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I am looking to have a 21,000 gallon IG pool installed, and the builder is suggesting a single speed over a 2 speed pump. Is there any advantage of this? I would think a 2 speed would be better to run the filtration system on, and is more cost effective.
The only negatives I can think of are that they cost a bit more the single speed and the efficiency at high speed is generally not as good as an equivalent HP single speed pump. The low speed however, more than makes up for the initial cost and the high speed costs. You will save quite a bit over the life of the pump.
I have a 22,000 gal IG with spill over spa and swim out. So take this for what its worth. Went with upgraded system. 2spd pump, 500lb sand filter and SWG. By upgrading the system I went from 1 skimmer, main drain, 2 returns in pools and 1 1/2" pipe, 1.5hp pump. To 2 skimmers, 2 main drains, 4 returns in pool and 2 1/2" pipe. Run the pump on High for 1hr then low for 8 and high for 1hr. Has worked very well so far. Pool was finished last August so still playing. I also had them add a autofill, overflow drain during construction, I did the plumbing for this. No charge for installing it in the pool wall.
Other than initial cost, I know of no problems--and LOTS of advantages. I was shocked to see that my filter (200# sand) works BETTER at low speed. The water seems to have more time to filter.
Lots quieter, too. I rarely run at full speed except when backwashing.
Svengali,
One big negative is that a 2 speed pump may not prime itself if turned on without prime while on low speed setting. This may lead to a ruined pump. There are 2 speed controllers that handle this, but to my knowledge, these are all pretty expensive.
I started a project to build my own 2 speed controller, but so far I have not finished it.
Jim