Consulting-Specifying Engineer - September 2008 - (Page 16)

M/E Roundtable appliances can be used, reducing the diffusion of the make-up air into the space. CSE : What are the advantages of direct-drive motors and belt-driven motors? Are certain applications ideal for each? Rivet: Direct-drive motors are most applicable when maintenance is a concern and when air volume and static pressure requirements are low enough McGuire: Personally, I like using directdrive motors for most grease hood exhaust designs. The prime advantages come from knowing that the fan itself is running when electricity is on. In addition, proper selection will limit failure during times of increased temperatures in the airstream. The belt-driven fans must have cowls over the belts to keep them out of the airstream. The significant problem is that of belt maintenance. The higher temperatures can lead to shortened life for belts. test is a visual one made by a UL inspector, who observes the removal of visible cooking vapors. If, in the judgment of the inspector, the hood captures and contains this visible effluent, then the tested exhaust airflow rate passes the test. What UL 710 does not test for is the amount of heat escaping the hood at a given airflow. Listed hoods can have a fire damper to protect ductwork and maintain temperatures below 375 F or can function without a fire damper. UL 710 does not cover evaluation of the exhaust hoods with respect to their grease extraction efficiency. UL 1046test protocol was established for grease filters used in exhaust systems with Type I restaurant-type cooking equipment. Grease filters are investigated to insure they remove grease from the effluent—drain-off of the collected grease—in such a manner that it does not fall back onto the cooking surface, and limit the projection of flames into the exhaust ductwork when fire breaks out on the upstream face of the filter, and after exposure to grease-laden air. UL Subject 762, “Power Roof Ventilators for Restaurant Exhaust Appliances” covers roof- or wall-mounted ventilators for restaurant exhaust appliances. Melink: The International Mechanical Code, NFPA 96, and the listed hood performance ratings provided by the manufacturer are the main ones. However, state and local codes may be different and dictate other approaches to designing and installing the kitchen ventilation system. Rivet: I agree. The most recognized code in the kitchen ventilation industry is the International Mechanical Code (IMC 2006). In some areas, the International Building Code 2006 is realizing greater recognition. The predominant standard in commercial kitchen is NFPA 96, 2008 edition. McGuire: Local codes always dictate the minimal permissible levels of design, but that may not be the correct way to engineer the system. The engineer must remember that a code only dictates the worst design permitted by law. NFPA 96 Personally, I like using direct-drive motors for most grease hood exhaust designs. The prime advantage comes from knowing that the fan itself is running when electricity is on. to meet direct-drive performance limitations. Benefits include: • Elimination of bearings and belts that wear over time, mitigating maintenance on the fans • Elimination of energy losses due to belts; thus, direct-drive fans are in general slightly more efficient • Reduced risk of downtime due to broken belts. Belt-driven motors are ideal for most applications because they have very broad performance ranges and provide greater flexibility in the field for balancing. Benefits include: • Performance flexibility; different belt and pulley combinations can be used to adjust for slight variations in static pressure and air volume • High air volume and high static pressure capabilities • Lower cost; typically, they are less expensive than direct-drive motors. Melink: From reduced maintenance and fire safety concerns to improved air balance and energy efficiency, direct-drive fans are the way of the future. Disadvantages include slightly higher cost, a motor that is more exposed to the airstream on up-blast fans, and a motor that is typically more difficult to replace if that ever becomes necessary. But the advantages of direct-drive far outweigh the disadvantages. C S E : W h at c o d e s / st a n d a r d s d o engineers need to be aware of when working in these facilities? D’Antonio: The following codes, standards, and test protocols govern commercial kitchen ventilation. The 2006 International Mechanical Code addresses commercial kitchen hoods, exhaust ducts, and exhaust equipment in Sections 506 and 507. “Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations,” in NFPA 96, details the minimum fire safety requirements related to the design, installation, operation, inspection, and maintenance of all public and private cooking operations, excluding single-family residential usage. These requirements include, but are not limited to, all manner of cooking equipment, exhaust hoods, grease-removal devices, exhaust ductwork, exhaust fans, dampers, fire extinguishing equipment, and all other auxiliary or ancillary components or systems that are involved in the capture, containment, and control of grease-laden cooking effluent. The 2007 ASHRAE Handbook: HVAC Applications addresses kitchen ventilation. UL 710 test protocol was established to determine minimum exhaust rates for 400, 600, and 700 F surface temperature appliances. The airflow portion of the 16 Consulting-Specifying Engineer • SEPTEMBER 2008

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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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