What is an Inverter or Variable Speed Drive?

Inverter drives are often called Variable Speed Drives (VSD), Variable Frequency Drives (VFD), frequency controllers or speed controllers.

An inverter is able to take 230 volts or 400 volts power at 50 hertz and can change it to a variable voltage and frequency output. This enables the pump or motor to rotate at varying speeds according to the frequency of the output.

Inverter drives allow the user to control the speed of the motor or pump to meet with the exact demands of the system or process that it carries out.

Without the inverter drive, the motor or pump will either be at full speed, or switched off.

The purpose of having the inverter is to control a process accurately, for example in the case of a cold water booster system, so we can control the speed of the pump to keep a constant pressure, regardless of the demand for water.

This control makes the process very energy efficient and as the motor or pump is not working at full speed, there is reduced wear and tear on the motor.

If a pump needs to run at full speed all the time, an inverter will not make it more efficient.


What applications are suitable for inverters and what benefits can be achieved?

Application one: cold water boosting
The traditional way of boosting cold water involves having a pump which only has two settings, on or off, with a pressure vessel/s to absorb the excess water supplied by the pump and maintain a flow of water while the pump is in use.

As the pump on a traditional system can only be on or off, the water pressure tends to peak when the pump starts up and then drop off very quickly when the pump turns off. This results in fluctuating water pressure, which is unpleasant for the user and can also cause unnecessary stress on the pipe-work and valves.

With an inverter driven cold water booster system, the pumps vary the speed to meet the demand by maintaining a constant pressure. This way the user has a more pleasant experience by having the water flow consistently from a tap or shower. The constant pressure means the pipe-work is not subject to varying stresses, and the reduced pump speed saves power and wear on the pumps.

There is typically a 30-40% power saving between a fixed speed booster set and a modern variable speed booster set.

With a traditional set, the excess pressure also leads to a higher water consumption, which does not occur on a variable speed drive because of the constant pressure.


Application two: heating and cooling pumps

Heating and cooling systems are designed to cope with the extremities of weather. More often than not, however, this full capacity is rarely required.

It is possible to determine the demand for heating or cooling by measuring the temperature of the water as it leaves the boiler or chiller and then measuring the temperature upon the water’s return. Once the demand is determined, the pumps can be adjusted accordingly.

This can result in up to 60% power savings, reduces wear and tear on the whole system and reduces the amount of fuel/electricity required by the boilers or chillers.


Application three: level control

By monitoring the level of fluid in a tank with a pressure transducer connected to an inverter, we can maintain a constant level of water/fluid in a tank. This is often used in industrial processes such as waste effluent and is more energy efficient than the traditional stop-start level control.


Application four: sewage and storm water pump stations

Using inverter drives to control sewage and storm waste water pumps allows us to reduce the number of blockages that can occur in the pump.

This is achieved by monitoring the amount of power the pump is using, when the power increases due to a blockage or restriction within the pump, the pump is stopped and then rotated in the opposite direction (switching direction several times) to remove the blockage from the pump.

This application has reduced blockages in some systems by up to 80%.

Furthermore, sewage and storm water pumps benefit from inverters because they allow the pumps to operate at a speed to match the water inflow to the pump station, which again reduces the amount of energy used.


Benefits of using variable speed drives

• Energy savings

• Improved control

• Reduced wear and less maintenance

• Reduced stress on pipe-work, valves and associated systems

• Better motor protection


Troubleshooting and inverter issues

Troubleshooting on most inverters is often simplified by the error being displayed on the screen of the inverter. Typical errors include overheating,
or failure of the control circuit.

Inverters that do not have a display will usually have a red or orange light to indicate there is an error.

A typical inverter life-span is 10-15 years on an industrial quality inverter. Some of the lighter duty inverters are expected to last around five years with correct maintenance.


Energy facts

A pump running at 80% speed uses only half the amount of power it would at full speed.

95% of the time, pumps don’t run as efficiently as they could do.

If you are experiencing issues with inconsistent water pressure, wasting energy or need help understanding your variable speed drives, please contact Dura Pump, mail@durapump.co.uk

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We are driven by our vision, where we see: A world where pump reliability is paramount.

We see ourselves: Satisfying the pump user through effective and efficient fluid management


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Dura Pump Ltd
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