Plumbing the panels

[Naptown]

For example I would prefer to see a 15 deg rise with a flow rate of 5 gpm instead of a 25 degree rise with a flow rate of 2 gpm (the 5gpm yields 50% more BTU) as long as you aren't increasing your pumping costs very much.

A simple flow meter, and two temp gauges will do the trick but many people don't have those toys in the workshop.

In red above means the temperature rise through the collectors not in the tank which would mean less BTU's going in.
needed to clarify as it was confusing to me at first and contrary to how it works considering the sentence above it refers to the tank temperature.

[Designer_Mike]

If your flow is on the low side, you might be better off with them in series and then you ensure you are getting even flow throughout the entire array and maximizing gain.

You just need to look at the pressure loss charts. You may drive the flow rate down a bit due to increased pressure...but that might actually reduce your pump electrical consumption (splitting hairs here)...and you may marginally increase your output since the panels will be more efficient with the higher flow rate which will create turbulence and improve heat transfer.

Lets say you ran 1/2" tube up to them and you have them in parallel. Depending on the pump you may get 3 gpm through the pipe to the roof (just guessing at a number)....now you split it up three ways and one panel takes two since there is little resistance and the other two share the last gpm...and those have a much higher temperature rise but you incorrectly think they are producing more....in reality, you are capturing much less since the flow rate is so slow....increasing the flow rate through each panel to 3 gpm (by putting them in series) will dramatically raise the turbulent flow and improve heat transfer.

If you had perfectly even flow through each panel compared to plumbing them in series it would probably be hard to measure the difference, but as you have very uneven flow, I wouldn't be surprised to hear you doubled the production rate.

You could easily experiment with different set ups just for curiosity. Unless you have a flowmeter on the pipe, you can't simply use outgoing water temp as the only parameter. You really need to look at the temp rise for your entire storage tank over the entire day.
For example I would prefer to see a 15 deg rise with a flow rate of 5 gpm instead of a 25 degree rise with a flow rate of 2 gpm (the 5gpm yields 50% more BTU) as long as you aren't increasing your pumping costs very much.

A simple flow meter, and two temp gauges will do the trick but many people don't have those toys in the workshop.

[aztom]

Thanks so much for all your help. I've got it jerry-rigged balanced by restricting the flow in or out of one panel or another. I also bled it again and got more air out of the system.
It seems to be doing much better now.

[russ]

Water will always follow the path of least resistance.

The 'reverse parallel' arrangement makes all runs the same length so equal pressure drops.

Nothing to do with venturi effect.

[aztom]

I think the larger manifold is a good idea, if not just right at the spot where it T's, to reduce the venturi effect.
As far as reverse parallel goes, I had just the opposite effect from what you might expect, as the nearest panels got the least water flow..

[aztom]

No. I don't have them plumbed in reverse parallel. This is my first feeble attempt at this stuff, and I didn't research it out enough beforehand obviously.

[Naptown]

Are they plumbed in reverse parallel?

[russ]

Sizing problem - there is inadequate pressure drop across the panels to cause the water to follow the three paths. Easiest solution (to me) is placing a hand valve in the inlet and compare the outlet temps -adjust the valves to get equal temps

Water is lazy - it always follows the route of least resistance.

[Mike90250]

Like batteries in parallel, water panels in parallel will exhibit uneven flow.

2 in parallel can be easily resolved like batteries, - plumb them on the diagonal ! Add a 3rd, and you are on your own.

Ideas - large 1.5" manifold, like a battery bussbar ?

[aztom]

Hi! I'm new here so bear with me.
I just plumbed three 3x6 ft. solar hot water panels. They're plumbed in parallel, with 1/2" copper T's for bottom feed, and T's at the top for hot water return.
Water doesn't circulate in the first two panels, only the end panel has circulating water in it.
I don't know why no water is going through the two nearest panels, but I think it may be because of the T's at the bottom feed. I'm thinking they may not be getting pressure from the pump because of the venturi effect. Water rushing straight through the T's may actually be pulling water down from the panels, instead of pressurizing the panels.
What do you think, and how can I solve this without plumbing them in series?
Thanks in advance, Tom.