Upsize Pump And/Or Piping?

[ChuckDavis]

Hi Mark,

Thanks for your reply. I did have some weirdness with the filter this spring. (Due to bad instructions from the manufactureer a 2-part "floc" product might have reacted inside the filter instead of in the pool.) But..........just today I followed a suggestion and compared backpressure with the filter set on "Filter" and on "Bypass/Recirculate." The difference is only 1 lb., which indicates pretty free flow through the filter.

I do have a bypass on the heater, but we are wimps and use the heater all the time. As noted above, putting the heater on bypass drops the filter backpressure by around 5 lbs. at high speed and 1-2 lbs. at low speed. With the heater on bypass the low speed is able to (barely) operate the water feature and chlorinator.

The check valve is a Jandy.

I've wondered if something "changed" in the heat pump during the (North Carolina) winter or spring startup. In the fall I disconnected all the plumbing to the heater and covered all the open ends with tie-wrapped screen to keep critters out. I did use a garden hose to flush the heater this spring, running the water in both directions.

(We don't close our pool, so the pump was in use - under timer control - all winter.)

My timer only controls the low speed on the pump, so I'm having to run the pump 7x24 at high speed. I'm now using a robotic cleaner, so I am wondering about changing to a 1-speed motor that the timer/controller could control.

Seems like I'm having to reengineer the system while holding the inground piping, filter and heat pump constant. Any and all suggestions would be appreciated.

[mas985]

So just for clarification. Everything was working perfectly fine before you installed the heat pump, correct?

Also, maybe I misunderstood your first post. The 3 PSI rise in the filter, was that due to the heat pump or something wrong with the filter?

It sounded like low speed was working ok with the heat pump but then something happened after than and now it doesn't work? I am trying to understand the history.

Low speed flow rates are going to be half of high speed, so you can't expect all that much out of low speed. While you don't have any lift with low speed (water feature is at same height as pump correct?) the extra head loss in the heater might be enough to reduce the flow rate to a level that is not all that useful.

[mas985]

Let me clarify a few things.

First, there is no limit to flow rate in pipe. The 8 ft/sec is a recommendation.

Second, the head loss in the plumbing is dependent on the flow rate. So on low speed, the head loss is about 1/4 of high speed.

Third, the suction side should have very low head loss since there are three pipes.

I can calculate the approximate head loss in your plumbing but I need a little more information.

What is the approximate length of your suction runs?

For the return to the pool, how many return eyeballs are in the pool and what are their sizes (e.g. 1", 3/4")?

How many 90s do you have in the heat pump install and overall on the pad equipment?

What other fittings do you have on the pad?

With this information, I can determine what the filter pressure should be given your setup and we can see if there might be an issue.

[ChuckDavis]

Suction Side:

Skimmer1 through and including mainfold - estimated 84 ft., 2x45's, 4x90's
Skimmer2 through and including manifold - estimated 36 ft., 2x45's, 4x90's
Main Drain through and including manifold - estimated 45 ft. (including pool depth), 2x45's, 2x90's
Manifold to pump - 2x90's

Pressure Side:

Pump to filter - 1x90
Filter - Tagelus TA-60, 24", zeolite media
Filter through and including heat pump bypass - 4x90's
Bypass to heat pump through and including bypass - 3x90's, 4x45's, approximately 30 ft. to heat pump and back
Bypass to (but not including) manifold - 1x90, Jandy check valve, unused Nature2 cartridge holder
Manifold to returns - Single 1.5 inch pipe, 4x90's, probably one 90 underground to split between 2 returns
Manifold to water feature - at least 5x90's

All piping is 1.5 inch
All valves are 2 inch valves with reducing couplers

Returns:

I am using Heat Snorkels (www.heatsnorkel.com). They each have a 1 inch side jet and a 3/4 inch eyeball. I removed one of the Heat Snorkels and there was no change in backpressure.

Backpressure Readings - High Speed (See notes below):

Filter on Filter, heat pump in circuit - 23 lbs
Filter on Filter, heat pump bypassed - 20 lbs
Filter on Bypass, heat pump in circuit - 22.5 lbs
Filter on Bypass, heat pump bypassed - 17.0-17.5 lbs

Backpressure Readings, Low Speed:

Filter on Filter, heat pump in circuit - 5.5 lbs
Filter on Filter, heat pump bypassed - 4.5 lbs
Filter on Bypass, heat pump in circuit - 5.5 lbs
Filter on Bypass, heat pump bypassed - 3.5 lbs

All backpressure readings are with water feature turned off.

All backpressure readings were double-checked. The 2.5-3.0 lb difference between Filter and Filter Bypass with the heat pump bypassed is notably different than the 0.5 lb difference between Filter and Filter Bypass with the heat pump in the circuit. I don't know if this could represent reaching (or exceeding) the top end of the performance capability of the pump and/or the zeolite filter media having possibly been clogged by the 2-part "floc" product that may have reacted inside the filter due to incorrect instructions from the manufacturer.

[ChuckDavis]

Hi Mark,

Have you had a chance to calculate the head on the suction side of my system?

On the pressure side, I'm thinking that I should add 2-3 lbs to the current top end of 23 lbs when back-calculating the head. As noted above it seems like the extended run to the heat pump might have exceeded the top end performance of the existing pump.

One of the online pool supply outfits recommended a 1.5 hp one-speed Pentair Energy Efficient Whisperflo pump or a variable speed pump and also changing all the above-ground piping to 2 inch. What is your opinion of these recommendations? Looking at the performance curves for a Whisperflo, and using 75 ft. of head and 50-60 gpm it looks like a 3/4 or 1 hp unit would work, but I definitely don't want to end up undersized again.

Thanks again.

[mas985]

Sorry, I must have missed your post.

With heater, I would expect about 15 PSI and with heater bypassed, I would expect 11 PSI so there is a large dependency somewhere. I am not sure where it could be. With the pressure differentials you are measuring it doesn't seem like it would be the heater or filter. Removing those does not change the pressure much. But this is probably the cause of all your problems.

Also, the 1.5 HP Whisperflo is going to be a much bigger pump than you have now so I would not recommend that.

[ChuckDavis]

Does 15-16 lbs of backpressure with the filter on either Backwash or Rinse tell you anything? Do those readings somewhat correspond with your projected pressures? (See below, also.)

All the above ground piping was replaced last year as part of a complete refurb. (Piping size was kept at 1.5 inches.) The backpressure didn't change much from before the refurb.

What I have downstream from the heater bypass is a Nature2 cartridge holder (G Series, part of original system, currently empty but used previously), a Jandy check valve (2 years old) and a Rainbow chlorinator (part of original system). There is a 1.5 inch manifold with one 1.5 inch branch to the pool returns and a 1.5 inch branch to a water feature. Underground piping is, of course, a mystery.

The Jandy check valve has unions, so I removed it and left the pipe open at that point. With the heater bypassed I got 13 lbs of backpressure and with the heater in circuit I got 20 lbs.

I then reconnected the upstream side of the check valve, but left the downstream side open. With the heater bypassed I got 17 lbs. of backpressure and with the heater in circuit I got 23 lbs.

I appears that the check valve is contributing 3-4 lbs of backpressure.

Visual inspection and manual operation of the check valve showed apparently normal operation, although the spring-loaded flapper does seem fairly strong.

According to the Jandy spec sheet, the check valve is supposed to cause no more than 0.5 lbs of pressure drop (1 ft of head) up to 50 gpm and no more than 1.0 lbs of pressure drop (2 ft. of head) up to around 90 gpm.

With the check valve fully reinstalled, I recorded pressures with one or both of the 1.5 inch pool return and water feature lines turned on. Normally I have the water feature valve partially open.

Here is the various data that I have, sorted by backpressure:

Through filter, Nature2 (empty), open pipe - 13 lbs ****
Through filter, backwash - 15-16 lbs
To filter, rinse - 15-16 lbs
Through filter, Nature2, check valve, open pipe - 17 lbs ****
Bypass filter, through Nature2, check valve, chlorinator, pool return (full) + water feature (partial) - 17-17.5 lbs
Through filter, Nature2, check valve, chlorinator, pool return (full) + water feature (full) - 18 lbs
Through filter, Nature2, check valve, chlorinator, pool return (full) - 20 lbs
Through filter, Nature2, check valve, chlorinator, water feature (full) - 20 lbs
Through filter, heater, Nature2, open pipe - 20 lbs ****
Bypass filter, through heater, Nature2, check valve, chlorinator, pool return (full) + water feature (partial) - 22.5 lbs
Through filter, heater, Nature 2, check valve, open pipe - 23 lbs ****
Through filter, heater, Nature2, check valve, chlorinator, pool return (full) + water feature (partial) - 23 lbs <normal operation>

The check valve would appear to be a problem. Are there any more smoking (or bubbling) guns hidden in all this data?

If replacing the check valve doesn't allow the chlorinator and water feature to (again) function with the 1.5 hp Super Pump on low speed, do you think that there would be a benefit from changing the above ground piping to 2 inch? (The chlorinator was just barely working at low speed.) Would the overall performance of the system improve? Would the pump run more efficiently? The three 1.5 inch suction lines could be put into a 2 inch manifold. The 1.5 inch pool return and 1.5 inch water feature line could come off a 2 inch manifold.

Thanks again.

[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.)