Optimizing Daily Run Times with A Variable Speed Pump

Example on using a Pump Curve: With a pool, pump, filter, and automatic pool cleaner installed, it’s time to set the pump to maximize efficiency.

To accomplish this, we will need:

• Total Dynamic Head.

• Pool volume (or dimensions).

• Desired Turnover Rate in GPM.

• System limits.

• Pump make/model. The easiest way to determine the total dynamic head for an existing pool is by obtaining a vacuum pressure reading at the pool pump and a pressure reading at the filter.

This is accomplished by removing the pump’s drain plug, likely located near the bottom of the strainer basket, and replacing it with a vacuum gauge.

Begin by relieving the pressure in the system at the filter. Unscrew the drain plug at the pump and install the vacuum gauge.

Next, obtain a pump performance curve for the pump in question and set the pump to a speed listed on the curve. Record the vacuum pressure at the pump and the pressure reading at the filter.

• Multiply the vacuum pressure reading (in inches of mercury, inHg) by 1.13 to convert to feet of head.

• Multiply the filter pressure reading (in psi) by 2.31 to convert to feet of head.

• Add the two values together to obtain the total dynamic head at that flow rate.

Repeat these steps at two additional pump speeds.

Field Example: 12,930-gallon pool Let’s walk through these calculations with a real-world setup:

• 12,930-gallon pool.

• 2-Inch plumbing.

• Pentair SuperFlo Variable Speed pump.

• Pentair Clean & Clear Plus Cartridge Filter (CCP420).

• Pentair Rebel suction-side cleaner. (See accompanying graphic using pressure readings at 3,000, 2,200, and 1,400 RPM.)

Begin by taking filter pressure measurements and vacuum pressure measurements, noting the pump’s RPM.

At 2,200 RPM, the measured filter pressure is 7 psi, and the vacuum is 6 inHg. Convert to head:

• 7 psi × 2.31 = 16.17 ft.

• 6 inHg × 1.13 = 6.78 ft.

•Total Dynamic Hd = 22.95 ft ≈ 23 ft.

Using the pump curve:

• At 2,200 RPM and 23 ft of head, flow is approximately 43 GPM.

Repeat this process at other speeds:

• 3,000 RPM → approx. 63 GPM.

• 2,200 RPM → approx. 43 GPM.

• 1,400 RPM → approx. 27 GPM. Now let’s decide on turnovers.

• Minimum: 1 turnover every 24 hrs.

• Standard: 1 turnover every 12 hrs.

• Heavy use/commercial: 1 turnover every 8 hrs.

Let’s opt for 1 turnover every 12 hours, which is the same as 2 turnovers per day, for optimal sanitation.

To achieve 2 turnovers for 12,930 gallons of water, we need to move a total of:

• 12,930 gallons × 2 = 25,860 gallons/day.

• 25,860 ÷ 24 ÷ 60 ≈ 18 GPM. To meet this, we can run the pump at 18 GPM for 24 hours, which can be achieved at low speeds (around 600 RPM). Lower RPMs are more energy efficient, since power usage increases roughly cubically with speed.

System Limits Pipe size: 2-inch plumbing. 2-inch plumbing should not exceed flow rates of 75 GPM.

Filter: The Pentair Clean & Clear Plus Cartridge Filter (CCP420) should not exceed 150 GPM.

Cleaner: The Pentair Rebel cleaner will probably not function at 18 GPM. The Rebel suction-side cleaner requires at least 25-28 GPM to function reliably. At 600 RPM and 18 GPM, the flow is probably not sufficient.

From field experience, the cleaner works best between 2,200 and 2,400 RPM.

Pump Runtime Plan:

Here’s a practical runtime plan:

1. 600 RPM for 22 hours → 22 hr × 18 GPM × 60 min = 23,760 gallons.

2. 2,200RPMfor2hours(cleaner)→ 2hr×43GPM×60min=5,640gallons.

Total: 28,920 gallons, comfortably exceeding the 2-turnover target.

Adding a Water Feature

Let’s add a solar heater to complicate the situation slightly.

All of the earlier pressure readings were taken with a solar water heater turned off. With a solar heater on, where a diverter sends water to the roof to be heated, the total dynamic head will increase at each of the water velocities. (See accompanying graphic.)

With the solar diverter valve open:

• 3,000 RPM → 46 ft of head → 53 GPM.

• 2,200 RPM → 25 ft of head → 38 GPM.

• 1,400 RPM → insufficient to reach the roof.

Here are our new goals:

• 2 turnovers a day, which will move a total of 25,860 gallons.

• Solar heating needed midday for about 6 hours.

• Suction side cleaner operation.

• Maximum efficiency otherwise.

PumpRuntimePlanwithSolar: 1. 2,400 RPM for 6 hours (solar heating) → 6 hr × 41 GPM × 60 = 14,760 gallons.

2. 2,200 RPM for 2 hours (cleaner) → 2 hr × 38 GPM × 60 = 4,560 gallons.

3. 600 RPM for 6 hours (filtration) → 6 hr × 18 GPM × 60 = 6,480 gallons.

Total: 25,800 gallons, just about perfect for 2 turnovers.

Figure 1. Reading a Pump Curve. Pentair SuperFlo VS Pump. Red Traces: TDH without water feature. Green Traces: TDH with solar on.

Figure 2. Total dynamic head measurements from pressure readings at specified pump speeds