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Can You Really Reduce Your Electricitiy Bill

With recent large increases to commercial and domestic electricity tariffs and promises of more to come, everyone wants to know how to reduce their electricity consumption. This can be done but it is neither simple nor easy. In this article we will review some strategies for saving power ? and debunk some of the scams around!

By John Cameron*

The review of the FutureWave Energy Saver for swimming pool pumps in the June 2011 issue of SILICON CHIP has created a lot of interest.

It really does work, unlike most energy saving gadgets promoted to an uninformed public.

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The FutureWave Energy Saver was reviewed back in the June 2011 issue. It’s one device which really can cut your electricity bill if you have a pool!

There are two main types of energy ‘saving’ devices sold over the Internet, at flea markets and unfortunately, by some retailers who should know better.

Most are so-called power factor correction devices or devices which are claimed to “clean up” or otherwise fix your “dirty” or “unusable” power. These provide no benefit to domestic consumers and have been frequently discredited. (See the November 2007 and May 2008 issues of SILICON CHIP).

Less common power saving products are voltage reduction devices for electrical motors. They vary the voltage to the motor, depending on the load. More on these devices later.

Possibly some readers may have suspected that the FutureWave device reviewed in the June 2011 issue was just another device varying the voltage fed to the motor. But the review gave a different picture.

It is intended for controlling swimming pool pumps which are driven by induction motors.

The FutureWave reduces the supply frequency fed to the motor, as well as manipulating the voltage and waveform.

The end result is reduced motor power consumption while still providing adequate torque and power output.

This is the real advantage of the FutureWave compared to anything else on the market.

It was determined by the developers of the FutureWave Energy Saver, after studying pump curves and graphs of pool pumps and much testing, that dropping pump speed below 1700 RPM, the resulting flow rate drops is not adequate for effective filtering.

Hence the lowest flow setting on the FutureWave is 31.5Hz, giving a pump speed of around 1800 RPM (for a 2-pole induction motor with a nominal speed of 2850 RPM) and allowing flow rates to be maintained to adequately maintain filtering and cleaning performance.

On average. this will provide a power saving of about 70%,

Where do the savings come from?

The savings come about because swimming pool pumps are over-specified for normal water filtering. The FutureWave provides large savings by reducing the flow rate through the pool’s plumbing to a rate better suited for efficient pumping and filtering.

So why is the pump not the ideal size for normal water filtering? It is basically because a larger pump with enough power output is required to prime the pool’s plumbing system, run a pool cleaner and provide adequate flow to perform backwashing.

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We looked at this "Electicity Saving Box" back in November 2007 and proved it wasn’t even worth the box it came in . . . nothing has changed, except now there are lots more of them around. Don't believe the claims: they’re a con!

The FutureWave allows the pump to prime the pools plumbing system before its energy saving mode kicks in. It will then reduce the power consumption whilst providing adequate flow rates to operate the pool cleaner (eg, Kreepy Krauly). A pump has to be able to pump 120-180 litres/minute against a reasonably high ‘head’ (eg, the depth of the pool plus height of pump above the pool) to keep the cleaner operating.

When the cleaner is not in use, ie, when the pool water is simply being filtered, the pump does not slow down. It continues to pump hard, forcing lots of water though the system.

This is not efficient because the friction loss in the PVC pipes of the typical swimming pool rises as roughly the square of the water flow.

So when you double the flow rate the friction loss of a system increases by a factor of four. In other words, you need four times the power to pump 240 litres/minute around a pool system compared to 120 l/min.

This was seen with figures given in the June FutureWave article. A 40% reduction in motor power frequency and thus water flow gave over a 60% reduction in power consumption. Halving the water flow rate would give a 75% reduction in pump energy needs.

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