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SDJunkMan

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Reply with quote  #1 
It seems like most of you use polycarbonate as glazing, but I was wondering if anyone has tested single vs thermopane glass in a collector.

When I first decided to build a collector, I was looking for some glass for the glazing, and came across a construction site where they were tearing down an old building. I asked about the Windows, and was told I could have them if I got them out before the excavator got to them. They are appx 44" x 66", which is about perfect for the collector I plan to build.

Unfortunately, that was a few years ago, and now that I am finally getting around to building the collector, some of the Windows have delaminated. This is not really a problem, but I need to decide if I should use the glass that hasn't separated or a single pane fron one that has delaminated.

The single pane would make the collector lighter, but would the collector preform better with the thermopane. The thermopane would have less heat loss, but may reduce the amount of light that gets in to the collector.

Ideally, I would build 2 collectors, and test them side by side, but it has taken me years to get started on the first one, and it still isn't finished.🙄


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Jeff
Black Hills of South Dakota

gbwillson

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Reply with quote  #2 
SDJunkMan-

I remember solar enthusiast and engineer, Nick Pine, ran the numbers and found that in very cold climates twin wall glazing performed better. But this was in reference to polycarbonate glazing, not glass. Double-pane glass can have a lot of variables, such as the amount of lead in the glass, distance between layers, and low-E coatings. 

If I had free windows like you do, I'd have to strongly consider using them. But if I had to purchase glazing I'd look no further than twin wall polycarbonate panels. It's light, virtually unbreakable, and easy to work with. You can buy it at Menard's where it is often on sale for as low as $30 for a 4x8 sheet. 

Also note that some collector designs work better than others in frigid weather. Collectors that isolate the air from the cold glazing or operate using a high velocity of air are best in the coldest climates.

https://www.menards.com/main/building-materials/roofing-soffits-gutters/specialty-roofing/4-x-8-polycarbonate-clear-twinwall-panel-6-mm/p-1496848120528-c-5819.htm?tid=-3673411028269853346&ipos=10

Greg in MN
SDJunkMan

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Reply with quote  #3 
Greg,

Being frugal (cheep) I plan to use one of them on the first collector, but may try a test later. I have 2 Windows that I would like to add collectors to after I get the first one built, they are each about 44" wide, and are side by side, so I think they would be a good test location.

I don't think our winters are as cold as yours in Minnie, we do get some real cold days, but on average, it isn't too bad. I am planning on building a passive unit that attaches to a window as my first project (a plan from Mother Earth news) It was originally going to be a back pass, but after finding this forum, I am thinking a 2 or 3 screen collector.

Jeff,
Black Hills of South Dakota

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Jeff
Black Hills of South Dakota
gbwillson

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Reply with quote  #4 
Jeff,

If you are considering a "Heat Grabber" type collector as your window heater it's pretty easy to build. The Heat Grabber backpass design keeps the warmed air away from the cold glazing. 

Several years ago when I was testing my ZeroPass versus a 2-screen collector in a vertical configuration, I noticed the ZP didn't do as well as the 2-screen. This was with both collectors back at a 60˚ angle. My thoughts were that the 2-screen warms the air primarily when the air passes through the screen layers. While the ZP warms the air as it passes between the screen layers. So while passive, the ZP air would enter the collector box, rise up against the cold glazing where it would stay until finally exiting the collector. My point is that while I think screen does better at transferring heat to the air, you may want to consider that when passive, air will rise up against the cold glazing and performance will be diminished. But...What if you made the unit vertical instead if tilted back at an angle? This would allow the air to stay between the screen layers. And the unit could still be as wider than the window for added performance.

Any testing of passive collectors will gain you little information towards a design that uses a fan. Passive units are about simplicity, lowest cost, and being able to operate without power. However, a powered unit is far more efficient at collecting heat, and can be made in almost endless design configurations. It takes very little airflow to overcome the tendency for warm air to rise, which makes powered units far more versatile as the air can move in any direction.


Greg in MN






SDJunkMan

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Reply with quote  #5 
Greg,

I guess I didn't think about the difference between a vertical collector and a angled collector.

A vertical collector would not work in the two windows that I want to start with, but I could possibly use one in the pair of Windows tat I was going to use to test difference collectors.

With the initial collector, my goal is just to put some heat into the basement. My primary heat source is a Buck stove on the main floor. My house has hot water heat, and unless it's very cold, the boiler rarely comes on. Unfortunately this doesn't put much heat into the basement. I don't use the basement much in the winter (probably because it's so darn cold), but warming up the basement would also warm up the rest of the house. Eventually I would like to add collectors to the upper part of the house, using a permanent wall mounted collector, and possibly a pair of passive window units on my deck, that I could remove in the summer. Most of it depends on my success with the initial collector. Getting the wife's approval is no problem, she is all for " free" heat, and I don'have any close neighbors or a homeowners assn. to worry about.

So, back to the passive angled window collector, would the back pass be my best option? I'm off work the next couple of days, and hope to get to work on something before winter sets in.

Jeff
Black Hills of South Dakota

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Jeff
Black Hills of South Dakota
gbwillson

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Reply with quote  #6 
Jeff-

I want to double check when I said vertical as I may have been unclear. I meant mounted flat, against the side of the house, instead of tilted back at an angle. I don't mean 8' tall and 4' wide, as I assume this would block the windows. Am I correct?


Greg in MN
SDJunkMan

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Reply with quote  #7 
Greg,

No, I understood that you meant flat against the wall.  The angled collectors I want to build will be 44" x 66" (the size of the glass that I have).  If I build one flat against the wall, it will probably be 44" x 66" (using 2 panes of glass side by side) as that will fit between the upstairs and downstairs windows, unless I decide to go a long low collector (44"x 264" using the glass I have, or something with the polycarbonate that Menards sells).

Jeff
Black Hills of South Dakota

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Jeff
Black Hills of South Dakota
gbwillson

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Reply with quote  #8 
For a passive unit like the Heat Grabber design I don't think any matrix-type design would work. The backpass-type keeps the heated air away from the cold glazing. You will be able to heat a small room, but the amount of heat gained from a small passive collector is limited. 

To heat a large area, you need a very large passive unit, or an efficient active unit. The 44"x264" unit you described would do a great job of heating a home. My 4x16 ZP is normally routed in and out of the basement workshop. The residual heat keeps the house cozy usually until the next morning. But as an experiment, I routed the output to the main floor and in short order, it was almost 90˚F! I switched it back to the workshop. 

Greg in MN
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