Sizing a new pump

[igraham]

I'm trying to figure out how to size a new pump. The pool is 33k gallons, so at 8/hrs per turnover, that is 68 GPM. At 12/hrs per turnover, it is 45. Average head feet is 45. The piping is 1.5".

1) Should I be sizing based on turning over 2x or 3x per day?
2) One pump i'm looking at is Pentair SuperFlo 1.5HP 2-Speed Pool Pump #340043. At high speed, that is 80 GPM at 45 feet, which seems like overkill and I could go with the 1hp instead at about 60GPM at 45 feet. However, I assume that most of the time I would be running on low speed. How do I therefore figure out which HP to go with?

 

[bobodaclown]

Hello,
This article may help. http://www.troublefreepool.com/content/152-determine-pump-run-time
Why not go with a 1hp 2-speed motor. Whats wrong with the current pump? There are two sides to the pump. The wet end (pump) and the motor. Usually all that's required is a new/reconditioned motor and new shaft seal and you're good to go. You can easily replace a single speed motor with a 2 speed motor.

 

[igraham]

There is a small crack in the pump casing. I may be able to deal that and then just get a new motor - not sure though. But where there is one crack, there may be more to come.

I forgot to not me that we currently do not hear the pool, but am going to be getting a heat pump. Does that affect the HP I need? Once the pool is warm, I don't see running the heater for more than a few hours per day.

 

[bobodaclown]

No not really. Most pumps on high speed move enough water, on low that may be another story. What are your electric rates? If they're more than $.30 KWH then look at a Variable Speed Motor, otherwise a 2-speed is fine. I run mine 90% on low. High speed when I check the pressure to clean the filter or for the fountain to spray higher.

 

[Isaac-1]

It is our experience that sizing pumps based upon turns per day is a general rule of thumb that has been taken to the point of a law. In general many / most pools can operate with no issues on far less than the industry standard suggested turns per day.

If you want the short version, a typical pool the size of yours with no water features will do just fine on a 1 - 1.5 HP 2 speed pump running on low when not vacuuming, backwashing, etc. with run times of 4-10 hours per day determined through experimentation.

As to the pump you are looking at make sure it will accept a 1.5 inch input pipe, many newer 1.5 HP pumps have 2 inch intake fittings.

 

[igraham]

Electric rates are about $.16/kWh so will go with 2 speed.

On the pipe fittling, can I use a pipe converter at the pump to go from 1.5" to 2"?

 

[Isaac-1]

You can, when it comes to inlet pipe for a pump you want a length of straight pipe going into the inlet, not an Elbow or reducer right at the inlet fitting.