Appliance Design - November 2007 - (Page 42)

GAS TECHNOLOGY MODULATION MIGRATION A blower valve developed by GTI. Burner for steam generator. Source: GTI More precise control benefits a growing number of applications. G by larry adams 42 applianceDESIGN November 2007 as modulation systems have evolved in the last 20 years, spreading in use from the large-scale boilers of a couple decades ago to applications today such as residential furnaces, commercial food service equipment, water heaters and other gas appliances. Some modulating systems modulate gas only, but more efficient systems modulate both air and gas that is inputted to a gas-fired appliance. Variable control of gas flow can be accomplished by means of a multi-position valve or pressure regulator to control the flow of gas into the combustion chamber, or by using a variable-speed premix blower to regulate the air/gas mixture headed to the burner. By using modulation, the unit stays on for a greater length of time, but at a lower firing rate, reducing the number of on/off cycles and reducing the amount of time the burner spends firing at full rate. This is unlike traditional gas-fired systems that are either 100 percent on or 100 percent off. The core concept is already well established in large-scale commercial heating applications. Now, the roster of modulating appliances includes commercial foodservice appliances and residential appliances such as gas furnaces, water heaters, cooking equipment, and even fireplaces. This short, and certainly incomplete list is most likely to grow as the benefits of modulation such as improved performance, precise control, better energy efficiency, lower emissions and consumer’s personal comfort in heating applications, all begin to outweigh the drawbacks of higher cost and complexity. The technology migration may be sped along as the experience from the earlier applications provides a knowledge base from which to evolve. “It isn’t a great leap like it was for other technologies such as going from directspark ignition to hot-surface ignition systems,” says Denny Gambiana, vice president at Varidigm Corp., Plymouth, Minn., a manufacturer of burner controls. “Those were different technologies that had to be proven throughout the industry. Modulation had already existed on boilers and big systems for decades, so the change should be more intuitive.” There are two approaches to modulation — multi-stage and variable modulation. For multi-stage products, which some experts say is not “true” modulation, the unit may have one or more fixed levels of output that are less than full. www.applianceDESIGN.com http://www.appliancedesign.com

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Appliance Design - November 2007 Contents Editorial Shipments/Forecasts News Watch Today’s LEDs are Brighter and More Colorful than Previous Versions, Allowing Designers More Opportunities to Improve and Differentiate Their Products. When Converting from CCFL to LED Backlights in LCD Panels, New Driving Methods are Needed. Electrowetting Technology Allows Displays to be Designed in an Extensive Range of Colors. Noise Problems are Not Always Easy to Find or Fix, but Acoustic Labs Can Help Designers Ferret Out the “Good” Noise from the “Bad.” A New Sanitization Protocol for Clothes Washers Combines the Best of Three Well-Established Provisions to Ensure Efficiency, Quality and Safety. Stricter EMC Requirements Raise the Bar for Appliances with Electronic Controls and Require Testing to New Levels. Despite Added Cost and Complexity, Gas-Modulating Systems have Migrated from Large-Scale Boiler Applications to Smaller Residential and Commercial Furnaces and Appliances. A New Treatment Technology Hardens the Surface of Light Alloys such as Aluminum and Magnesium and Expands Their Potential Applications. DesignMart Advertiser’s Index Association Report: AHAM

Appliance Design - November 2007

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