Variable Speed Pumps. What Are They and How Do They Work?

Variable Speed Pumps. What Are They and How Do They Work?

One of the biggest advances in this industry in the past 25 years has been variable speed pumps. As the world becomes more conscious of energy use and greenhouse gas emissions, surprisingly estimates have found that 10% of electricity use in the world is from pumps. Whether it’s the mains water pump to make the taps work, the sewerage pump to pump it away, the air conditioning pump to cool the building, pumps use a lot of electricity and are not very efficient. In fact an EU study found that 2/3 of all pumps installed are inefficient and use up to 60% too much electricity, if efficient pumps and motors were installed, there would be an overall reduction of 5% in Europe’s electricity usage. That is the power usage of 83 million people!

Pumps as a piece of machinery have not advanced a whole lot in the past 50 years. There has been some advances in materials and construction, but overall a pump generally has an impellor that spins driven by a motor and this is used to move water. The biggest gains have been found in electric motor design and the switching and control systems that are attached. The piece of technology that is most widely used is the variable speed motor driver (VFD or VSD), so what is a VFD and how does variable speed technology work?

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When a pump driven by an electric motor turns on, the motor starts spinning and accelerates to its maximum speed. In Australia, most electric motors spin at 2950 rpm as we have a 50 Hz electrical supply. This means that the pump will be spinning at this speed and will be able to pump water to its maximum volume and flow. Say for example that a pump produces 50L/min at 400kpa (a large house pump). If you only have one small tap partly open, the water coming out will be at about 400kpa but there will be nowhere near 50L/min of flow coming out. So the pump is only producing 5-10L/min out of the tap, it is still using the full amount of power to operate the electric motor. Over the life of a normal house pump of 5-10 years, this amount of wasted power can easily add up to the cost of the whole pump.

This is the pressure and flow on a conventional pump. This has varying pressure and uses lots of electricity.















With a variable speed pump, a pressure sensor is mounted on the outlet of the pump, and this measures the operating pressure of the pump. The VFD controller will be set so that it keeps the outlet pressure of the pump constant, no matter what flow is required out of the pump. If the same pump as before is instead a variable speed then the outlet pressure can be set to 300kpa. If only 5L/min is required, then the motor will slow down in speed until it can maintain 300kpa at that flow. This means that the motor instead of using 6 Amps, will be using possibly 1or 2 Amps to do the work and over time this saves a massive amount of power.

VFD pump curve

This is the pressure and flow of a VFD pump. This keeps pressure constant and saves electricity.















The other benefit of using a variable speed pump is that it provides you with a constant water pressure supply. This is because you can set an operating pressure on the controller and the pump maintains this, it stops the pressure and flow spikes that occur with most conventional house and irrigation pumps. These type of pumps have been used for years to provide towns and cities with constant water pressure and with developments in technology, the common house pump now provides this benefit.

The best VFD house pump on the market is the CME Booster from Grundfos. The CME 3-62 is the most common model for a residential house, which we have them in stock and it costs $1,890. The CME is a bit of a step up in price compared to a normal house pump but with the power savings and constant mains style pressure, the extra cost up front is easily repaid in comfort and efficiency later on. There are also bore pumps and larger irrigation pumps available with variable speed too and allows your pumps to be much more efficient and flexible. Call us, email us or come and see us today to see how we can get you pumps running more efficiently and saving you money.