Appliance Design - April 2008 - (Page 24)

COOLING TECHNOLOGIES NIST Helps Heat Pumps Boost Output Researchers at the National Institute of Standards and Technology (NIST) have developed a testing apparatus that uses a high-resolution camera to track — with laser-illuminated dust particles — the motion and distribution of air flow in finned-tube heat exchangers. Data from these laboratory experiments are being compared with computer simulations of air flow performed with computational fluid dynamics (CFD) software. Once accurate CFD models are developed and validated, engineers can use them as the basis for design changes to coil assemblies and refrigerant circuitries to accommodate the existing air distribution. The NIST program, partially sponsored by the Air-Conditioning and Refrigeration Technology Institute (ARTI), could increase finned-tube heat exchanger heating or cooling capacity by five percent, resulting in improved heat pump efficiency. Additionally, such improvements could lead to reduced heat exchanger size, thereby reducing material cost and the amount of refrigerant needed. The NIST study results on home airsource heat pumps will be issued in 2009 and are also expected to be applicable to large heat exchangers used in commercial buildings and refrigeration systems. < Microchannel coil used in Carrier's AquaForce air-cooled chiller. For example, some York air conditioners made by Johnson Controls and some chillers by Carrier Corp. are successfully using the technology. The York products use microchannel brazed heated exchangers from Delphi Corp., Troy, Mich.; technology that Delphi had developed for the automotive market and transitioned to non-automotive applications. The microchannel products used by Carrier are supplied by a different vendor and are based on a Carrier-developed design. Testing by these companies and independent researchers has found that microchannel technology offers improved overall system performance. Carrier Corp., for instance found that the microchannel technology offers heat transfer and thermal performance improvements of 10 percent, a 20 percent lower air-side pressure drop, a refrigerant charge reduced by 20 to 40 percent and a 50-percent coil-weight reduction. And similar results have been found in academic research studies. Researchers at the University of Maryland’s Center for Environmental Energy Engineering have tested microchannel and fin-and-tube heat exchangers. In one scenario, researchers Yunho Hwang, Rin Yun, and Reinhard Radermacher used a commercially available 7-kW capacity residential air conditioning system that had a traditional fin-and-tube condenser as its base system. After testing the base unit with the fin-and-tube condenser, the condenser was replaced by a microchannel heat exchanger with the same face area, and then tested under identical conditions. The system with the microchannel heat exchanger had a reduced refrigerant charge 24 applianceDESIGN April 2008 of 10 percent, while the coefficient of performance (COP) increased by 6 to 10 percent and the SEER increased by 7 percent. One of the first microchannel heat exchangers to hit the market was the PF2 from Modine Mfg. The PF2 cooling core technology, which stands for Parallel Flow Plate Fin, is an all-aluminum brazed heat exchanger. The heat exchanger uses the flat aluminum fins and each tube has microchannel passages for the refrigeration. The tubes and the serpentine fins, which have a silicon-aluminum cladding on it, are metallurgically bonded to protect it against corrosion and damage. Johnson says that the technology is just now beginning to take off, that the slow pace of implementation is picking up as designers grow more comfortable with it. Designers had gotten very proficient with working with copper round tube plate fin design, as well as designing the packaging and cabinets around RTPF. They were also leery about the increase in tooling costs that might accompany a redesign, he says. Designers can continue to use the same cabinets, but to gain the most out of the microchannel technology it is best to redesign the unit around the MCHX technology, Johnson says. In some cases, integrated MCHX technology could be a simple matter of a drop-in, but in other applications a redesign might be beneficial to proper function. “If the current package has a very deep RTPF coil, meaning that if it has 4 to 6 or more rows, than it is going to be very difficult to replace all of that surface area with a single row microchannel coil,” Johnson says. In this case, designers would more than likely need to reconfigure these systems to “reduce A sheet of laser light illuminates the surface of the heat exchanger during the air velocity measurement experiment. www.applianceDESIGN.com http://www.appliancedesign.com

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Appliance Design - April 2008 Contents Editorial Shipments/Forecasts News Watch A Variant of Thermoacoustic Refrigeration Known as Acoustic-Stirling is Expanding Its Range Outside Cryocooling Into More Conventional Applications Such As Refrigeration and Air Conditioning Free-Piston, Stirling Coolers Are Now Showing Up in Mainstream Applications As Costs Come Down and Heat Transport Solutions Are Devised Heat Exchanger Innovations Are Helping To Improve the Overall Efficiency of Vapor Compression Systems Environmental Concerns Have Once Again Ignited a Debate Over Refrigerants A New Glass Ceramic Material for Induction Cooktops Can Be Decorated In a Variety of Glimmering Metallic, 3-D Looks That Can Employ a Number of Shades, Patterns, Styles, Colors, Intensities, and Textures Colorful, Reflective Coatings for Glass Create a Variety of Design Options To Help Designers Establish a Unique Look for Their Products Appliance Designers Faced With Different Motor and Drive Options Need To Understand the Differences and Tradeoffs Before Choosing A New MEMS Valve Offers a Number of Advantages Over Solenoids In Certain Applications, Including the Opportunity To Cut Energy Use The AHR Expo Set Attendance Records and Showcased Thousands of Innovative New Products Classifieds Design Marts Advertiser’s Index Association Report: CEA

Appliance Design - April 2008

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