Greater efficiency with VS pumps
The major contribution to lowered energy use for Variable-Speed pumps is reduced flow rates. The inability to control the unnecessarily high flow rate for filtration purposes is the main reason why single speed pumps are not energy efficient.
It should also be noted that the permanent magnet motors incorporated on Variable-Speed pumps are inherently more efficient than the induction motors on single speed pumps.
This is because not all of the energy that goes into the motor is conserved as work at the shaft. Some of this energy is lost with the heat due to various mechanical resistances.
Because of their design, Variable-Speed pumps inherently lose less energy, compared to traditional pumps.
This leads to upper limits on the efficiencies possible for each type of motor.
Some consumers are interested in comparing the efficiencies of the two types of motors performing the same job, comparing apples to apples rather than energy efficiencies based on reduced flow rates.
Specifically, what is the energy consumption difference between a Variable-Speed pump and a single speed pump that are both producing the same amount of work at the shaft?
For a given pool with given hydraulic characteristics, what is the energy consumption difference if a single speed induction motor is unbolted from the pump and replaced with a Variable-Speed permanent magnet motor?
The amount of power produced by the motor divided by the motor’s efficiency is equal to the amount of power required to work.
Power out/Efficiency = Power in
Assume we wish to accomplish one horse power (HP) work at the shaft. If the single speed induction motor is rated 75% efficient, and the Variable-Speed permanent motor is rated 92% efficient and 1 HP = 746 Watts, then:
Single speed power requirement = 746 W / .75 = 995 Watts needed ——— Variable-Speed power requirement = 746 / .92 = 811 Watts needed
This shows that the Variable-Speed permanent magnet motor requires less energy to accomplish the exact same.
Variable-Speed pumps are more efficient, but are there additional advantages?
The answer is a resounding yes!
One benefit is their extremely quiet operation. Variable-Speed pumps are quiet for two reasons. The first reason has to do with the low speed they run for normal filtration.
Most everyone is familiar with the varying levels of noise produced by an area fan when it is operating at different speeds.
At its highest speed, the fan is quite loud, while it is much less audible when it is running at its lowest speed. Such is the case with Variable-Speed pumps: since they are running at the lowest possible speed, they produce less noise. The second reason they are so quiet is due to the totally enclosed fan cooled motor design, which insolates whatever noise produced.
An added advantage of the totally enclosed motor design is improved protection of the motor from the elements. Newer pumps also feature built-in diagnostics that enable them to protect from common conditions that lead to pump damage such as overheating, freezing, and voltage irregularities.
Another common benefit enjoyed by owners of Variable-Speed pumps is their durability. This is because they are designed with superior bearings and the shafts are better balanced to a tighter tolerance, producing far less heat and vibration.
Furthermore, the motor is operated by permanent magnets on the rotor that don’t require electricity to induce a magnetic field as is the case with an induction motor. This means that the rotor spins with the same revolutions per minute as the stator’s magnetic field, resulting in no “slip” or lag time between the speed of the rotor and stator. In short, there is less stress on the pump components which translates to a longer pump life.
Because they can be operated over a wide range of speeds, there is no issue if other equipment or features are added to the pool such as adding a solar system, changing the filter type, or installing fountains. Any changes made to the pool can be accommodated by simply setting a different optimum operational speed.
This also means that it’s possible to control the height and flow of various water features such as deck jets, fountains, and waterfalls.