investindy said:21000gal pool
3 turns a day this equals 21000x3 = 63,000gallons pumped per day
63000 gallons / (60x24) = 43.75 gallons needed per minute [60minutes an hour x 24 hours]
My pump pressure shows 28PSI thus 28x2.31 + 5 = 70 for head pressure
- Look at a pump manufacturers chart for something with 70lbs head pressure and a GPM of 44, for my needs around 3/4HP
- If I wanted the most energy efficient it would be around 1Hp but then I would get 65GPM so I would only need to run my pump (21000/(65*60)) = 5.4 hrs day for one turn.
Not quite that easy...
Your head pressure is 'dynamic' because it changes with water flow. That means when you change the pump size, the head will change with it.
You need to start with your GPM at the known head level and then find your target GPM. To find the new head:
New Head = Known Head X ( Target GPM / Known GPM )^2
So, let's say you have 63 GPM @ 46' Head and you need to get to 75 GPM. The increased water flow will bring your TDH from 46' up to 66'.
You can then use that new head level and your target GPM to size your pump.
*Thanks to Pentair for doing the math for me on the example.