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Single Speed vs. Two Speed Pumps

 
The benefits of a two speed pump have to be seen to be believed.  Most pool guys will never even think to recommend this, but it just makes way too much sense to be ignored.

Think about it . . . the two-speed pump addresses the biggest concerns that pool owners have about their pumps, that being cost of operation and quietness of operation.

If you live in California, you may be eligible for a rebate directly from your power company for the purchase of a 2 speed pump (up to $600.00).

Cost of Operation

Energy efficiency is a big issue with consumers and with power companies these days, although many pool guys still don't think much about it. 

Consider the following real-life comparison:

Pool #1 - The Traditional Approach                 Cost:  $51.90 per month

This 25,000 gallon pool has a normal 1.5 HP pool pump.  It runs 8 hours per day.  It pumps about 80 gallons per minute, which means that it circulates 38,400 gallons each day.  The pump draws 9.0 amps at 240 volts.  At a cost of 10 cents per kilowatt hour, that translates to a cost of $1.73 per day or $51.90 per month to operate the pool. 

Pool #2 - The 2 Speed Approach                     Cost:  19.50 per month

This 25,000 gallon pool has a two speed 1.5 HP pool pump.  It runs 12 hours per day in low speed. In low speed it pumps about 40 gallons per minute which means that it circulates 28,800 gallons each day.  (Remember that the pool only needs to turn the water over once each day).  The pump draws 2.25 amps at 240 volts in low speed.  At a cost of 10 cents per kilowatt hour, that translates to a cost of $0.65 per day or $19.50 per month to operate the pool. 

The only time you really need to turn it to high speed is for backwashing or vacuuming, or if you need to increase the flow rate temporarily.

Take a look at the chart to see how this works out:

Pool

Hours/Day

Flow Rate

Gal/Day

Amp Draw

Daily Cost

Cost/Flow*

Pool #1

8

80 GPM

38,400

9.0

$1.73

4.5 cents

Pool #2

12

40 GPM

28,800

2.25

$0.65

2.25 cents

*cost per thousand gallons of water pumped

In this example you are moving less water, but the reality is that most pumps are oversized and as a result the pools are over-circulated.  The 2 Speed pump provides just the circulation that your pool needs at a fraction of the cost.

Keeping the pool circulating a longer period of time each day has a couple of advantages:

  • The longer periods of circulation will help to reduce the occurrence of algae.

  • If you have a salt system, you can run the system many more hours per day and get increased chlorine production if needed.

Quietness of Operation

The 1.5 HP pump will typically make quite a bit of noise.  This is partly the result of pump noise but more the result of water flowing through the pump and the piping.

The 1.5 HP Two Speed pump on low speed will make very little noise, just a low hum.  This is because it is working under much less pressure and the turbulence in the piping is non-existent.

What about Total Dynamic Head?

If you look at the pump curves for two speed pumps, you will notice that when the two speed pump is on low speed, it operates at a very low level of Total Dynamic Head.  How can it possibly run, if the pool has a TDH of 50 ft?  The answer is that when you reduce the flow, you greatly reduce the friction loss.  In other words, you cut the friction loss (as expressed in TDH) of a system by a factor of 4 when you cut the flow in half.

In this example, the pool system which runs at 50 ft of TDH, will now produce 12 ft of TDH.  The flow at high speed is approximately 88 gallons per minute, while it is calculated at about 42 GPM in low speed.

WHAT ABOUT SOLAR SYSTEMS?  When a pool has a solar system mounted on the roof, a two speed pump may not be the answer.  This is because the rise to the roof creates 10 ft or more of static lift, and that number does not change when you put a pump in low speed and reduce the flow through the system.  With a solar system, it is often better to use a smaller single speed pump, such as a 3/4 HP pump that will give you adequate lift at all times.

 

WIRING A 2 SPEED PUMP

One thing that scares people is hooking up a 2 speed pump.  It is a little different from hooking up a regular pump.  You have to have some way to change from high to low speed.

There are several possible ways to control a 2 speed pump

1.  Toggle Switch - Whisperflo 2 speed pumps come with a toggle switch on the back of the motor.  You will run the pump in low speed normally but manually switch it up to high speed for vacuuming, or backwashing or using the spa.

2.  Air Switch - you can buy a two speed air switch to change from high to low speed.  This allows you to run air tubing to wherever you want to locate the air button.

3.  Two Speed Timer - there is an Intermatic timer (T106) that controls high/low speed.  You would use a normal timer to control the on/off function and then use a two speed timer to control the high/low function.

4.  Electronic Control - if you have a control system such as a Aqualink or Compool, you can wire up a two speed relay to control the high/low speed function of the pump.

As always, if you have questions, feel free to call us at 1-800-394-6131 for assistance.  We are committed to providing the highest level of customer service and technical support in the industry.



Take a look at our 2-speed and variable speed Pool Pump selections.

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