Best panel header tilt for drainback?

RyanW

I am getting really close to mounting 8 AET32 panels in two rows of 4 flat to my 5/12 pitch roof.    I plan on cocking them at an angle to effectively give the headers a tilt so that they will drain out.    I originally planed on a fall of 1/4" per foot which means that the array which would be roughly 16' square would be cocked about 11".    That sure would look funny.  



 In doing some more research I find folks like Dr Ben in his top ten mistakes video <a href="http://www.solarhotwater-systems.com/">http://www.solarhotwater-systems.com/</a> recommends a drop of only  1" for 20 feet!   That seems really low to  me.  



  I am now looking at a fall of 2" over the 16' which would mean that the panels would be cocked 5 inches.       Is this enough and what do you all normally try to attain.

Thanks

Ryan

Kevin_in_Denver_2

1" Header?

1/4" is overkill in some cases.



With a 1" header, Dr. Ben's recommendation is  fine, as long as all the lower headers line up well and look straight.   Just imagine a a perfectly level 1" pipe open at one end.   It would still drain almost completely.   But settling of the structure or the mounting hardware could tilt it the wrong way.



Note that in 1/2" pipe and smaller, the capillary effect messes things up, and more tilt is  probably required.

RyanW

Headers

Yes these AET panels do have 1" headers.   The harp lines are 1/2" copper and are tilted with the roof at 5/12" pitch so drainage in them should be fine.    The roof is made up of scissors trusses and I like the idea of putting a bit of extra tilt for potential roof sagging.



So is 1/8" per foot a good slope?

Ryan    

Kevin_in_Denver_2

should work

But if you are still worried, there's another way to do it:

shoot for level, and feed the lower header from both ends.  

hot_rod

glycol

is used in DB in some installations up north if you don't want to pitch the collectors. This also allow you to mount the collectors and piping without pitching them.



You do still take the glycol penalty for heat transfer of course.



Pay attention to the piping pitch also, maybe consider a Coaxial Hydrovent from Radiant Engineering. This device assures the piping and collectors drains down quickly and completely.



hr

ABSolar

Panel tilt

Hi RyanW,

I don't see how you arrive at 11" tilt using 2 rows of 4 panels using the 1/4" tilt per foot rule.  I get 4" of tilt (across tops of panels) per 4 panel array (16'-0" not including between panel connections)  If you were referring to the array being cocked down along the long sides of the collectors, the "out of square" is essentially the same (4"), assuming no/ little space between upper and lower arrays, because you still have 16'-0 (a square).

16'-0" x 1/4"/ ft = 4" tilt per array.  If the 2 arrays are in the same row, you can install them pitched as a "chevron" pattern.  If one array is above the other, pitch them both the same direction.  For what it's worth, you could lessen the pitch to 1/8" per foot.  Water will seek the low point.  Heck, 60'-0" gutters can be pitched just one inch and still drain to the downspout hole.   I would DEFINITELY use 3/4" diam. piping minimum for drainback.

Feel free to correct my line of thinking on this panel layout...

ABSolar

Coaxial hydrovent - what !?!

Hey HR,

I had to google that one, only to find reference back on the wall in 2008.  At first, I thought you might be kidding, sort of like a muffler bearing for a car..  Did  Dale at Radiant Engineering ever start marketing that drainback facilitator?  More succinctly, do you still swear by them for speeding up the drainback process?

It would seem to me that the concentric tube only allows the air to go as high as the concentric tube top before re-entering the return pipe from the collectors.  So the improvement would only affect X number of feet of piping.  Am I missing some water flow logic here?

RyanW

funny math

Yes I guess I was not totally clear on that.   I also was working towards a 4" vertical elevation drop over the array.   That means that I have to rotate the array almost 11" on my 5/12 pitch roof.     To get 4" of vertical change I have to move the panels 9.6" horizontally.    The roof plane is the hypotenuse  of the two which comes out to 10.4"    I bumped that up to 11" to accommodate the unions between the panels.  



The panels are on the back side of the house so I decided to play it safe and go for the 1/4" slope in-case the trusses ever settle.    Yesterday was a big day here as I got some help from my pops and a friend.   We put up the racking that I had prepared to attach them to the standing seams.    I had to use rails to make sure that all of the s5! clamps rested on top of the perlins under the roof.   6 hours later the panels were on the roof.   All went well except the next to last panel was warped a bit so getting the unions to match was a bit difficult.   I am attaching a few photos of the system.   Sure looks like some one messed up with a tape measure!

RyanW

More drainback piping quesitons

The panels are up and now I have to connect them to the tank!    I would love some feedback before I start sweating joints and cutting holes in my roof.  



I have two rows of 4 AET 4x8 panels piped in reverse return.   I just did a bit of dry fitting and took some photos of them to see what you all think before I cut holes in my roof.   The boots are high temp silicone which is why they are orange.   

All pipes are 1" type L



Pictures

1: the supply side.   The pipe has to penetrate the roof to the left of the roof seam to get on the correct side of a rafter.



2,3 Hot return  Option A    This is what I am planing on doing as I think it should fill all of the panels, is the simplest and looks the best.  The array pushed up very close to the ridge cap!



4,5 Option B    Karl Northwind was worried about the upper array filling properly and so this option would force the water to climb a bit more before returning down to the tank.    I am not sure if this is nessisary but it is a great use of street 45s.   I think that this would force the upper panels to fill better before any water heads back down but it also adds more curves to resist flow.    Also more sweat joints to leak and the pipe bump does show over the ridge cap.   



Which would you do?

Thanks

Ryan

Dr_Ben

1" in every 20 feet

If you guys want a full explanation of why I recommend a tilt of 1" in every 20 feet, tune in to my next solar Q&A webinar at noon on May 16th. Here's the link:



http://www.solarhotwater-systems.com/webinars/



I'd be more than happy to discuss that or any other solar thermal questions you may have. You're also free to share your comments and/or experiences related to solar.



Hope to see you there!

Dr. Ben



PS - Ryan, I can also give you some input on your piping layout if it's not too late.