We are in our first full season with our pool. I'm quickly learning that our pool builder didn't understand the finer points of pool equipment. I am considering replacing our 1.5 HP SF 1.5 (Jandy Model SHPF1.5) single speed pump with either a two speed or a variable speed pump. I currently run our current pump for 8 hours per day (~1 turn) which gives me perfectly clear water but isn't long enough for my SWG to generate enough chlorine even with the SWG set to 100%. A lower speed pump will allow me to run the pump longer to generate more chlorine while lowering my electric bill. My spa jets run on a separate pump, and my Polaris runs off of a separate booster pump. Therefore, it will be rare for me to need to run the filter pump at high speed.
I just installed a flow meter to get idea of how much water I'm pushing through my system. With my filter pressure gauge half way between clean and dirty (which is about as dirty as I let it get), I'm moving 71 GPM. With my multiport on recirc, I move 92 GPM. I have three suction side feeds into the pump and three pressure side returns to the pool. All piping is 2".
Looking at the pump curve for my pump at this link, I think I have about 72 feet of head. With a flow rate of 71 GPM and 72 feet of head, from the formula in http://www.troublefreepool.com/hydra...head-t915.html I think I have a plumbing factor of 0.0142 (between curves B and C).
My heater and SWG have a minimum flow rate requirement of 30 GPM. If I was to install a pump that gave me 30 GPM, I would turn over my pool water 1.4 times in 24 hours. I think that rate would work very well given that I only turn over the water a little more than once per day now with very good results.
I'd love to get a variable speed pump, but the upfront cost will make the payback very long. Therefore, I think I need to get a standard two-speed. Looking at the curves for the Whisperflo two speed pumps at low speed, the following pumps would give the following approximate flow rates:
WFDS4 (1HP - 1/8HP): 34 GPM
WFDS6 (1.5HP - 3/16HP): 37 GPM
WFDS8 (2HP - 1/4HP): 40 GPM
On to my questions:
Am I approaching this correctly?
Given all of the calculations above, am I cutting things too close if I got the WFDS4? I need a flow rate of 30 GPM to run my SWG and heater.
Thanks for your help!