Consulting Specifying Engineer Jan/Feb 2015-CSE : Page-34

VFD, motor strategies for energy efficiency A variable frequency drive (VFD) often is specified to reduce operational cost for pumps, fans, compressors, or any similar equipment with variable load profiles that may be found in a typical building. Here’s how to specify a VFD to meet load conditions while achieving efficiency. BY JOHN YOON, PE, LEED AP, McGuire Engineers Inc., Chicago Learning objectives Ⅲ Review the evolution of efficiency standards and how they relate to the specifica-tion of VFDs and motors. Ⅲ Understand how a standard induction motor uses (and wastes) electricity. Ⅲ Introduce some emerging standards and technologies related to VFDs and motors. Ⅲ Examine common pitfalls in specifying motors and VFDs. M otors get no respect. Although they’re pres-ent in many of the sys-tems that we design and they often drive the overall energy usage profile of a building, they usually end up as an afterthought. Traditionally, mechanical, electrical, plumbing (MEP), and fire protection designs for buildings have been focused on system level considerations of health/ safety, functionality, and initial capital cost. However, the adoption of more stringent energy codes and standards has put greater emphasis on energy efficiency in our designs. While this emphasis on energy effi-ciency may seem like a relatively recent development, it is the direct evolution of federal legislation that was passed almost 40 years ago in response to the 1973-74 oil crisis. The key is to recognize that this is all part of an ongoing progression and that efficiency requirements will only become more stringent. So while many building owners will be more than satisfied with minimal code-compliant designs, as pro-active engineers and designers, there is a need to understand how the components in the systems we design use power and how they can be optimized without com-promising those traditional design values. In some cases, there may be technologi-cal “dead ends” in the individual system components that may require emphasis on different solutions for energy efficiency. In most design methodologies, you look for the “bang for the buck”—high-impact, low-cost solutions first. The question is, what uses the most electricity in our designs? Although we may not think of motors specifically when considering the energy use of any particular building sys-tem, the electrical usage associated with motors is “hidden” in most commercial building energy use categories. From a broader perspective, electric motor driven systems represent more than a third of the total electricity demand for the United States and between 43% and 46% globally per statistics from the International Energy Agency. Total motor energy usage for the industrial sector out-strips commercial usage by roughly 3:1. Of total power used by motors worldwide, approximately 68% is used by medium-sized motors from 1 to 500 hp, which cov-ers the vast majority of motors used in building systems. A business concept known as “disrup-tive innovation” describes an innovation that redefines or replaces a market by offering improved simplicity, function-ality, and affordability. They typically Motors are everywhere 34 Consulting-Specifying Engineer • JANUARY/FEBRUARY 2015

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