System optimisation
- Introduction
- Optimising pump and fan applications
- Assessment framework
- Pump and fan characteristics
- Control options
- Fine-tuning pump and fan applications
- Control technologies
Pump and fan characteristics
Pumps move mainly incompressible fluids (like water) and fans move compressible fluids (gases like air). Pumps and fans each come in two basic types:
Pumps
- Centrifugal - fluid is spun around and ejected by centrifugal action. These are the most common pumps used in industry.
- Positive displacement - a set volume of fluid is physically moved, often by a piston. These pumps are less common, and are used for thick and viscous fluids under high pressure or where the delivery flow must be precise.
Fans
- Centrifugal - the same principle as the centrifugal pump. These are generally higher efficiency, up to 80 per cent, with the exception of the radial fan, which is around 50 per cent to 60 per cent but does not clog easily.
- Axial propeller-based fans - generally these low efficiency fans are used in free air or where space is at a premium. Aerofoil section blade fans are the exception, with high efficiencies - up to 90 per cent.
The Motor Solutions Online system optimisation information focuses on centrifugal pumps and fans, since these offer the greatest opportunity for energy savings.
Performance characteristics
The performance characteristics of pumps and fans are most often presented in a graphic form called 'characteristic curves'. These curves describe characteristics of available head (pressure) and efficiency and power consumption, from zero to maximum flow. A family of performance curves can exist for various impeller diameters.
Understanding performance curves enables you to check the performance of existing pumps, and identify opportunities for reducing your operating costs. For example, reduced operating costs can often be achieved by machining a pump impeller to get a better match between pump performance and the system requirements.
Performance curves are available from your equipment manufacturer and are often found in equipment operating manuals.
A typical pump curve
This is an animated graphic showing a typical pump curve. It will keep cycling so do not worry if you miss it the first time.
System curve
A pump or fan can operate at any point on its performance curve. The actual operating point is determined by the system requirements of flow and pressure. It is important that you select or modify your pump or fan so the operating point occurs in a zone of high efficiency. As you can see, pump efficiencies can vary significantly. In the diagram below, for example, efficiencies vary from 40 to 80 per cent.
In the next example, a system curve is superimposed on the pump curves so you can see the operating point.
Load duty cycle
The load duty cycle depicts the operating points and their percentage of total operating time. Analysis of the load duty cycle is the key to determining the most viable optimisation techniques.
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