Appliance Design - April 2009 - (Page 22) COOLING TECHNOLOGIES up to 1,800 BTU/h, enough to perform well in many refrigerated appliances. In a recent test with a 7.0 cu. ft. commercial refrigerator/freezer, the compressor was able to maintain a minus 20 DegF evaporator temperature, and a refrigerator compartment temperature below 40 DegF with an ambient of 110 DegF. These findings suggest that the mini-compressor has sufficient capacity to cool many types of appliances, both mobile and stationary. Fig. 4 shows the comparative sizes of the mini-compressor with a commonly used reciprocating compressor. Key comparative performance parameters are shown in Table 2. For appliance designers, a striking, but seldom used parameter is that of cooling power density, both volumetric and by weight. The inference to be drawn from this comparison is that a large reduction in both space and weight can be achieved using the minicompressor. Such factors have historically been used in mobile refrigeration systems only. But now, this device can be considered in some stationary appliances, which is highly unusual for a DC-powered compressor. A small vapor-compression system can have large performance and efficiency advantages over thermoelectric coolers that have been used in some small appliance products. When the mini-compressor is used in a refrigeration system together with a high-performance condenser, the complete refrigeration system can be incorporated within a form factor as small as 200 cu. in. This permits a major space reallocation in the cabinet, reducing the volume needed for the refrigeration system and providing considerably more volume for product storage. There’s also a weight reduction of approximately 10 lbs. from the use of mini-compressors, anothType Refrigerant Volume, In.3 Weight, Pounds Speed, RPM Capacity, BTU/h (ASHRAE) Cooling Power Density, BTU/In3 Cooling Power Density, BTU/lb Fig. 4. Mini-compressor next to reciprocating compressor of equivalent capacity. er benefit to the product being cooled. Numerous types of refrigerated appliances can benefit from a compressor size and weight reduction, and some of the more pertinent examples are listed in the Potential Applications box. In addition to those existing appliances, the mini-compressor is also an enabling technology, that is, it presents an opportunity to conceive and develop new generation cooling products that have not yet been imagined. For example, personal cooling systems using a body-mounted chiller continue to be an intriguing product concept. Such systems have a myriad of applications that could benefit first responders, motorcyclists, multiple sclerosis patients, victims of sports or burn injuries, wheelchair users, and industrial workers operating in a high-heat environment. The surging solar power market will also provide significant growth opportunities for DC compressors as the emergence of low-cost solar power spurs the development of DC-powered refrigerators, freezers, air conditioners, and other cooling appliances. Rotary R-134a 11 1.3 1,800-7,000 950* 86.3 730.7 In addition to form and function, the appliance designer also needs to recognize that a DC-powered appliance presents its own unique challenges. It’s no secret that DC compressors are higher in cost than their AC counterparts. This cost difference is due to the higher cost of DC motors, the need for a separate motor-drive controller, and that there are far fewer DC compressors produced on the world market. In addition, a separate power supply might be needed to convert an AC power source to DC. So, despite the many virtues of a small DC compressor, it may not be suitable in the most price sensitive products. Nonetheless, the introduction of an innovative mini-compressor that significantly reduces the weight and space allocation in a refrigerated appliance fulfills a growing need for compact thermal management systems. The compressor is reasonably quiet, provides high cooling power, precision control, and unique flexibility. All that remains to be proven is its long term reliability and dependability. < For more information, email: info@aspensystems.com Reference: 1. “Experimental Evaluation of Aspen Miniature Rotary Compressor,” Abhijit A. Sathe, Eckhard A. Groll, and Suresh V. Garimella, Cooling Technologies Research Center, 19th Annual Compressor Engineering Conference at Purdue University, West Lafayette, Ind., July 2008. Reciprocating R-134a 130 9.5 2,000-3,500 764 5.9 80.4 Table 2. Comparison of specifications between mini-compressor and a reciprocating compressor of equivalent capacity. 22 applianceDESIGN April 2009 www.applianceDESIGN.com http://www.appliancedesign.com
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