Overcompensation has been a standard practice in engineering to ensure a system can handle whatever the user or environment might throw at it. In a world where excessive Energy use is both impractical and costly, this practice must be revisited.

　　Energy accounts for the largest part of the total cost of operating a pump or fan motor.
　　Of all resources on which modern manufacturing is dependentCONTROL ENGINEERING China版权所有, energy is arguably the most fundamental. It is also a resource that has long been taken for gra

nted. However, rising energy prices and compliance concerns related to greenhouse gas emissions in some industries are increasingly leading operators to critically assess their energy usage.
　　Lack of standards = inefficiencies
　　A recent presentation to the American Council for an Energy Efficient Economy referenced a study that looked into the internal practices of a leading chemical company and of two major engineering contractors that company used on recent projects. The focus of the study, “Energy Efficiency for Industry,” was to identify whether the size of the installed pumps matched the real need. The results showed that 90% of the pumps were not correctly sized. If such a high percentage of installations are incorrectly matched in this company, how many are equally mismatched in other companies around the world?

　　The "true" condition of this sample application, 100 units of flow, requires 4www.cechina.cn,000 units of pressure (point "a")

　　Ten percent reserve "b" is added to the fan specification "a", to be on the safe side concerning maximum flow.
　　This example further illustrates the problem faced by system design engineers. When projecting a systemCONTROL ENGINEERING China版权所有, there is a degree of uncertainty as to the shape of the system. Friction控制工程网版权所有, pipe cross section changes, and the number of 90-degree turns in the final pipe layout all take their toll. These factors add to the risk that the expected operating conditions will not be met. As a resultwww.cechina.cn, there are three basic ways to address the chan