Plant Services - September 2007 - (Page 47) EFFICIENCY HVAC Table 1.Summary of industrial refrigeration energy e ciency improvement opportunities Strategy 1 2 3 4 5 6 7 8 9 10 Energy e ciency opportunity Floating head pressure control Raise suction pressure VFD for evaporator fans VFD for compressors VFD for evaporative condenser fans Heat recovery (oil cooling) Improved compressor sequencing and capacity control Improve hot gas defrost dwell period Convert liquid injection oil cooling to external oil cooling Reduce parasitic loads Capital cost New L n/a L L L M L L M M Retro t L L-M L-M H L M L-M L H M Operational risk L M L L L L L M M L Value H H M M L-M M M L-M M L For more information EEG1 Section 4.1 EEG Section 5.1 Cold Front2 Vol. 4 No. 4, 2004 Cold Front Vol. 4 No. 3, 2004 Cold Front Vol. 4 No. 2, 2004 Cold Front Vol. 6 No. 4, 2006 EEG Section 6.3, IRC TechNote: 2002 EEG Section 5.4 EEG Section 6.2.2, Cold Front Vol. 3 No. 3, 2003 Cold Front Vol. 5 No. 3, 2005 L = low, M = medium and H = high. 1 EEG is the Industrial Refrigeration Energy E ciency Guidebook, Reindl, D. T., Jekel, T. B., and Elleson, J. S., IRC, (2004). 2 Cold Front is the IRC’s quarterly newsletter available at www.irc.wisc.edu/?/newsletter. Compressor + evaporator (kW/ton) • Industrial refrigeration systems are custom-engineered to meet a plant’s specific process needs. is makes prescriptive energy conservation measures difficult to identify because each system is “one-of-a-kind.” • Food production facilities often require continuous refrigeration. Energy efficiency improvement measures that require shutdown are difficult to implement. • Because refrigeration uptime is crucial, plants’ operations staff are often risk-averse concerning any changes that might undermine their ability to provide “cold” to the production floor. Load down, e ciency up 2.4 Fixed speed Duty cycling 2.2 Variable speed Tspace=-20°F Nevap=7 TDdesign=8.4°F 2.0 Plant operations professionals are pushing to reduce overall energy consumption. Consider these 10 ideas aimed at improving industrial refrigeration system efficiency. Each is proven to work. You just need to evaluate them for implementation in your plant’s context. 1.8 1.6 50 60 70 80 Evaporator part-load ratio 90 100 1. Floating head pressure control Figure 1. The e ciency advantage of a variable-speed evaporator fan increases as the cooling load decreases. Many plants operate their refrigeration systems with higher than necessary head (condensing) pressures. Although the ability to reduce a system’s head pressure is limited by ambient conditions, many plants can operate with considerably lower minimum head pressures. If your ammonia-based refrigeration system’s head pressure never falls below 125 psig, you might have an opportunity to improve system efficiency. A useful guideline says you can expect the efficiency of your system’s compressors to improve by 1.3% for each degree F in lower saturated condensing temperature (1°F is about 3 psig for ammonia). S 2. Raise suction pressure/temperature If your plant uses evaporator pressure regulators on all of its loads, it might make sense to raise your system’s suction pressure set point. You can expect your system’s compressor capacity to improve by 2.5% for each degree F increase in saturated suction temperature. Efficiency increases depend on the starting point of your suction pressure increase, but improvements in the range of 2% for each degree F increase in saturated suction temperature are possible. 47 .PLANTSERVICES. http://www.irc.wisc.edu/?/newsletter http://www.PLANTSERVICES.com
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