Flow Control - Jan 2012
applications corner by David W Spitzer Success at Last It Took a Few Years But The Variable Speed Drive Was Justified O ver the past couple of months I was irked that the extractor feed pump operated at full speed with its flow being throttled by a control valve located in plain sight approximately 1 meter above the pump discharge It seemed straightforward to me that it would be much more efficient to reduce the pump speed so that the pump output could match its load thereby eliminating not only the dissipation of hydraulic energy across the control valve but eliminating the control valve entirely Having successfully demonstrated that the energy savings could be accurately predicted I was ready to apply variablespeed I endured walking by the extractor feed pump with its control valve installation for some years until new motor controls needed to be located in a new motor control center The extractor pump variable speed drive was then justified using calculated energy savings plus an energy savings rebate from our power provider We Know Flow drive technology to the extractor feed pump Energy consumption was calculated for full speed operation and then for reduced speed operation Energy savings on the order of 15 percent were not sufficient to justify the project that included the purchase of the variable speed drive modification of a motor control center and control wiring modifications to accommodate the proposed variable speed drive Notwithstanding the inability to justify this project this exercise made it clear that in new installations aside from being more energy efficient the installed cost of variable speed drive control is less expensive than the cost of installing control valves and bypasses in sizes up to a few inches In larger applications the cost of a variable speed drive can be far higher than that of a control valve installation However the energy savings associated with large equipment can be much larger and handily justify a well conceived variable speed drive project I endured walking by the extractor feed pump with its control valve installation for some years until new motor controls needed to be located in a new motor control center The extractor pump variable speed drive was then justified using calculated energy savings plus an energy savings rebate from our power provider It may have taken years but the extractor feed pump and other pumps in the unit could finally operate with their control valves wide open FC David W Spitzer is a regular contributor to Flow Control with more than 35 years of experience in specifying building installing startup troubleshooting and teaching process control instrumentation Mr Spitzer has written over 10 books and 150 technical articles about instrumentation and process control including the popular Consumer Guide series that compares flowmeters by supplier Mr Spitzer is a principal in Spitzer and Boyes LLC offering engineering expert witness development marketing and distribution consulting for manufacturing and automation companies He can be reached at 845 623 1830 www spitzerandboyes com NOTE David W Spitzers Variable Speed Drives Principles and Applications for Energy Cost Savings is available for purchase through ISA at isa org spitzer and boyes llc complete consulting services We help suppliers with market research comparative analysis technology transfer expert testimony seminars We help end users with sensor and flowmeter selection training and seminars troubleshooting advanced control complex problems For more information visit www spitzerandboyes com or call 1 845 623 1830 14 January 2012 Flow Control Page 1 Circle 10 or Request Info Instantly at www FlowControlNetwork com
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