Consider Two-Stage Systems to Save Power
Consider Two-Stage Systems to Save Power (2010)-In recent years, many low-temperature ammonia refrigeration systems using screw compressors have used single-stage compression to satisfy refrigeration loads in lieu of traditional two-stage systems. This paper compares performance data for both types of systems and estimated operating costs based on total brake horsepower (BHP) requirements for each type of system. The performance data shows that two-stage systems provide significant power savings without significantly increasing system complexity. The data also provides guidance for when to specify two-stage systems over single-stage systems. Performance charts are presented for low-temperature saturated evaporating temperatures ranging from ?20?F to ?45?F. The charts show total system BHP requirements and estimated costs for the required total BHP at each low-temperature. Total BHP includes compressor BHP, condenser BHP, and recirculation pump BHP. The typical system used for the comparison is based on 300 tons of low-temperature refrigeration load and 200 tons of high-temperature refrigeration load. The system used for comparison is comprised of one low-temperature recirculator operating at various low temperatures, one hightemperature recirculator operating at +25?F saturated evaporating temperature, rotary screw refrigeration compressors with thermosyphon oil cooling, and evaporative condensers operating at 95?F saturated condensing temperature. The system loads and operating temperatures are typical of many refrigeration systems.
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