Hershey’s ChocolateWorld Data Center (Hershey, Pennsylvania, USA)
A number of independent third-party studies detail the consequences of oil fouling, which include: • A drop in heat transfer ratio from 1.0 to 0.65 at oil concentrations as low as 10 percent. 2 • A loss of 10 percent efficiency after five years, 20 percent efficiency loss after 10 years in oil-lubricated chillers at Tsinghua University, China. 3 • As much as 30 percent performance degradation in other cases. 4 Performance degradation over time is not only due to oil fouling. Another study shows that traditional oiled compressors, specifically screw compressors, suffer significant performance degradation due to excessive bearing wear, capacity slide damage, and other factors over years of operation. 5 This study concluded that screw compressor wear significantly impacts performance by the fifth year of operation, and subsequent performance degradation was found to be as high as 26 percent on average after 15 years of operation. To avoid mechanical wear and oil-related performance problems, Danfoss offers variable-speed centrifugal semi-hermetic compressors that employ oil-free magnetic bearings. With Danfoss Turbocor® compressors, chiller manufacturers are able to eliminate complex oil management systems that conventional chillers need to lubricate mechanical compressor bearings. Theoretically, an oil-free hermetic compressor design avoids the frictional inefficiency, degradation and maintenance issues associated with conventional oiled compressors. But how does it compare in actual practice after years of operation? To find out, Danfoss initiated a research project in 2018 to compare the present-day performance of DanfossTurbocor® compressors in operation for 10 or more years with their performance when originally installed. The
and 38,928 hours of operation, respectively, resulting from 24/7 operation in data- center cooling for more than 10 years. In January 2018, the compressors were removed from the chiller and replaced with new TT300 compressors. The existing compressors were sent to Danfoss’ test laboratory at Innovation Park in Tallahassee, Florida. TT300 Compressor One tested at 48.0 kW per ton of refrigeration (TR) and Compressor Two, 49.0 kW/TR, at pressures, RPMs, and capacities shown in Tables 1 and 2. (Although no official test standard pertains to standalone centrifugal compressors, AHRI 540-2015 was used as a test reference as explained below.) These results fall within the AHRI 540- 2015 uncertainty limits for the verification of published ratings for an application envelope with 95 percent for minimum mass flow and minimum refrigerating capacity and with 105 percent maximum power input. These results were then compared with the original test parameters for each compressor when they were tested and shipped in 2007 from the Danfoss factory to the chiller manufacturer.
Application TheHershey Company is a global confectionery leader famous for its chocolates, sweets, and snacks. In 1973, it opened Hershey’s Chocolate World in Hershey, Pennsylvania, and then expanded to locations that today range from Times Square to Dubai to Shanghai. To serve chocolate customers and fans worldwide, Hershey’s Chocolate World also operates a data center located in Hershey. The data center operates around the clock using a chiller providing cooling for the electronic equipment. Cooling technology To handle these conditions, the data center employs one 180-ton (600 kWr) Smardt WA062.2 water-cooled chiller using two Danfoss Turbocor® TT300 oil-free centrifugal compressors. Optimized for R-134a refrigerant, each compressor provides up to a nominal 90 tons of refrigeration utilizing two-stage centrifugal compression. Performance testing The two compressors submitted for performance testing incurred over 38,967
study sought to determine if oil-free compressors experienced the same
performance degradation found in traditional oiled compressor types—or whether they maintained their original level of performance. The study confirmed that Danfoss Turbocor® compressors with oil-free magnetic-bearings maintained consistent performance over a 10-year period.
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