Giving the green light to variable-speed pumps
For more than a decade, I’ve been gradually improving the efficiency of my appliances and driving down my electricity consumption. One device had defied me, however. As hard as I looked, there did not seem to be a greener alternative to my 750 watt pool pump. Until now.
For the past 12 months, I have been testing the Viron P300 variable-speed pool pump, courtesy of the South African distributor, Fluidra . What makes this pump different is that it operates on a DC motor, so it can run at different speeds as needed. At the slowest setting, Eco, my Watts Up meter tells me the pump is using a mere 175 watts, less than a quarter of the consumption of the old pump. (A sixth, compared to the widely used 1.1 kw pumps.)
But does it work? The principle of a variable speed pump is that because a slower water flow is much more efficient, longer hours at lower speeds are the most economical way to pump enough water through the filter each day. But I have not significantly increased hours. For my 31,000 litre pool, I leave the Viron P300 on the Eco setting 8 hours a day, spring, summer and fall. And my pool stays clean. (As I have written here before, I radically cut back on pumping hours in the winter.)
The flow on the Eco setting is somewhat weaker than that of the old pump, but my Zodiac Genius still climbs the walls as long as the weir basket is clear. I think the slightly lower flow does make it more sensitive to a leaf-clogged weir, so I check it more often now. I am told that the Gemini and Kreepy Krauley pool cleaners might work even better with the lower flow because they use a hammer action, rather than a diaphram. I have not tested them on on this pump, however.
The Eco setting is not strong enough for backwashing, but that is the joy of a variable-speed pump. Just push a button and the Clean setting sends a surge of water through the filter. My measurements indicate the Clean setting uses 505 watts, still significantly less than a 0.75 kw or 1.1 kw AC pump, and with a stronger flow than a 0.75 kw can create. Beyond Eco and Clean is the Turbo setting, more suited to a fire engine than to anything I need to do with my pool.
I calculate that I am saving 4.6 kilowatt hours every day and R150 each month with the Viron P300. For someone like me who was sitting on a daily consumption just a little above Johannesburg’s magic cutoff point of 16 kWh a day, the savings could be much greater. The municipality offers a Lifeline Tariff as well as affordable rates for prepaid meters for those who keep their average consumption below 500 kWh hours a month, or 16 kwh a day. Qualifying for the lifeline tariff could save me about R3000 a year.
These savings come at a cost, however. A new Viron P300, manufactured in Spain with an Australian motor, sells for about R8300. By comparison, an ordinary AC pump from Speck costs about R2200 for the 0.75kw version. Leaving aside the Lifeline Tariff, it would take a few years of savings on utility bills to cover the difference, but there is no doubt that it is a good long-term investment. With a larger pool requiring more hours of cleaning per day, the DC pump would pay for itself more quickly.
Unfortunately, I did encounter one unexpected cost replacing my dead AC pump with a more environmentally friendly version. The Viron pump is larger, a few centimetres too large to fit in my existing pump box. A larger enclosure set me back R1800. If your box has little room to spare, check the measurements of any pump you might buy.
The Viron P300 is not the only variable-speed pump available now in South Africa. The IntelliFlo by Pentair costs more than double the price of the Viron P300, but has an extremely sophisticated controller. The pump can be programmed to run at different speeds at different times of the day. I have spoken to pool owners who splurged on the IntelliFlo pump and they were completely satisfied. Zodiac has also introduced the variable-speed FloPro ePump, which is worth investigating.
All of these pumps are astoundingly quiet compared to ordinary pumps. Standing at the far side of my pool from the pump box, I can only be certain the pump is operating if I can see the hose is pulsating.
I would love to say that I am finally at ease with the energy consumption that goes into my pool, but alas, I am a perfectionist. The ideal solution is so obvious, and yet no one offers it. A major expense of solar photovoltaic systems is the batteries that store the power for evenings and cloudy days and the inverter that converts the DC power produced by solar cells and batteries into household AC current. My pool pump has a converter to change AC current into DC for the motor. DC-AC, AC-DC—let’s call the whole thing off. Why shouldn’t solar panels send DC power directly to the pump’s motor, eliminating costly and troublesome components? (And getting Eskom out of my pool entirely.) It won’t worry me that the pump operates fewer hours under the winter’s low sun; that makes perfect sense. And if the pump slows down on cloudy days and stops at night, that’s fine too.
I’m not resting by the pool yet.