Need quieter pump and adding 160' Solar on roof

[zephans]

I'm planning on replacing my loud Waterco 2hp (max) pump with a quieter (and more efficient) pump. However I am almost ready to hook up and start using my 160' solar heating array .

QUESTION #1: Will a 3/4 hp pump be enough to get up to top and prime solar array 2 stories (25') above pool + 110' of mixed 1.5"-2" piping?

QUESTION #2: will 2-speed pump work on low once solar array is primed?

QUESTION #3: My WaterCo T450 sand filter says "Max flow=35 gal/min, max pressure=21 psi". Given most pumps have GPM > 60 I'm curious if


My initial guesses based on reading Hydraulics 101 topic:
#1: My initial guess is to buy a 3/4 HP (full rated) WhisperFlo 2-speed pump. This way I'll have enough suction to keep my Polaris Ranger vacuum moving on it's own when cleaning.

#2: I'm guessing 3/4 hp on low speed will keep enough pressure once solar array is fully primed… but I have no way to test this and calculating would be brutally tedious.

#3: I haven't pulled out a hose and 5gal bucket to measure my current GPM and I'm overloaded with other projects (such as plumbing up to the new solar array). I suspect after head losses I'm not pushing more than 35gal/min… or perhaps I am and that's why whenever I backwash I never see clear water no matter how long I run (because zeobrite is being blown out with water by current 2HP max pump ).



Plumbing specs & details:
Pool is a 2007 Diamond Star 54" Oval AG vinyl pool with original pump and filter kit + custom piping for solar array.

Pool volume:
12' wide X 24' long X 48" (4') Deep (even though pool is 54" high)
7,700 gallons per www.poolcalculator.com

Plumbing: ~138' total
14' 1.5" cheap flex hose
6' 1.5" spa flex hose (tigerflex?) from hard piping to pool return
8' 2" bypass route (core hard piping)
110' 2" solar heater route
15' up to roof base
15' over + 4' overhang
30' across parallel array + up to top of
20' back to pump corner
25' down
5' misc pipe routing
=110' total length
=138' total piping (118' 2" + 20' 1.5")

Pump:
Waterco AquaMite Series pump
110v 1ph. (Phase), 10.5A run - 12A max
110*10.5=1,155 Watts (1.16 kW)
1.155*1.38=1.5939 hp run (service load)
110*12=1,320 Watts (1.32 kW)
1.320*1.38=1.8216 hp max (peak load)

FYI: At $0.10 per kWh this is 12 cents to 18 cents per hour to run.

Model 2402200DU (2HP)

Pool Filter:
WaterCo T450
Max pressure: 21 psi
Nominal Diameter: 18"
Filtration area: 1,733 sq ft
Max flow: 35 gal/min
Filter media: 165 lbs (75 lbs ZeoBrite)

Solar array:
160 sq ft total surface (8' x 20')
1 4'x20' array (unknown mfg), 1.5" Male threaded manifold
2 2'x20' SolarBear array, 1" female threaded manifold
Base height from pool: 15'
Top height from pool: 19'

Head calculations based on Hydraulics 101:
Static Head for solar array = 25' (near pool bottom to top of pergola roof)
FYI: Pump should handle 2x static head to prime quickly.
Return Dynamic Head = 2.31 * Filter PSI
Clean filter typically runs 13 PSI with current 2hp max pump
2.31 * 13=30.03
Pipe dynamic head not calculated
~17 90' elbows
(yes, I've designed and built all my own plumbing and this is one area my inexperience probably shows)
20' 1.5" cheap flex hose (came with AG pool kit)
6' skimmer to pump
Someday I might get around to replacing cheap flex hose… if I need to.
140' 2.0" s40 pipe
=55' head not including pipe dynamic head


Thanks in advance for any answers, thoughts, or experience with similar or partially related configurations!

 

[mas985]

#1 Yes a 3/4 HP should be enough but you need to check the head curve. If the maximum head of the pump exceeds the height of the panels, then the pump should be able to prime the panels. A 3/4 HP whisperflo is more than enough.

#2 If you have a vacuum release valve on the panels, as is recommended, then no, the pump will not be able to keep the valve closed on low speed. Pressure drops significantly on low speed and even more at the top of the house so the vacuum release will likely be at negative pressure and open. Low speed will also not have enough head to pump to that height so water will probably not flow.

#3 A 2 HP pump should have quit a bit of pressure on a 1 1/2" pipe. My guess is that you are well over 35 GPM.

[edit] Re-read the post and saw the 13 PSI which would be about 40 ft of head. I don't have a head curve for that pump but if you have one, you can look up the flow rate.

 

[zephans]

Thanks for the quick reply Mas985. Glad to know I'm at least in the right ballpark.

I haven't found a vacuum release valve at Lowes or Home Depot. Instead I bought a small (3/4") check valve, 2" T, and threaded reducer bushing to build my own vacuum release. I figure Check valve will let air in but block water under pressure. if it doesn't work I could just cap it or thread in a real vacuum releas valve 8). If I want to be really sneaky I could add two 3/4" elbows (doing anyway to prevent gunk from falling in) and then extend the pipe down enough for me to slip on a cap whenever I want to prevent vacuum break (such as low speed pump + solar). My piping design skills are somewhere between McGyver and Rube Goldburg .

Additional thoughts & ramblings:
I have no idea why the pool bundle included such a large pump motor with a sand filter that is rated for max 35 GPM. (Actually given trend to oversize I'm not that surprised.) I'm surprised I haven't blown all the zeobrite out by now... but there'd be a bigger trail somewhere. It was good to finally calculate average cost per hour to run the pump. With the normal but loud noise it makes I figured it was sucking mucho dinero every time I turned it on. Therefore I haven't been running it nearly as long as I should (only 1h per day most days). That explains my perpetual cloudy water. Now that I figured it costs ~11-19 cents per hour I think I can run it a few more hours every day and try cleaning things up a bit more.

Funny thing about the 2HP pump and the cheap 1.5" flex hose from skimmer to pump. A couple times I have forgetten to clean the nylon I have over the skimmer and suction has been strong enough to collapse the cheap pipe . By some miracle both times nothing was damaged once I cleaned the nylon. I'll look for the 2HP pump head curve after I pour a structural support pad then hook piping up to the SHW roof I just finished building.

 

[mas985]

Although it is possible to run the solar on low speed without a vacuum release valve, I would not recommend it. First, you need a fairly decent flow rate for the panels to remain efficient. Low speed of a 3/4 HP pump will probably be less than optimal in terms of flow rate.

For example, I estimate for my pool that I get about 65 GPM with solar on and a 1 HP Northstar pump. If I drop that to a 3/4 HP Whisperflo, flow rate drops to 57 GPM so 1/2 speed is about 29 GPM which is pretty low for a solar panel and would drop the heat transfer with it. Your flow rates may be slightly different but probably not too far off.

Second, running at low speed without a vacuum release valve would create a vacuum at the top of the panels and with the low flow rates and high heat could collapse the tubes in the panel. Better to avoid this.

If you do go with a 2 speed pump, I would recommend running at full speed when the solar is on then when solar shuts off, run at low speed. If you think solar will be running most of the time, then I you might want to go with an Intelliflo pump. This pump will allow you to adjust for the minimum flow rate that is need to keep the panels efficient and help keep costs down at the same time. It will give you the most flexibility in adjustment but the downside of course is the cost.

A couple of other thoughts

Any inground pump is likely to be too much for your filter as they will all probably well exceed the 35 GPM. So if you go with an inground pump, you may also need to change the filter. In ground pumps tend to be much higher head pumps than AG pumps so for a given plumbing system will produce much higher flow rates than AG pumps.

Is there anyway to mount the panels closer to the ground so you can use a standard AG pump? Otherwise, you may need to replace the filter and some of your plumbing as well.

However, to prevent a vacuum at the top of the panels, I suspect that you will need at least 45 GPM which exceeds the filter specs anyway. So if you want to keep the filter, then you should probably keep the panels on the ground.