Pool plumbing question (1.5' to 2')
Thanks in advance for any feedback. I am looking for some confirmation of my analysis. I am an engineer, so I believe I understand the physics. However, I am not a plumber, nor am I a pool builder. I still feel my analysis is sound, but it conflicts with some pool builders. Hopefully, I won't screw up describing it. :)
While investigating whether my pool plumbing setup could support the new heat pump I just purchased, I noticed something concerning. I have a 32,000 gallon pool with a 60 sq inch DE filter and 2 HP motor. Unfortunately, the entire pool is plumbed with 1.5" piping. After researching, the theoretical "limit" on 1.5" PVC is 42 GPM. This means my pump is probably strained against the plumbing (thereby wasting electricity) and more importantly my turnover rate is suboptimal (probably 11 to 12 hours instead of 8 to 10).
After speaking to some pool builders, they suggest that it is impossible to fix without ripping out all the underground piping. This is where I totally disagree. Since all the intake pipes and return pipes are joined above ground, I believe a well designed and installed 2" solution would give the exact same benefit of 2" throughout. Here's why:
Since the theoretical limit of 1.5" is 42 GPM, each 1.5" will be limited by something close to that. However, I have 4 intake 1.5" (drains and 3 skimmers) and 3 return 1.5" (pool jets, stair jets, and swim out jets). Since each 1.5" intake can supply around 42 GPM, theoretically you can add each one for a 168 GPM flowrate. However, since these would be joined into a 2" junction, the limit would go back to the theoretical 73 GPM of a 2" pipe (as the slowest piping determines the limit). Therefore, whether I replaced all the piping to 2" or just the above ground piping to 2", by the laws of physics and simple engineering principles, my max flow rate would be exactly the same (again at or close to 73 GPM).
More importantly, for any pool that uses 2" for intake and return lines underground, they are probably wasting their money as they can't push more water than the 2" pipe that they all lead into (meaning into and out of the pump and filter). I have a couple of engineers that have checked my analysis and agree with me, but I haven't had any pool builders agree yet. After having a lengthy conversation with 1 pool builder, he did say that I am starting to make him rethink he thought for the last 25 years, but he wasn't ready to commit.
This website seems to back up my analysis. However, I would love to hear from some plumbers and pool builders that support my analysis (http://www.poolplaza.com/pool-pump-sizing-2.shtml). Or point out why it is wrong. If you need more details or I did a poor job of explaining, let me know.