Use of variable speed drives (VSDs)
Best Available Technique (BAT)
BAT is to optimise pumping systems by using variable speed drivers (VSDc)
Brief technical description
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:
- process control
- better system reliability
- energy savings.
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:
- 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.
Achieved environmental benefits
Some studies have shown that 30 to 50 % of the energy consumed by pumping systems could be saved through equipment or control system changes.
Electric motors driving a variable load operating at less than 50 % of capacity more than 20% of their operating time, and operating for more than 2000 hours a year should be considered for equipping with variable speed drives.
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.
Driving force for implementation
Energy and cost savings.
The optimisation techniques are widely used.