applications include large cooking operations, such as batch cooking or facilities that operate 12 to 24 hours per day. Melink: VFDs should be specified as much as possible so that direct-drive rather than belt-drive fans can also be specified. Since the belt is the weak link in the overall kitchen ventilation system, the more we design these out of kitchens, the better Demand ventilation is slowly but surely becoming an industry standard, and there is no reason to use both belt-drive fans and VFDs. CSE: How should engineers handle roof venting issues—stacks above rooflines, neighbors’ complaints, wind, etc.? D’Antonio: First, follow the code for venting requirements and always augment that with site-specific needs related to aesthetics, potential odor, and noise control. Mixed-use applications are typically problematic about odor control spreading to nearby residential units. Fan selection is also very important in this regard, with utility set fans providing the best throw distances. Select the lowest possible fan rpm to reduce noise and consider vibration control. Odor can be controlled to a greater level with various secondary particulate removal devices, which are located downstream of the primary filtration in the hood; however, these devices may be costly to install and maintain. Melink: Lower-cost aluminum up-blast fans usually work satisfactorily in lightand medium-duty applications. Rugged steel centrifugal fans usually work better in heavy-duty applications where there are high heat and grease loads. Properly designed parapet walls can help reduce the aesthetic, noise, and wind issues that can bother neighbors and adversely affect fan performance. McGuire: First, prevailing winds may be prevailing, but that does not mean they always blow in the same direction. Distances that may seem more than adequate for dilution of cooking odors be introduced in a variety of locations for this purpose. One example is to provide 85% to 90% of the exhaust requirement at or near the kitchen hood with the remaining 10% to 15% make-up introduced at the dining area HVAC unit. Since the kitchen exhaust is grease-laden air, it typically is not conducive to heat exchange. To effectively employ heat exchange on make-up air, a particulate removal system should be installed to treat exhaust stack efflu- Lower-cost aluminum up-blast fans usually work satisfactorily in light- and medium-duty applications. Rugged steel centrifugal fans usually work better in heavy-duty applications. can disappear as the chef begins to season the menu items. One of my tougher design situations was one in which we put a hood exhaust fan on the roof of a 10-story building. Its discharge was approximately 75 ft from the closest intake. Unfortunately, the ground-floor restaurant that the system served came up with a menu that used garlic to an extreme. Office tenants on the top half of the building began smelling garlic around 10 a.m. while the kitchen was preparing for a busy lunch schedule. The ultimate solution, which we used, contained a level of carbon filtration of exhaust air. Yes, we needed to filter the exhaust for odor control. It required an outlay for installation and a continuing maintenance cost, but it was the appropriate solution to the situation. CSE : How should engineers pro vide adequate make - up air for exhaust fans? For pre-conditioning air with heat exchangers? To avoid depressurization? D’Antonio: Make-up for commercial kitchen exhaust should be provided in a manner to maintain the kitchen area at a negative pressure with respect to the dining area. This will ensure proper odor control. Make-up air can ent. To avoid depressurization of the kitchen and to satisfy codes, the makeup air must be interlocked to operate with the exhaust fans. Melink: Ideally, the make-up air should be provided in a distributed rather than concentrated manner and as far from the hood as possible to minimize drafts that can interfere with proper hood capture. Most make-up air units have heating capability, but the trend is toward both heating and cooling/dehumidifying capability. Rivet: There are various ways to provide make-up air to the space so it is important to evaluate the source and the quality of the outside air being supplied before choosing how to introduce it. If using tempered air, the system should introduce the air using perforated ceiling diffusers evenly distributed throughout the room. Diffusing tempered air contributes positively to the comfort in the space. When supplying non-tempered or marginally tempered air, use supply plenums around the perimeter of the hood that introduce the air downward at low velocities, in order to keep the air near the hood, which reduces the negative effects the air could have on the comfort in the space. Also, a back/rear plenum that introduces air behind and below the Consulting-Specifying Engineer • SEPTEMBER 2008 15

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Consulting-Specifying Engineer - September 2008 Contents Viewpoint Letters News M/E�Roundtable Selecting Appropriate Egress Strategies Commissioning On-Site Electrical Systems Mentoring Control Engineers and Technicians Casting Call for Cx Case Study New Products Equipment Lifecycles Advertiser Index Green Space

Consulting-Specifying Engineer - September 2008

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