There are two main categories of swimming pool pumps from which to choose. You can either purchase a single speed or a variable speed design. Doing the pump sizing calculations can also help you understand what type to purchase for greatest energy efficiency. Let's do an example of sizing the two different types to illustrate the point.
Let's say you own, or are going to build, a fifteen thousand gallon pool and you want to turn the water over in the pool twice per day. That means your pump has to move 30,000 gallons of water per day (pool size times turns per day).
In our first example we are going to purchase a constant flow pump that turns itself on and off once per day. So, let's say you set the pump to run during the night when energy rates are at their lowest. You want the pump to run for six hours every night. Therefore, in six hours time the pump must move 30,000 gallons of water. If we convert six hours to minutes (6x60) we have 360 minutes. Thirty thousand gallons of water moved in 3600 minutes means you need to purchase an 83 gpm pump or larger. To make the pump smaller you can cycle more times per day.
In our second example, let's illustrate a variable speed pool pump which will run constantly throughout the day. You have the same fifteen thousand gallon pool that you want to turn every twelve hours or thirty thousand gallons of water to move daily. However daily is going to be 1440 minutes instead of 360 minutes as in the example using a single speed pump. Thirty thousand gallons divided by fourteen hundred forty minutes is 20.8 gpm or larger.
Now, here's the bonus for you. Not only can you purchase a smaller pump which saves on material and room but the smaller pump will keep your pool water healthier and save you money on energy. As for the health of your water it is easy to see that cleaning and mixing your chemicals constantly is better than letting the water sit and mixing it every so often with cleaning and chemicals. As for the energy savings, the physics of water hydraulics is it takes less energy to move water slowly than quickly. The speed of the water compared to the energy needed is an exponential, not linear, relationship. Savings of up to forty percent have been documented when installing variable speed pool pumps. The capital expense is sometimes greater but the long term savings will almost always go toward the energy efficient variable speed pool pump.
