Header slope in ganged evacuated tube collectors in a drainback system

[hermhart]

I understand that when using an evacuated tube collector panel in a drainback system, that the header should slope downward toward the inlet, and I'm told that this slope should be about 1" per foot. OK. If we have a single collector panel, OK. Let's think of 8' wide panels. So we're talking about a slope of 8" for the width of the panel. Now if we gang 2 or more panels together, what is a practical way to plumb that? Would we come up from inside the building with a single pipe and then when we get near the panel installation, that the plumbing would branch out with an inlet going to each of the separate panels? That way the panels would not be actually ganged. They would be fed from a common source via a branch network. This would mean that to keep the panels themselves more or less on the same elevation, that the branch point that serves the first panel would need to be 8" lower than the branch point that serves the second panel, etc. This doesn't seem very practical for panels that basically lie on a sloped roof. Or is there a different approach being used for this issue?

ps. I had a drawing, but the attachment isn't working.

[hermhart]

Here's my drawing.




panelslope.jpg

[Naptown]

Your drawing looks correct. the panels should be plumbed in parallel reverse configuration to even out flow and eliminate a series configuration

[hermhart]

Naptown,

It's not clear to me what you mean. My plan would be parallel plumbing from the branches. So, yes, it's parallel in that sense. But what do you mean by "reverse configuration to even out flow"? What is reversed? And how is flow evened out? And what about "eliminate series configuration"? The parallel panel system could be said to be in series with the pumping and other processing inside the building. Is that what you mean? Or is it something else?

Anyway if my drawing is correct, then as I see it if I basically have these panels mounted to a sloped roof, then the plumbing from the level of the panels down to the elevation of the lowest plumbing branch would have to be located in the attic area... in the space between the roof and the ceiling of the room below. So I am limited then 1) by that amount of space that's available, 2) by the amount of slope I put on the pipes, and 3) by the number of panels in the system. Am I thinking right?

Thanks

[russ]

Your layout and understanding are OK - Rich means to keep the pipe runs approximately the same length.

If you have one panel higher than the other I would put valves in the inlet to each panel to allow balancing of the flow when they are operating. If you can't balance the flow equally between the units you will lose substantial heat - one will be hotter than the others.

[Naptown]

This is what I meant it should eliminate the need for balancing valves.reverse prallel collector plumbing.pdf

[russ]

This is what I meant it should eliminate the need for balancing valves.[ATTACH=CONFIG]1444[/ATTACH]

If all panels are at the same elevation it may but no guarantee.

[hermhart]

Naptown,

I meant for the panels to all be at the same elevation or height. In my drawing the pipes are not at the same height because of slope. Is slope not critical in the plumbing for a drainback system? Also both your drawing and mine show the piping to be of differing lengths. Is that OK if the panels themselves are the same height? Otherwise, your drawing differs from mine in that you also show the outlet. I left that off for simplicity.

Thanks to you both for your help with this issue.

[Naptown]

Try this schematic with panels all on same level but sloped. all inlet and outlet piping is sloped also keep all pipes the same length or you will need the balancing valves and flow meters etc.
If you can set vertically with one collector above the one below it will work easier.reverse prallel collector plumbing horizontal.pdf

[Naptown]

If all panels are at the same elevation it may but no guarantee.

elevation makes no difference the outlet is still at the highest point so flow will be equal.

[hermhart]

Do you need a vacuum breaker in drainback, as opposed to closed loop?

[Naptown]

I have never not installed one in a drain back if that's what you mean. It helps with draining down quickly and if by chance you overfill your drainback tank so air cannot be introduced into the collector lines the system will not drain.

[hamish]

yep vacuum breaker a must to send the liquid on its way, you need to check its function,

sometimes the heat jams them shut. Give it a few taps and you will hear the air sucking

in as it opens. Post a few pics when it up and running so we can admire your work.

[Art VanDelay]

No Vacuum Breaker in drainback

Vacuum breakers will suck. Literally

http://www.heatinghelp.com/forum-thread/131460/Drain-back-solar

[Naptown]

Vacuum breakers will suck. Literally

http://www.heatinghelp.com/forum-thr...ain-back-solar

The problem herin lies with a delicate balance to allow the air bubble to reenter the tubing breaking the vacuum. It would also as described in that post require a pressurized drain back tank.