More than 90% of the total cost of ownership of a pump comes from energy consumption, outweighting servicing, maintenance and replacement parts.
There are various approaches used to control the flow rate of a pump, but they all come with their own inefficiencies. However, there are tried and tested solutions for efficiently managing the performance of pumps in the form of Variable Frequency Drives (VFDs) – also known as Variable Speed Drives (VSDs).
VFDs, which have been available since the 1980s, are used to regulate motor speed in applications including conveyor systems, fans and pumps. This article explains why a VFD is the most energy-efficient method of controlling pump flow, as well as other ways they help reduce the TCO of a pump.
Traditional approaches to designing pump control solutions can be highly energy efficient in applications where little operational variation is required. For example, if the pump is running at maximum flow, then it is highly efficient. But introducing some variation in the flow causes the energy efficiency to drop away. Here are some commonly used approaches to controlling flow and saving energy:
These pump flow control methods do provide practical solutions in some applications with specific requirements, where either control, energy efficiency or both are not primary factors. But when sustainability and TCO are priorities, there are more effective solutions.
Simply put, pumps with VFD motor starters are more energy efficient in most pumping applications because they provide variable flow rate control that delivers energy efficiencies during operation. Furthermore, VFDs are also intrinsically more efficient because of the affinity laws.
When coupled with appropriate sensors and transducers, the VFD-controlled pump motor will provide pumping power according to the demand requirements of the system, rather than at either peak operating output or at a suboptimal and lower efficiency output. Running motors constantly at full speed lowers operational lifespans.
If the motor is not subject to the electrical overload and mechanical shocks of on/off and reversing flow control, instead soft starting and stopping, less strain is placed on the motor and the wider system, protecting seals, joints and pipelines. When damaged, these system elements can interrupt flow and reduce efficiency. The undamaged mechanical elements of the motor will run smoothly without additional friction and wear. An added benefit of reduced pump motor shocks for reducing TCO is lower maintenance requirements.
The affinity laws, or pump laws, are a range of formulae with variables including head, flowrates, impellor diameter and shaft speeds. Even allowing for the underlying assumptions, the laws clearly demonstrate that running a pump motor at lower rates reduces energy consumption. A 25% decrease in pump motor speed can reduce energy consumption by 60%.
VFDs are the most energy efficient method of controlling flow. When combined with the maintenance reductions and reduced failure risk that VFD pump motors enjoy, the initial investment in VFDs leads to a much lower TCO, as well as optimising pump energy efficiency.
Dalroad helps end users and electrical contractors in a wide range of industries to select the best VFD for their pump. Contact our team of experts today for no-obligation advice and recommendations.
