Loss of pressure when adding basic solar heater

[onlinestoreca]

We are new to owning a pool. We had a sailboat on the east coast of Canada and enjoyed it greatly when we actually sailed. It was very inconvenient to get to the boat, then there was a lot of work prepping, and if you forgot something it was an hour back to the house and an hour back to the marina. Weeknights were difficult to pull off so it was basically nice weekends.

Now we open up a patio door and there's a pool off the deck. We think we are going to like it

We have a 16' x 48" round above ground pool and that is all we think we really need. Although that is what I said about a 26' sailboat -lol, and that changed quickly.

I hooked up a solar heater, just a cheapie, basically black tubing that lies on the ground. Trying to stay cheap until we learn if we will actually use a pool. When I attach the solar heater, the water pressure drops dramatically. The water that was coming into the pool was definitely warmer though and I could see it making a difference over time.

I expected some drop, but the drop was a lot. The pump is 1500 gph, the hose is 1-1/2" for the pump to the pool. I have to reduce the hose to 1-1/4" where it attaches to the solar heater.

I am going to install a bypass valve to keep the water pressure up and hope this works, unless there is a better suggestion. I am also not sure what size hose to use in the bypass, I was thinking 1-1/4", but maybe that doesn't matter.

Thanks for any ideas, or for mentioning something of which I am not thinking.

Scott

[mas985]

If you are trying to force all of the water through a small panel, that could be your problem. The extra head loss in the panel can reduce flow rates significantly. Your best best is put in a bypass and adjust it so that the filter pressure does not go up by more than a few PSI when solar is engaged.

[PoolDoc]

Add to what Mark said, the fact that most "1500 gph" pumps are low pressure devices with very little reserve capability.

You may need a standard AG pool pump, to drive the water through the panels.

[Watermom]

I don't send all of my water through my solar panels. I usually only open the valve maybe half-way.

[BigDave]

My two cents, sorry to be contrary:
If you find flow is inadequate for filtration with the solar panels on and you'd like to get maximum heating from the panels, plumb a bypass around the panels and run all the water the pump can move through the panels when the sun shines and bypass the panels - pumping only through the filter when it's dark.

[mas985]

Higher flow rates do equate to higher thermal transfer efficiency but only up to a point. Most manufactures recommend 0.1 GPM/sq-ft of panel to obtain maximum efficiency and forcing more water than that through the panels won't get much more heat into the pool but it will lower the electrical efficiency of the pump. For most panel setups, optimum efficiency is achieved at a point that is 3-5 PSI above the operating point without the solar panels.

[BigDave]

Agreed, but, in this case the OP has a low volume, low pressure pump that is unlikely to overwhelm the capacity of the panel. The observation of warmer water returning from the panel demonstrates this. Flow rates approaching the panel's capacity would be less noticeably warmer.

[mas985]

It depends on the size of the panels but typical AG panels are 2'x20' or 40 sq-ft and I got the impression there is only one which would require only 4 GPM. So most of the flow rate can probably bypass the panels and still provide pretty good heat transfer. But once the OP posts back, perhaps he can tell us the size of the panel.

[CarlD]

sometimes it's simpler. I re-routed soft panels when I had them so the water went in one corner and out the other, and ALL the return water passed through them. The efficiency of heating was amazing that way.
It's fundamental to thermodynamics that the faster the water flows through the panels without cavitating, the more heat is transferred. Usually, the limiting factors are a loss in pressure, or more pressure than the panels can tolerate before they start to fail and leak.

I successfully ran a 4'x10' (same as a 2x20) with a little tiny Intex cartridge pump this way, and was able to heat my parents' 13k AG with only 6 hours of direct sun a day. For both, I did it by re-routing the panels so water went in one corner and out the furthest.

[Air_Cooled_Nut]

There are many factors that can affect pressure drops: http://www.pipeflow.com/pipe-pressure-drop-calculations

Also, though the pressure may have dropped that doesn't necessarily mean the flow has. Time how long it takes to fill a gallon bucket from the solar output and the normal output (basically the end of the hose that connects to the pool to keep things consistent).