Living sustainably

Energy efficiency

System optimisation

  1. Introduction
  2. Optimising pump and fan applications
  3. Control technologies

Assessment framework

When improving the efficiency of centrifugal pump and fan systems, it is important that the savings justify the expense and effort. The four-step assessment framework outlined below will help you identify cost-effective opportunities for energy savings on your site, which require minimum effort.

Step one: initial plant review

You can use this table to collect basic plant information for an initial review of your energy-saving opportunities. Or you can develop a more systematic review process by incorporating efficiency and load data into your plant inventory, as outlined in Motor Solutions Online Reference manual inventory.

Plant identity Weekly operating hours Motor size HP Operating requirements (steady, variable) % average throttling at outlet Other
e.g. cavitation blocked filters

The following rules of thumb will help you prioritise these opportunities:

  1. The longer the operating hours the higher the potential savings. Applications that operate more than 80 hours a week are likely to represent the best opportunities.
  2. Applications that have the highest horsepower are likely to produce the highest savings.
  3. Steady applications with more than 10 per cent throttling represent opportunities for improved pump efficiency, often at little cost.
  4. Variable applications that use throttling as a form of control and operate below full load for a significant length of time offer potential opportunities for higher efficiency through improved control technologies.
  5. Applications that have blocked filters, cavitation or poorly maintained pipe-ductwork can deliver savings with improved maintenance. 

Step two: gathering data

To examine in more detail the best opportunities determined in your initial review, you will need to collect more data. The purpose of gathering this data is to develop a system performance curve and apply this to the pump (fan) diagram to establish the specific operating points. This step may require the assistance of a qualified engineer, or your pump or fan supplier.

You will require:

From this data, you can establish the system resistance curve and the load duty cycle. When you consider this information in conjunction with the pump and fan characteristic curves, you will develop a full understanding of the performance enhancement opportunities.

Step three: technical options review

Systems can be classed as one of three types:

  1. steady: constant load single operating point
  2. discrete: two to four operating points
  3. variable: greater than four operating points.

Investigate the following options, including estimated costs and savings. Your equipment supplier may be able to help with this analysis.

Steady Discrete Variable
Reduction of impeller diameter Multiple speed motors Variable speed drive
Variable inlet guide vanes for fans Variable inlet guide vanes for fans Variable inlet guide vanes for fans + multiple speed motor
High efficiency motors  High efficiency motors High efficiency motors
Equipment upgrade (new pump) Booster pump/fan<

Booster fan + variable inlet guide vanes

Step four: economic assessment

The last step is to determine which option presents the best opportunity for your site. The best way to do this is to compare the life cycle cost of each option using a 'net present cost' calculation (available in most spreadsheets). This will take into account the capital cost, running costs and your company's investment criteria. It is important you also keep in mind other benefits such as reduced noise, higher reliability and less maintenance that may tip the balance and justify greater expenditure to improve efficiency.

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