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dbc

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Posts: 242
Reply with quote  #61 
Jim,  Thank you for the excellent suggestions, although I think most of them will need to wait for a future build.

I didn't really have an 'engineering concept' for the white paint; it was mostly because I used white paintable silicone on the frame joints.  I figured if I missed a spot or if the paint flaked off, it wouldn't show.  It could just as easily be black or some other dark color, and if there's a performance advantage I'm all for it.

I used the same angle hold-downs on my 2x16 ZP, and they seemed to work OK that time.  I didn't test with a heat gun, but I did probe around with a light feather when the collector was operating and I didn't detect any leaks that way.  Last time I used a silicone gasket under the glazing (I set wax paper strips over the wet silicone and set the glazing on it gently.  I removed the wax paper after the silicone cured).  This time I used synthetic felt gaskets wrapped in high-temp foil tape (your idea as I recall).  These are glued to the frame.  I pressed down on the glazing when I marked the angles for the holes.  It went together really tight; in fact I had to elongate a few of the holes slightly because I couldn't press down hard enough to line the holes up for the screw.  I will check it with the fan running.

I can leave the cross-bars unpainted to retain the reflective properties, or even wrap them in foil tape to make them even shinier.  That's a great idea about using 1/4 x 1 bar on edge; it would be stiffer that way, and shading would only be an issue early and late in the day.  I need to find a better source for aluminum angle, bar, etc.  Home Depot is really expensive, which is why I went with EMT.

Here is the first of my planned tie-plates to hold the cross-bars.  The bottom is just tied with twine at the moment:

Glazing clamp 01, 061218.jpg 

Glazing clamp 02, 061218.jpg 

The biggest inefficiency in this scheme is that it requires a second piece of EMT on the back side.  If I had thought of it (much) earlier, I could have installed more T-nuts in the plywood that lines the track frame.  Then I could have just screwed the plates into the T-nuts with machine screws.  I could still do it with wood screws, but I chose not to, so I can take the cross-bars on an off more than maybe once.  I also thought of flattening and bending the ends of the EMT, but I passed on that idea for the same reason.

An unforeseen consequence is that the angle bracket for mounting the collector is too close to where I wanted to put the first cross-bar.  I wanted to center the cross bar over the end of the screen frame, but I had to put it about 3/4 inch to the left to clear the bracket.  It's still over the edge of the screen frame, so it should work OK.

For what it's worth, I also have some plastic insulating washers I can put onto the conduit connectors.  Don't know if they really add anything; I may leave them off.  I probably will squirt some silicone in the ends to keep the wasps out:

Glazing clamp 03, 061218.jpg

dbc

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Posts: 242
Reply with quote  #62 
I decided I don't like my latest cross-bar plan either.  Spacing is real critical - too tight and it wants to dent the frame when you pull it together, too loose and it wants to slide around and scuff everything.  It was also difficult to hold everything in place and put it together on the collector.  The left back brace was too close to the in/out ducts.  Finally, the whole thing was just too ugly.

So - I'm going to screw into the frame.  My new 'backup' plan is to cut the tie plates even with the back, screw them to the frame and fit the EMT cross bars across the front and through the matching holes in the tie plates.  Instead of using the conduit connectors (too ugly), I'll cut the EMT just long enough to pin it outboard of the tie plates.  It won't draw your eye as much.

Before I do that, I want to get a couple more sticks of EMT, and flatten and bend the ends.  If it fits right, I can just screw that to the frame and be done with it - one piece, nothing to rattle in the wind.
gbwillson

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Reply with quote  #63 
A few random thoughts...

T-nuts don't hold up well in anything but hardwood, so they likely would strip out. I can't imagine the exterior color of a collector box would make much difference in performance, or at least a difference that is measurable. Once you have the collector mounted take a look at the collector from where passers-by might see it. I think you will find that the shiny EMT would look better painted black over the glazing and white in front of the frame like you had suggested. Again, the improvement from any reflection off of the EMT would not be measurable, and would not be worth degrading the aesthetics of your build. 

I agree that the second piece EMT across the back is a bit much, especially if it gets in the way during mounting. Is the flat stock you used to hold the EMT aluminum? If so, you could heat it up and put a 90˚ bend in to hook to around the back of the collector, thus eliminating the EMT across the back. Or maybe a simple hook or protrusion from the side could hold the plate with a hole in it, in place? 

Greg in MN
dbc

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Posts: 242
Reply with quote  #64 
Thanks, Greg.  I'm pretty far off the nearest public road, so I don't get many passers-by, at least not the two-legged variety.  Still, I see the collector every day, and I want to feel good about how it looks.  Part of the fun is to make it look as good as I can.  It may not always show, but I do try to do at least a craftsmanlike job, within the limits of my skill, budget, and 'rough' shop facilities.  I know I have a long ways to go to match some of the artists on SimplySolar.

The glazing cross-bar question is still dogging me - I kind of like Jim's idea of using aluminum flat bar on edge.  1/4 x 1 is too expensive (for this box), but maybe 1/8 x 1 or 1/8 x 3/4 is rigid enough?  I figured you could screw some angle pieces perpendicular to the sides of the frame extending out a short way in front of the glazing and bolt the flat bar to them.  if you inverted the angle, by cutting out one side where it fit against the frame, leaving the full angle profile for the extended part only, the whole thing would fit within the outline of the collector, instead of sticking out above and below.  Also thinking of using chain-link fence tension bar for the cross-bars.  They're available at HD and cheap ($5 for a 48 inch length), and 48 inch would be just long enough if the angle brackets were inverted.  You could cut out one side of the angle where it sits against the frame, and leave the full angle profile for the part that extends in front.  That way the whole thing would fit within the outline of the collector frame.  The tension bar is really stiff too, at least edgewise.  Square tubing or angle would also work, and attach the same way.

I am hesitating on flattening and bending the EMT, because I have found that it's tricky to get both flattened ends in the same plane.  If they aren't exactly the same, one 'ear' or the other will sit at a slight up or down angle against the mating surface.  I used this technique to make 45 degree angle braces on both wall-mounts, and one end always looked slightly crooked.

Regarding the paint color, I always figured if you had the whole inside lined with 1 inch insulation, with all the corners sealed, there wouldn't be much thermal coupling between inside and outside.  The glazing would probably be most of it, no matter what color the frame was painted.  I guess I also went with white because the soffits, fascia, gutters, and downspouts are white.  I don't know, maybe bronze or some earth-tone would look good too.

It's odd, but I have always had good results using T nuts in plywood.  They only work one way - pulling something against the front (pulling the T nut prongs into the back).  I guess you could over-torque them, and I can see how you'd have trouble if the plywood ever got wet.  I used 8 T nuts (5/16 inch) to attach my 4x8 2-screen collector to its mount, and they held tight for 4-5 years (I'm removing it as we speak).  That collector had a 3/4 plywood back (and weighed a ton), which is why I haven't used T nuts for that application again.  If I build another collector with a track frame (did I say that?), I may omit the plywood altogether from the sides, and use Rivnuts for attaching things.  Rivnuts fasten directly to sheet metal and give you an inside machine thread.

For this round, I have some 1 inch Palram Woodtite screws, galvanized, with sealing washers, to screw through the frame into the plywood inside.

Late edit:  I made a bent conduit prototype, 12 inch span.  Pretty funky:

4) Bent EMT clamp prototype, 061318.jpg

gbwillson

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Reply with quote  #65 
Could you rip some of the stud track into L-shaped corners to use as cross braces. I'm not sure how stiff it would be, but if you have some scrap track laying around...

Fence stretcher bars are quite hard. Bert made some comments when he was playing around with frameless screens about how hard they were to drill through. They are tough, but are they stiff and thick enough to resist bending? 

Greg in MN


dbc

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Posts: 242
Reply with quote  #66 
The stretcher bar surely isn't stiff enough on the flat, but it might be if installed edgewise to the glazing.  Even then, depending on how it was attached, it may still twist and bow mid-span 'like a banana'.  I don't know; maybe you really need 1/4 inch thick bar.

I kind of doubt ripped stud track would be stiff enough to span 4 feet, at least not the 25 ga. they sell around here.  A ripped stud, which has more ribbing and a rolled lip might work, though.  You could rip it twice, once along each side of the wiring knockouts, and end up with two 1 1/6 in. x 1 1/4 in. angles, with the rolled lip on the 1 1/4 side.  I'll have to make that the new 'Plan B'.  I already got the EMT, so I'll probably try that first, at least make the braces and see how they fit.
Bruce

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Posts: 97
Reply with quote  #67 
Looking good, Don...I love your craftsmanship!  I have to ask (knowing little about air heaters) how much pressure are we talking here?  It seems to me that a 1/2 inch conduit will hold a lot of tension pressure over a four foot span.  I am playing with the idea of running a full ten feet span and am planning to anchor the 10 foot (does anyone know if you can get longer pieces?) every 4 feet with 6 inch long bolts inserted through the conduit, dividers, screen frame edges, iso and 1/2 inch plywood back with fender washers. That will sandwich everything together, I think.  Not sure if I will use 1/4 bolts or some 3/8 inch all thread I already have. I thought I was overbuilding (a family trait..."Hell for strong, but not so good fer purty") but you guys have me wondering if I am.  

My water heater collector has two 4x8 sheets of 6mm twinwall that I have very little flex coming from the no-pressure (other than wind and temp changes) so how much pressure can I expect?  It seems to me that my 8 inch ductwork should relieve most of it?
gbwillson

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Reply with quote  #68 
Don-

Just a thought...what if you only had a single brace running down the middle of the collector horizontally? An 8' horizontal brace would also help seal the divider between the two sides and the return. You'd have to check how well is seals the two manifolds, but with the manifolds only being 2' wide, and the direction of the glazing ribs, I'm guessing it would be effective with only the single brace.

Greg in MN



Bert

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Posts: 528
Reply with quote  #69 
Greg that's a good idea. With the middle divider it wouldn't shade much either. But it would have to be stiff enough to not bow over that span.
Maybe on edge or more likely an L angle.
Or could it be connected to the divider?

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Bert K.
Michigan

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dbc

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Posts: 242
Reply with quote  #70 
Bruce - Not sure what the air pressure is inside the collector, or even how to measure it, but generally it would depend on the output of your fan (or fans), and on the internal resistance of the airflow path.  I'm speaking here of a collector where the fan is on the input side.  I can also say that twin-wall is pretty flexible, and I can see it push out against the cross bars on my 2x16 collector when the fan starts.  With only a 2 ft span, the flexing was pretty easy to control.  You could check out Bert's ZP build for more info on this; he even posted a short video of the flexing before he added cross braces.  His is bigger, 4x20 I think, and he has a more powerful fan.  I like your idea of through-bolting.  Krautman Craig did that, and even used half of the bolts to mount the collector.  I think it would be best to avoid drilling and bolting through the twin wall, but right next to it or between sheets would be OK.

The main reason you want to keep the glazing pressed down is so the air stays between the screens (talking about a ZP) instead of going in front, by the glazing.  I have an additional problem on the current build due to the U-turn layout, where I want to prevent leakage over the divider, short-circuiting the intended air flow path.  Unfortunately, the divider is not structural (just a piece of 1-inch polyiso).

Greg - That was the first idea I thought about.  Th idea was to run a single brace lengthwise down the center, and fit some bands around the short direction (top to bottom) to keep it down if it flexed too much.  My concern was exactly what you have identified - the seal at the manifolds.  I tried to figure out a cross or t-shaped brace that would work in both directions, but I never came up with anything that I thought would work that wasn't too bulky.  I haven't screwed the cross braces to the collector yet, so I can still try things.

Bert - I probably answered your question in the first paragraph above, but I think I'm out of luck attaching anything to the divider.  I wish I had a structural center, but then I would have probably needed a structural back panel to attach it to, which I don't have either.  'Bad Planning' should be the name of this project.

Anyway, here are the cross braces I made yesterday (one of them).  Still need to drill holes in the ears, clean 'em up and paint.  Or try something else:

1) EMT clamp 01, 061418.jpg 

2) EMT clamp 02, 061418.jpg 

 

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