Solar heater question... directionally challenged!!!

[tmurphy]

So we are just hooking up a new solar heater system for our little 14'x42" intex pool.
We are locating the blankets on the roof of our shed and there are 2 2'x10' blankets.
We are not using the pool pump to pump through because we actually have solar panels on the shed powering the 1/4hp submersible pump and the pool pump runs at night and is too powerful for the solar panels to power.
So this is free energy!!!

So... as we are setting up and determining how to arrange everything (we previously had one of those garbage 3'x'3 Game solar blanket things) the diagram below shows that we should have the inlet at the bottom and the outlet at the top.
Is there any reason we can't do it the other way around?
Hubby is figuring it might be a little easier on the pump to pump it straight up and then have gravity help pull it through the tubes of the heater, rather than pump it up to the bottom and have the pump have to push it through all the way up.

I'm sure there is no reason why we can't do it the other way around.... but why would they suggest doing it wit the inlet at the bottom instead of at the top?

Photo by Tammy Murphy - Google Photos
Just click on the link for the picture of the diagram.....

 

[tmurphy]

nobody?

 

[sbcpool]

Fluid dynamics are weird. Whether you have a 1 square inch column of water 33 feet high or 12 trillion gallons of water 33 feet high, the pressure at the bottom is the same per unit area. It sounds intuitive enough, but the consequences can be strange. I don't think reversing the flow will have any effect on your pump because either way it sees a column of water as tall as the highest point in the system. If you're not sure, experiment. Science is fun.

 

[pooldv]

Solar panels need to fill from the bottom up. The few times I have seen people accidentally plumb them backwards they have issues. There is someone on TFP now who just had to replumb his panels because the installer plumbed them backwards and there were problems with air in the lines and panels. I have never seen any solar panel manufacturer recommend top down plumbing.

 

[Isaac-1]

Plumb bottom up, otherwise the water is trying to fight past the air bubble as they try to rise to the highest point.

 

[chiefwej]

As others have said it needs to be pumped from bottom up or you won't get the air out, also you might remember that warm water rises.

 

[Pool Clown]

Aside from how the water flows (bottom to top, top to bottom, etc.) There is a more potentially serious issue here. The diagram you posted shows the panels plumbed in series. Your panel size, and the amount of panels may not make a difference here, but if you had a hot tub and wanted to add panels, it may. Having the panels in series will increase the temp of the water each time the water passes through a panel. Your typical heat rise through the WHOLE solar system should only be about 4 degrees. Panels should be plumbed in parallel. Running the water through in series would have a higher heat rise if you were to add panels. This configuration (current amount and size of panels) would probably not be a problem for a typical size pool, but you have a smaller pool and you will be able to raise the temp faster. There will probably be no problem in your case, just wanted to make you and anyone else considering a DIY solar setup aware of the hot water potential, especially when the system first cycles on.

Until the panels completely purge and you begin to get constant flow, you will experience a temporary warmer, (potentially hotter) than normal output.

 

[borjis]

Until the panels completely purge and you begin to get constant flow, you will experience a temporary warmer, (potentially hotter) than normal output.

Indeed you will.

The highest return temp I ever had was during a sweltering weekend 2 weeks ago. The return water came back through nearly 120 degrees!
It sat there for a good minute before settling down to 94.

 

[tmurphy]

Thanks for the explanations everyone.... and the warning Pool clown!
We welcome the hotter temps! but will use caution when first powering on the system, there is usually nobody in the pool at that time anyway.
The panels are 2x10 and at this time that is all our shed roof can accommodate. The other side of the roof is partially shaded by a tree, that may change when we move to a bigger, permanent above ground pool.
But our kids are still young and we still have a rather large playset taking up a good portion of that backyard so until that goes, we are dealing with a smaller pool.... which for smaller kids... is ok.
Only a year or two more though and we are moving up though so we will definitely keep that in mind if and when we add more panels.