Appliance Design - November 2007 - (Page 44)

GAS TECHNOLOGY often employ variable-speed conditioned air blowers and variable-speed exhaust blowers, both of which require more complicated control schemes than constant-speed blowers. So adding variable firing capacity to a gas appliance requires more than just substituting a modulating burner in the design. The whole system needs to be redesigned. Bosch and Rheem offer tankless, gas water heaters that use modulating systems. Bosch features it on about 60 percent of its product line. Rheem offers the technology in all of its tankless water heaters, says Peter Blaha, product manager for specialty products, Rheem Water Heaters. The modulating valve allows the tankless heater to adjust for the amount of water flowing through it. Rheem’s RTG-74 model, which has a maximum flow of 7.4 gallons per minute, would not require the heater’s maximum output if only one faucet was in use. But, if additional faucets, showers, or clothes washers were running, and more hot water was needed, the system would detect the increase in water flow and send a signal for more heat. The modulating valve would adjust to provide more fuel and a hotter flame to deliver the increased demand for heat. With this type of unit all of the hot water needs can be met, says Blaha. “If we utilized an ‘on/off type device’ for our tankless heaters, it would be extremely inefficient,” says Blaha. “With the modulating gas valve, Rheem's tankless heater range for the 74 model is from 19,000 BTUs to 199,000 BTUs.” Fig. 1. Comparative drying curves show how drying times are reduced by using a gas modulated clothes dryer. The technology was developed by the Natural Gas Technologies Centre, Quebec. they work reliably for a long time. When you get to modulating, you are adding a complexity and cost to the product.” Despite the increased cost and complexity, Johnson believes in modulation, and every gas-fired product that comes through his center is looked at with an eye toward integrating this technology. One of his most successful projects is a pizza oven, which is being actively marketed, that makes a pizza in six or seven minutes. It features an airflow and combustion system that increases pizza production rates while maintaining cooking quality. “A lot of the big chains want consistency, they want the same pizza whether you get it in Wichita or Moscow,” says Johnson. “That is where that precision really comes in handy.” Commercial cooking equipment in general is a growing area for modulation, ovens in particular. But the concept has also shown up in an upscale residential gas cooktop. Caldera Corp., Stowe, Vt., uses a modulation system to control its Arrow Gastop, which features five burners, with each providing 21 different settings. The lowest setting delivers 185 BTUs per hour and the highest cranks out 18,000 BTUs/hr. At the simmer settings, the unit does cycle on and cycle off to keep the BTUs at a consistent point. Company founder Al Shute says the Arrow Gastop uses a touch-control interface to control the flame. A variable-capacity gas valve that could be electronically controlled was needed to make the product a success, but Shute could not find one on the market and so began a multi-year research project to develop a valve that would work with his system. The modulating valve worked so well that Shute created a spin-off company called CompuValve to license the technology. 44 applianceDESIGN November 2007 While the modulating systems can make cooking better, it can also make homeowners more comfortable in heating applications. York and Rheem, for example, are among those gas furnace companies offering two-stage and variable modulating units. York’s 9.M and 9.C Series Affinity Modulating Furnace continually adjusts the firing rate in 1 percent increments between 35 percent capacity and 100 percent. Rheem offers two-stage furnaces that can run between 70 and 100 percent capacity and a variable-modulation furnace that operates between 40-percent and 100-percent capacities. While modulating furnaces do offer the users more precise temperature control enhancing personal comfort, they also illustrate the issue of added complexity, as they The Bosch 2400E tankless water heater uses a gas modulating system. 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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