The Pros and Cons of the variable speed pool pump.
Variable speed pumps have been around for a few years now and a host of unforeseen issues has arisen for the residential pool owner and/or pool service person. We came across a blog on a US website that sums it up pretty well in our opinion.
The set up:
The standard rule for pool water circulation in the warm months is to have the complete body of water turned over a minimum of 1 ½ times (ideally 2 times) in 24 hours through the pool filter, thus a 20,000 litre capacity pool requires a minimum of 30,000 litres to be pumped in a 24 hour period. Again, it would be preferable to pump 40,000 litres to assure that any miscalculation of total litres and pump flow of litres per minute is taken into account. To assure one has the correct litre pump rate a flow meter/check valve should be used to take into account the ‘head pressure’ (e.g. resistance) which can vary from pool to pool. Additionally, a dirty filter or suction cleaner can reduce the flow rate appreciably Once the proper flow rate is ascertained, the pool owner and/or service person must calculate the litres of water in the swimming pool. Armed now with the accurate flow rate and the calculated total litres of water in a swimming pool, it is now a simple matter of the hours to run the pool pump in a 24 hour period to achieve the standard rule of turnover rate for the body of water.
But that is not necessarily the end of the action required and is most definitely not the end of the story.
What the pool industry is finding out the hard way is with the slower the rate of water flow (even though the required turnover rate is achieved) certain pools are now having water maintenance ‘problems’, whereas with the prior single speed pumps there was not an issue.
What is happening to swimming pools that once were not a problem when the pools had a 1 or 2 horsepower single speed pump but are now having water issues with a variable speed pump? This scenario has been voiced by many professional service persons of 20 and 30 years’ experience recently. What many in the industry are realising is the circulation speed is as important as turnover rate in certain pools. Swimming pools have various styles with a multitude of water return line placements, making each pool unique in its own way, thus having its own potential water condition problems. This uniqueness maybe a contributing factor to water pool issues if the water is not circulated properly into all areas with sufficient force.
One can envision a fast narrow raging river and the agitation it applies to the side banks and obstacles in its path. Now envision a wider meandering river through the back ‘forty’ acres, peacefully making its way to the main river. Let’s assume for the sake of this argument the volume of water moved by both rivers is somewhat equal. Which of the two do you think has the more ‘cleaning’ (debris movement) power?
The same (with some alteration to the aforementioned scenario) can be said for the slow speed and high speed setting of the variable speed pump. One knows that the higher speed setting is required to activate pools with in-floor cleaning pop ups, whereas, a lesser setting may only push up the ‘pop ups’ a portion of the way, thus limiting the power of the in-floor cleaning system.
The same holds true for the ‘power ‘ to move water along the side walls, into the ‘standing’ water ‘ areas, the sharp rough corners, and the movement of the surface water into the skimmer collection area. We have all seen an object floating on the water’s surface that never seems to make it to the skimmer basket. This condition is due to the problem of a resistance on the surface of the water that is not overcome by the circulation power of the pool pump on a too low of speed setting.
By turning up the speed to its highest setting, the skimmer basket collects a greater amount of the surface material, whereas a speed setting that is too low will never force the floating object to enjoy the company of the skimmer basket and subsequent trash bin.
The bottom line:
The circulating power of water (along with the correct turnover rate) is a major determining factor in the proper care of a swimming pool. Selecting a low setting to save on the monthly electrical bill can cause a much greater cost down the road in the corrective action required to restore the pool water that has not been circulated and/or turned over sufficiently.
The closing note:
Brushing the pool’s entire surface is analogous to a low pressure power wash cleaning of one’s concrete sidewalk or patio deck. Therefore one must brush, brush, and brush some more for good measure. End extract.
So who really benefits from the purchase of a variable speed pool pump? Our opinion is that it is rarely the pool owner.
If that is the case why are they so vigorously marketed and even attract a rebate in some states? The latter provides a clue. Rebates schemes are only put in place if there is a cost benefit for the paymaster. In the case of “energy saving” pumps it is the electricity suppliers that are the main beneficiaries, followed by pump retailers who increase their sales margin selling you a more expensive “energy saving” pump.
Residential and commercial development is increasing demand from electricity suppliers. The problem is, the generating capacity & supply network infrastructure is not keeping up with growth. This is causing a growing concern that during times of peak demand the current infrastructure will eventually not be able to cope. The two biggest consumers of power in a residential property are usually air conditioners & pool pumps. On a hot summers day, hundreds of thousands of households are creating peak demand from the supply network. Brainwave…. Why not encourage the pool owner to reduce the power/turnover of the pump and run the pump for longer hours thereby spreading the load over a longer period, reducing the peak demand and taking the pressure off the supply network. Great in theory bad news if you think it will save the consumer money.
Lets look at a few figures. You can buy a reasonable quality standard pool pump for around $400. A variable speed pump will cost anywhere between $800 & $2500 depending on quality and specification. On pump purchase alone you need to save $400 – $2100 on electricity costs over the life of the pump just to break even on investment. It is to early to confirm, but it would be fair to assume that the lifespan of the pump is likely to be greatly reduced compared to a standard pump due to the extended daily runtime required to achieve the required filtration. But that’s not the end of it. If you are one of the majority that use a salt or mineral chlorinator the news just gets worst. The life of the cell plates is largely determined by the amount of hours they are energised. If you are running the pump three times longer to achieve the required water turnover the cell plates will only last a third of the time. Replacement cell plates cost $200 – $800 depending on model. Add to this the additional costs manifesting from poor water flow rates and the extra ware & tare on filter and other equipment and it is easy to see that the installation of a multi speed pump could result in a very poor investment and is unlikely to save the consumer a cent once all the hidden costs are factored in.
If there was any advantage running a pool at reduced power and lower flow/turnover rates the use of lower powered standard pumps would have replaced the more common 1 – 1.5hp pump years ago? All of the above reinforces our opinion that the installation of the more expensive variable speed pump option will most likely increase pool operating costs. As always we encourage you to do your own research, hopefully this will give you a more informed base from which to start.
Update: We recently tested a range of standard and variable speed pumps to determine which models would be the most economic for the pool owner over a five year period when both purchase and power costs are taken into consideration. It may come as a surprise to learn that in our tests all the standard pool pumps provided a better return on investment than the variable speed versions. To see the results click here