Pressure sensors enable variable speed pumps to optimise pump speed and maintain constant outlet pressure for reliable water supply, says Dan Mullen.
02 September 2019 | Dan Mullen
Variable speed pumps (VSPs) use a variable frequency drive (VFD) or variable speed drive (VSD) to optimise the pump speed and power consumption, while maintaining the constant outlet pressure of the pump. In such scenarios, pressure sensors are essential.
What does the pressure sensor do?
It converts the outlet pressure to an electrical signal, which the VFD uses to adjust the pump's speed. It is either included as an integral part of the pump design or mounted externally. In many cases, a high cut-out pressure switch is mounted to prevent the pump from outputting extreme pressure. An additional pressure sensor can also be mounted on the inlet of the pump to monitor efficiency.
What are the benefits of VSPs with sensors?
- Efficiency: Pumps with VSDs and pressure sensors maintain constant pressure output and are therefore up to 30 per cent more efficient than 'traditional' technologies.
- Reliability: VSPs run at lower speeds and without a stop-start cycle, so there is less stress on the pump, making it more reliable with less downtime and maintenance.
- User experience: Even in challenging environments, such as high-rise buildings, a constant, reliable water pressure can be maintained. Users can modify the pressure supply depending on load and preference.
- Connectivity: VSPs can also be linked with the IoT, providing data to be used when a problem is identified, such as a burst pipe or leak, or to determine water usage. Building managers can remotely monitor and regulate water use, as well as respond in an emergency by either turning the water systems off to reduce spillage, or by allocating the highest water press to combat emergencies, such as fighting fires on the higher levels of a building.
Where are VSPs used?
Previously used in large commercial or industrial applications, this cheaper and smaller technology means it can be used in residential applications.
Demand has also increased because water delivery is challenging amid spreading urbanisation and less consistent municipal water and power supply.
It is difficult to maintain a constant water pressure to every storey of a high-rise building, but sensors detect variations in water pressure to determine when the pump needs to work a little harder to maintain a constant pressure and when it can relieve the pressure, but without the extremes of being either fully 'off' or fully 'on'.
Pumps work more efficiently if they are run at a constant rate; they are also less prone to failure, with all of the associated costs of ongoing repair and maintenance.
For example, 60/70CP range pressure sensors can be used in industries that require the pumping of liquids with a high degree of reliability (10 million cycle lifespan), such as oil. They are also robust enough to withstand damaging pressure spikes and hydraulic shocks.
What are some of the core considerations?
- Installation costs: The upfront cost of parts for the VSP will be more expensive in the immediate term, but the return on investment can be quickly realised in energy savings alone. And there is little if any difference (in terms of complexity) between installing a VSP and a fixed-speed system.
- Maintenance time frames and operational costs: Permanent magnet motors produce far less heat and vibration than traditional induction motors, resulting in not only less stress and wear on pump components, but on other equipment too. The net result is a dramatically longer life than 'traditional' systems and fewer maintenance issues.
Dan Mullen is product line manager at Sensata Technologies