A pump application might need to cover several duty points, of which the largest flow and/or head will determine the rated duty for the pump. A control and regulation system is important in a pumping system so as to optimise the duty working conditions for the head pressure and the flow. It provides:
●better system reliability
For any pump with large flow or pressure variations, when normal flows or pressures are less than 75 % of their maximum, energy is probably being wasted from excessive throttling, large bypassed flows (either from a control system or deadhead protection orifices), or operation of unnecessary pumps.
The following control techniques may be used:
●shut down unnecessary pumps. This obvious but frequently overlooked measure can be carried out after a significant reduction in the plant’s use of water or other pumped fluid (hence the need to assess the whole system)
●variable speed drives ( on the electric motor) yield the maximum savings in matching pump output to varying system requirements, but they do have a higher investment cost compared to the other methods of capacity control. They are not applicable in all situations, e.g. where loads are constant (see Section 3.6.3)
●multiple pumps offer an alternative to variable speed, by pass, or throttle control. The savings result because one or more pumps can be shut down when the flow of the system is low, while the other pumps operate at high efficiency. Multiple small pumps should be considered when the pumping load is less than ha lf the maximum single capacity. In multiple pumping systems, energy is commonly lost from bypassing excess capacity, running unnecessary pumps, maintaining excess pressure, or having a large flow increment between pumps
●controlling a centrifugal pump by throttling the pump discharge (using a valve) wastes energy. Throttle control is, however, generally less energy wasteful than two other widely used alternatives: no control and by pass control. Throttles can, therefore, represent a means to save pump energy, although this is not the optimum choice.
The applicability of particular measures, and the extent of cost savings depend upon the size and specific nature of the installation and system. Only an assessment of a system and the installation needs can determine which measures provide the correct cost-benefit. This could be done by a qualified pumping system service provider or by qualified in-house engineering staff.
The assessment conclusions will identify the measures that are applicable to a system, and will include an estimate of the savings, the cost of the measure, as well as the payback time.
Pumping systems often have a lifespan of 15 to 20 years, so a consideration of lifetime costs against initial (purchase) costs are important.
Pumps are typically purchased as individual components, although they provide a service only when operating as part of the system, so a consideration of the system is important to enable a proper assessment of the cost-benefit.
Energy Efficiency (2009) 3.8.5