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solardan1959

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Reply with quote  #31 
Mark,
  Not sure what you mean by a plenum with the screen collector.  Most do not use a plenum as it is not needed with a screen collector.  The Screen would be cheaper, easier, and perform as well or better. (I feel better) 
I just made a long horizontal screen section here, probably a better place to talk about this: 

Dan

Scott Davis

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Reply with quote  #32 
I agree with Dan.  While we have yet to have anyone do side by side tests with large scale, horizontal collectors, I think both will work really well and my guess is that the screen would likely be superior.
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jkknutson@centurytel.net

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Reply with quote  #33 

the best hot air collector

I have been running a 4'x8' solar hot air panel for 5 years and want to start manufactering them.
I have a snap disc controller running a Fantech model FG4 110 cfm FAN @ 50 PASCALS (.2 inches of water). this fan works great it runs all day without letting anything to get too hot. The solar panel came with a PV powered fan that could not keep up and alowed the plastic vent pipe to melt, 160 degrees, so I put an ac powered fan in instead. I would use the FG5 next time to increase cfm to 130 while still using only 20 watts.
I want to start building prototypes to test against each other and would like to know what works best collector, glazing  and boxes so far so I can take solar hot air to the next step, and not reinvent the wheel.

Jeff Knutson
a-a exteriors.com

Scott Davis

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Reply with quote  #34 
Hi Jeff,

Right now the double layer screen, hot air collector is the design to beat!

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Jp27300

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Reply with quote  #35 
Dan,

Do you have any more data on 2 screen vs 3 screen?

The 2 screen collector I've built seems to allow alot of light through, so I think 3 or 4 screens even would work better, although I';m concerned about airflow through a 4 screen perhaps.


Also I was wondering how you "glued" the mylar (like one of those space blankets?) to the Foam insulation?

I have issues with odors and am trying to keep anything out of the box that might off gas over time.

Was wondering what might work.  Maybe even Elmers glue.

Jeff NH

Seatec

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Reply with quote  #36 
My screen panel I am build has a plenum top and bottem to help balance the air flow. I will have 4 screens, 2 aluminum pass through and 2 fiberglass , starting off at the bottem as zero pass. Just experimenting with the screens, but still think the flexable tubes will be the best panel.

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netttech

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Reply with quote  #37 
JP,

I've glued down Mylar using 3m spray glue. I used the mylar for my parabolic trough panels. The glue worked well for gluing mylar.

Yea it had a smell during the application but went away in a couple of days. Of course parabolic troughs is for hot water & not hot air.

I have no idea if it generated any smell.

Jeff
Central IL
solardan1959

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Reply with quote  #38 
Jp27300,
   No I have no numbers but my three layer seems to consistently run hotter by a few degrees and it has slightly more flow than the two layer.  But since I opened up all the vents it would be very hard to determined flow accurately for an individual collector.
   I got my Mylar as a donation from Greg Wilson and he gave me a can of spray adhesive similar to what nettech used.  I also have used some spray adhesive from big box or craft stores.  Try to enlist some help when you apply the Mylar as two people can more easily apply the Mylar to the sticky surface.

Seatec,
   I think you do nice work!  I like what you now doing with vents, the equal flow all across the panel has to be better at extracting heat from all the absorber.  Greg and I both spent some time in this area and did some experimenting with pushing and pulling air.  The most interesting thing that came out of that was how differently air flows when you are pushing as apposed to pulling air.  basically if you change how you get your air through there you will have to completely redo you vents. (pretty much reverse them)

Dan
gbwillson

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Reply with quote  #39 
Quote:
Originally Posted by solardan1959
Jp27300,
   No I have no numbers but my three layer seems to consistently run hotter by a few degrees and it has slightly more flow than the two layer.  But since I opened up all the vents it would be very hard to determined flow accurately for an individual collector.
   I got my Mylar as a donation from Greg Wilson and he gave me a can of spray adhesive similar to what nettech used.  I also have used some spray adhesive from big box or craft stores.  Try to enlist some help when you apply the Mylar as two people can more easily apply the Mylar to the sticky surface.

Seatec,
   I think you do nice work!  I like what you now doing with vents, the equal flow all across the panel has to be better at extracting heat from all the absorber.  Greg and I both spent some time in this area and did some experimenting with pushing and pulling air.  The most interesting thing that came out of that was how differently air flows when you are pushing as apposed to pulling air.  basically if you change how you get your air through there you will have to completely redo you vents. (pretty much reverse them)

Dan




3M Super 77 is a great product for adhering mylar to your insulation. It's carried by most big box stores. As Dan mentioned, get help when applying the mylar, if possible. If you do apply mylar yourself, try this.
Apply adhesive and mylar along only one narrow edge. Once this has dried, you can apply the remaining mylar as the dried edge allows you to pull out all of the wrinkles and lay the smooth mylar down into the spray adhesive. Essentially, the 1st glue strip becomes your "helper".

Greg in MN[wave]
Julian Jameson

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Reply with quote  #40 
Just wanted to add an update to an assertion I made on the forum, back on the 13th Oct.

We have two side-by-side 4'x8' collectors mounted on the south wall of our home. The house is on a hill top in mostly-open land, in Nova Scotia. The prevailing wind comes from the north-west (or thereabouts).

The two collectors are almost identical. Their elements are overlapping dual screens in a through-pass configuration. The manifolds are all open to the sun. One of the collectors has screen in the open manifolds whereas the other does not (they're just open 'black boxes').

We have monitoring equipment attached to both collectors that allows logging of temperatures (all inlets and outlets) as well as data regarding the speeds of the fans. Depending on which software tool I use, data can be logged each hour (where it is averaged) or each second.

From the data, we have consistently found that, on any given day, the output from each collector varies compared to the other collector. Some days they have around the same output, other days #1 is considerably better than #2 and vice versa.

The sensors are all in the same places, the fans are identical. There is a small gap between the actual collectors but it's just a few inches.

I think one of the factors causing the variance is exposure to the wind (where one collector may have more cooling gusts blowing over the glazing, or external pressure changes, compared to the other). With the prevailing winds, one collector definitely has more exposure to wind than the other (it might even shield the other, to some extent). Obviously that all changes when the wind direction changes.

The other theory I have is to do with the azimuth angle of the sun.

In terms of exposure by the sun and [azimuth] angle of incidence, collector #1 lags collector #2 by almost 15 minutes.

I think what is happening is that once the sun transitions into and out of the period where the solar radiation becomes the most focused (for sake of argument, the two hour period around the solar noon), if any significant changes occur in the atmosphere during this time, then one collector can be affected more detrimentally than the other.

Outside of those transition periods there is still (up to) 15 minute difference in solar focus cast on the collectors so, again, any atmospheric conditions may affect the collectors in slightly different ways during these times.

Anyway, thought I'd share this as it the somewhat "random" variance between the two collectors seems to solidifying as a fact.

For testing of side-by-side panels (depends on the location, of course) it might be worth considering that a more accurate comparison could come from having the panels next to each other in a vertical configuration (if possible), rather than horizontal.

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