Many industrial systems, whether machine-integrated or not, use pumps of all types and sizes that operate without attracting attention. However, these pumps sometimes cause considerable energy expenditure which can be significantly reduced by opting for better equipment and improving its operating conditions.
Potential improvement measures
Schedule appropriate modes of operation
Often, the pumps operate continuously at full power while demand fluctuates (during machine stoppages, or if their operating conditions change).
Intermediate demand should be managed by varying the speed of at least one pump, rather than by archaic energy-consuming control processes such as bypass circuits or flow restriction valves. This is because the power absorbed varies according to the cube of the flow rate pumped: speed variation is the best way to reduce the energy consumption of pumping systems in this case.
Furthermore, the need for operational safety encourages the use of redundant control modes. This causes additional energy costs, which can be avoided by using efficient and reliable regulation.
Potential savings:
- up to 50% by stopping unnecessary pumps (ON/OFF);
- up to 90% by using variable speed drives (VSD). [1]
Schedule quality preventive maintenance
Monitoring the operational data of the distribution networks is a first step in managing the actual operating conditions and detecting faults. Here are some examples of issues to monitor:
- measure pressure losses caused by clogging in elements such as heat exchangers, cooling circuits or filters;
- dirt and corrosion in pipes, which increase energy losses;
- repair water leaks; avoid purges of “anti-freeze” water in winter.
Upstream, regular maintenance of the pumps ensures optimal and economical operation. Some examples of actions to be implemented:
- detect and remedy operating conditions provoking cavitation and are destructive to the pump;
- check the discharge pressure: a value that is too high relative to a determined reference means wasted energy;
- check the mechanical transmissions: these elements are involved in the overall efficiency of a pumping system;
- carrying out overhauls in good time helps to avoid breakdowns and efficiency losses (the clearance between rotor and stator increases as the pump wears and increases energy losses).
Size the installations correctly
Appropriate sizing of the pump and motor is extremely important. Indeed, these elements must operate close to their point of maximum efficiency. However, these elements are often greatly oversized, meaning that they actually operate at less than their optimum efficiency, leading to a drop in overall efficiency as well as higher investment costs.
When designing new projects or replacing old pumps, the question of pump system sizing is a necessity because the additional energy costs due to non-optimal efficiency will have consequences throughout the lifetime of the equipment.
On existing installations, it is not always necessary to replace the pump. The balance between the pump and the demand can be achieved through correct adjustment of the pump rotor diameter according to the manufacturer's specifications. This operation makes it possible to significantly reduce the pressure and flow rate of the pump, and therefore the power consumed.
Select the most advantageous components
European directives relating to eco-design have introduced requirements relating to the minimum efficiency of pumps, circulators and electric motors. This forces equipment manufacturers to design more energy-efficient products: the end user is the primary beneficiary.
The replacement of pumps and drive motors should be prepared on the basis of a technical and economic study on the lifetime of the product (10 to 15 years), in order to fully appreciate the savings in terms of energy costs.
Optimise the configuration of the pipe network
- Water will flow more freely in pipes that are large, as short and as straight as possible and without singularities such as changes in direction or restrictions in cross-section;
- during modernisations, it is useful to check the sizing of the pipes in relation to actual needs.