In the Polaris pool cleaner thread the subject of variable speed
pool pumps came up. Which got me thinking about them
again because a friend who has a pool with a single speed
pump is considering options. Doing a bit of research, here's
what I have concluded and I wanted to see if anyone has
First, it looks like because of the design of the variable speed
permanent magnet motors, they are inherently more efficient
so you use about 15-20% less energy even at full speed.
Second, the biggest savings in energy come from slowing
the pump down, reducing the flow resistance. That means
you can run the pump for say 4 times as long, at 1/4 the
flow rate, move the same amount of water, but save 70 to
80% or so in energy.
However, the price of these pumps is very high. A complete
new pump runs from $900 to $1200 dollars online. The next
obvious problem is that they typically have only a 1 yr
warranty. I found an online story where a guy bought
a Pentair Intelliflow one where one of the two small control
boards failed shortly after the warranty ended. He says
Pentair will not sell the replacement board as a seperate
part or take pumps back for repair. He would have to buy
a whole new pump. It looks like Jandy, another major
manufacturer, does sell parts, but the equiv part for their
pump would be $400.
So, this got me to thinking. It appears to me the biggest
part of the energy savings can be obtained by just going
to a dual speed pump. And since my friend has a working
pump that is about 5 years old, I'm thinking the most
cost effective solution is to just replace the motor with
a dual speed motor. We could do that for under $300.
With the variable speed pump, assuming we bought the
lowest cost one, by my calcs, with the energy savings
it would take almost 4 years
to break even. With the dual speed motor, it would take
less than 2 years. The pool is seasonal, used 3.5 months
a year. And it looks to me like the additional savings in
energy going with the true variable speed pump is only
about $50 more a year over the dual speed. And then
what happens if the fancy electronics on this motor,
which sits outside all year, fails at say year 3, 5 etc?
The only other advantage of the variable is you can fine
tune it to run at exactly the speed you want, but I don't
see a compelling need for that. Also, there aren't any
utility rebates available here that would alter the
equation. So, it seems for this app, the variable speed
makes no sense. If you had a pool running year round,
higher cost electric, rebates, etc, then the results
might be different.
So, swap out the motor for the dual speed for $300? Any other
thoughts, issues I missed?