Upsize Pump And/Or Piping?

[ChuckDavis]

A few more thoughts after a bit of sleep and a cup of coffee..............

The 1.5 inch piping for the returns is a single pipe leaving the equipment shelter. It splits somewhere underground. Does that still count as a 2 inch?

I've been working up some numbers using a Hayward pump sizing worksheet. For an 8-hour turnover I need around 32 GPM. Maximum flow with 1.5 inch pipe and 8 ft/sec is supposed to be 51 GPM. With the water feature I probably want to be at the high end. 24 PSI of backpressure equals 55 ft of head, plus an estimated 12 ft of friction loss on the suction side, yielding 67 ft. of head. This is a little outside the curve for my pump, but I'm getting away with it. (Low speed isn't supposed to be able to overcome more than 18 ft of head, so I'm surprised it works at all with the heater on bypass.)

I have an inquiry into the (mechanical) controller mfr to see if I can wire it so that the timer controls high speed operation (essentially abandoning low speed).

Would it make any sense to increase the size of the runs to/from the heat pump to 2 inches, leaving everything else at 1.5 inches? High speed works OK (although the performance curve says it's a bit undersized), and I'm leaning towards giving up on using the pump at low speed.

Thanks again.

[ChuckDavis]

I was writing my post while yours came in, so I just saw your post.

Everything worked fine last year even after installing the heat pump (although low speed was marginal). Something changed over the winter that added 2-3 psi of backpressure. I had thought that the "floc" might have munged up the filter media, but the difference between running the filter on "filter" and "bypass" is only 1 lb.

Perhaps something got damaged or plugged in the heat pump over the winter. I did cover the open connections with screen to keep critters out. I gravity drained the heat pump (I don't have a shop vac), so maybe there was some freeze damage if there was water left inside. I did use a garden hose to run water through the heat pump in both directions before hooking it back up this spring. Do you thing that might have damaged something? (I'm having trouble getting hold of the heat pump mfr.)