WARNING: Some pool companies are claiming to offer a little magic box that will save electricity on your pool pump, and they even go as far as to say that you will save electricity on all appliances in your house with this little magic box.
In principle these little magic boxes are just a few capacitors, and attempts to be a Power Optimizer Corrector (POC).
Some good advice : Put your dog on them if they knock on the door. If you don’t have a vicious dog, put you neighbours dog on them.
When we talk about electricity, we refer to energy in Kilowatt-hour abbreviated as KWh. KWh implies a Kilo (that is 1000) Watts of power for one hour. Note that we use power and energy.
Think of Power as the speed at which you use Energy – and power multiplied by the time in hours as the total Energy you use in KWh.
In terms of cost, a KWh from Eskom costs about R 1.50 if you are lucky. So if your pool pump uses 1.1 KW and you run it for 8 hours per day, it will cost you about R 13.20 per day (for 8.8 KWh).
If you want to conserve energy, you have to think of how much power each appliance uses, and the length of time you use it. Some devices, for example a kettle use 2 KW but we only use it for 3 minutes at a time, so boiling a Kettle takes 0.1 KWh to boil.
So in general: Devices that are used to heat anything use the most power and devices that have electric motors are next. Then lights, which use less power, but stay on for long and lastly electronic devices.
The background: Sometimes you will see people referring to KVA (Kilo-Volt-Ampere) instead of KW. Watts is Volts times Amps, so why use VA? It gets complicated so settle for this. If you have devices that work on magnetic principles such as electric motors, then you need 15% more Volt-Ampere than Watt. Else think of it as the same.
Is Power Factor Correction an Option for domestic?
Electrical motors use Resistive and Inductive power. The inductive power is essentially not energy, but you still pay for it because Eskom measures the total amount of apparent power to determine your maximum demand (and rightfully so).
To explain it, we have to resort to vector algebra, which I won’t do here, but suffice to say that by adding a capacitor to your power load, you can cancel the inductive loads and therefore save power.
In an industrial environment these devices can save lots on maximum demand. However, these are huge machines and huge capacitors.
When looking at the savings on small electric motors – 1.1 Kw pool pump for example, the savings are insignificant.
Ask yourself the question – if this was possible, and the claims of up to 44% savings could be achieved, and take into consideration that there is about 700 000 domestic swimming pool pumps in South Africa, which would consume as much electricity as a medium sized town like Stellenbosch, surely it would have been feasible for ESKOM to offer these little magic boxes to all for free ??
Variable Speed Pumps
The easiest way of explaining this, would be to refer to motor vehicles – a 3.0 litre beast, would consume much more fuel than an economic 1.3 litre – point taken – there would be a huge difference in power.
As with motor vehicles, and new high powered small capacity engines, that runs extremely efficient, new pool pumps has been introduced into the market lately.
Speck BADU®Eco Touch
Due to highly innovative motor technology, the new Speck BADU®Eco Touch pump is revolutionizing energy consumption, operating costs, water quality and lower CO2 emissions in swimming pools and koi ponds.
The system is simple but brilliant: the lower the motor speed, the lower the energy consumption!
Looking at fundamental pump characteristics
A Speck BADU®Eco Touch swimming pool pump was installed on an existing 50 000 L domestic pool. This pump is driven by an innovative brush-less dc motor, of which the rotational speed can be varied digitally with a 3-speed manual control.
The energy consumption for each speed was measured. The power input of any such pump need to be known, or measured, because often only the output power of pumps are indicated. It should be mentioned that there is a significant difference between conventional induction motors, and the Speck BADU®Eco Touch pump, which has a much higher efficiency.
Observations
It was clear that the stronger pump were actually wasting energy usage, and it could be mentioned that by just downsizing the conventional pool pump from a nominal 1100 watt to a smaller nominal 450 watt, the same volume of water will be moved through the filter at only 50 % of the previous energy consumption. Filtering will also be more effective because the water movement through the sand is slower. As a matter of fact, the smaller motor can drive the automatic cleaner as effectively as the big motor.
The most important fact conveyed visually, however, is that there seems to be no real lower limit to the energy that will turn the pool water around for filtering purposes, and in the extreme a variable speed pump with digital control can be set to run continuously at very low speed/power, and to only speed up occasionally for a short period to operate the automatic cleaner, which needs at least 100 watt to function. See results further on, of an experiment to determine how long such a cleaner needs to run daily.
Note that the key effect here is variable speed, and not motor efficiency, which contributes only a minor share to minimising energy for pumping a fixed volume of water.
Also very significant is the “unintended energy demand result” of automated sanitisers like salt water chlorinators, UV exposure, and oxygenator/ionisers, which prescribe varying, but long, periods of water flow irrespective of the strength and consequential energy usage of the pump. A minimal energy pump setting seems to be the answer to this dilemma, and will enable total eco-friendly swimming pools that have very small carbon footprint, and chemicals-free water.
A long term experiment with filtering and automated cleaner time periods
Because it is difficult to find out why private pool owners are advised to run their automatic cleaners and filters for so many hours every day, it could be helpful to look at an 8 month history (half a winter + half a summer) of a medium-sized pool (50 000L) in a city garden, where a focused effort was made to maintain it to a similar standard as neighbourhood pools, but using 5 % of the energy, or less.
Basically energy is required to sweep or suck the bottom clean and deposit the waste material (dust/sand, leaves, dead algae) into a strainer or filter. It is also necessary to circulate water through a fine filter (most commonly sand) to catch suspended particles. An automatic pool cleaner was attached during this experiment, but no other devices. Sanitising and algae control was done manually. The same adjustable 3-speed pump was used for the experiment, and it was found that the lowest setting (300 watt) could still drive the pool cleaner with vigor, with a circulation of 7300 L/hour through the system.
In summary: a 300 watt pump is sufficient to drive a pool cleaner system for long periods, but if the pool is in a bad shape, it will need the medium or high setting and a few back-washings to clear it up first. The cleaner moves at a speed of 4 meter/min across the bottom, and can theoretically sweep the pool in less than 30 minutes. In practice, with some prodding not to skip some areas, one hour is sufficient. The clarity of the water was as good as that of neighbouring pools that filtered for extensive periods daily. It was thus demonstrated over a prolonged period (8 months) that it is possible to maintain this pool, running the filter pump for only one hour per day, on average, and using less than 10 Kwh/month.
Conclusion
The bottom line is therefore that the energy cost of a domestic swimming pool can be reduced dramatically without sacrificing water quality, and for some installations the price differential between traditional pumps and a Speck BADU®Eco Touch swimming pool pump, can be recouped in less than a year, depending on requirements. It has been shown that long hours of swimming pool filtering and automatic cleaner operation to maintain clean internal surfaces and clear water is unnecessary and wasteful in energy usage. A low power pump motor (300 watt) can drive a cleaner as effectively as a strong motor (1100 watt), and one hour’s operation per day can be sufficient for a medium-sized domestic swimming pool (50 000 liters). If pool chemicals are manually administered, no extra pump time is required, and the monthly energy requirement to maintain the swimming pool, can be as low as 10 Kwh. If in-line sanitising is implemented, additional energy will be consumed, because longer water circulation times are required, but in view of the previous analysis there is hope that this unintended energy demand can also be drastically reduced, to the same level as that of the automatic cleaner.
